TEST OF PRESTRESSED CONCRETE T-BEAMS RETROFITTED FOR SHEAR AND FLEXURE USING CARBON FIBER REINFORCED POLYMERS

Transcription

1 TEST OF PRESTRESSED CONCRETE T-BEAMS RETROFITTED FOR SHEAR AND FLEXURE USING CARBON FIBER REINFORCED POLYMERS Alison Agapay Ian N. Robertson Prepared in cooperation with the: State o Hawaii Department o Transportation Highways Division and U.S. Department o Transportation Federal Highway Administration Research Report UHM/CEE/04-08 August 2004 i

2 Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 4. Title and Subtitle Test o Prestressed Concrete T-Beams Retroitted or Shear and Flexure using Carbon Fiber Reinorced Polymers 5. Report Date August Perorming Organization Code 7. Author(s) Alison Agapay, Ian N. Robertson 8. Perorming Organization Report No. 9. Perorming Organization Name and Address Department o Civil and Environmental Engineering University o Hawaii at Manoa 2540 Dole St. Holmes Hall 383 Honolulu, HI Sponsoring Agency Name and Address Hawaii Department o Transportation Highways Division 869 Punchbowl Street Honolulu, HI Work Unit No. (TRAIS) 11. Contract or Grant No. HiDOT Project # Type o Report and Period Covered Final 14. Sponsoring Agency Code 15. Supplementary Notes Prepared in cooperation with the U.S. Department o Transportation, Federal Highway Administration 16. Abstract In 1997, a precast prestressed T-Beam in the Ala Moana Shopping Center Parking Garage was strengthened in lexure using carbon iber reinorced polymer (CFRP). When the old parking garage was demolished in June 2000 to make way or a new multilevel parking garage, this beam and two control beams were salvaged and transported to the University o Hawaii at Manoa Structural Testing Laboratory or testing. This report presents testing o the strengthened beam and a control beam. It also describes the retroit procedures during ield application o the CFRP strips, beam recovery, and preparation or laboratory testing. In addition, a step-by-step analysis o the predicted strengths is presented. To ensure lexure ailure, the beams were retroitted in shear with CFRP. Two types o wrapping scheme were used and anchorage was provided or the shear retroit. The let hal o each beam was retroitted with 3 wide double layer CFRP stirrups. The right hal o each beam was retroitted with 12 wide CFRP sheets. Ater lexural testing, each hal o each beam was recovered or shear testing. Flexural test results indicate that the CFRP strengthening provided a 71% increase compared with the control specimen without reducing the beam s ductility. The lexural capacity o the strengthened beam was 21% greater than predicted by ACI 440R-02. The two T-Beam tests with CFRP sheets or shear strengthening produced 7% and 16% increases in the shear capacity when compared with the control beam without CFRP shear strengthening. These increases are below the 42% increase predicted by ACI 440R-02. Because o conservatism in the estimate o concrete and internal steel stirrup contribution to the shear capacity, the ailure shear strength o the beams with CFRP sheets was still slightly greater than the ACI 440R-02 prediction or ultimate shear capacity. The shear tests indicated delamination o the CFRP stirrups and sheets occurring prior to the maximum shear load. Anchorage at the top and bottom o the beam web helped prevent complete delamination o the CFRP; however urther anchorage development is required to improve the strength o the CFRP shear retroit. 17. Key Word Prestressed T-beam Carbon Fiber Reinorced Polymer Flexural Strengthening Shear Strengthening 18. Distribution Statement 19. Security Classi. (o this report) Unclassiied 20. Security Classi. (o this page) Unclassiied 21. No. o Pages Price Form DOT F (8-72) Reproduction o completed page authorized

3 ABSTRACT In 1997, a precast prestressed T-Beam in the Ala Moana Shopping Center Parking Garage was strengthened in lexure using carbon iber reinorced polymer (CFRP). When the old parking garage was demolished in June 2000 to make way or a new multilevel parking garage, this beam and two control beams were salvaged and transported to the University o Hawaii at Manoa Structural Testing Laboratory or testing. This report presents testing o the strengthened beam and a control beam. It also describes the retroit procedures during ield application o the CFRP strips, beam recovery, and preparation or laboratory testing. In addition, a step by step analysis o the predicted strengths is presented. To ensure lexure ailure, the beams were retroitted in shear with CFRP. Two types o wrapping schemes were used and anchorage was provided or the shear retroit. The let hal o each beam was retroitted with 3 wide double layer CFRP stirrups. The right hal o each beam was retroitted with 12 wide CFRP sheets. Ater lexural testing, each hal o each beam was recovered or shear testing. Flexural test results indicate that the CFRP strengthening provided a 71% increase compared with the control specimen without reducing the beam s ductility. The lexural capacity o the strengthened beam was 21% greater than predicted by ACI 440R-02. The ailure shear strength o the beams with CFRP sheets was slightly greater than the ACI 440R-02 prediction. The shear tests indicated delamination o the CFRP stirrups and sheets occurring prior to the maximum shear load. Anchorage at the top and bottom o the beam web helped prevent complete delamination o the CFRP; however urther anchorage development is required to maximize the strength o the CFRP shear retroit. iii

4 AKNOWLEDGEMENTS This report is based on a Masters thesis prepared by Alison Agapay under the direction o Dr. Ian Robertson. This research project was unded by research grant No rom the Hawaii Department o Transportation (HDOT) and the Federal Highway Administration (FHWA). The contents o this report relect the views o the authors, who are responsible or the acts and accuracy o the data presented herein. The contents do not necessarily relect the oicial views or policies o the State o Hawaii, Department o Transportation or the Federal Highway Administration. This report does not constitute a standard, speciication or regulation. In addition to the primary sponsors, a number o individuals and companies have made signiicant contributions to this research project. The authors would like to acknowledge and thank the ollowing: Drs. Gregor Fischer and Si-Hwan Park or their eort in reviewing this report. Timothy Goshi or assisting with the construction o the test rame, and in preparing the beams or testing. Kainoa Aki or programming the LAB VIEW data acquisition system, monitoring the instrumentation during each test, and assistance with installing the CFRP retroit. Gaur Johnson or assistance preparing the beams or testing and recording crack development. Stephanie Fung or assistance with data recording during the tests. Laboratory technicians, Andrew Oshita and Miles Wagner, or their advice during construction o the test rame, and general assistance during laboratory testing. The authors are extremely grateul to Adriano A. B. Bortolin o Sika Products, USA, or providing valuable inormation concerning the original CFRP application, at iv

5 which he was the Sika representative. Sika Products, USA, also donated all o the CFRP materials required or laboratory shear retroit o the test beams. Brian Ide o Martin and Chock, Inc., the structural engineer responsible or the original CFRP strengthening design, provided detailed inormation regarding the design and installation o the original lexural strengthening. The authors are also indebted to Chandler Rowe and his colleagues at Plas-Tech Ltd., Honolulu, Hawaii, or donating their labor and expertise in the repair o the beams and or installation o the shear retroit materials. v

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7 TABLE OF CONTENTS AKNOWLEDGEMENTS... IV LIST OF FIGURES... XI LIST OF TABLES... XIX 1 INTRODUCTION BACKGROUND OBJECTIVE Use o CFRP or lexural strengthening Use o CFRP or shear strengthening SUMMARY LITERATURE REVIEW INTRODUCTION CFRP FLEXURAL STRENGTHENING CFRP SHEAR STRENGTHENING CHAPTER SUMMARY ALA MOANA BEAM REPAIR BEAM RECOVERY AND REPAIR INTRODUCTION EPOXY CRACK REPAIR EPOXY MORTAR SPALL REPAIR TOP SLAB REPLACEMENT TEST SETUP AND BEAM LAYOUT INTRODUCTION TEST APPARATUS BEAM SHEAR RETROFIT CFRP Shear Stirrups CFRP Shear Sheets BEAM TEST CONFIGURATION AND INSTRUMENTATION T-Beam 1 Layout and Instrumentation T-Beam 1L Layout and Instrumentation vii

8 5.4.3 T-Beam 1R Layout and Instrumentation T-Beam 2 Layout and Instrumentation T-Beam 2L Layout and Instrumentation T-Beam 2R1 Layout and Instrumentation T-Beam 2R2 Test Setup and Layout MATERIAL PROPERTIES CONCRETE COMPRESSIVE STRENGTHS TOP SLAB CONCRETE MODULUS OF RUPTURE STEEL REINFORCEMENT TENSILE STRENGTHS CFRP MATERIAL PROPERTIES CFRP PULL-OFF TESTS THEORETICAL BEAM STRENGTHS NOTATION FLEXURAL STRENGTH OF T-BEAM FLEXURAL STRENGTH OF T-BEAM 2 (W/CARBODUR STRIPS) Flexural Capacity o a Reinorced Concrete Beam with CFRP Nominal Flexural Capacity o a Prestressed Concrete Beam with CFRP Calculation o the Predicted Flexural Strength o T-Beam SHEAR STRENGTH OF T-BEAM 1 (WITHOUT SHEAR RETROFIT) SHEAR STRENGTH OF T-BEAM 2R1 (PLAIN CONCRETE) SHEAR STRENGTH OF T-BEAM 1L (W/CFRP STIRRUPS) SHEAR STRENGTH OF T-BEAM 2L (W/CFRP STIRRUPS) SHEAR STRENGTH OF T-BEAM 1R (W/CFRP SHEETS) SHEAR STRENGTH OF T-BEAM 2R2 (W/CFRP SHEETS) RESULTS AND DISCUSSION T-BEAM 1 RESPONSE ACI 318 Predicted Flexural Capacities Slab Reinorcement Strain Gage Readings Concrete Strain Gage Readings Vertical Delection Strains in the CFRP stirrups and sheets T-BEAM 2 RESPONSE viii

9 8.2.1 Failure mechanism or T-Beam Slab Reinorcement Strain Gage Readings Vertical Displacement rom LVDT Readings Carbodur Strip Strain Gages ACI 440 VERSUS EXPERIMENTAL MOMENT CAPACITY SHEAR STRENGTH OF T-BEAM 2R1 (PLAIN CONCRETE) SHEAR STRENGTH OF T-BEAM 1L (CFRP STIRRUPS) Measured strain in the CFRP stirrups SHEAR STRENGTH OF T-BEAM 2L (CFRP STIRRUPS) Strain Gage Readings or CFRP Stirrups SHEAR STRENGTH OF T-BEAM 1R (CFRP SHEETS) Strain Gage Readings or CFRP Sheets Carbodur strip strain gages SHEAR STRENGTH OF T-BEAM 2R2 (CFRP SHEETS) Strain Gage Readings attached on CFRP Sheets COMPARISON OF THE SHEAR STRENGTHS OF THE T-BEAMS TESTED IN SHEAR ACI 440 VERSUS EXPERIMENTAL SHEAR CAPACITIES SUMMARY AND CONCLUSION SUMMARY CONCLUSIONS Flexure Tests Shear Tests APPENDIX A REFERENCES ix

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11 LIST OF FIGURES FIGURE 1-1 DAMAGED BEAM IN THE ALA MOANA PARKING GARAGE PRIOR TO 1997 REPAIR... 2 FIGURE 1-2 ELEVATION OF REPAIRED T-BEAM SHOWING THE TOP FLANGE AND JOISTS... 3 FIGURE 3-1 CROSS SECTION OF T-BEAM FOR CARBODUR STRIP INSTALLATION FIGURE 3-2 SURFACE PREPARATION PRIOR TO CFRP APPLICATION FIGURE 3-3 SIKA CARBODUR STRIPS BEING PREPARED FOR INSTALLATION FIGURE 3-4 APPLICATION OF CFRP STRIPS FIGURE 3-5 WET LAY-UP ANCHORAGE WRAP AT END OF CFRP STRIPS FIGURE 3-6 SIKA WET LAY-UP WRAPS AT CONCRETE SPALLS FIGURE 3-7 REPAIRED BEAM IN SERVICE FIGURE 4-1 SAW CUTTING COLUMN CAPITAL TO REMOVE PRECAST PRESTRESSED BEAM FIGURE 4-2 CABLE SUPPORT DURING BEAM REMOVAL FIGURE 4-3 INJECTION PORT PLACEMENT FIGURE 4-4 EPOXY INJECTION FIGURE 4-5 PRIMING THE REPAIR CONTACT SURFACE FIGURE 4-6 FORMING THE REPAIR AREA FIGURE 4-7 POURING EPOXY MORTAR PATCH MATERIAL FIGURE 4-8 COMPLETED SPALL REPAIR FIGURE 4-9 TYPICAL T-BEAM CROSS-SECTION FIGURE 4-10 T-BEAM 1 FLANGE LAYOUT FIGURE 4-11 T-BEAM 1 FLANGE REINFORCEMENT LAYOUT FIGURE 4-12 PLYWOOD BLOCK-OUTS FOR CFRP SHEAR STIRRUPS FIGURE 4-13 T-BEAM 1 TOP FLANGE CONCRETE PLACEMENT FIGURE 5-1 SCHEMATIC LAYOUT OF TEST SETUP FIGURE 5-2 DETAIL OF FINAL TEST FRAME DESIGN FIGURE 5-3 TEST FRAME DETAILS FIGURE 5-4 TEST FRAME UNDER CONSTRUCTION (SHORT COLUMNS) FIGURE 5-5 COMPLETED TEST FRAME WITH T-BEAM 1 READY FOR LOADING FIGURE 5-6 SHEAR RETROFIT LAYOUT FOR T-BEAM FIGURE 5-7 SLOTTED HOLES IN TOP SLAB FOR CFRP SHEAR STIRRUPS FIGURE 5-8 CONCRETE SURFACE PREPARATION USING NEEDLE GUN FIGURE 5-9 ROUGHENED WEB FOR 3 WIDE STIRRUPS xi

12 FIGURE 5-10 CFRP STIRRUPS BEING SATURATED WITH SIKADUR HEX FIGURE 5-11 SIKA 30 HI MOD GEL EPOXY USED TO PREPARE SURFACE FOR CFRP FIGURE WIDE DOUBLE LAYER CFRP STIRRUPS WRAPPED THROUGH SLOTTED HOLES FIGURE 5-13 CFRP STIRRUPS IN PLACE, BOTTOM TRIMMED AFTER CURING FIGURE 5-14 INSTALLATION OF STEEL TUBE ANCHORAGE FOR 3 WIDE CFRP STIRRUPS FIGURE 5-15 COMPLETE INSTALLATION OF ANCHORAGE FOR 3 WIDE CFRP STIRRUPS FIGURE 5-16 ROUGHENED WEB AND HI MOD GEL APPLICATION FOR 12 WIDE SHEETS FIGURE 5-17 CFRP SHEETS SATURATED WITH SIKADUR HEX FIGURE 5-18 INSTALLATION OF CFRP SHEETS AS SHEAR REINFORCEMENT FIGURE 5-19 SIKA 30 HI MOD GEL EPOXY BED AT RE-ENTRANT CORNER OF CFRP SHEETS FIGURE 5-20 TUBE ANCHORAGE SET IN EPOXY BED AT RE-ENTRANT CORNER OF CFRP SHEETS 52 FIGURE 5-21 TELESCOPE SPLICE IN STEEL TUBE ANCHORAGE FIGURE 5-22 COMPLETE INSTALLATION OF MECHANICAL ANCHORAGE FOR 12 CFRP SHEETS 53 FIGURE 5-23 T-BEAM 1 LAYOUT AND INSTRUMENTATION FIGURE 5-24 T-BEAM 1 IN THE LOAD FRAME READY FOR TESTING FIGURE 5-25 T-BEAM 1 READY FOR TESTING CENTER VIEW FIGURE 5-26 LAYOUT AND INSTRUMENTATION OF T-BEAM 1L FIGURE 5-27 T-BEAM 1L READY FOR TESTING FIGURE 5-28 FLEXURAL STRENGTHENING OF T-BEAM 1R USING PRE-CURED CARBODUR STRIPS FIGURE 5-29 T-BEAM 1R LAYOUT AND INSTRUMENTATION FIGURE 5-30 T-BEAM 1R READY FOR TESTING FIGURE 5-31 STEEL REACTION BRACKETS AT BOTH ENDS OF T-BEAM FIGURE 5-32 T-BEAM 2 TOP FLANGE REINFORCEMENT AND STRAIN GAGE LAYOUT FIGURE 5-33 T-BEAM 2 SLAB LAYOUT PRIOR TO CONCRETE POUR FIGURE 5-34 T-BEAM 2 BEING PREPARED FOR SHEAR RETROFIT FIGURE 5-35 BEAM SHEAR RETROFIT LAYOUT FOR T-BEAM FIGURE 5-36 SIKA 30 HI MOD GEL EPOXY BEING APPLIED TO THE CFRP STIRRUPS FOR EVEN SEATING OF THE ANCHORAGE ANGLES FIGURE 5-37 CFRP ANGLES INSTALLED AS ANCHORAGE FOR CFRP SHEAR REINFORCEMENT.. 71 FIGURE 5-38 ELECTRICAL RESISTANCE STRAIN GAGES INSTALLED ON THE CARBODUR STRIPS.. 72 FIGURE 5-39 T-BEAM 2 LAYOUT AND INSTRUMENTATION FIGURE 5-40 T-BEAM 2 TEST SETUP FIGURE 5-41 T-BEAM 2L BEING PREPARED FOR SHEAR TESTING xii

13 FIGURE 5-42 T-BEAM 2L LAYOUT AND INSTRUMENTATION FIGURE 5-43 T-BEAM 2L IN TEST SETUP FIGURE 5-44 WEDGE ANCHORS INSTALLED ON PRESTRESSED STRANDS AT END OF T-BEAM 2R FIGURE 5-45 T-BEAM 2R1 LAYOUT AND INSTRUMENTATION FIGURE 5-46 T-BEAM 2R1 IN TEST SETUP FIGURE 5-47 T-BEAM 2R2 LAYOUT AND INSTRUMENTATION FIGURE 5-48 T-BEAM 2R2 IN TEST FRAME FIGURE 6-1 CONCRETE CORE SAMPLE TAKEN FROM A T-BEAM WEB FIGURE 6-2 DYNA Z16 PULL-OFF TESTER FIGURE 6-3 TYPICAL LOCATIONS OF CFRP PULL-OFF TESTS FIGURE 7-1 CROSS-SECTION OF T-BEAM FIGURE 7-2 STRESS AND STRAIN DISTRIBUTION OF A REINFORCED CONCRETE BEAM WITH CFRP UNDER FLEXURE AT ULTIMATE LIMIT STATE CONDITION FIGURE 7-3 STRESS AND STRAIN DISTRIBUTION OF A PRESTRESSED CONCRETE BEAM UNDER FLEXURE AT THE INITIAL CONDITION (PRIOR TO APPLICATION OF CFRP) FIGURE 7-4 STRESS AND STRAIN DISTRIBUTION OF A PRESTRESSED CONCRETE BEAM WITH CFRP UNDER FLEXURE AT ULTIMATE LIMIT STATE CONDITION FIGURE 7-5 T-BEAM 2 TRIBUTARY WIDTH AT ALA MOANA PARKING GARAGE FIGURE 7-6 SECTION PROPERTIES OF THE PRECAST PRESTRESSED BEAM SECTION FIGURE 7-7 SECTION PROPERTIES OF THE COMPOSITE SECTION FIGURE 7-8 STRESS AND STRAIN DISTRIBUTIONS FOR T-BEAM 2 AT THE INITIAL CONDITION FIGURE 7-9 STRESS AND STRAIN DISTRIBUTIONS FOR T-BEAM 2 AT ULTIMATE STATE CONDITIONS FIGURE 7-10 T-BEAM 1 LAYOUT FOR SHEAR STRENGTH CALCULATION FIGURE 7-11 SHEAR CAPACITY AND SHEAR DIAGRAM OF T-BEAMS 1 AND FIGURE 7-12 T-BEAM 2R1 LAYOUT AND SHEAR AND MOMENT DIAGRAMS FIGURE 7-13 T-BEAM 1L LAYOUT AND SHEAR AND MOMENT DIAGRAMS FIGURE 7-14 CROSS SECTION OF T-BEAM 1L SHOWING CFRP STIRRUP LAYOUT FIGURE 7-15 T-BEAM 2L LAYOUT AND SHEAR AND MOMENT DIAGRAMS FIGURE 7-16 CROSS SECTION OF T-BEAM 2L FIGURE 7-17 T-BEAM 1R LAYOUT AND SHEAR AND MOMENT DIAGRAMS FIGURE 7-18 CROSS SECTION OF T-BEAM 1R SHOWING CFRP SHEET LAYOUT FIGURE 7-19 T-BEAM 2R2 LAYOUT AND SHEAR AND MOMENT DIAGRAMS xiii

14 FIGURE 7-20 CROSS SECTION OF T-BEAM 2R2 SHOWING CFRP SHEETS FIGURE 8-1 T-BEAM 1 READY FOR FLEXURAL TESTING FIGURE 8-2 MID-SPAN MOMENT DISPLACEMENT RELATIONSHIP FOR T-BEAM FIGURE 8-3 T-BEAM 1 MID-SPAN CONDITION CORRESPONDING TO SIX DUCTILITY LEVELS FIGURE 8-4 T-BEAM 1 SLAB REINFORCEMENT STRAIN GAGE READINGS FIGURE 8-5 STRAIN READINGS FOR STRAIN GAGES 4-6 (T-BEAM 1) FIGURE 8-6 STRAIN READINGS FOR STRAIN GAGE 1-4 (T-BEAM 1) FIGURE 8-7 REPRESENTATION OF THE VERTICAL DEFLECTION OF T-BEAM 1 FROM LVDT READINGS FIGURE 8-8 STRAIN READINGS FROM GAGES ATTACHED TO CFRP STIRRUPS AND SHEETS (T- BEAM 1) FIGURE 8-9 T-BEAM 2 READY FOR FLEXURAL TESTING FIGURE 8-10 MID-SPAN MOMENT-DISPLACEMENT RELATIONSHIP FOR T-BEAM FIGURE 8-11 T-BEAM 2 CONDITION CORRESPONDING TO SIX DUCTILITY LEVELS FIGURE 8-12 FLEXURE-SHEAR CRACK FORMED OUTSIDE OF THE LEFT LOAD POINT (T-BEAM 2) FIGURE 8-13 DELAMINATION OF CARBODUR STRIPS INITIATING AT THE FLEXURE-SHEAR CRACK FIGURE 8-14 CARBODUR STRIPS DELAMINATED FROM BEAM AND PULLING OUT OF CFRP WRAP ANCHOR FIGURE 8-15 STRAIN READINGS FOR SLAB REINFORCEMENT STRAIN GAGE (T-BEAM 2) FIGURE 8-16 STRAIN READINGS FOR STRAIN GAGES 4-6 (T-BEAM 2) FIGURE 8-17 STRAIN READINGS FOR STRAIN GAGES 1-4 (T-BEAM 2) FIGURE 8-18 REPRESENTATION OF THE VERTICAL DEFLECTION OF T-BEAM 2 FROM LVDT READINGS FIGURE 8-19 T-BEAM 2 BEAM SOFFIT SHOWING LOCATION OF STRAIN GAGES FIGURE 8-20 STRAIN READINGS OF STRAIN GAGES FIGURE 8-21 STRAIN READINGS OF STRAIN GAGES FIGURE 8-22 STRAIN READINGS OF STRAIN GAGES FIGURE 8-23 STRAIN READINGS OF STRAIN GAGES FIGURE 8-24 STRAIN READINGS OF STRAIN GAGES FIGURE 8-25 STRAIN READINGS OF STRAIN GAGES FIGURE 8-26 STRAIN READINGS OF STRAIN GAGES xiv

15 FIGURE 8-27 WEB-SHEAR CRACKS FORMING AWAY FROM THE MID-SPAN OF BEAM AS CONFIRMED BY CARBODUR STRAIN READINGS FIGURE 8-28 STRAIN READINGS FOR GAGES ON THE FIRST CARBODUR STRIP FIGURE 8-29 STRAIN READINGS FOR GAGES ON THE SECOND CARBODUR STRIP FIGURE 8-30 STRAIN READINGS FOR GAGES ON THE THIRD CARBODUR STRIP FIGURE 8-31 STRAIN READINGS ON THE FIRST CARBODUR STRIP CORRESPONDING TO THE SIX DUCTILITY LEVELS FIGURE 8-32 STRAIN READINGS ON THE SECOND CARBODUR STRIP CORRESPONDING TO THE SIX DUCTILITY LEVELS FIGURE 8-33 STRAIN READINGS ON THE THIRD CARBODUR STRIP CORRESPONDING TO THE SIX DUCTILITY LEVELS FIGURE 8-34 PLOT OF NORMALIZED ACI 440 PREDICTION AND EXPERIMENTAL MOMENT CAPACITIES FIGURE 8-35 TEST SETUP AND SHEAR SPAN OF T-BEAM 2R FIGURE 8-36 SHEAR-DISPLACEMENT RELATIONSHIP FOR T-BEAM 2R FIGURE 8-37 T-BEAM 2R1 CONDITION AT CRITICAL STAGES DURING THE TEST FIGURE 8-38 FAILURE OF STEEL SHEAR REINFORCEMENT AT FAILURE SHEAR CRACK FIGURE 8-39 SHEAR REINFORCEMENT ANCHORAGE FAILURE AT BASE OF WEB FIGURE 8-40 TEST SETUP OF T-BEAM 1L (CFRP STIRRUPS) FIGURE 8-41 SHEAR-DISPLACEMENT RELATIONSHIP FOR T-BEAM 1L FIGURE 8-42 T-BEAM 1L CONDITION AT VARIOUS STAGES IN THE SHEAR-DISPLACEMENT RESPONSE FIGURE 8-43 FLEXURAL FAILURE OF T-BEAM 1L FIGURE 8-44 DELAMINATION OF CFRP STIRRUPS FROM T-BEAM 1L FIGURE 8-45 STRAIN READINGS FROM STRAIN GAGE FIGURE 8-46 STRAIN READINGS FROM STRAIN GAGE FIGURE 8-47 STRAIN READINGS FROM STRAIN GAGE FIGURE 8-48 STRAIN READINGS FROM STRAIN GAGE FIGURE 8-49 STRAIN READINGS FROM STRAIN GAGE FIGURE 8-50 STRAIN READINGS FROM STRAIN GAGE FIGURE 8-51 STRAIN READINGS ON STRAIN GAGE FIGURE 8-52 STRAIN READINGS FROM STRAIN GAGES FROM THE FIRST TEST OF T-BEAM 1L xv

16 FIGURE 8-53 STRAIN READINGS FROM STRAIN GAGES FROM THE SECOND TEST OF T-BEAM 1L FIGURE 8-54 T-BEAM 2L TEST SETUP FIGURE 8-55 INITIAL CONDITION OF T-BEAM 2L BEFORE TESTING FIGURE 8-56 SHEAR DISPLACEMENT CURVE FOR T-BEAM 2L FIGURE 8-57 T-BEAM 2L CONDITION AT VARIOUS STAGES DURING TESTING FIGURE 8-58 SHEAR FAILURE AND TENDON END ANCHORAGE SLIP FIGURE 8-59 RUPTURE OF GFRP ANGLE AT THRU-BOLTS FIGURE 8-60 AREAS OF CFRP DELAMINATION ON T-BEAM 2L FIGURE 8-61 BUCKLING OF CFRP STIRRUPS AT FAILURE FIGURE 8-62 STRAIN READINGS FROM STRAIN GAGES 1 AND FIGURE 8-63 STRAIN READINGS FROM STRAIN GAGES 2 AND FIGURE 8-64 STRAIN READINGS FROM STRAIN GAGES 3 AND FIGURE 8-65 STRAIN READINGS FROM STRAIN GAGES 4 AND FIGURE 8-66 STRAIN READINGS FROM STRAIN GAGES 5 AND FIGURE 8-67 STRAIN READINGS FROM STRAIN GAGES 6 AND FIGURE 8-68 T-BEAM 1R TEST SETUP FIGURE 8-69 SHEAR-DISPLACEMENT CURVE FOR T-BEAM 1R FIGURE 8-70 T-BEAM 1R CONDITION AT VARIOUS STAGES DURING SHEAR TESTING FIGURE 8-71 T-BEAM 1R CONDITION AT CFRP DELAMINATION FIGURE 8-72 T-BEAM 1R CONDITION AT FAILURE FIGURE 8-73 STRAIN READINGS FROM STRAIN GAGES FIGURE 8-74 STRAIN READINGS FROM STRAIN GAGES FIGURE 8-75 STRAIN READINGS FROM STRAIN GAGES FIGURE 8-76 STRAIN READINGS FROM STRAIN GAGES FIGURE 8-77 STRAIN READINGS ON THE CARBODUR STRIPS FROM STRAIN GAGES FIGURE 8-78 T-BEAM 2R2 TEST SETUP FIGURE 8-79 SHEAR-DISPLACEMENT CURVE FOR T-BEAM 2R FIGURE 8-80 T-BEAM 2R2 CONDITION AT SEVEN STAGES FIGURE 8-81 DELAMINATION OF THE CFRP SHEET FIGURE 8-82 RUPTURE OF GFRP ANGLES AT THRU-BOLTS FIGURE 8-83 STRAIN READINGS FROM STRAIN GAGES FIGURE 8-84 STRAIN READINGS FROM STRAIN GAGES FIGURE 8-85 STRAIN READINGS FROM STRAIN GAGES xvi

17 FIGURE 8-86 SHEAR-DISPLACEMENT CURVES FOR ALL SHEAR TESTS FIGURE 8-87 NORMALIZED ACI 440 PREDICTIONS VERSUS EXPERIMENTAL SHEAR CAPACITIES xvii

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19 LIST OF TABLES TABLE 6.1 CONCRETE COMPRESSIVE STRENGTH AND MODULUS OF ELASTICITY TABLE 6.2 MODULUS OF RUPTURE TEST TABLE 6.3 STEEL REINFORCEMENT TENSILE STRENGTHS TABLE 6.4 CFRP MATERIAL PROPERTIES TABLE 6.5 PULL-OFF TEST RESULTS xix

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21 CHAPTER 1 1 INTRODUCTION 1.1 Background Carbon Fiber Reinorced Polymers (CFRP) has become a valuable material or repairing and retroitting damaged or deicient structures. Numerous research studies have shown that CFRP sheets or strips bonded to the concrete surace can substantially increase lexural, shear and compressive strength o concrete members. The literature review in Chapter 2 summarizes a number o research studies on the use o CFRP or lexural and shear strengthening o concrete beams. During a routine structural inspection o the Ala Moana Parking Garage in the late 1990 s, a number o large lexural cracks were noted on the bottom o a precast prestressed concrete beam along with severe spalling damage to the beam ledges (Figure 1-1). The beam spans 30 rom center to center o supporting columns. The beam is a precast prestressed T-Beam supporting joists and a slab acting as the top lange o the beam (Figure 1-2). The damaged beam was repaired in 1997 using CFRP materials. Chapter 3 provides a description o the original beam repair. In 2000, the portion o the Ala Moana Parking Garage around this beam was demolished to allow or a new multilevel parking structure. This beam, along with two identical undamaged beams, was salvaged in June 2000 or testing in the University o Hawaii at Manoa Structural Testing Laboratory (UHM-STL). During demolition, beam recovery, and transportation, minor damage was caused to the beam webs. This damage 1

22 was repaired and the top slab reinstated at UHM-STL prior to testing. Chapter 4 describes the beam recovery and repair operations. The research program reported here involved lexural and shear testing o two o the beams salvaged rom the Ala Moana Parking Garage. One un-strengthened beam was used as the control specimen. This beam is reerred to as T-Beam 1. The second beam is the strengthened beam reerred to as T-Beam 2. The third beam will be used in a uture research study on CFRP shear retroit o cracked beams. Considerable instrumentation was installed to monitor the beams during testing. The layout o this instrumentation or each test, and the precise test setup or each loading condition, are described in detail in Chapter 5. Material properties or the beams and CFRP materials are presented in Chapter 6. Predicted strengths o the control and strengthened beams are presented in Chapter 7. The results o the lexural and shear testing are presented in Chapter 8. Finally Chapter 9 presents a summary and conclusions or this research project. Figure 1-1 Damaged beam in the Ala Moana parking garage prior to 1997 repair 2

23 30' BEAM ELEVATION Figure 1-2 Elevation o repaired T-beam showing the top lange and joists 1.2 Objective The primary objective o this research program was to evaluate the use o CFRP material as a retroit or damaged or deicient prestressed concrete beams. The repaired beam, T-Beam 2, was the irst application o CFRP material or strengthening o a concrete structure in the State o Hawaii. The Hawaii Department o Transportation (HDOT) unded this research program in order to evaluate the use o CFRP or retroit o deicient bridge structures across the state. Because o similarities between the Ala Moana beams and typical prestressed AASHTO bridge girders, the results o this study should provide valuable insight into the likely perormance o bridge girders retroitted with CFRP materials. Very ew tests have been conducted on ield applied CFRP ater exposure to service conditions. The precast prestressed beam tested in this study was retroitted or lexure with CFRP applied under ield conditions. It was then in service or three years and 3

24 spent an additional eighteen months exposed to exterior environmental conditions prior to testing. Initial theoretical strength calculations or T-Beam 1 and T-Beam 2 indicated that the addition o CFRP to increase the lexural capacity o T-Beam 2 resulted in a shear critical ailure mode i the beam were tested under the proposed laboratory conditions. To reduce the potential or a shear ailure and ensure the desired lexural ailure o T-Beam 2, the shear spans o both beams were increased or the laboratory loading and CFRP shear retroit was applied prior to lexural testing. Two shear retroit techniques were employed on each beam, namely external CFRP shear stirrups on the let hal o the beam and CFRP sheets on the right hal o the beam. Subsequent to lexural testing, each o the beam shear spans was tested in shear to evaluate the perormance o the CFRP shear retroit Use o CFRP or lexural strengthening Prior laboratory research studies have shown that external application o CFRP in the tension zone o a lexural member can dramatically increase the lexural capacity o the member (Chapter 2 Literature Review). The externally applied CFRP adds to the tensile capacity o the existing internal non-prestressed or prestressed tension reinorcement, thereby increasing the lexural capacity. The high tensile strength o CFRP materials provides signiicantly increased capacity or relatively small amounts o added material. The relatively high modulus o elasticity o CFRP also enhances the post-cracking lexural stiness o the member. Care must be taken not to increase the lexural tension reinorcement to the point where compression ailure o the concrete governs the lexural strength o the beam. 4

25 T-Beam 2 was retroitted with three pre-cured carbodur strips epoxied to the bottom o the beam. The ends o these tension strips were restrained at the ends o the beam by means o uni-directional CFRP abric wraps. Chapter 5 provides a detailed description o the lexural strengthening o T-Beam Use o CFRP or shear strengthening Shear strengthening using CFRP has proved eective in a number o prior experimental studies (Chapter 2 Literature Review). In many o these previous studies, the CFRP shear reinorcement was bonded to the beam web without any anchorage at the top and bottom o the web. Failure o the CFRP shear retroit was usually the result o de-bonding o the CFRP rom the concrete surace. The relatively low tensile strength o the surace concrete controls the pull-o strength and thereore precipitates the debonding ailure. Few studies have considered mechanical anchorage o the CFRP shear reinorcement at top and bottom o the beam. Such anchorage may improve the perormance o the shear reinorcement and so was used in the tests reported here. Two types o shear strengthening were installed on T-Beam 1 and T-Beam 2. The let hal o each beam was retroitted with external CFRP stirrups placed at 12 on center, between the internal 3/8 diameter steel stirrups. Each stirrup consisted o a 3 wide double layer o CFRP abric extending rom the bottom o the beam, up the side o the web, through a slot in the top slab, continuously over the top o the web and down the other side o the beam. In order to prevent premature delamination o the CFRP stirrups at the re-entrant corner at the bottom o the web, mechanical anchorage was provided in the orm o steel tubes or GFRP angles with steel bolts through the beam web. 5

26 The right hal o each beam was retroitted in shear with 12 wide single layer sheets o CFRP epoxied to both sides o the beam web. The shear sheets were installed at 18 on center so as to leave a 6 gap between the sheets to allow moisture and vapor to escape rom the beam concrete without aecting the bond between CFRP and concrete. Each sheet extended rom the bottom o the web to the soit o the top slab. In order to prevent premature delamination o the CFRP sheets at the re-entrant corners at the bottom o the slab and at the bottom o the web, mechanical anchorage similar to that used or the shear stirrups was installed at both locations. A detailed description o the shear retroit o each beam is provided in Chapter Summary The objectives o this research program are summarized below. 1. To determine the increase in lexural strength o the precast T-Beam as a result o the ield applied CFRP lexural reinorcement. The perormance o the strengthened T-Beam 2 will be compared with the control specimen, T-Beam 1, and with the results o previous experimental studies. 2. To evaluate the use o CFRP in the orm o stirrups and sheets or shear retroit o prestressed concrete beams. The eect o mechanical anchorage provided at the re-entrant corners o the CFRP shear reinorcement will also be evaluated. 3. Compare shear test results with previous experimental studies and with the strength predicted by the recently published ACI 440R-02 committee report on the use o externally bonded FRP. 6

27 4. To determine the ailure mechanism o the CFRP lexural and shear retroit systems used on the T-Beams. 5. To recommend appropriate CFRP lexural and shear retroit methods or prestressed concrete bridge girder beams. 7

28 8

29 CHAPTER 2 2 LITERATURE REVIEW 2.1 Introduction Since the late 1980 s, research into the use o Fiber Reinorced Polymers (FRP) or external repair and retroit o concrete lexural members has progressed rapidly. Researchers have considered various types o FRP, dierent application techniques and various loading conditions. The majority o this research has been perormed in the laboratory on small-scale reinorced concrete specimens. Limited research is available on the perormance o ield applied FRP and on the application o FRP materials to prestressed concrete beams. This chapter presents some o the recent research using Carbon Fiber Reinorced Polymer (CFRP) or lexural and shear strengthening o reinorced concrete members. 2.2 CFRP Flexural Strengthening Numerous research programs have studied the perormance o CFRP as lexural strengthening or reinorced concrete beams. These studies considered dierent methods o wrapping the CFRP onto the concrete member. Some also investigated the eect o rate o loading on the perormance o the strengthened concrete member. Research has also been perormed on the use o CFRP as coninement or partially corroded concrete members. Spadea et al. 1 studied two methods o adding CFRP or lexural strengthening o reinorced concrete members. In the irst method, two layers o CFRP were bonded to the tension ace o the specimen and wrapped up the vertical aces o the beam to one 9

30 third o the beam height. In the second method, our layers o CFRP were bonded in the same manner as beore with the addition o end anchorage wraps near the supports that extended to the top o the vertical aces o the beam. Both CFRP strengthening methods produced higher lexural strengths than the control beam, reaching the calculated theoretical strengths. However the lexural ductility o the beams was reduced compared with the un-strengthened control specimen. The irst application method exhibited a sudden ailure mode due to debonding o the laminate. This method showed a loss in ductility o between 45% and 65%. The second method showed a sudden ailure mode due to shear at the supports. Although the end anchorages were eective at restraining debonding o the lexural FRP, shear cracks near the supports opened up and the internal shear stirrups ruptured, precipitating a brittle shear ailure. This second method showed a loss in ductility o between 25% and 40%. Spadea et al. 2 also tested a number o beams retroitted with only one sheet o CFRP laminate bonded to the tension zone o the specimens. Testing included a control specimen, a strengthened specimen without end anchorage, and a strengthened specimen with anchorage at the ends o the CFRP near the supports. The retroitted specimens were less ductile than the control specimen. Their ductility was reduced by 30-65% compared with the control beam. Results showed that the strengthened specimens without end anchorage ailed suddenly with the debonding o the laminate. Specimens with the anchored laminate perormed very well with increases in lexural capacity o 30% to 70% and did not exhibit premature debonding o the CFRP. The specimens with anchored CFRP were more ductile than those without anchorage. 10

31 GangaRao and Vijay 3 conducted a study o 24 beams that compared dierent types o FRP lexural retroit. They divided the beams into six groups. The irst group included the control specimens. The second group o beams had steel plates bonded to the tension ace or lexural strengthening. The rest o the groups were retroitted with CFRP wraps with dierent anchorage systems. Some o the beams were subjected to bending to induce lexural cracking prior to strengthening with CFRP. The third and ourth groups had CFRP wraps extending 90% up the vertical aces and along the ull length o the beam. The ith and sixth groups had CFRP wrapped up the ull height o the vertical aces and along the ull length o the beam. All o the repaired specimens showed improvements in lexural perormance. The beams retroitted with CFRP perormed better than the steel-plate reinorced beams. Some o the specimens ailed in shear so the theoretical bending moments were not reached. The perormance o repaired damaged beams and repaired undamaged beams was similar. Fanning and Kelly 4 tested ten rectangular beams that were 9-10 in length. Two beams were used as control specimens. Eight o the beam specimens were retroitted with CFRP composites o dierent lengths in the tension zone o the beam. For the beam retroitted with CFRP over the ull span length, the ends o the CFRP were anchored at the supports. No anchorage was provided or shorter CFRP retroits. Results showed an increase o 40% in overall stiness and a minimum o 50% increase in ultimate load or the beams retroitted with CFRP over the ull span length. Specimens with shorter lengths o CFRP showed no signiicant increase in strength. Beams without anchorage ailed due to CFRP plate peel-o. 11

32 Shahawy et al. 5 experimented on ull-scale T-girders that were preloaded at dierent stress levels and then repaired with two dierent CFRP wrapping techniques. Both wrapping techniques had no additional anchorage. The irst wrapping technique consisted o two layers o CFRP on the tension ace extending our to six inches up the sides o the beam web. The second wrapping technique consisted o two layers o CFRP on the tension ace with wraps extending up the ull side o the beam web. The preloading o the beams had no eect on the perormance o the CFRP. The partially wrapped specimens had less strength than the ully wrapped specimens. In addition, ailure o the partially wrapped specimens resulted rom sudden delamination o the CFRP. White et al. 6 conducted a study o reinorced concrete beams subjected to a high rate o loading. A total o nine beams were tested with one being the control specimen. Eight o the specimens were retroitted with two types o CFRP. The irst was an S-type consisting o pultruded CFRP laminates. The second was an R-type consisting o prepreg sheets. No anchorage was provided or the CFRP on any o the specimens. A number o loading cycles were used. These included one slow stroke to ailure, one ast stroke to ailure, one stroke to 150 kn at a slow rate ollowed by a ast stroke rom 150 kn to ailure, and twelve ast loading cycles to 120 kn ollowed by ast loading to ailure. Specimens subjected to the high rate o loading had an increase o 5% in lexural capacity, stiness, and energy absorption over slowly loaded beams. Masoud et al. 7 investigated the retroit o corroded reinorced beams using CFRP. The beams were cracked under typical service load conditions. An electrical current was passed through the longitudinal reinorcements and wet-dry cycling applied to the beam 12

33 to accelerate corrosion o the reinorcing bars. Two techniques were used to repair the beams with CFRP. The irst involved ully wrapping the tension ace and both sides o the beam with CFRP. A horizontal strip o CFRP was placed at the top edge o the wrap on both sides o the beam web or anchorage. The second scheme was the same as the irst with the addition o one longitudinal CFRP sheet added to the tension ace. The objective o this repair was to conine the concrete cover as opposed to actual lexural strengthening. Results showed that an increase in strength was observed or all o the strengthened specimens under monotonic loading. The test also showed that strengthened specimens had better atigue lie over un-strengthened specimens. Bonacci and Maalej 8 also investigated the repair o corroded reinorced concrete beams with CFRP beore and ater sustained loads were applied. The beams were divided into groups where one group had more corrosion than the other. The beams were retroitted with CFRP on the tension ace o the beam. Some had no anchorage while others had anchorages provided at the ends and at mid-span o the beam. Results showed that the CFRP repair increased the beam strength and decreased delection. Delamination o the CFRP started in the mid-span region and continued to the supports. The CFRP lexural retroit applied to the T-Beams in this research program has similarities to many o the examples described in the literature. Pre-cured CFRP strips were bonded to the tension ace o the beam over its ull length. Hand lay-up CFRP sheets wrapped up the sides o the web were used to provide anchorage at the ends o the tension strips. These beams were thereore expected to perorm similar to those in the literature review. In contrast to the specimens presented in the literature review, the T- 13

34 Beams in this program are precast prestressed concrete beams as opposed to the reinorced beams used in most prior research. Because o the predicted increase in lexural strength due to the addition o CFRP lexural strengthening, T-Beam 2 might experience a shear ailure prior to lexural ailure. Since the primary intent o this project was to determine the lexural perormance o the ield-applied CFRP, it was important to prevent a premature shear ailure. Two types o CFRP shear retroit were investigated on T-Beam 1 so as to validate their eectiveness beore applying them to T-Beam 2. The two shear retroit systems consisted o CFRP stirrups and sheets as described later in this report. The ollowing section provides a review o literature on experimental programs investigating FRP shear retroit o concrete beams. 2.3 CFRP Shear Strengthening A number o laboratory experimental research studies have been perormed on shear strengthening o reinorced concrete beams using CFRP materials. These studies considered dierent wrapping conigurations o CFRP on the concrete surace. Some o the conigurations used CFRP ully wrapped on all our aces o a rectangular beam, CFRP on the sides and bottom o the beam, and CFRP on the beam sides only. Studies also considered CFRP bonded at dierent angles on the sides o the beam. Some o these studies investigated dierent anchorage systems to provide better attachment between the CFRP and the concrete. Sheikh et al. 9 investigated 5/6 th scale models o beams rom a building that was damaged by unexpected loads during the irst two years o service. The beams were cast with a haunch to simulate being ramed into the walls and to orce shear ailure to occur 14

35 within the shallow section o the beam. The repaired beam was completely wrapped on all sides o the shallow section to prevent shear ailure. The beams were subjected to a single point load at the edge o the haunch section. The control beam ailed in shear at a load o 1,700 kn while the retroitted beam ailed in lexure at a load o 2,528 kn. The ailure o the beam changed rom a brittle shear ailure to a more ductile lexural ailure. The mid-span delection o the repaired specimen was 10 times greater than that o the control specimen. Czaderski 10 experimented with specimens retroitted with preabricated L-shaped CFRP stirrups as shear reinorcement. A total o ive specimens were tested o which two were control specimens. One control specimen was a beam that had internal steel shear reinorcement while the other did not have internal steel shear reinorcement. The remaining three specimens were retroitted with the L-shaped stirrups spaced equally along the length o the shear span and overlapped on the bottom o the beam. The specimens were subjected to increasing static loading until ailure. The test results showed an increase o the shear strength with the beams retroitted with the L-shaped stirrups. The retroitted specimens also exhibited greater ductility than the control specimens. The bottom overlapped ends o the L-shaped stirrups tended to separate rom one another at ailure. Chaallal et al. 11 tested reinorced concrete beams retroitted with CFRP stirrups bonded to the sides o the beam at various angles. Three groups o beams were tested. The irst group had internal steel shear reinorcement but wasn t retroitted with CFRP stirrups. The second group did not have enough internal steel shear reinorcement and wasn t retroitted with CFRP stirrups. The third group was the same as the second group 15

36 but it was retroitted with CFRP stirrups at 90 degrees to the horizontal and 45 degrees to the horizontal. The CFRP retroit was applied to the two vertical aces o the beams. The beams were subjected to our-point bending. Results showed an increase in strength o about 70 percent and increased stiness or the repaired beams. The 45-degree CFRP stirrups perormed better than the 90-degree CFRP stirrups. Failure occurred due to delamination o the CFRP stirrups rom the surace o the concrete. For more extreme loading, U-shaped retroit stirrups were suggested. Triantaillou 12 tested eleven reinorced concrete beams strengthened with CFRP stirrups at various angles on the vertical sides o the beam. Two beams were used as control specimens. Three o the beams were itted with CFRP stirrups oriented at 45 degrees to the horizontal. The rest o the beams were itted with CFRP stirrups oriented at 90 degrees to the horizontal. Internal steel shear reinorcement was not included in order to orce shear ailure in each specimen. The beams were loaded in our-point bending. Results showed an increased in shear strength between 65 and 95 percent over the control specimens. Failure was initiated by shear cracking ollowed by peeling o the CFRP shear stirrups. Results also showed that the 45 degrees CFRP shear reinorcement was more eective than the vertical CFRP shear reinorcement due to the ibers being more nearly perpendicular to the shear cracks. Al-Sulaimani et al. 13 conducted research on sixteen beams with various conigurations o CFRP shear reinorcement. The beams were divided into our groups. The irst group was used as the control. All o the retroitted beams were preloaded until shear cracks ormed. The load was then released and the beams were repaired. The irst retroit method consisted o bonding CFRP stirrups to the sides o the beam in the shear 16

37 span area. The second retroit method consisted o CFRP sheets bonded to the whole sides o the beam. The inal retroit method consisted o CFRP sheets that continuously wrapped on the bottom side o the beam along the ull span length. The specimens were all tested in our-point loading. Results showed that the stirrups and sheets bonded to the sides o the beams produced a similar increase in strength. They also had similar ailure modes where both delaminated at the bottom o the member. The CFRP sheets that wrapped at the bottom side o the beam prevented shear ailure and caused the specimens to ail in lexure. The continuity o the wrap repair reduced the stress concentrations that were present in the stirrups and sheets. All orms o shear repair also increased the beam stiness. Schuman and Karbhari 14 conducted research on hal-scale cantilever T-Beams retroitted or shear with wet lay-up CFRP. They investigated the eect and beneits o anchoring the CFRP shear stirrups to the side o the beam. Two types o CFRP retroit were considered. The irst consisted o U-Shaped CFRP stirrups bonded to the bottom and sides o the beam. The second consisted o L-Shaped CFRP stirrups that were placed in an oset coniguration so as not to overlap on the bottom o the beam. All shear stirrups were anchored at the top o the web using steel plates and expansion anchors embedded into the top slab. Five sets o specimens were tested with dierent anchorage conigurations. The irst specimen was the control. The second specimen was retroitted with the U-Shaped stirrups without anchorage. The third specimen was retroitted with Oset L-Shaped stirrups with 3/8 diameter anchor bolts extending 4 into the top slab. This anchor embedment did not extend past the internal steel stirrups. The ourth specimen was also retroitted with the Oset L-Shaped stirrups using 3/8 diameter 17

38 anchor bolts extending 6 into the top slab. The embedment o the anchors was now deep enough to pass the internal steel stirrups and slab reinorcement. The last specimen was also retroitted with the Oset L-Shaped stirrups but using ½ diameter anchor bolts extending 6 into the top slab. The test results showed that there is little or no beneit in using CFRP shear stirrups without anchorage. The third specimen only showed a slight increase in strength and ductility. The ourth and ith specimens showed considerable increase in strength, ductility, and stiness. The test also showed that there was a strong dependence on both the anchor size and embedment depth o the anchorage system. Many o the studies described above relate to the type o shear retroit used or the T- Beams in this research program. However, most o the studies ound in the literature were applied to reinorced concrete beams without internal steel shear reinorcement, while the T-Beams in this study are prestressed beams with internal steel shear reinorcement. Based on the literature review, two shear retroit systems were considered, consisting o CFRP stirrups and sheets. The CFRP stirrups were installed on both vertical sides o the T-Beam web and wrapped over the top o the web through slots in the top slab. The CFRP sheets were installed on the two vertical sides o the T-Beam web. The shear retroit was not extended around the soit o the beam so as not to introduce additional restraint to the ield-applied CFRP lexural retroit. The shear retroits were anchored at top and bottom o the web by means o steel tubes or GFRP angles with bolts passing through the web. More detail o the shear retroit systems is provided in Chapter 5. 18

39 2.4 Chapter Summary Numerous research projects have investigated lexural strengthening o reinorced concrete members using various CFRP retroit systems. All o the repaired specimens showed some increase in lexural capacity. Specimens that were damaged prior to strengthening behaved like specimens that were not damaged prior to strengthening. End anchorages helped prevent early debonding o the CFRP, thus increasing the lexural strength. Failure o the beam was generally associated with delamination o the CFRP. There have also been many research projects involving reinorced concrete members retroitted with dierent CFRP shear strengthening conigurations. Beams that were retroitted with CFRP on just two sides did not perorm as well as beams that had continuous CFRP on three sides or with a complete wrap. Specimens that were retroitted with CFRP at an angle perormed better than specimens that had CFRP attached vertically. The retroitted beams generally ailed upon delamination o the CFRP rom the concrete surace. However, the addition o eective anchorage or the ends o the CFRP increased the shear capacity and ductility o the concrete member. Failure now depends on the anchorage and not on delamination o the CFRP. 19

40 20

41 CHAPTER 3 3 ALA MOANA BEAM REPAIR In 1997, during a structural inspection o the parking garage at the Ala Moana Shopping Center, signiicant lexural cracking and ledge spalls were noted on one o the precast prestressed T-Beams supporting the elevated parking level. This beam was repaired using epoxy-modiied mortar to repair the spalls and CFRP materials to improve the lexural capacity. The repair was designed by Martin and Bravo Structural Engineers, Honolulu, Hawaii. Figure 3-1 shows a cross section o the beam strengthening using three pre-cured CFRP carbodur strips. These strips extended the ull length o the beam soit and anchored at the ends by 6 wide double ply wet lay-up CFRP wraps extending up both sides o the beam web. The repairs were perormed by Concrete Coring o Hawaii in the presence o the Martin and Bravo design engineer and a representative rom the CFRP supplier, Sika Products USA. A rotary grinder was used to remove paint and weak concrete paste beore installation o the CFRP material (Figure 3-2). This surace preparation is necessary to provide a suitable bond between the CFRP and the concrete. The result was a smooth surace similar to ICRI-CSP surace proile A slightly higher surace proile such as ICRI-CSP 3-4 is normally speciied or CFRP applications. Once the concrete suraces were prepared, three 4 wide pre-cured CFRP Sika carbodur strips and two 6 wide Sika Wrap Hex 103C uni-direction sheets were prepared or installation (Figure 3-3). A uniorm thin layer o Sikadur 30 Hi-Mod Gel two-part 21

42 epoxy was applied to the soit o the beam. The pre-cured CFRP strips were pressed onto this epoxy layer using a roller (Figure 3-4). The 6 wide wet lay-up sheets were saturated in Sikadur Hex 300 two-part epoxy and then applied at each end o the beam to anchor the lexural strips (Figure 3-5). In addition, Sika Wrap Hex 103C was used to wrap the epoxy mortar patches at the ledge spalls at third points along the span (Figure 3-6). Once the epoxy had cured, the beam was painted with exterior quality latex paint and put back into service (Figure 3-7). Figure 3-1 Cross section o T-Beam or carbodur strip installation 22

43 Figure 3-2 Surace preparation prior to CFRP application Figure 3-3 Sika carbodur strips being prepared or installation Figure 3-4 Application o CFRP strips 23

44 Figure 3-5 Wet lay-up anchorage wrap at end o CFRP strips Figure 3-6 Sika wet lay-up wraps at concrete spalls Figure 3-7 Repaired beam in service 24

45 CHAPTER 4 4 BEAM RECOVERY AND REPAIR 4.1 Introduction The portion o the old Ala Moana Parking Structure containing the repaired T-Beam was demolished in June 2000 to make way or a new multilevel parking structure. During demolition, the repaired T-Beam and two nominally identical un-repaired T- Beams were salvaged or testing. The top slab orming the lange o the T-Beams was removed, along with the transverse joists, to acilitate shipping o the salvaged beams. This removal was perormed using a demolition rig with large hydraulic pincer. Removal o the top slab over the precast beam web occasionally resulted in spalling o concrete at the top o the web. These spalls were repaired once the beams were delivered to UHM- STL as described later in this chapter. The top slab was also reinstated at UHM-STL. Removal o each beam was perormed using the demolition rig and a large diameter concrete saw. The precast prestressed web section o each beam was removed by saw cutting through the cast-in-place column capital at each end o the span (Figure 4-1). This enabled recovery o the entire precast section o the beam without damaging any o the prestressing steel or altering the prestress in the beam. During saw cutting, the beam was supported by two cables rom the demolition rig (Figure 4-2). Because o the negative bending induced by the sel-weight o the beam, lexural cracking occurred in one o the beam webs. These cracks were repaired once the beam was delivered to UHM-STL as described later in this chapter. 25

46 Figure 4-1 Saw cutting column capital to remove precast prestressed beam Figure 4-2 Cable support during beam removal 26

47 4.2 Epoxy Crack Repair During handling o one o the control specimens, negative bending cracks ormed in the beam web. These cracks were not anticipated to aect the lexural strength o the beam during testing since they did not extend into the prestressed bulb at the base o the beam. However, they would aect the stiness o the beam during lexural testing and may jeopardize the shear strength o the beam and so were repaired prior to replacement o the top slab. The cracks were repaired by Plas-Tech Ltd., Hawaii, using a Sika epoxy injection system. Injection ports were epoxied onto the crack at 2-inch intervals and the surace o the crack was sealed with Sika epoxy modiied mortar (Figure 4-3). The cracks were then injected using Sika epoxy modiied mortar and allowed to cure beore handling the beam (Figure 4-4). Figure 4-3 Injection Port Placement 27

48 Figure 4-4 Epoxy Injection 4.3 Epoxy Mortar Spall Repair During demolition o the top slab and supporting joists, portions o the beam webs were damaged by concrete spalls. None o the spalls aected the internal lexural and shear reinorcement in the precast prestressed beams, however, in order to restore the beams to their original condition, these spalls were repaired prior to replacement o the top slab. The spall repairs were perormed by personnel rom Plas-Tech Ltd., Hawaii, using a Sika epoxy mortar patching system. The contact surace was primed using Sika epoxy modiied mortar (Figure 4-5) and ormed with plywood (Figure 4-6). A two part Sika epoxy modiied mortar was mixed with clean silica sand and poured into the orm (Figure 4-7). The patch material was allowed to cure beore removal o the orm (Figure 4-8). 28

49 Figure 4-5 Priming the repair contact surace Figure 4-6 Forming the repair area 29

50 Figure 4-7 Pouring epoxy mortar patch material Figure 4-8 Completed spall repair 30

51 4.4 Top Slab Replacement To acilitate transportation o the beams rom the Ala Moana Shopping Center to UHM-STL, the top slab and supporting joists were removed during demolition. In order to replicate the T-Beam behavior o the in-situ beam, a concrete lange was poured onto the recovered precast beams prior to testing. The eective lange width suggested by the ACI Building Code or the in-situ condition is 77.5 inches. Because o limitations o the test rame used to test the beams, the lange width over hal o the beam was reduced to 66 inches (Figure 4-10). This slight reduction in lange width was not anticipated to aect the beam lexural perormance. The 4.5 inches thick top lange was reinorced according to the original design documents or the parking garage (Figure 4-9). The slab reinorcement consisted o two layers o grade 60 #3 reinorcing bars running both transverse to the beam axis and longitudinally. In the transverse direction, the bottom bars were spaced at 12 on center and the top bars were spaced at 7 on center (Figure 4-11). In the longitudinal direction, the bottom bars were spaced at 6 on center and the top bars were spaced at 12 on center (Figure 4-11). Some o the transverse reinorcing bars were relocated to avoid the 3 openings ormed or the proposed CFRP shear reinorcing stirrups. These openings were ormed by means o plywood block-outs (Figure 4-12). The block-outs were located at approximately 12 inches on center so as to all between the original internal steel shear reinorcement. In order to monitor strains in the top slab reinorcement, six electrical resistance strain gages were bonded to the surace o longitudinal bars in the top slab. Four strain gages 31

52 were located along the top center longitudinal bar while two gages were located on slab top bars to one side o the beam web at mid-span (Figure 4-11). The existing steel shear reinorcement in the precast beams consisted o double leg #3 reinorcing bars at a nominal spacing o 12 inches on center along the ull length o the beam. Each bar consisted o a straight vertical section in the beam web, with no hook or anchorage at the bottom o the beam, and a 90 degree bend into the top slab at the top o the beam. During demolition o the top slab, some o the 90 degree bend extensions had been removed or damaged. These stirrups were repaired by welding #3 bar extensions to reinstate the original anchorage into the top slab. The concrete was supplied by Hawaiian Cement Ready Mix and poured in place. For T-Beam 1, the top slab was poured directly on the precast beam web (Figure 4-13). For T-Beam 2, Corr Bond was applied to the top o the beam web to improve the bond between the top o the precast beam and the concrete slab. The top slab concrete was wet cured or 7 days and then exposed to the laboratory environment while waiting or testing. 5'-6" 42" 1 Slab Reinorcement 2-leg #3 12" o.c " 1'-62" 1 52" " (10) 3 8"Ø Stress-relieved 2 3 8" prestress strands 52" 1 1'-4 1 2" MIDSPAN BEAM SECTION Figure 4-9 Typical T-Beam cross-section 32

53 3" TYP 5'-6" 6' 3" wide crp stirrups (typ) 14' " 9' " Figure 4-10 T-Beam 1 lange layout 3" TYP 5'-6" 6' 3" wide crp stirrups (typ) 6" TYP 14' " Bottom Reinorcement Layout 9' " 1' TYP 3" TYP 5'-6" 1'-11" 4'-2" " 3 4 " 3" wide crp stirrups (typ) 3' " 1 4 " 3 2' " " " 1' " 1' TYP 6' 14' " 9'-9 1 7" TYP 2 " Top Reinorcement Layout and Strain Gage Locations Figure 4-11 T-Beam 1 lange reinorcement layout 33

54 Figure 4-12 Plywood block-outs or CFRP shear stirrups Figure 4-13 T-Beam 1 top lange concrete placement 34

55 CHAPTER 5 5 TEST SETUP AND BEAM LAYOUT 5.1 Introduction This chapter describes the test setup and specimen details or the prestressed concrete T-Beams tested in this program. The testing apparatus was constructed speciically or this project, but was conigured so that it could be modiied and re-used or uture testing in the UHM-STL. The CFRP shear strengthening applied to each T-Beam to preclude premature shear ailure is described, along with all instrumentation placed on the beams during testing. The test routine and data recording procedures are also presented. 5.2 Test Apparatus In the Ala Moana Shopping Center Garage, the prestressed T-Beams supported transverse joists at 7 eet on center, which in turn supported the parking level slab. The majority o the load applied to the T-Beams was thereore applied by the transverse joists at 3.5 eet on either side o the beam mid-span. I the repaired T-Beam with lexural CFRP were tested under point loads at the locations o the original joists, the beam might ail prematurely in shear. In order to avoid this shear ailure, additional CFRP shear strengthening was applied to both beams as described later in this chapter. In addition, the load points were relocated to 2 eet either side o the beam mid-span so as to increase the shear span. The T-Beams in this program were tested under 4-point loading. Figure 5-1 shows the original schematic o the test setup. Based on the anticipated lexural capacity o the strengthened beam, a 200,000 lb capacity hydraulic actuator supported by a two-post 35

56 rame was initially considered or the test setup. However, since the beams were to be retroitted or shear, it was decided that, subsequent to lexural testing, each o the shear spans would be tested to determine the shear capacity o the two retroit systems. This would require a 300,000 lb capacity hydraulic actuator supported by a our-post rame. The inal test rame coniguration is shown in Figure 5-2 and Figure 5-3. A Load Frame 200 Kip Actuator Load Cell Spreader Beam Test Beam A TEST SETUP ELEVATION SECTION "A-A" Figure 5-1 Schematic Layout o Test Setup The our-post rame consists o our 4 x 6 steel tube columns with a 1.75 diameter high-strength threaded steel rod inside each column. The rods extend rom the top o the rame and pass through the 2 thick laboratory strong-loor. They were pre-tensioned to approximately 25% o their capacity beore testing. The 300,000 lb 30 stroke hydraulic actuator is suspended rom a steel cross-head at the top o the our tube columns. The cross-head was constructed rom two W24 wide lange beams welded side-by-side and supported on double W12 wide lange beams supported on the tube columns (Figure 5-3). The rame was designed so that during testing o the T-Beam specimens, the compression orce applied by the actuator is transerred by the cross-head to the our 1.75 diameter 36

57 high-strength steel rods. Numerous web stieners were installed in the W24 and W12 beams to acilitate this load transer. In order to test the T-Beams or this project, the our-post rame had to extend 19 eet above the laboratory strong-loor (Figure 5-2). However, this encroached on the travel o the overhead crane and so limited the use o the laboratory on the ar side o the rame. In order to retain the our-post rame or uture testing, but also maintain ull crane unction, the tube steel columns were spliced at 2/3 rd height. Figure 5-4 shows the test rame in the short coniguration during construction. Figure 5-5 shows the test rame with the column extensions in place. In order to stabilize the rame, adjustable crossbracing was installed above the test specimen (Figure 5-5). A load spreader beam was abricated rom two W24 wide lange beams to distribute the actuator load to the load points at 2 eet either side o the beam mid-span (Figure 5-3). W8 wide lange beams were used to abricate pin and roller supports or each end o the test beam (Figure 5-3). Fabrication o the test rame was perormed over an 8 month period in UHM-STL. 37

58 6" 6' 6" 6" 1' 2'-0" 1" Detail 1 6'-7" 22' 15'-4" 6" 2" 1' 9" 1" 2' " Detail 3 2' " Detail " 1' " 2' 12" Figure 5-2 Detail o Final Test Frame Design 38

59 6" 6' 2-W12 Beams (Typ) 6" 1' 6" 6" 3' 6" 2'-0" Plate Stieners Actuator Swivel Head 1" DETAIL 1 - CROSS-HEAD FRAMING 2-W24 Beams 1' 1'-6" 6" W8x48 1/2" Plate Stieners 3" 8 1 2" 1/2" 8" 2' DETAIL 2 - PINNED SUPPORT Swivel Head Load Platen Steel Plate Stieners 2-W24 Beams 2'-0" 4'-0" Cement Grout DETAIL 3 - SPREADER BEAM Figure 5-3 Test Frame Details 39

60 Figure 5-4 Test Frame under Construction (Short Columns) Figure 5-5 Completed Test Frame with T-Beam 1 ready or loading 40

61 5.3 Beam Shear Retroit T-Beam 1 was the irst beam to be prepared or testing as the control specimen. During the demolition o Ala Moana Parking Garage, the original top slab and joists were removed to acilitate shipping o the beams to UHM-STL. The top slab was reconstructed as described in Chapter 4 to act as the top lange and compression zone o the beams. In order to avoid premature shear ailure o the strengthened beam, CFRP shear reinorcement was installed on T-Beam 2 prior to lexural testing. Two types o shear strengthening were considered or this application. In order to evaluate these two options, they were applied to T-Beam 1 and tested in shear ater completion o the lexural test. The two shear retroit systems installed on T-Beam 1 consisted o 3 wide double layer CFRP stirrups installed on the let hal o the beam and 12 wide single layer CFRP sheets installed on the right hal o the beam (Figure 5-6) CFRP Shear Stirrups CFRP shear stirrups were used to retroit the let hal o T-Beam 1 (Figure 5-6). Each stirrup consisted o a double layer o 3 wide CFRP unidirectional abric extending rom the bottom o the beam on one side o the web, through the top slab and down the other side o the web. In a normal application, the stirrup would extend under the beam soit to orm a lap splice, so as to create a continuous hoop. However, since the primary intent o this program was to evaluate the original ield application o the CFRP carbodur lexural strengthening, the additional restraint provided by ull hoop stirrups would have altered the lexural perormance o T-Beam 2. 41

62 To maintain continuity at the top o the beam, the stirrups were passed through slots abricated in the top slab. In a ield application, this would require cutting slots in the top slab to acilitate the stirrup installation. To prevent premature delamination o the stirrups at the re-entrant corner at the bottom o the web, steel tubes with thru-bolts were installed to restrain the stirrups. The layout or the shear retroit o T-Beam 1 is shown in Figure 5-6. The existing internal #3 reinorcing stirrups were located at approximately 12 on center. In order to avoid conlicts at the top o the beam, the 3 wide double layer CFRP stirrups were located between the existing steel stirrups. This resulted in a 12 center-to-center spacing or the 3 wide CFRP stirrups. The contribution o these stirrups to the shear capacity o the beam is computed in Chapter 7. Plywood saddles were used as block-outs to create the slots in the top slab. Ater the concrete slab had set, the saddles were removed using a pneumatic chipping hammer and power drills. The plywood saddles proved diicult to remove, and so high density Styrooam was used to create the saddles or T-Beam 2. Figure 5-7 shows the slotted holes ater the saddles were removed. The top o the web at the slotted holes had small holes due to entrapped air under the saddles. These holes were illed with epoxy mortar prior to installation o the CFRP stirrups (Figure 5-11). A pneumatic needle gun was used to roughen the surace o the web to remove the surace cement paste and improve the bond between the CFRP and the concrete. For each o the 3 wide double layer CFRP stirrups, a 3 wide strip o concrete was roughened on both sides o the beam web (Figure 5-8). The resulting surace condition was similar to ICRI surace proile #

63 Internal shear stirrups (typ) CL " 1' TYP 2' Let Support 7" " 10" 1' " 12" 1' " " 1' " " 1' " 91 2 " " Let Span (3" wide double layer CFRP Stirrups) 24' 6" TYP 1'-6" Right Span (12" wide CFRP Sheets) Right Support TBEAM " TYP 5'-6" 6' 3" wide CFRP stirrups (typ) 14' " 9' " CONCRETE SLAB Figure 5-6 Shear retroit layout or T-Beam 1

64 Figure 5-7 Slotted holes in top slab or CFRP shear stirrups Figure 5-8 Concrete surace preparation using needle gun Figure 5-9 Roughened web or 3 wide stirrups 44

65 Beore installation o the CFRP materials, a total o twenty-our 3 wide CFRP strips were cut rom standard 24 wide CFRP unidirectional material. Each 3 wide CFRP stirrup contained 12 CFRP tows. The strips were saturated in Sikadur Hex 300 epoxy in preparation or installation (Figure 5-10). Sika 30 Hi Mod Gel epoxy was applied to the roughened suraces o the concrete as a bonding agent (Figure 5-11). It was also used to ill the air holes on top o the web. The 3 wide double layer CFRP stirrups were then installed rom the top o the slab going through the slotted holes and down the sides o the web. A roller was used to press the CFRP into place and remove any air bubbles between the CFRP and the concrete surace. Figure 5-12 shows the slotted holes with the 3 wide double layer CFRP installed in place. Ater installation, the epoxy was allowed to cure or ive days beore the excess bottom CFRP was removed with a grinder (Figure 5-13). In order to prevent premature delamination o the CFRP stirrups at the re-entrant corner at the base o the web, mechanical anchorage was provided in the orm o steel tubes with thru-bolts passing through the beam web. Three quarter inch diameter holes were drilled through the web midway between the CFRP stirrups. The steel tube was provided in two sections rather than a continuous member so as not to enhance the beam bending capacity. The two sections o tube were 1.25 x 1.25 and 1.5 x 1.5 with 1/8 wall thickness. These pieces it inside each other to orm a telescopic joint midway along the stirrup hal o the beam. Thru-bolts made rom 5/8 diameter threaded steel rod were used to anchor the steel tubes on either side o the web. Beore installation o the tube steels, a bed o Sika 30 Hi Mod Gel epoxy was spread over the bend in the CFRP so as to 45

66 provide even load transer between the CFRP stirrup and steel tube. The nuts were snug tightened and the epoxy allowed to cure or ive days (Figure 5-14 and Figure 5-15). 46

67 Figure 5-10 CFRP stirrups being saturated with Sikadur Hex 300 Figure 5-11 Sika 30 Hi Mod Gel epoxy used to prepare surace or CFRP Figure wide double layer CFRP stirrups wrapped through slotted holes 47

68 Figure 5-13 CFRP stirrups in place, bottom trimmed ater curing Figure 5-14 Installation o steel tube anchorage or 3 wide CFRP stirrups 48

69 Figure 5-15 Complete installation o anchorage or 3 wide CFRP stirrups CFRP Shear Sheets The right hal o T-Beam 1 was retroitted with 12 wide CFRP sheets as shear reinorcement (Figure 5-6). The surace preparation or the CFRP sheets involved roughening o the concrete surace o the web and a 4 return under the top slab using a needle gun (Figure 5-16). Sika 30 Hi Mod Gel Epoxy was then applied or each 12 CFRP sheet (Figure 5-16). The irst 12 CFRP sheet was located 18 rom the right support, just inside the thickened anchorage zone o the prestressed beam. The sheets were spaced at 18 on center so as to leave a 6 gap between sheets to allow or moisture in the beam to escape. 49

70 Figure 5-16 Roughened web and Hi Mod Gel application or 12 wide sheets Figure 5-17 CFRP sheets saturated with Sikadur Hex 300 Figure 5-18 Installation o CFRP sheets as shear reinorcement 50

71 The 12 wide CFRP sheets were cut rom the standard 24 wide CFRP roll and saturated with Sikadur Hex 300 epoxy (Figure 5-17). Sika 30 Hi Mod Gel epoxy was applied to the roughened suraces o the concrete as a bonding agent (Figure 5-16). The CFRP sheets were then installed on the web (Figure 5-18). A roller was used to press the CFRP onto the concrete and to remove air bubbles. At the top o the web, our inches o the 12 CFRP sheet was bonded underneath the slab as a return so that mechanical anchorage could be installed at both the top and bottom o the web to prevent premature delamination o the CFRP sheets at the re-entrant corners. A 2 x 4 timber was used to hold the CFRP in place under the slab while it was being rolled onto the web. Ater installation, the epoxy materials were allowed to cure or ive days. The excess CFRP at the bottom o the beam was then removed with a grinder (Figure 5-18). Anchorage o the CFRP sheets was provided using steel tubes and threaded rods as described earlier or the CFRP stirrups. A bed o Sika 30 Hi Mod Gel epoxy was placed in the CFRP bends at all anchorage locations so as to provide even load transer rom the CFRP to the steel tubes (Figure 5-19). The bottom anchorage was identical to that used or the stirrups except that the threaded rod thru-bolts were located at the center o the 6 gap between CFRP sheets (Figure 5-20). A telescopic joint o the steel tube is shown in Figure For the top anchorage, a 2 x 1.5 by 1/8 thick continuous steel tube was used. There was no need to splice the tube since its contribution to the compression lange is negligible. Thru-bolts made rom 5/8 diameter threaded steel rod were used to anchor the tube steel on either side o the web (Figure 5-22). The nuts were snug tightened and the epoxy allowed to cure or ive days. 51

72 Figure 5-19 Sika 30 Hi Mod Gel epoxy bed at re-entrant corner o CFRP sheets Figure 5-20 Tube anchorage set in epoxy bed at re-entrant corner o CFRP sheets 52

73 Figure 5-21 Telescope splice in steel tube anchorage Figure 5-22 Complete installation o mechanical anchorage or 12 CFRP sheets 53

74 5.4 Beam Test Coniguration and Instrumentation Both T-Beam 1 and T-Beam 2 were instrumented with strain gages installed on the top slab reinorcement, slab and precast beam concrete, and on the CFRP shear reinorcement. In addition, dial gages and LVDTs (linear variable displacement transducers) were used to monitor the vertical delection o the beams. Ater testing each beam in lexure, the remaining beam halves were tested in shear to evaluate the ultimate perormance o the CFRP shear retroit schemes. These hal beams were also instrumented extensively to monitor the CFRP strains. In the sections below, each beam test coniguration and instrumentation layout is presented in detail. The results o the tests are presented in Chapter T-Beam 1 Layout and Instrumentation T-Beam 1 was tested under our point loading over a span o 24 eet (Figure 5-23). It was supported at each end by pinned supports. It was loaded with two point loads located 4-3 apart, centered at the beam mid-span. The load was applied in displacement control. Displacement increments started at and increased to as the test progressed. Figure 5-23 shows the layout and instrumentation or T-Beam 1. A total o 25 strain gages were installed on the beam. Strain gages 1-6 were installed on the longitudinal reinorcement in the concrete top slab. These gages were Micro-measurement electrical resistance gages CEA UN-350 bonded to the surace o the reinorcement ollowing the manuacturer s instructions. Strain gages 7-21 were Micro-measurement electrical resistance gages EA-06-20CBW-120 designed or bonding to concrete. They were installed on the top slab concrete surace and along the bottom o the beam to 54

75 determine the curvature o the beam. Data rom these strain gages were used in another project to evaluate a strain-based delection monitoring system 16. Strain gages were installed on the CFRP shear reinorcement to monitor strains in the CFRP during lexural testing. Three LVDTs were supported on independent uni-strut rames so as to record the vertical delection o the top slab (Figure 5-23). LVDT3 was placed at mid-span o the beam, but slightly to one side o the beam centerline so as to avoid intererence with the steel spreader beam. The other two LVDTs were located in the right shear span as shown in Figure Dial gages were also installed on the concrete top slab directly over the supports to record any settlement o the supports during testing. Figure 5-24 shows T-Beam 1 in the test rame immediately prior to testing. Figure 5-25 shows a close-up view o the center section o T-Beam 1 prior to testing. 55

76 P CL P 4'-3" " 2' DIAL GAGE Let Support " 2'-3" 1' " '-5" 1'-4" 1'-10" '-3" " 15 8'-1" " " 2" Let Span (3" wide double layer CFRP stirrups) LVDT ' LVDT 2 LVDT 1 12' 6'-9" 3'-9" ' 13 1'-5" " " " 8' '-3 1 2'-2 1 " 4 " 2 " Right Span (12" wide CFRP sheets) DIAL GAGE 1' " Right Support T-BEAM " TYP 1' " 5' " 8' 8' " 5'-4" 2' " 5'-6" ' 14' " 9' " CONCRETE SLAB Figure 5-23 T-Beam 1 Layout and Instrumentation

77 Figure 5-24 T-Beam 1 in the load rame ready or testing Figure 5-25 T-Beam 1 ready or testing center view 57

78 5.4.2 T-Beam 1L Layout and Instrumentation Ater lexural ailure o T-Beam 1 at mid-span, the let hal o the beam, which was retroitted in shear with 3 wide double layer CFRP stirrups, was tested as T-Beam 1L (Figure 5-26). It was supported on a 10 span and subjected to two point loads located 1-2 apart, centered at mid-span. Several o the strain gages rom T-Beam 1 were still unctioning ater the lexural test and were monitored during testing o T-Beam 1L. Strain gages 7-9 and were the original strain gages attached to the concrete surace. Additional strain gages were installed on the CFRP shear stirrups to monitor their perormance. Several o the CFRP stirrups were selected and the strain gages located based on likely shear crack locations. Strain gages were attached to the CFRP retroit (Figure 5-26). Three LVDTs were located on the top slab to measure the vertical displacement o the specimen. LVDT3 was placed at mid-span o the beam. LVDT1 was placed directly over the let support, while LVDT2 was placed at quarter span (Figure 5-26). Initially, T-Beam 1L was supported with two pin supports. However, during testing, signiicant deormation o the supports indicated that they were experiencing inward lateral load due to shortening o the span. The resulting tension in the bottom o the beam would likely aect the shear and lexural capacities o the beam. The beam was unloaded and one o the supports modiied to provide a roller support. The beam was then re-loaded with one pinned support and one roller support as shown in Figure Figure 5-27 shows T-Beam 1L in the test rame ready or testing. 58

79 CL P 1'-2" P " 2' 6" 1 1/2" x 1 1/2" x 1/8" hollow tube steel " LVDT 1 LVDT 2 LVDT 3 5' 2'-3" 3' " 2'-9" 1'-9" 25 pinned support '-5" 1'-4" 1' " 1'-6" 10' T-BEAM 1L 5'-6" " 28 1'-6" 1' TYP 3' 2' 1'-2" ' " 11" existing shear stirrups (typ) roller support 1 1/4" x 1 1/4" x 1/8" hollow tube steel 3" double layer CFRP stirrups Sika 30 Hi Mod Gel epoxy Hollow tube steel 2'-4 1 anchors nuts & bolts 2 " " 1' " T-BEAM 1L CROSS SECTION Figure 5-26 Layout and Instrumentation o T-Beam 1L

80 Figure 5-27 T-Beam 1L ready or testing T-Beam 1R Layout and Instrumentation T-Beam 1R is the right hal o T-Beam 1 recovered ater lexural ailure at mid-span. It was retroitted with 12 wide CFRP sheets with 6 spacing between sheets. Based on the test results rom T-Beam 1L, it was determined that additional lexural strengthening was necessary to ensure ailure in shear. Thereore, three pre-cured carbodur strips were installed under the soit o T-Beam 1R. Technicians rom Plas-Tech Ltd. installed the pre-cured carbodur strips (Figure 5-28). A lexural retroit or T-Beam 1R was necessary due to the lexural ailure observed in T-Beam 1L. Three 4 wide pre-cured carbodur strips were installed as lexural reinorcement on the soit o the beam. Prior to installation, the beam soit concrete was roughened with a pneumatic needle gun. Sika 30 Hi Mod Gel epoxy was used as the bonding agent. It was applied on the surace o the concrete and on the carbodur strips. The strips were then placed along the beam soit and pressed into place with a roller. 60

81 The ends o the CFRP carbodur strips were wrapped with Sika Wrap Hex 103C unidirection abric to resist end delamination. These anchorage sheets were saturated with Sika Hex 300 epoxy or the wet lay-up application. The end supports were located under these CFRP wraps to enhance anchorage o the carbodur strips. Figure 5-28 shows the installation o the pre-cured carbodur strips and CFRP wraps on T-Beam 1R. T-Beam 1R was supported over a 10-2 ½ span by a pinned support and a roller support (Figure 5-29). Two point loads were applied to the top lange as described or T- Beam 1L. A total o 32 strain gages were installed on the beam. Strain gages 1-12 were installed on the steel tubes to determine the level o strain in the anchorage tubes during testing. Strain gages were installed on the CFRP shear sheets to monitor their perormance during shear testing. Strain gages were the original concrete strain gages installed on T-Beam 1. Strain gages were installed on the three carbodur strips at mid-span to monitor the tension strains in the lexural retroit. Three LVDTs were also installed to monitor vertical delection o the beam. LVDT3 was placed at mid-span o the beam. LVDT1 was placed directly over the right support and LVDT2 was placed at quarter span. Figure 5-29 shows the instrumentation and layout o T-Beam 1R. Figure 5-30 shows T-Beam 1R in the test setup ready or testing. 61

82 T-Beam 1R prepared or carbodur strip installation by Plas-Tech technicians End anchorage provided by Sika Wrap Hex 103C wraps Completed Sika Wrap Hex 103C anchorage at each end o beam Final T-Beam 1R retroitted in lexure Figure 5-28 Flexural strengthening o T-Beam 1R using pre-cured carbodur strips 62

83 CL P P Spliced steel tubes 1'-2" LVDT 3 LVDT 2 LVDT 1 2" x 1 1/2" x 1/8" 5' " Steel tube 2'-4" 6" 2" " " 2" " 23 2 " /4" " " 2 " ' " Roller Support " Pinned Support A 1 1/2" x 1 1/2" x 1/8" Steel tube B 6" TYP 10' " T-BEAM 1R 1'-6" 1 1/4" x 1 1/4" x 1/8" Steel tube Pre-cured carbodur strips 5'-6" " BOTTOM OF BEAM 5'-6" " 12" CFRP sheets Sika 30 Hi Mod Gel epoxy CFRP sheets wrapped around soit to restrain precured carbodur strips 1' " " SECTION A Steel tube anchors with thru-bolts 2' " CFRP overlap rom bottom o beam 12" CFRP sheets Steel tube anchors Sika 30 Hi Mod Gel epoxy " 2' " with thru-bolts Pre-cured carbodur strips 1' " SECTION B Figure 5-29 T-Beam 1R Layout and Instrumentation

84 Figure 5-30 T-Beam 1R ready or testing T-Beam 2 Layout and Instrumentation T-Beam 2 was the strengthened beam with the ield-applied pre-cured carbodur strips. Due to the presence o pre-cured carbodur strips attached to the beam soit with CFRP wraps at each end, the test setup and layout o T-Beam 2 was slightly dierent to that used or T-Beam 1. In order to avoid increasing the end anchorage o the CFRP carbodur strips, the support reactions could not be located under the ends o the beam as was the case or T-Beam 1. Instead, steel plate supports were abricated and attached to the ends o the beam using an epoxy bond, expansion anchors and prestress anchors on the tendon extensions (Figure 5-31). The existing CFRP that was wrapped around the repaired ledges at the third points o the beam span were removed so that the only anchorage or the carbodur strips was at the ends o the beam. The slab reinorcement layout is the same as used or T-Beam 1. Six strain gages were attached to the slab longitudinal reinorcement at the same locations as T-Beam 1 (Figure 5-32). 64

85 Let End Pinned Support Steel Reaction Bracket Right End Roller Support Figure 5-31 Steel reaction brackets at both ends o T-Beam 2 A bonding agent (Corr Bond) was applied to the top o the precast beam web to improve the bond between the top o the web and the concrete slab. The concrete slab dimensions were 4.5 thick, 5-4 wide, and long. The width o the concrete slab was 2 less than the slab on T-Beam 1 to allow or additional clearance in the load rame. High density Styrooam was used to create the saddle blockouts or the 3 wide CFRP stirrups (Figure 5-33). This simpliied the construction and demolition o the saddles compared with the plywood saddles used in T-Beam 1. Figure 5-32 shows the concrete slab layout and reinorcement o T-Beam 2. Figure 5-33 shows the slab reinorcement and high density oam blockouts prior to pouring. 65

86 5'-4" 3" wide CFRP stirrups (typ) 24'-10" Top Slab Layout 5'-4" 6" TYP 24'-10" 1' TYP Slab Bottom Reinorcement Layout 1'-11" 3' " 1'-11" 1' TYP 5'-4" ' 4 5 1' 6 24'-10" 7" TYP Slab Top Reinorcement and Strain Gage Layout Figure 5-32 T-Beam 2 top lange reinorcement and strain gage layout 66

87 Figure 5-33 T-Beam 2 slab layout prior to concrete pour T-Beam 2 was strengthened in bending at the Ala Moana Parking Garage. The precured carbodur strips were anchored at both ends o the beam with CFRP wraps. Because o the concrete damage at third points along the span o the beam, it was also wrapped with CFRP at these locations adding additional restraint to the carbodur strips. The CFRP wraps at the third point locations were removed prior to the shear retroit to release the additional restraints on the pre-cured carbodur strips. Figure 5-34 shows the locations where additional CFRP wraps were removed prior to the laboratory beam shear retroit. 67

88 CFRP wraps removed Figure 5-34 T-Beam 2 being prepared or shear retroit The beam shear retroit layout or T-Beam 2 is shown in Figure The beam shear retroit had basically the same procedure as T-Beam 1. Ater the concrete slab was cured, the CFRP blockouts were removed to orm the slotted holes. The Styrooam blockouts were much easier to remove than the plywood blockouts used in T-Beam 1. Locations o the existing reinorcing stirrups were recorded prior to the slab pour so that the CFRP shear stirrups could be placed between them. The locations o the CFRP stirrups and sheets were roughened to produce better bonding and remove surace cement paste. The mechanical anchorage or the shear retroit was the same layout as or T- 68

89 Beam 1, except that Glass Fiber Reinorced Polymer (GFRP) angles were used instead o the steel tubes (Figure 5-36 and Figure 5-37). These angles were 3 x 3 with a thickness o ¼. Because they are non-corrosive, these GFRP angles are ideally suited or retroit o structures exposed to external weather conditions. The 3 wide double layer CFRP stirrups and 12 wide CFRP sheets were prepared and installed in the same manner as the wet lay-up method described or T-Beam 1. There were a total o twenty-two 3 wide double layer CFRP stirrups and ourteen 12 wide CFRP sheets. Ater the CFRP shear retroit was installed and allowed to cure, the anchorage angles were installed. Since the angles stiness is signiicantly lower than the steel tubes used or anchorage in T-Beam 1, it was assumed that they would not contribute much to the bending strength o the beam. They were thereore installed as continuous sections or each o the beam hal spans. Three quarter inch holes were drilled through the web between the CFRP shear stirrups and sheets, avoiding the internal steel stirrups. Sika 30 Hi Mod Gel epoxy was used or the load transer between the CFRP and the anchorage angles. Figure 5-36 shows the epoxy being applied on the CFRP. Figure 5-37 shows the completed installation o the GFRP angle anchorages. 69

90 CL BEAM SOFFIT Existing shear stirrups (typ) 10" 7" 8" 1'-4" 1' 11" 1'-1" 10" 1'-2" 1' 1'-1" 1' 1'-1" 1' 1'-1" 1' 11" 1'-2" 10" 1'-3" 1'-1" 10" 10" " 2' Let Support A 1'-1" 10" 1' 1' 1' 1' 1' 1' 1' 1' 1' B Let Span (3" wide double layer CFRP stirrups) 25' " 1' 6" 1' C 6" 1' 6" 1' 6" 1' 6" 1' 6" Right Span (12" wide CFRP sheets) 1' 6" A Right Support T-BEAM 2 ELEVATION 70 5'-4" 3" wide CFRP Stirrups (typ) 5'-4" 24'-10" CONCRETE TOP SLAB 5'-4" " 5'-4" " Existing CFRP wrapped around beam end to restrain ield-applied carbodur strips 1' " 2' " existing pre-cured carbodur strips 3" Double layer CFRP stirrups Sika 30 Hi Mod Gel epoxy 1' " 3" x 3" x 1/4" GFRP angles Thru-bolts 2' " " existing pre-cured carbodur strips 12" CFRP sheets Sika 30 Hi Mod Gel epoxy 1' " " 2' " existing pre-cured carbodur strips 3" x 3" x 1/4" GFRP angles secured with Thru-bolts SECTION A SECTION B SECTION C Figure 5-35 Beam shear retroit layout or T-Beam 2

91 71 Figure 5-36 Sika 30 Hi Mod Gel epoxy being applied to the CFRP stirrups or even seating o the anchorage angles 3 wide CFRP stirrups with anchorage angles 12 wide CFRP sheets with anchorage angles in place Figure 5-37 CFRP angles installed as anchorage or CFRP shear reinorcement

92 T-Beam 2 was supported with a pin and roller. It was supported outside the ends o the precast beam rather than underneath the beam. Supporting the beam underneath the CFRP wrapped ends would have added extra restraining orce to the pre-cured carbodur strips. Thereore, two steel plates were abricated and attached at the ends o the beam (Figure 5-31). They were attached to the beam by means o epoxy, expansion bolts and anchoring them to the prestressed strands with prestressed anchors. The pin and roller supports were placed underneath these steel brackets. Most o the instrumentation o T-Beam 2 was ocused on the pre-cured carbodur strips. A total o 27 strain gages were installed. Strain gages 1-6 were installed on the longitudinal reinorcement in the concrete slab. The rest were installed on the carbodur strips. Strain gages 7-27 were installed on the pre-cured carbodur strips. Three rows o strain gages were attached on the same location o the three pre cured carbodur strips. Figure 5-38 shows a row o strain gages installed on the pre-cured carbodur strips. Figure 5-38 Electrical resistance strain gages installed on the carbodur strips 72

93 In addition, three LVDTs were placed on top o the concrete slab to measure the vertical delection o the beam. There were no dial gages placed on the support because no settlement o the supports was experienced during testing o T-Beam 1. Figure 5-39 shows the overall layout and instrumentation o T-Beam 2. T-Beam 2 was tested on a 25-8 ½ span rom pinned support to roller support. It has a longer span than T-Beam 1 due to the supports being located under the steel brackets outside the beam ends. It was loaded with two point loads located 4-3 apart centered on the beam mid-span. The loading routine was the same as that used or T-Beam 1. Figure 5-40 shows T-Beam 2 in the load rame ready or testing. 73

94 CL 1' " ' ' ' ' " 8' " ' BOTTOM OF BEAM " 2' 10" 7" 8" 1'-4" Existing shear stirrups (typ) 1 3 4" 1' 11" 1 2" 1'-1" 10" 2 1'-2" P 1' 2" LVDT 1 1'-1" 3 3" 1' 4'-3" 1 7 8" 1'-1" 5 & 6 4 P 1' 1'-1" 1' 12'-5" 6'-9" LVDT 2 LVDT 3 11" 1'-2" 10" 1'-3" 1'-1" 3'-9" 10" 10" Let Support 1'-1" 10" 1' 1' 1' 1' 1' Let Span (3" wide double layer CFRP stirrups) 25' " 1' 1' 1' 1' 1' 6" 1' 6" 1' TBEAM 2 Figure 5-39 T-Beam 2 Layout and Instrumentation 6" 1' 6" 1' 6" 1' 6" 1' 6" Right Support Right Span (12" wide CFRP sheets)

95 Figure 5-40 T-Beam 2 test setup 75

96 5.4.5 T-Beam 2L Layout and Instrumentation Ater lexural testing o T-Beam 2, the let-hand section o the beam was recovered and re-tested in shear as T-Beam 2L. This section had shear retroit consisting o 3 wide double layer CFRP stirrups. The pre-cured carbodur strips on the soit o the beam had delaminated during lexural testing o T-Beam 2. These strips were reinstated with a new layer o Sika 30 Hi Mod Gel epoxy to maintain the increased bending capacity o the beam. Wet lay-up Sika wraps were installed at each end o the carbodur strips to improve anchorage. In addition, to simulate typical shear retroit, the CFRP stirrups were extended around the bottom o the beam by splicing a 3 wide double layer o Sika Wrap with 4 minimum overlap at the bottom o the original CFRP stirrups. Figure 5-41 shows T-Beam 2L ready or retroitting with the carbodur strips and CFRP wraps extensions. Figure 5-41 T-Beam 2L being prepared or shear testing 76

97 Because o the o-center lexural-shear ailure o T-Beam 2, the let section o the beam was considerably shorter than T-Beam 1L, the let section o T-Beam 1. T-Beam 2L was supported by pin and roller supports placed as close as possible to the ends o the beam, creating a span length o 7-5. The right support was directly below the wrapped end o the carbodur strips, while the let support was beyond the end o the strips. The beam was loaded by means o a single point load acting on an area measuring 16 by 21 placed o-center to create a 1.5:1 shear span to depth ratio in the right side o the beam (Figure 5-42). Because o the inclined prestress strands in the let side o the beam, the shear capacity o this portion is greater than the right side. Shear ailure was thereore anticipated, and occurred, in the right portion o the beam. A total o 12 strain gages were installed on the irst two 3 wide double layer CFRP stirrups adjacent to the right support. Six strain gages were placed on stirrups on the ront o the beam and the other six were placed at the same locations on the stirrups on the back o the beam (Figure 5-42). An LVDT was placed at the loading location to measure the vertical delection. During loading, a shear crack ormed between the let support and the end o the carbodur strips on the soit o the beam. In order to avoid premature ailure, the load was removed and the let support relocated to bear directly under the CFRP wrap at the ends o the carbodur strips (Figure 5-42). The beam was reloaded until shear ailure occurred in the right shear span. Figure 5-43 shows T-Beam 2L in the test rame ready or testing. 77

98 P & LVDT 2'-10" 1'-4" 3'-3" 2'-3" 10" 7" 8" 1'-4" 1' 11" 1'-1" 10" 1'-2" 4 1 2" 2' 4 3 4" 1" " " Existing shear stirrups (typ) 5 1 2" 2 7 8" First Loading Second Loading Let Support 1'-1" 10" 1' 1' 1' 1' 7'-5" 6'-9" T-BEAM 2L Right Support Existing prestress strands 1-6 Front strain gages 7-12 Back strain gages BOTTOM OF BEAM Figure 5-42 T-Beam 2L Layout and Instrumentation Figure 5-43 T-Beam 2L in test setup 78

99 5.4.6 T-Beam 2R1 Layout and Instrumentation Ater testing T-Beam 2 in lexure, the right portion o the beam was recovered and used or two shear tests, designated T-Beam 2R1 and T-Beam 2R2. T-Beam 2R1 was perormed on the center section o the original T-Beam 2 to determine the original shear capacity o the beam without any shear retroit. Two o the 12 wide CFRP shear retroit sheets were removed to allow or shear ailure in the let shear span (Figure 5-45). The carbodur strips providing lexural strengthening were still intact on this portion o the beam. In order to prevent anchorage slip o the prestressing strands at the damaged let end o the beam, wedge anchors were installed on each strand as shown in Figure T-Beam 2R1 was simply supported on a 12-8½ span by pin and roller supports (Figure 5-45 and Figure 5-46). The load was applied on a 16 by 21 area located ocenter so as to induce a shear ailure in the un-retroitted section o the beam. An LVDT was placed at the loading location to measure the vertical delection. No strain gages were monitored during testing o this un-retroitted beam section. Figure 5-44 Wedge anchors installed on prestressed strands at end o T-Beam 2R1 79

100 P & LVDT Existing shear stirrups (typ) 1' 1'-1" 1' 1'-1" 1' 11" 1'-2" 10" 1'-3" 1'-1" 10" 10" 1' Let Support 3' " 1' 6" 1' 6" 1' 6" 1' 6" 1' 6" 1'-4" Right Support 12' " TBEAM 2R1 BOTTOM OF BEAM Figure 5-45 T-Beam 2R1 Layout and Instrumentation Figure 5-46 T-Beam 2R1 in test setup 80

101 5.4.7 T-Beam 2R2 Test Setup and Layout T-Beam 2R2 was the second shear test perormed on the right hand section recovered rom the T-Beam 2 lexural test. T-Beam 2R2 was perormed to evaluate the 12 wide CFRP shear reinorcement sheets installed on the right hal o T-Beam 2. In order to simulate typical shear retroit, the irst two CFRP sheets rom the let support were extended around the soit o the beam by means o spliced 12 wide CFRP sheets as shown in Figure The prestressed strands at the let end o the beam were anchored by means o wedge anchors similar to T-Beam 2R1 shown in Figure The pre-cured carbodur strips were still intact on the soit o this portion o the beam. No additional repair was needed. T-Beam 2R2 was simply supported over a 9-0 span with pin and roller supports as shown in Figure A total o nine strain gages were installed on the irst two 12 wide CFRP sheets rom the let support. T-Beam 2R2 was loaded on a 12 x 36 area located at mid-span, simulating a line load. An LVDT was placed at the loading location to measure vertical delection. Figure 5-47 shows the instrumentation and layout o the beam. Figure 5-48 shows T-Beam 2R2 in the test rame ready or testing. 81

102 Existing shear stirrups (typ) P & LVDT 11" 1'-2" 10" 1'-3" 1'-1" 10" 10" 5" 4" 2" " " 1 4 3" " " 4" " " 1' " 1" 12 1 " 1' 6" 1' 6" 1' 6" 1' 6" 1' 6" 4'-6" 9' Let Support T-BEAM 2R2 Right Support BOTTOM OF BEAM Figure 5-47 T-Beam 2R2 Layout and Instrumentation Figure 5-48 T-Beam 2R2 in Test Frame 82

103 CHAPTER 6 6 MATERIAL PROPERTIES Material properties o the T-Beam concrete, reinorcing and prestressing steel, and CFRP carbodur strips and wet lay-up wrap were determined through coupon testing perormed ater the T-Beam tests. These material properties were required or strength calculations in Chapter 7, Theoretical Strengths o T-Beam 1 and T-Beam Concrete Compressive Strengths Two compressive strengths were determined or each T-Beam. The compressive strength o the concrete used in the top slabs was determined using 6 diameter by 12 long concrete cylinders cast when the T-Beam top slabs were poured. They were tested in compression on the same day as the lexural tests on the T-Beams. The compressive strengths o the precast prestressed beams were determined by testing concrete cores taken rom the web and anchorage blocks. Ater all testing had been perormed on the T- Beams, 4 diameter by 5.5 long concrete cores were drilled rom un-cracked sections o the precast beam web and anchorage blocks using a core drill as shown in Figure 6-1. The cores were tested in compression and the resulting strengths adjusted according to ASTM C42-99 due to their non-standard cylinder size. From these compressive strengths, the modulus o elasticity o the concrete was estimated using the expression, E = 40 c (ksi) 17. Table 6.1 shows the average and standard deviation or concrete compressive strengths and corresponding modulus o elasticity values determined rom these tests. 83

104 Figure 6-1 Concrete core sample taken rom a T-Beam web Table 6.1 Concrete Compressive Strength and Modulus o Elasticity Top Slab, 6 x 12 cylinder Precast Beam, 4 x 5.5 cores Avg. c (psi) Std. Dev. (psi) No. o samples Avg. c (psi) Std. Dev. (psi) No. o samples T-Beam T-Beam Modulus o Elasticity, E = 40 c (ksi) Top Slab Precast Beam T-Beam T-Beam

105 6.2 Top Slab Concrete Modulus o Rupture Two rectangular beams were cast during the pouring o the concrete top slab or T- Beam 2 to perorm modulus o rupture tests according to ASTM C The beams were 6 x 6 x 18 long and loaded at third points along the span. Table 6.2 lists the results o the rupture tests. Table 6.2 Modulus o Rupture Test Beam Load (lbs) M (lb-in) r (psi) Avg Steel Reinorcement Tensile Strengths Internal shear stirrups and prestressing strands were recovered rom the T-Beams ater all tests were complete. The shear stirrups were two-legged #3 deormed reinorcing bars. The prestressing strands were 3/8 nominal diameter seven-wire stressrelieved strands with a design nominal tensile strength o 250 ksi. Coupons o these materials were prepared and tested in tension to determine their yield and ultimate strengths. Table 6.3 lists the yield and ultimate strengths o the shear stirrups and prestressing strands. 85

106 Table 6.3 Steel Reinorcement Tensile Strengths Description No. o samples Yield Stress Avg. y (ksi) Std. Dev. (ksi) Ultimate Stress Avg. u (ksi) Std. Dev. (ksi) T-Beam 1 T-Beam 2 Shear stirrups Prestress strands 272 Shear stirrups Prestress strands CFRP Material Properties The 4 wide pre-cured carbodur strips and the Sika Wrap Hex 103C uni-direction wet lay-up material were tested ater all T-Beam tests were complete. Samples o the carbodur strips were recovered rom locations where they appeared undamaged and still in good condition. Double layer 12 x 12 wet lay-up samples o the Sika Wrap Hex 103C were made at the same time as the shear retroit o the beam webs. Coupons o these materials were cut and tested in tension to determine their tensile strength and modulus o elasticity. Table 6.4 lists the tensile strength and modulus o elasticity o these materials. Table 6.4 CFRP Material Properties Tensile Strength Modulus o Elasticity CFRP Material Avg. CFRP (ksi) Avg. E CFRP (ksi) Carbodur strips Sika Wrap Hex 103C

107 6.5 CFRP Pull-o Tests Pull-o tests were perormed on the CFRP to determine the bond strength between the CFRP and the precast concrete. Tests were perormed on the CFRP shear stirrups, CFRP shear sheets and the pre-cured carbodur strips. The tests were made at locations where the concrete was un-cracked and the bond between CFRP and concrete was still intact. The tests were perormed using the DYNA Z16 pull-o tester shown in Figure 6-2. Figure 6-3 shows typical locations where the pull-o tests were perormed. In all cases, ailure occurred in the concrete substrate, and not in the CFRP or the epoxy bond. Figure 6-2 DYNA Z16 Pull-O Tester Figure 6-3 Typical locations o CFRP pull-o tests 87

108 Table 6.5 lists the pull-o test results rom T-Beam 1 and T-Beam 2. All o the pullo tests exceeded the 200 psi minimum recommended by the ACI 440R-02 report or CFRP installation 18. Table 6.5 Pull-o Test Results No. o Samples Stress (psi) Std. Dev. (psi) Comment T-Beam 1 T-Beam 1R Concrete ailure T-Beam 1L Concrete ailure T-Beam 2 T-Beam 2R Concrete ailure 88

109 CHAPTER 7 7 THEORETICAL BEAM STRENGTHS This chapter presents predicted strength calculations or the T-Beams tested in this program. In the irst section o this chapter, the lexural strength o T-Beam 1 is predicted using the ACI Building Code. The lexural strength capacity o T- Beam 2 with CFRP lexural strengthening is predicted using the ACI 440R-02. The strain-compatibility methodology proposed by ACI 440R-02 or non-prestressed beams is presented in detail. Adjustments are proposed or application o the ACI 440R-02 methodology to prestressed concrete beams. This methodology is then applied to the T- Beam 2 section properties. The rest o the chapter presents shear strength predictions or the original T-Beam without retroit and or the CFRP retroitted beams. The ACI 440R-02 approach to predicting the contribution o CFRP shear reinorcement is introduced. Shear strength predictions are presented or T-Beam 2R1 (concrete beam without CFRP shear retroit), T-Beam 1L and T-Beam 2L (with CFRP shear stirrups), and T-Beam 1R and T-Beam 2R2 (with CFRP shear sheets). The predicted strengths are compared with the observed strengths in Chapter Notation A = nt w = area o CFRP external reinorcement A s = area o non-prestressed steel reinorcement A = area o precast prestressed concrete section cp A cs = area o concrete slab 89

110 A cc = area o composite section A = 2nt w = area o CFRP reinorcement within spacing s v A ps = total area o prestressed strands a = β c 1 = depth o equivalent rectangular stress block b = width o the compression lange c = depth o the neutral axis C E = environmental reduction actor d = centroidal depth o a non prestressed reinorcement measured rom top o beam d = depth o CFRP shear reinorcement d p = centroidal depth o prestressed strands measured rom top o beam e = eccentricity o the prestressed tendons e = eccentricity o the prestressed tendons at center c e = eccentricity o the prestressed tendons at support e E = modulus o elasticity o the concrete slab c E = tensile modulus o elasticity o CFRP E p = modulus o elasticity o prestressed concrete E ps = modulus o elasticity o prestressed tendons E s = modulus o elasticity o steel c = measured compressive strength o concrete ' c = speciied compressive strength o concrete bs = bottom stress level in the concrete slab o a prestressed concrete section due to the dead load o the concrete slab bp = stress level in the bottom o the prestressed beam section due to the prestressing orce and dead load o beam = stress due to prestress at tension iber ce cp = stress level in the prestressed beam section at the level o the prestressed tendons = stress due to un-actored dead load at tension iber d = eective stress in the CFRP; stress level attained at section ailure e u = design ultimate tensile strength o CFRP * u = ultimate tensile strength o the CFRP material as reported by the manuacturer = stress level o the prestressed tendons attained at section ailure p pc = compressive stress in concrete at centroid o composite section pe = eective prestressing stress o the prestressed tendons due to P e pi = initial prestressing stress o the prestressed tendons 90

111 ps = stress in prestressed reinorcement at nominal strength pu = ultimate strength o prestressing tendons s = stress in non-prestressed steel reinorcement tp = stress level in the top o the prestressed beam section due to the prestressing orce and dead load o beam ts = stress level in the top concrete slab o a prestressed beam section due to the dead load o the concrete slab = speciied yield strength o non-prestressed reinorcement y h (i.e. h c ) = overall thickness o member I c = moment o inertia o composite prestressed section I = moment o inertia o precast prestressed beam section p k 1 = modiication actor applied to κ v to account or the concrete strength k 2 = modiication actor applied to κ v to account or the wrapping scheme l = member span length L = active bond length o CFRP laminate e M = cracking moment cr M d = moment at section due to un-actored dead load (sel-weight o precast and topping) M = dead load moment o the prestressed concrete beam dp M ds = dead load moment o the concrete slab o a prestressed concrete beam M max = maximum actored moment at section due to external loads (not including dead load) M n = nominal lexural capacity n = number o plies o CFRP reinorcement n c = modular ratio s = shear stirrup spacing s = CFRP shear reinorcing spacing P e = eective prestressing orce o the prestressed tendons I c S bc = ybc = bottom section modulus o the composite section I p S bp = y = bottom section modulus o the prestressed beam I b c S bs = = section modulus to the bottom o the concrete slab o a composite ybs section 91

112 I p S tp = = top section modulus o the prestressed beam y I t c S ts = = top section modulus o the composite section yts t = thickness o the concrete slab t = nominal thickness o one ply o the CFRP reinorcement V c = nominal shear strength provided by concrete V cw = nominal shear strength provided by concrete when diagonal cracking results rom excessive principal tensile stress in the web V d = shear orce at section due to un-actored dead load (sel-weight o precast and topping) V = nominal shear strength provided by CFRP stirrups V i = actored shear orce at section due to externally applied loads occurring with n M max V = nominal shear capacity V = vertical component o eective prestress at section p V s = nominal shear strength provided by steel stirrups w = width o the CFRP reinorcing plies w d = sel-weight o prestressed beam and concrete slab w = sel-weight o prestressed beam dp w ds = sel-weight o concrete slab y bs = distance rom the centroid o gravity o a composite prestressed beam section to the bottom o concrete slab y b = distance rom the centroid o gravity o a prestressed beam section to the bottom o the prestressed beam section y bc = distance rom the centroid o gravity o a composite prestressed beam section to the bottom o the composite prestressed beam section y t = distance rom the centroid o gravity o a prestressed beam section to the top o the prestressed beam section y ts = distance rom the centroid o gravity o a composite prestressed beam section to the top o concrete slab β 1 = ratio o the depth o the equivalent rectangular stress block to the depth o the neutral axis ε b = strain level in the concrete substrate developed by a given bending moment (tension is positive) ε bi = strain level in the concrete substrate at the time o the CFRP installation (tension is positive) 92

113 ε cu = maximum usable compressive strain o concrete (0.003) ε e = eective strain level in CFRP reinorcement; strain level attained in section ailure ε u = design rupture strain o CFRP reinorcement ε s = strain level in the non-prestressed steel reinorcement ε bp = initial strain level in the bottom prestressed concrete substrate due to bp (i.e. strain level in the concrete substrate at the time o the CFRP installation) ε cp = initial strain level o prestressed concrete substrate at the level o the prestressed tendons ε bs = initial strain level in the bottom concrete slab substrate o the prestressed concrete due to bs ε p = strain level o the prestressed tendons attained in section ailure ε pe = eective strain level o the prestressed tendons due to pe ε py = yield strain level o the prestressed tendons ε tp = initial strain level in the top prestressed concrete substrate due to p tp ε ts = initial strain level in the top concrete slab substrate o the prestressed concrete due to ts κ m = bond dependent coeicient or lexure κ v = bond reduction coeicient Aps ρ p = bd = ratio o prestressed reinorcement γ = actor or type o prestressing tendon p ψ = additional CFRP strength-reduction actor 93

114 7.2 Flexural Strength o T-Beam 1 The predicted nominal lexural capacity o T-Beam 1 was based on ACI building code. The mid-span cross-section o T-Beam 1 is shown in Figure 7-1. b = 66" 42" 1 Slab Reinorcement 2-leg #3 12" o.c " 1'-62" 1 dp = 24.65" 52" " (10) 3 8"Ø Stress-relieved 2 3 8" prestress strands 52" 1 1'-4 1 2" MIDSPAN BEAM SECTION Figure 7-1 Cross-section o T-Beam 1 The nominal lexural capacity was calculated using the ollowing ormula, M n = A ps ps d p a 2 where γ p pu d ps = pu 1 ρ p + ( ω ω' ) (ACI , Eq. 18-3). β1 ' c d p Since there was no mild tension steel in the T-Beam and the eect o the compression steel in the lange was negligible, ps was simpliied to, ps = pu γ p 1 ρ p β1 pu ' c 94

115 0.05( ' c 4000) where β = The lexural capacity o T-Beam 1 was predicted using the measured material property values. For ' c = 5396 psi or the concrete slab (Table 6.1), β = The area o one 3/8 diameter seven wire stress-relieved prestressing strand (grade 250) is in 2. The area o ten strands is thereore A ps = in 2. The width o the lange is b = 66" (Figure 7-1). The depth o the centroid o the prestressed strands is d p = 24.65". For stress-relieved tendons, γ p = Based on coupons tests, the ultimate strength o the prestressing tendons is pu = 272 ksi (Table 6.3). Substituting gives: ps = = x 66x ksi. From internal orce equilibrium, the depth o the concrete compression block is: Aps ps a = = 0.85 c b ' = 0.71". Note that c ' or the equivalent rectangular stress block is based on the concrete slab concrete cylinder tests. The depth o the equivalent rectangular stress block is less than the thickness o the concrete slab, thereore the nominal lexural capacity o T-Beam 1 is given by: M n = A ps ps d p a 0.71 = = 5228 kip - in = 436 kip - t

116 Using the nominal material strengths o ' c = 4000 psi or the top slab and pu = 250 ksi or the prestressed strands, the nominal lexural capacity o T-Beam 1 is M = 397 kip-t. n 7.3 Flexural Strength o T-Beam 2 (w/carbodur strips) The ACI 440R-02 report suggests a methodology or computation o the nominal lexural capacity o a reinorced concrete beam retroitted in lexure with CFRP bonded to the tension surace. The calculation is based on the ultimate limit state condition o the beam s stress and strain. However, the ACI 440R-02 report does not consider prestressed concrete members. An understanding o the stress and strain distribution o the reinorced concrete beam was helpul in the development o the equations used or calculating the nominal lexural capacity o a prestressed concrete beam retroitted with CFRP in lexure Flexural Capacity o a Reinorced Concrete Beam with CFRP 19 The stress and strain distribution o a typical reinorced concrete beam retroitted with CFRP is shown in Figure 7-2. The ACI 440R-02 procedure used to arrive at the nominal lexural strength o the beam satisies the strain compatibility and orce equilibrium o Figure 7-2. It also considers potential controlling ailure modes as compressive concrete crushing or CFRP debonding. 96

117 b c ε cu β c c ' h d (Neutral Axis) ε s e s e s ε e ε bi ε b Figure 7-2 Stress and strain distribution o a reinorced concrete beam with CFRP under lexure at ultimate limit state condition To determine the lexural strength o the beam, several equations must be satisied by trial and error. For an assumed depth o the neutral axis, c, the strain level o the CFRP is computed as: ε h c c e = ε cu ε bi κ mε u (ACI 440R-02, Eq.9-3) 1 ne t or ne t ε u where, κ m = (ACI 440R-02, Eq.9-2) or ne > t 60ε u ne t The let side o ACI 440R-02 equation 9-3 is based on strain compatibility o the beam section assuming concrete crushing, while the right side represents the CFRP debonding ailure mode. I the let side o the equation controls, the ailure mode o the section is concrete crushing, while debonding governs i the right side o the equation controls. The concrete ailure strain level is usually taken as

118 The initial strain level in the concrete at the level o the CFRP, ε bi, is computed considering the load experienced by the beam immediately prior to application o the CFRP. Usually, this load is the dead weight o the beam and any supported slab. It is appropriate to subtract the initial strain level rom the total strain level to get the eective strain level o the CFRP. Unless the beam is shored to relieve some o the existing dead load, this initial strain level must be considered when computing the strain in the CFRP. A bond dependent coeicient, κ m, is provided in the calculation as a saety actor against CFRP debonding. Since the tensile stress-strain relationship or the CFRP is linear until ailure, the stress level in the CFRP is given by: = ε (ACI 440R-02, Eq. 9-4). e E e Based on the strain level o the CFRP and the initial strain level o the concrete, the strain level o the non-prestressed steel reinorcement is determined using strain compatibility o the beam section as: d c ( ε + ε ) ε s = e bi (ACI 440R-02, Eq. 9-8). h c Assuming perectly elastic-plastic behavior or the non-prestressed steel, the stress level in the steel is given by: s = E ε (ACI 440R-02, Eq. 9-9). s s y Having determined the stresses in the CFRP and steel reinorcement or the assumed neutral axis depth, c, internal orce equilibrium is checked using: 98

119 As s + A e a = β 1c = (ACI 440R-02, Eq. 9-10). ' 0.85 b c The equivalent rectangular stress block (Whitney stress block) is used to estimate the compressive stress in the concrete compression zone or both potential ailure modes. I the value o c determined rom ACI 440R-02 equation 9-10 diers rom the assumed value, the new value o c is used as the next assumed c and the process repeats. Iteration o these equations continues until the neutral axis depth determined rom ACI 440R-02 equation 9-10 agrees with the assumed value. The nominal lexural capacity o the CFRP retroitted concrete beam is then determined as: a a M n = As s d + ψ A e h (ACI 440R-02, Eq. 9-11). 2 2 A reduction actor o ψ = is applied to the lexural strength contribution o the CFRP reinorcement Nominal Flexural Capacity o a Prestressed Concrete Beam with CFRP Since the ACI 440R-02 equations were developed or non-prestressed concrete beams, it was necessary to modiy these equations to determining the nominal lexural capacity o a prestressed concrete beam retroitted with CFRP. The modiied system is also based on strain compatibility and orce equilibrium o the prestressed member. The equations dier rom those presented in Section due to the presence o a prestressing orce in the steel and concrete, and the dierence in stress-strain response o prestressing steel compared with non-prestressed reinorcement. The stress and strain distributions in the beam at both initial and inal conditions are considered in this derivation. The initial condition represents the beam condition at the 99

120 time the CFRP retroit was applied. Usually, the stress and strain distribution in the beam at the initial condition is a unction o the level o prestress and the dead weight on the beam. A typical stress and strain proile o a prestressed concrete beam at the initial condition is shown in Figure 7-3. In order to generalize to a composite T-Beam section, this derivation considers a composite section with a non-prestressed top slab. b t c εtp ε ts ε bs tp ts bs h d p (Neutral Axis) ε pe ε cp ε bp pe cp bp Figure 7-3 Stress and strain distribution o a prestressed concrete beam under lexure at the initial condition (prior to application o CFRP) The stress levels in the concrete at the initial condition are: M ds ts = Sts E E c p M ds bs = Sbs E E c p tp = P A cp e P M ee + S S tp dp tp M S ds bs P P e M e e dp bp = + + Acp Sbp Sbp M S ds bc tp and cp = ( h d p ) + bp h t bp 100

121 The corresponding strain levels in the concrete at the initial condition are: ε ts = E ts c ε bs = E bs c ε tp = E tp p ε bp = E bp p ε tp ε bp ε cp = + h t ( h d p ) ε bp In addition to the stress and strain levels in the concrete, the stress and strain o the prestressed tendon at the initial condition are: = pe P A e cp ε pe = E pe ps where P e is the eective prestress ater losses at the time o installation o the CFRP. These values make up the stress and strain proile o Figure 7-3. It is likely that the majority o the precast prestressed concrete beam section will be in compression at the initial condition. In particular, the bottom ibers may be subjected to signiicant compression at the time o FRP application, as opposed to the small tensile strain in the bottom ibers or a non-prestressed beam. Once the initial condition has been determined, the stress and strain proiles or the inal condition are developed as shown in Figure 7-4. The inal condition is the ultimate limit state o the beam in lexure. 101

122 b t c ε cu β1c 0.85 ' c h d p (Neutral Axis) ε pe ε ε p cp p p ε bp e e ε e Figure 7-4 Stress and strain distribution o a prestressed concrete beam with CFRP under lexure at ultimate limit state condition At the ultimate limit state, the beam section experiences tension rom the neutral axis to the bottom o the section. The dotted line represents the initial strain condition o the prestressed concrete. Since the prestressing tendons were bonded to the concrete, the additional elongation o the tendons started at the initial condition. In addition, the CFRP elongation also started at the initial condition when the whole section was still in compression. To arrive at the nominal lexural strength o the prestressed concrete beam, several equations are developed which must satisy the strain compatibility and orce equilibrium o Figure 7-4. Also, the concrete strain levels must be checked according to the mode o ailure, namely concrete crushing or CFRP debonding. As beore, this new set o equations is satisied by iteration. For an assumed depth c, the strain level o the CFRP is computed rom: ε = h c c e ε cu + ε bp κ mε u. 102

123 Note that ε bp and ε bi have the same meaning, although the irst is or a prestressed beam while the second is or a non-prestressed beam. They both represent the initial strain at the bottom concrete iber beore the CFRP was applied. In the case o the prestressed beam, the strain in the CFRP at the ultimate limit state is the sum o this initial concrete compressive strain and the strain corresponding to crushing o the compression concrete at the top o the beam. Since the tensile stress-strain relationship or the CFRP is linear until ailure, the stress level in the CFRP is given by: = ε. e E e Based on the initial tensile strain in the prestressing steel and the compressive strain in the concrete at the level o the prestress steel centroid, the strain level o the prestressed steel at the ultimate limit state is determined rom strain compatibility as: d p c ε p = ε cu + ε cp + ε pe c. The strain level o the concrete at the centroid o the prestressing steel and the eective prestress strain in the prestressing steel due to the prestressing orce minus losses, are added to the strain induced in the prestressed tendons at the ultimate bending capacity. The stress corresponding to this strain must be determined rom the stressstrain relationship or the prestressing steel. I ε p ε py, then p = E p ε p. 103

124 I ε p > ε py, then p is determined rom the stress-strain relationship or the prestressing steel with a limit o, where, p ps ps γ p pu A u = pu 1 ρ p + ' ' β1 c bh c. This expression or ps takes into account the contribution o the CFRP lexural reinorcement. With the stresses in the CFRP and prestressing steel determined or the assumed neutral axis depth, c, internal orce equilibrium is checked using: Aps p + A e a = β 1c =. ' 0.85 b c Iteration o these equations is required until the neutral axis depth determined rom this equation matches with the assumed value. Once satisied, the nominal lexural capacity o the CFRP strengthened prestressed concrete beam computed as: a a M n = Aps p d p + ψ A e h Calculation o the Predicted Flexural Strength o T-Beam 2 This section presents the computation o the nominal lexural capacity o T-Beam 2 using this modiied ACI 440R-02 procedure or prestressed beams. In its initial condition in the Ala Moana Parking Garage, the beam supported a tributary width o 30 over a 30 span. The dead load supported by the beam at the time o retroit application is assumed to be the sel-weight o the precast beam and the weight o 30 tributary width o slab. Figure 7.5 shows the cross-section o the beam used to calculate this dead load. 104

125 30' Acp Acs Figure 7-5 T-Beam 2 tributary width at Ala Moana Parking Garage The initial dead load on the beam was thereore determined as ollows: Unit weight o concrete: 150 lb/t 3 Weight o precast beam: A cp = 198 in w dp = 150 = 206 lb/t 144 Weight o concrete slab: Acs = = 1620 in w ds = 150 = 1688 lb/t 144 Dead load moment: 2 w 2 dpl 206x24 12 M dp = = = 178 kip-in (precast) 2 2 wdsl 1688x30 12 M ds = = = 760 kip-in (concrete slab) Note that the precast sel-weight is supported by the precast member over a span o 24 eet, while the topping slab was added once the precast beam was installed on the column capitals, representing a span length o 30 eet. The precast section was shored during addition o the topping slab. Any continuity at the supports has been neglected to simpliy the computation o dead load moments. The initial stress level in the prestressing steel at the time o CFRP application was determined as ollows: With = 250 ksi, and 0.75 = = ksi. pu pi = pu Assuming 20% prestress loss, 0.80 = = 150 ksi. pe = pi Thereore, P A = = 120 kips e = pe ps 105

126 Material properties o the prestressed beam rom Table 6.1 are: ' ' = 9023 psi (concrete slab) and = 8397 psi (precast) c c E = 4800 ksi (concrete slab) and E = 4665 ksi (precast) c p Section properties: Precast Section: 15" 24" 9" cgp cgs e = 5.15" Figure 7-6 Section properties o the precast prestressed beam section I = in 4 y = 9" y = 15" p b t I p S bp = = 1119 in 3 I p S tp = = 672 in 3 y 9 y 15 = b = t 106

127 Composite Section (Flange transormed to equivalent width): 64" x 1.03= 66" 9.1" cgc 4.6" 19.4" Figure 7-7 Section properties o the composite section I = in 4 y = 19.4" y = 4.6" y = 9.1" c bc I c S bc = = 2363 in 3 I c S bs = = 9966 in 3 y 19.4 y 4.6 = bc = bs I c S ts = = 5038 in 3 Ec 4800 n c = = y 9.1 E 4665 = ts Initial Condition Stresses: = p M ds Ec 760 ts = = 1.03 = ksi S E 5038 ts p M ds Ec 760 bs = = 1.03 = ksi S E 9966 bs p bs ts tp = P A cp e P M ee + S S tp dp tp M S ds bs = x = = ksi bp = P A cp e P M ee + S S bp dp bp M + S ds bc = x = = ksi 107

128 tp bp cp = ( h d p ) + bp h t = ( ) = ksi and = 150 ksi. Initial Condition Strains (10-6 ): pe ts bs ε ts = = = = 32.3 ε bs = = = = E 4800 E 4800 c tp bp ε tp = = = = 5.79 ε bp = = = = 145 E 4665 E 4665 p c p ε pe = E pe ps = = = 5260 ε tp ε bp ε cp = ( h d p ) + ε bp h t = Figure 7-8 and Figure 7-9show the stress and strain proiles across the mid-span ( ) = = 123 cross-section or T-Beam 2 in lexure at the initial and ultimate loading conditions respectively. cgc Strain (10 ) Stress (ksi) Figure 7-8 Stress and strain distributions or T-Beam 2 at the initial condition 108

129 neutral axis 'c cgc 5260 ε p p e ε e -6 Strain (10 ) Stress (ksi) Figure 7-9 Stress and strain distributions or T-Beam 2 at ultimate state conditions Ater iteration the neutral axis depth converged to c=0.93. The ollowing calculations show the inal iteration loop. Strain level o the CFRP at the ultimate limit state is: ε e h c = ε cu + ε bp c κ m ε u where the CFRP debonding ailure mode coeicient is: κ m = 1 60 ε 1 60 ε u u 1 ne ne t t or ne or ne t t lb > lb / in / in and ne t = = lb / in > lb / in, thereore: κ m = ε u ne t * u C E u 0.85 x 406 where: ε u = = = = E E rom CFRP tests Thereore, κ m = = x and, κ = 0.53x0.014= mε u 109

130 h c Finally, ε e = ε cu + ε bp = = 0.089> c 0.93 The stress level in the CFRP is then: e = E ε e = = 177 ksi. The strain level in the prestressed steel at the ultimate limit state is: ε p d ε cu c + ε c p = cp + ε pe = = This strain exceeds the yield strain o the prestressing steel assumed to be ε = 0. 01, thereore the stress in the prestressing steel must be determined rom the stress-strain curve or the tendons. Reerring to the stress-strain relationship suggested by Nawy (2003) or stress-relieved 250 ksi tendons, the stress at ε > is = 250 ksi 20. p p py Checking ps : Thereore, β = ( ' c 4000) 0.05( ) β = 0.85 = 0.85 = 0.60 < ps γ p pu A u = pu 1 ρ p + ' β1 ' c bh c = = ksi Thereore, = 246 < 250 ksi. p = ps Checking the assumed neutral axis depth c: a = β A + A = 0.85(9.023)(64) ps p e 1 c = = ' 0.85 cb 0.604" 110

131 a Thereore, c = = = 0.93" which agrees with the assumed depth c. β The nominal lexural capacity o T-Beam 2 is then given by, a a M n = A ps p d p + ψ A e h = = = 7185 kip in = 599 k t

132 7.4 Shear Strength o T-Beam 1 (without shear retroit) The shear strength o T-Beam 1 was calculated using the ACI provisions or shear strength o composite prestressed concrete beams. T-Beam 1 spanned 24 t and supported two point loads at 25.5 inches rom mid-span as shown in Figure The shear strength analysis and shear proile along the length o the beam are developed in this section " existing shear stirrups (typ) 1' TYP P 4'-3" CL P 2' 24' TBEAM 1 Figure 7-10 T-Beam 1 layout or shear strength calculation Concrete T- Beam properties: Prestressed Beam Section: c' := 8413 psi pu := psi pi := psi pe := psi A ps := 0.8 in 2 cgs c := 3.85 in rom bottom cgs e := 10.5 in rom bottom E ps := ksi y := psi or stirrups h := 24 in b := 66 in b w := 5.5 in L := 24 t Topping Slab: ct' := 5396 psi h c := 28.5 in d p := in P e := pe A ps P e = lb 112

133 1. Calculate the location o the section centroid: i. prestressed section ii. composite section A cp := 198 in 2 E p := 4669 ksi prestressed E c := 3938 ksi topping E c y b := 9 in n c := n E c = 0.84 p y t := 15 in A cc := 445 in 2 y bc := 18.6 in I p := in 4 y ts := 9.9 in I c := in 4 I p S bp := S y bp := in 3 I c S bc := S b y bc = in 3 bc I p S tp := S y tp := in 3 I c S ts := S t y ts := in 3 ts e c := y b cgs c e c = 5.15 in Eccentricity o prestress tendons at center := e e = 1.5 in Eccentricity o prestress tendons at support e e y b cgs e 2. Compute concrete shear capacity based on lexure-shear cracking, V ci : A cp w d := W 144 d 0.52 W u := 1.2W d W u = 0.62 kl = kl Assuming normal weight concrete Beam sel weight plus topping sel weight 43 P l 1.6 P u := 1.6 P l P u = 43 kips V i () x M cr () x V ci ( x) := 0.6λ c' b w d p () x + V d () x + 1.7λ c' b () x w d p () x M max := kips Live load at each load point corresponding to lexural ailure o the beam. λ := 1.0 or normal weight concrete. d p () x := x i x i x < 5.67 x 1, := t Compute shear capacity at 1 t intervals rom support to load point. W u L V u ( x) + P 2 u W u x L V d () x W d x 2 := Factored shear orce at section x. := Shear orce at x due to un-actored dead load. := () V d () x actored shear orce at x due to external load. V i () x V u x 113

134 x = V d () x = V u () x = V i () x t kips kips kips V u0 := V u ( 0) V u0 = k Factored shear orce at support V d0 := V d ( 0) V d0 = 6.19 k Un-actored shear orce due to dead load at support = M d () x W d x ( L x) 2 M u () x W u x 2 V u ( 0) x 2 := Moment at section x due to un-actored dead load := Moment at section x due to actored load M max () x M u () x M d () x x := Maximum actored moment at section x due to external loads (not including dead load) = M u () x t M cr () x = M d () x k t I cc := 6 c' + y ce () x d () x bc ( ) = M max () x k t = kips t 114

135 Eccentricity o prestress at section x, 4 strands harped at section x=5.67 t rom support e c e e ex ():= e e + x i x < 5.67 e 5.67 c = 5.15 d () x ce () x M cr () x 5.15 i x M d () x e e = 1.5 := Stress due to un-actored dead load at section x S bp P e P e ex () + A cp S bp := Stress due to prestress at tension iber at section x I c 6 c' y ce () x d () x bc ( ) := Cracking moment x = ex () = ce () x = d () x = M cr () x t in psi psi k = M max () x = V ci ( x) := max 0.6 λ c' b w d p () x V d () x + V i () x M cr () x M max () x, 1.7λ c' b w d p () x 1000 x = d p () x t = V i () x = M cr () x = M max () x = V ci () x = kips 115

136 3. Compute concrete shear capacity based on web shear cracking, V cw ( ) b w V cw ( x) := 3.5λ c' pc () x d p () x + V p () x A ps pe P e := P 1000 e = 120 kips pe = psi cgs e = 10.5 in at the support cgs c = 3.85 in at center Vertical component o eective prestress at section x is: V p () x := ( ) P e cgs e cgs c 68 0 i x > 5.67 i x 5.67 y := y bc y bp y = 9.6 in distance between centroid o precast and composite sections pc () x P e P e ex () y := + A cp I p M d () x y 12 I p V cw () x 3.5 λ c' b w d p () x := pc () x b w d p () x + V p () x x where λ = 1 or normal weight concrete. = d p () x = pc () x = V p () x = V cw () x t ksi kips kips = 116

137 4. Shear Strength o Concrete, V c : ( ) V c ( x) := min V cw ( x), V ci ( x ) Shear strength o concrete x = V ci () x t = V cw () x = V c () x kips kips kips 5. Compute concrete shear capacity o steel stirrups, V s : Two - leg #3 12 in o.c. Although the bottoms o the stirrups are not anchored with a hook, the ull capacity o the stirrups is assumed in these calculations. = A s := 0.22 in 2 s := 12 in V s () x A s y d p () x := 1000s 6. Compute combined concrete and steel stirrup shear capacity, Vn: V n () x := V c () x + V s () x x = V c () x t = V s () x = V n () x = kips 117

138 7. Plot the Shear Capacity Proile or T-Beams 1 and 2 Figure 7-11 shows the applied shear diagrams or T-Beams 1 and 2 based on their lexural capacities, and the shear strengths or the T-Beams without CFRP shear reinorcement. The shear applied to T-Beam 1 exceeds the beam capacity over a 2 eet distance adjacent to the load points. For T-Beam 2, the applied shear exceeds the beam capacity or 5 eet on either side o the point loads. It was concluded that the shear capacity o both T-Beams should be increased by means o a CFRP shear retroit to reduce the potential or shear ailure during the lexural testing. Shear Force (kips) Shear Capacity Proile o T-beam1 Vci(x) Vcw(x) Vc(x) Vs(x) Vn(x) T-beam1 Shear Diagram T-beam2 Shear Diagram Span length o beam (t) Figure 7-11 Shear capacity and shear diagram o T-Beams 1 and 2 118

139 7.5 Shear Strength o T-Beam 2R1 (plain concrete) The shear capacity o T-Beam 2R1 was determined according to ACI provisions or non-composite prestressed concrete beams. It was analyzed as a noncomposite section because the dead weight o the beam was neglected. The nominal shear capacity is based on contributions rom the concrete and steel stirrups. Figure 7-12 shows T-Beam 2R1 test layout at ailure, along with the corresponding shear and bending moment diagrams. Pu=185 k existing shear stirrups (typ) 1' 1'-9 3 1' 4 " 1' 1' 1' 1' 6" 6" 6" 6" 6" 3' " 12' " TBEAM 2R1 Vu= V(kips) Mu=2664 M(kip-in) Figure 7-12 T-Beam 2R1 layout and shear and moment diagrams 119

140 T-Beam 2 Section Properties: ' = 8397 psi b = 5. 5 in d = in c w S = 1119 in 3 I = in 4 A = 198 in 2 bp c y = 19.4 in P = 120 kips λ = 1. 0 NWC bc e p cp Concrete Shear Strength: V c is lesser o V ci or V cw Calculation o V ci : V = kips u M = 2664 kip-in u Pe Pe e x5.15 pe = + = + = 1.16 ksi A S cp bp I c ' M (6 ) 1.16 cr = c + pe = = kip-in ybc ' Vu M cr ' Vci = 0.6λ c bwd p + 1.7λ c bwd p M u V = + = = 193 kips = 21.1 kips 1000 ci Thereore, V = 193 kips. ci Calculation o V cw : Pe pc = = 606 psi A 198 V p = cp = 0 ' ( ) ( ) c pc bwd p + V = = Vcw = λ p kips 1000 Thereore, V = kips. c 120

141 Strength o Shear Stirrups: Two - leg #3 12 in o.c, assuming ull anchorage at top and bottom o web: A = 0.22 in2 s = 12 in v Av yd p 0.22x50900x24.65 Vs = = = 23 kips 1000s 1000x12 Thereore, the nominal shear capacity o T-Beam 2R1 is: V V + V = = 91.1 kips. n = c s 121

142 7.6 Shear Strength o T-Beam 1L (w/cfrp stirrups) The shear capacity o T-Beam 1L was determined according to ACI and ACI 440R-02 guidelines. The concrete and existing steel stirrup contributions to the total shear strength were computed based on the ACI code. The CFRP shear retroit contribution was computed according to the recommendations in the ACI 440R-02 report. Figure 7-13 shows the T-Beam 1L test layout at ailure, and the corresponding shear and bending moment diagrams. Pu=87.5 k 1'-2" Pu=87.5 k " 1' TYP existing shear stirrups (typ) 2' 6" 2' " Vu= ' TBEAM 1L V(kips) 87.5 Mu=2319 M(kip-in) Figure 7-13 T-Beam 1L layout and shear and moment diagrams 122

143 T-Beam 1 Section Properties: ' = 8413 psi b = 5. 5 in d = in c w S = 1119 in 3 I = in 4 A = 198 in 2 bp c y = 18.6 in P = 120 kips λ = 1. 0 NWC bc e p cp Concrete Shear Strength: V c is lesser o V ci or V cw Calculation o V ci : V = 87.5 kips u M = 2319 kip-in u Pe Pe e x5.15 pe = + = + = 1.16 ksi A S cp bp I c ' M (6 ) 1.16 cr = c + pe = = kip-in ybc ' Vu M cr ' Vci = 0.6λ c bwd p + 1.7λ c bwd p M u V ci = + = = 157 kips = 21.1 kips 1000 Thereore, V = 157 kips. ci Calculation o V cw : Pe pc = = 606 psi A 198 V p = cp = 0 ' ( ) ( ) c pc bwd p + V = = Vcw = λ p kips 1000 Thereore, V = kips. c 123

144 Strength o Shear Stirrups: Two - leg #3 12 in o.c., assuming ull anchorage at top and bottom o the web: A = 0.22 in2 s = 12 in v Av yd p Vs = = = 23 kips 1000s Contribution o CFRP shear retroit ( V ) based on ACI 440R-02 report procedure: 5 2 " d=24.65" 2' cgs " 1' " Figure 7-14 Cross section o T-Beam 1L showing CFRP stirrup layout CFRP Stirrups Properties: Two sided stirrups: ψ = (ACI 440R-02, Table 10.1) ε κ ε (ACI 440R-02, Eq. 10-6b) e = v u d = 24.65" n = 2 plies s = 12" w = 3" t = 0.039" E = ksi * = 139 ksi C = u E 124

145 Calculation o V : A v ed V = (ACI 440R-02, Eq. 10-3) s e E v = ε (ACI 440R-02, Eq. 10-5) e A = 2nt w (ACI 440R-02, Eq. 10-4) k v k1k2l = 486ε e u 0.75 (ACI 440R-02, Eq. 10-7) * Ce u 0.85x139 ε u = = = (ACI 440R-02, Eq. 8-4) E Le = = 0.924" (ACI 440R-02, Eq. 10-8).58 ( nt E ) ( 2x0.039x ) = ' 8413 k 1 = c = = (ACI 440R-02, Eq. 10-9) 4000 d 2Le x0.924 k2 = = = (ACI 440R-02, Eq ) d k v = k1k2l 486ε e u 1.64x0.925x0.924 = = x0.011 thereore k = v ε = k ε = 0.262x0.011 = thereore ε = e v u e = E ε e = x0.003 = 31.8 ksi A v = 2 nt w = 2x2x0.039x3 = in 2 A v ed 0.468x31.8x24.65 V = = = 30.6 kips s 12 Thereore, the nominal shear capacity o T-Beam 1L is: e ( ) = Vn = Vc + Vs + ψ V = x = kips. 125

146 7.7 Shear Strength o T-Beam 2L (w/cfrp stirrups) The shear capacity o T-Beam 2L was determined according to ACI and ACI 440R-02 guidelines. The concrete and existing steel stirrup contributions to the total shear strength were computed based on the ACI code. The CFRP shear retroit contribution was computed according to the recommendations in the ACI 440R-02 report. Figure 7-15 shows the T-Beam 2L test layout at ailure, and the corresponding shear and bending moment diagrams. Pu=289 k 2'-2" 1'-4" 3'-3" 1' " " 2' existing shear stirrups (typ) 1'-1" 10" 1' 1' 1' 6'-9" TBEAM 2L 168 1' existing prestress strands V(kips) Vu= Mu=2360 M(kip-in) Figure 7-15 T-Beam 2L layout and shear and moment diagrams 126

147 T-Beam 2 Section Properties: ' = 8397 psi b = 5. 5 in d = in c w S = 1119 in 3 I = in 4 A = 198 in 2 bp c y = 19.4 in P = 120 kips λ = 1. 0 NWC bc Concrete Shear Strength: V c is the lesser o V ci or V cw. Calculation o V ci : V = 121 kips u M = 2360 kip-in u Pe Pe e x5.15 pe = + = + = 1.16 ksi A S cp bp I c ' M (6 ) 1.16 cr = c + pe = = kip-in ybc e p cp V ci = M ' u cr 0.6λ c bwd p + 1.7λ M u V ' c b w d p V = + = = 214 kips ci = 21.1 kips 1000 Thereore, V = 214 kips. ci Calculation o V cw : Pe pc = = 606 psi A 198 = cp 127

148 V p = 0 ' ( ) ( ) c pc bwd p + V = = Vcw = λ p kips 1000 Thereore, V = kips. c Strength o Shear Stirrups: Two - leg #3 12 in o.c., assuming ull anchorage at top and bottom o the web: A = 0.22 in2 s = 12 in v Av yd p Vs = = = 23 kips 1000s Contribution o CFRP shear retroit ( V ) based on ACI 440R-02 procedure: " d=24.65" 2' cgs " 1' " 3.85" Figure 7-16 Cross section o T-Beam 2L CFRP Stirrups Properties: Completely wrapped: ψ = (ACI 440R-02, Table 10.1) ε = ε (ACI 440R-02, Eq. 10-6a) e u d = 24.65" n = 2 plies 128

149 s = 12" w = 3" t = 0.039" E = ksi * = 139 ksi C = Calculation o V : u E A v ed V = (ACI 440R-02, Eq. 10-3) s e E v = ε (ACI 440R-02, Eq. 10-5) e A = 2nt w (ACI 440R-02, Eq. 10-4) * Ce u 0.85x139 ε u = = = (ACI 440R-02, Eq. 8-4) E ε = ε = x0.011 = thereore ε = e u e = E ε e = x0.004 = 42.4 ksi A v = 2 nt w = 2x2x0.039x3 = in 2 A v ed 0.468x42.4x24.65 V = = = 40.8 kips s 12 Thereore, the nominal shear capacity o T-Beam 2L is: ( ) = Vn = Vc + Vs + ψ V = x = kips. e 129

150 7.8 Shear Strength o T-Beam 1R (w/cfrp sheets) The shear capacity o T-Beam 1R was determined according to ACI and ACI 440R-02 guidelines. The concrete and existing steel stirrup contributions to the total shear strength were computed based on the ACI code. The CFRP shear retroit contribution was computed according to the recommendations in the ACI 440R-02 report. Figure 7-17 shows the T-Beam 1R test layout at ailure, and the corresponding shear and bending moment diagrams. Pu=131 k 1'-2" Pu=131 k 2' " 6" TYP 10' " 1'-6" Vu=131 TBEAM 1R V(kips) 131 Mu=3553 M(kip-in) Figure 7-17 T-Beam 1R layout and shear and moment diagrams 130

151 T-Beam 1 Section Properties: ' = 8413 psi b = 5. 5 in d = in c w S = 1119 in 3 I = in 4 A = 198 in 2 bp c y = 18.6 in P = 120 kips λ = 1. 0 NWC bc e p cp Concrete Shear Strength: V c is lesser o V ci or V cw Calculation o V ci : V = 131 kips u M = 3553 kip-in u Pe Pe e x5.15 pe = + = + = 1.16 ksi A S cp bp I c ' M (6 ) 1.16 cr = c + pe = = kip-in ybc V ci = M ' u cr 0.6λ c bwd p + 1.7λ M u V ' c b w d p V = + = = 153 kips ci = 21.1 kips 1000 Thereore, V = 153 kips. ci Calculation o V cw : Pe pc = = 606 psi A 198 = cp V p = 0 131

152 ' ( ) ( ) c pc bwd p + V = = Vcw = λ p kips 1000 Thereore, V = kips. c Strength o Shear Stirrups: Two - leg #3 12 in o.c., assuming ull anchorage at top and bottom o the web: A = 0.22 in2 s = 12 in v Av yd p Vs = = = 23 kips 1000s Contribution o CFRP shear retroit ( V ) based on ACI 440R-02 code: " d=20.15" cgs " 2' 1' " 3.85" Figure 7-18 Cross section o T-Beam 1R showing CFRP sheet layout CFRP Sheets Properties: Two sided sheets: ψ = (ACI 440R-02, Table 10.1) ε κ ε (ACI 440R-02, Eq. 10-6b) e = v u d = 20.15" n = 1 ply 132

153 s = 18" w = 12" t = 0.039" E = ksi * = 139 ksi C = Calculation o V : u E A v ed V = (ACI 440R-02, Eq. 10-3) s e E v = ε (ACI 440R-02, Eq. 10-5) e A = 2nt w (ACI 440R-02, Eq. 10-4) k v k1k2l = 486ε e u 0.75 (ACI 440R-02, Eq. 10-7) * Ce u 0.85x139 ε u = = = (ACI 440R-02, Eq. 8-4) E L = = 1.38" (ACI 440R-02, Eq. 10-8) e.58 ( nt E ) ( ) = ' 8413 k 1 = c = = (ACI 440R-02, Eq. 10-9) 4000 d 2Le k 2 = = = 0.86 (ACI 440R-02, Eq ) d k v = k1k2l 486ε e u = = thereore k = v ε k ε = = thereore ε = e = v u e = E ε e = = 42.4 ksi A 2 nt w = = in 2 v = A v ed V = = = 44.4 kips s 18 Thereore, the nominal shear capacity o T-Beam 1R is: e ( ) = V V + V + ψ V = = kips. n = c s 133

154 7.9 Shear Strength o T-Beam 2R2 (w/cfrp Sheets) The shear capacity o T-Beam 2R2 was determined according to ACI and ACI 440R-02 guidelines. The concrete and existing steel stirrup contributions to the total shear strength were computed based on the ACI-318 code. The CFRP shear retroit contribution was computed according to the recommendations in the ACI 440R-02 report. Figure 7-17 shows the T-Beam 2R2 test layout at ailure, and the corresponding shear and bending moment diagrams. Pu=284 k existing shear stirrups (typ) 11" 1'-2" 10" 1'-3" 1' 1'-1" " 10" 10" 1' 1' 1' 1' 1' 6" 6" 6" 6" 6" 4'-6" Vu=142 9' TBEAM 2R2 142 V(kips) Mu= M(kip-in) Figure 7-19 T-Beam 2R2 layout and shear and moment diagrams 134

155 T-Beam 2 Section Properties: ' = 8397 psi b = 5. 5 in d = in c w S = 1119 in 3 I = in 4 A = 198 in 2 bp c y = 19.4 in P = 120 kips λ = 1. 0 NWC bc e p cp Concrete Shear Strength: V c is lesser o V ci or V cw Calculation o V ci : V = 142 kips u M = 3408 kip-in u Pe Pe e pe = + = + = 1.16 ksi A S cp bp I c ' M (6 ) 1.16 cr = c + pe = = kip-in ybc V ci = M ' u cr 0.6λ c bwd p + 1.7λ M u V ' c b w d p V = + = = 175 kips ci = 21.1 kips 1000 Thereore, V = 175 kips. ci Calculation o V cw : Pe pc = = 606 psi A 198 = cp V p = 0 135

156 ' ( ) ( x606) x5.5x c pc bwd p + V p = = Vcw = λ kips 1000 Thereore, V = kips. c Strength o Shear Stirrups: Two - leg #3 12 in o.c., assuming ull anchorage at top and bottom o the web: A = 0.22 in2 s = 12 in v Av yd p Vs = = = 23 kips 1000s Contribution o CFRP shear retroit ( V ) based on ACI 440R-02 code: " d=20.15" cgs " 2' 1' " 3.85" Figure 7-20 Cross section o T-Beam 2R2 showing CFRP sheets CFRP Sheets Properties: Three sided sheets: ψ = (ACI 440R-02, Table 10.1) ε κ ε (ACI 440R-02, Eq. 10-6b) e = v u d = 20.15" n = 1 ply 136

157 s = 18" w = 12" t = 0.039" E = ksi * = 139 ksi C = Calculation o V : u E A v ed V = (ACI 440R-02, Eq. 10-3) s e E v = ε (ACI 440R-02, Eq. 10-5) e A = 2nt w (ACI 440R-02, Eq. 10-4) k v k1k2l = 486ε e u 0.75 (ACI 440R-02, Eq. 10-7) * Ce u 0.85x139 ε u = = = (ACI 440R-02, Eq. 8-4) E L = = 1.38" (ACI 440R-02, Eq. 10-8) e.58 ( nt E ) ( ) = ' 8397 k 1 = c = = (ACI 440R-02, Eq. 10-9) 4000 d Le k 2 = = = 0.93 (ACI 440R-02, Eq ) d k1k2le kv = = = thereore k v = ε u ε k ε = = thereore ε = e = v u e = E ε e = = 42.4 ksi A 2 nt w = = in 2 v = A v ed V = = = 44.4 kips s 18 Thereore, the nominal shear capacity o T-Beam 2R2 is: e ( ) = V V + V + ψ V = = kips. n = c s (Note: CFRP shear contribution was identical or T-Beam 1R and T-Beam 2R2). 137

158 138

159 CHAPTER 8 8 RESULTS AND DISCUSSION This chapter presents the lexural and shear results o the T-Beams tested in this program. In the irst section o this chapter, the lexural results o T-Beam 1 and T-Beam 2 are presented and compared with the predicted strengths covered in Chapter 7. In the rest o the chapter, the shear results o T-Beam 2R1, T-Beam 1L, T-Beam 2L, T-Beam 1R and T-Beam 2R2 are presented and compared with the predicted strengths covered in Chapter 7. In addition, the beam response and ailure modes are discussed in detail. 8.1 T-Beam 1 Response Figure 8-1 shows the initial setup or testing T-Beam 1 in lexure. The beam was tested over a simply supported span o 24 eet with two equal line loads applied at 2-1½ either side o mid-span. A detailed description o the test setup and instrumentation is provided in Chapter 5. Figure 8-1 T-Beam 1 ready or lexural testing 139

160 The bending moment at mid-span o T-Beam 1 is plotted against the mid-span delection in Figure 8-2. The plot shows the T-Beam 1 test result and the ACI predicted lexural capacity based on nominal material properties and the lexural capacity based on measured material properties. Six signiicant stages in the beam response are identiied on the plot. Crack propagation in the mid-span region o the beam at each o these stages is shown in Figure 8-3. The irst lexural cracks were observed at mid-span at the bottom o the beam at a bending moment o 196 kip-t (Figure 8-3, Stage 1). As the load increased, these cracks extended up into the web and new cracks ormed below the load points. Apparent yielding o the prestressing steel occurred between a mid-span delection o 0.30 and 0.50 inch as indicated by the change o slope o the moment-displacement response ater 0.50 inch displacement (Figure 8-2, Stage 2). Based on the initial stiness o the beam and the peak load capacity, an estimate o the yield displacement, y, is shown in Figure 8-2. The lexural ductility o the beam at subsequent stages is determined by comparison with this displacement. The mid-span lexural cracks continued to open as the load was increased (Figure 8-3, Stages 3, 4 & 5). The beam exceeded the ACI capacity based on nominal material properties at a delection o 1.6 inches, representing a ductility level o 4.69 (Figure 8-2 Stage 4). The beam reached an ultimate bending moment o 424 kip-t at a mid-span delection o u = 3.06 inches beore rupture o one or more o the prestress strands resulted in a sudden drop in load (Figure 8-2). This represents a ductility o 9.0 when compared with y. Complete lexural ailure occurred when the remaining prestressed strands ruptured at the center crack (Figure 8-3, Failure). 140

161 8.1.1 ACI 318 Predicted Flexural Capacities The lexural capacities o T-Beam 1 predicted by the ACI code using nominal and measured material properties are shown in Figure 8-2. The predicted nominal lexural capacity was based on the nominal material properties assumed in the original ' design o the beam ( = 4000 psi and = 250 ksi). Subsequent to beam ailure, c pu concrete cores and steel coupons were recovered and tested as described in Chapter 6. Based on these actual measured material properties, the ACI lexural capacity was recomputed. Calculations o the predicted lexural capacities are provided in Chapter 7. The beam reached the predicted nominal lexural capacity o 397 kip-t at 4.69 (Figure 8-2, Stage 4). The beam continued to carry load beyond this point reaching an ultimate bending moment o 424 kip-t. This ultimate strength represented an increase o 7% over the ACI code nominal capacity. The beam never reached the predicted lexural capacity o 436 kip-t based on actual material properties. This predicted strength was 3% higher than the ultimate strength o the beam. The ACI predicted lexural capacity based on actual material properties thereore provided a reasonable estimate o the lexural capacity o the beam. y 141

162 Moment-Displacement Curve Ductility Ductility Ductility 8.2 FAILURE 142 Moment (kip-t) Cracking 2 - "Yielding" T-Beam 1 Test Result Mn (ACI ) - Actual Mn (ACI ) - Nominal 1 - Cracking 2 - "Yielding" 3 - Ductility Ductility Ductility 8.2 FAILURE 150 Ductility: µ = u / y = y = y 4.69 y 8.2 y u = Midspan Vertical Displacement (in) Figure 8-2 Mid-span Moment Displacement Relationship or T-Beam 1

163 Stage 1 - Cracking Stage 2 Yielding Stage 3 Ductility Stage 4 Ductility 4.69 Stage 5 Ductility 8.2 Stage 6 - FAILURE Figure 8-3 T-Beam 1 mid-span condition corresponding to six ductility levels

164 8.1.2 Slab Reinorcement Strain Gage Readings Six electrical resistance strain gages were attached to the longitudinal reinorcement in the concrete slab. The gage locations are described in Chapter 5 and shown in Figure 8-4. The strains recorded by these gages during lexural testing o T-Beam 1 are plotted against the applied mid-span moment in Figure 8-4. These readings indicate that the top reinorcing strains did not exceed 1200 microstrain in compression, indicating that the extreme iber compression in the concrete slab was well below the assumed ailure strain o 3000 microstrain. This conirms the theoretical computations showing that the beam ailure is controlled by yielding o the steel and not compression ailure o the concrete. Figure 8-5 shows the strain distribution across the lange at mid-span or each o the 6 stages identiied in Figure 8-2. As expected, the strains increase with increasing applied load. It is also evident that the strains are almost constant across the ull width o the lange, indicating that the entire lange width is eective. Figure 8-6 shows the strain readings rom strain gages 1-4 plotted along the hal span o the beam. These strain proiles are again plotted at each o the six stages noted in Figure 8-2. Theoretically the strain in the compression zone should be constant between the load points and decrease linearly between the load point and the support. This trend is visible in Figure 8-6, however gages 1 and 4 deviates rom the expected response. Gage 4 was located slightly lower in the lange than gage 3, and appears to be aected by crack propagation into the lange at the inal stages o the test. The lower than expected strains at gage 1 may indicate inadequate protection o the gage during concrete placement resulting in ailure o the bond between the gage and the reinorcing steel. 144

165 Slab Reinorcement Readings 3" TYP 5'-6" 1'-11" 3' '-2" 2 " 2'-01 2 " " " 4 " 3" wide crp stirrups (typ) " " 1' " 1' TYP 6' 145 9'-9 1 7" TYP 14'-21 2 " 2 " Strain 1 (End-Center o Slab) Strain 2 (Next to End) Strain 3 (Next to MidSpan) Strain 4 (Midspan) Strain 5 (O Center) Strain 6 (O-Center Edge) Strain (10^-6) Moment (kip-t) Figure 8-4 T-Beam 1 slab reinorcement strain gage readings

166 Slab Reinorcement Strain Gage Readings or " 1' " " 1 1 2' " 4 " Cracking 2 - "Yielding" 3 - Ductility Ductility Ductility 8.2 FAILURE Strain (10^-6) Right Hal Span o T-Beam 1 cross section (in) Figure 8-5 Strain readings or strain gages 4-6 (T-Beam 1)

167 Slab Reinorcement Strain Gage Readings or 1-4 P P existing shear stirrups (typ) 4'-3" " " " " CL " 4 2' 24' 5'-6" 4'-2" 1'-11" 1 2 3' " 3 2' " 4 6' 147 Strain (10^-6) Support 1 - Cracking 2 - "Yielding" 3 - Ductility Ductility Ductility 8.2 FAILURE 14' " 1 2 9' " 3 4 (Center Line) Let Hal Span o T-Beam 1 (in) Figure 8-6 Strain readings or strain gage 1-4 (T-Beam 1)

168 8.1.3 Concrete Strain Gage Readings Several 2 gage length strain gages were installed on the concrete surace o T-Beam 1 as described in Chapter 5. These strain gages were installed as part o another research project to develop a strain-based delection monitoring system 16. The intent o this project was to measure the beam curvature so as to determine the delected shape by double integration o this curvature. Once the concrete cracks in tension, the bottom strain gages no longer represent the average strain in the beam, so this strain-based delection system is only eective while the beam is un-cracked. Once cracks orm in the tension concrete, the strain in the concrete between these cracks deviates rom that anticipated by beam theory Vertical Delection The vertical delection o T-Beam 1 was recorded by three LVDTs (linear variable displacement transducers) installed on the top slab as described in Chapter 5. In addition, dial gages were installed at each end o the beam to monitor any support settlement. The dial gage readings indicated negligible settlement at the supports. The LVDT readings on one side o the beam span were mirrored to produce a complete delected shape at each o the six stages identiied in Figure 8-2. The resulting delected shapes are shown in Figure 8-7. These delection proiles conirm that the majority o the beam curvature is concentrated between the load points due to signiicant cracking in this region. This is particularly evident or the inal stages prior to ailure Strains in the CFRP stirrups and sheets Although shear ailure was not anticipated to control the ailure o T-Beam 1, our strain gages were attached to the CFRP stirrups and sheets as described in Chapter

169 These strain gages were installed to monitor the vertical strain in the shear retroit close to the supports. Figure 8-8 shows that the strains in the CFRP shear retroit were small throughout the test, never exceeding 21 microstrain. No shear cracking was observed in the shear spans during testing o T-Beam

170 Vertical Displacement rom LVDTs DIAL GAGE existing shear stirrups (typ) P CL 4'-3" LVDT 3 P LVDT 2 12' LVDT 1 6'-9" 3'-9" DIAL GAGE " 2' Dial Gage 0.5 Vertical Displacement (in) Mirror Image Mirror Image 24' Beam Span Length (in) LVDT 3 LVDT 2 Dial Gage LVDT Cracking 2 - "Yielding" 3 - Ductility Ductility Ductility 8.2 FAILURE Figure 8-7 Representation o the vertical delection o T-Beam 1 rom LVDT readings

171 Strain gage readings on rp stirrups and sheets existing shear stirrups (typ) P 4'-3" P CL " 1' " ' 2'-3" 1'-5" 1'-4" 1' " 3' 22 1'-5" 151 Moment (kip-t) Let Span (3" wide double layer CFRP stirrups) Right Span (12" wide CFRP sheets) 24' Strain 22 (Right Edge CFRP Sheet) 250 Strain 23 (Second Right Edge CFRP Sheet) 200 Strain 24 (Third Let Edge CFRP Stirrup) Strain 25 (Second Let Edge CFRP Stirrup) Strain (10^-6) Figure 8-8 Strain readings rom gages attached to CFRP stirrups and sheets (T-Beam 1)

172 8.2 T-Beam 2 Response T-Beam 2 was tested under the same loading conditions as T-Beam 1. However, the span length was increased to 25 eet and 8 ½ inches because the supports were located under steel brackets bolted to the ends o the beam. This was necessary to prevent the support condition rom providing additional restraint to the ends o the carbodur strips on the beam soit. Figure 8-9 shows the test setup or T-Beam 2. More detailed inormation on the test setup and instrumentation o T-Beam 2 is provided in Chapter 5. Figure 8-9 T-Beam 2 ready or lexural testing The mid-span bending moment-displacement response o T-Beam 2 is plotted in Figure 8-10 along with the response recorded or T-Beam 1. The plot also shows the 152

173 lexural capacity predicted by the modiied ACI 440R-02 procedure using measured material properties. Six signiicant stages in the beam response are identiied on this plot with associated damage conditions shown in Figure For ease o comparison, the response o T- Beam 1 and the ACI predicted lexural capacity is also plotted in Figure The irst lexural cracks were observed at mid-span at the bottom o the beam at a bending moment o 217 kip-t (Figure 8-11, Stage A). As the load increased, these lexural cracks extended up into the web and new lexural-shear cracks ormed below and outside the load points. Based on the change in slope o the moment-displacement response, yielding o the prestressing steel was considered to occur between mid-span delections o 0.30 and 0.50 inch. Based on the intersection o the initial and inal stiness tangents, the yield displacement was deined as y = inch (Figure 8-10). Subsequent to yielding, the stiness o T-Beam 2 with CFRP carbodur strips exceeded the stiness o T-Beam 1 without the carbodur retroit. As the load increased, the lexural cracks between the load points and the lexuralshear cracks outside the load points continued to open (Figure 8-11, Stages C, D, & E). The stiness o the beam remained relatively constant through these three stages. Failure occurred at a bending moment o 725 kip-t with a maximum mid-span delection o 4.03 inches when the carbodur strips delaminated rom the beam soit over the let hal o the span (Figure 8-11, Failure). Based on the deinition o yield displacement shown in Figure 8-10, the ultimate ductility o T-Beam 2 was Both in terms o ductility and total mid-span delection, 153

174 T-Beam 2 response was more ductile than that or T-Beam 1. The addition o CFRP carbodur strips as tension reinorcement has not reduced the ductility as observed in some prior research studies (Chapter 3). This is attributed to the relatively low reinorcement ratio or the original prestressed beams and to the presence o anchorage wraps to prevent premature delamination at the ends o the CFRP strips. During the lexural test o T-Beam 2, the response was similar to that or T-Beam 1 up to the yield point. Initially, T-Beam 2 was less sti than T-Beam 1 as a result o the longer span or T-Beam 2. However, the post-yielding stiness o T-Beam 2 was greater than T-Beam 1 and did not degrade as rapidly. At stage C in Figure 8-10, T-Beam 2 supported the same load that caused ailure in T-Beam 1, but at a third o the mid-span delection. The cracks in T-Beam 2 at this stage (Figure 8-11, Stage C) were signiicantly shorter and smaller than those at the same load in T-Beam 1 (Figure 8-3, Stage 5). The CFRP lexural reinorcement was instrumental in reducing the crack sizes and limiting the delection at the nominal moment capacity o the control beam. The ACI 440R-02 procedure was modiied or prestressed beams in Chapter 7. This procedure predicted a lexural capacity o 599 kip-t or T-Beam 2. T-Beam 2 exceeded this bending moment at a mid-span delection o 2.5 inches. The beam supported an ultimate moment o 725 kip-t, which is 21% greater than ACI 440R-02 predicted moment capacity. This ultimate capacity also represents a 71% increased over the ultimate capacity o T-Beam 1, while the ACI 440R-02 procedure suggests the increase to be around 37% compared with the ACI predicted lexural capacity based on measured material properties. 154

175 155 Moment (kip-t) B - "Yielding" A - Cracking C - Ductility Moment-Displacement Curve 4 D - Ductility E = Ductility 6.74 FAILURE (Max Load) FAILURE T-Beam 2 Test Result Mn (ACI 440R-02) - Actual T-Beam 1 Test Result Mn (ACI ) - Actual A - Cracking B - "Yielding" C - Ductility 2.42 D - Ductility 4.98 E = Ductility 6.74 FAILURE (Max Load) 0 y = y 4.98 y 6.74 y u = Midspan Vertical Displacement (in) Ductility: µ = u / y = 9.37 Figure 8-10 Mid-span Moment-Displacement Relationship or T-Beam 2

176 A Cracking B Yielding C Ductility D Ductility 4.98 E Ductility 6.74 FAILURE Figure 8-11 T-Beam 2 condition corresponding to six ductility levels

177 8.2.1 Failure mechanism or T-Beam 2 Failure o T-Beam 2 occurred when the CFRP strips delaminated rom the bottom o the beam over the let shear span. This delamination appeared to initiate at the base o a lexure-shear crack that had ormed just outside the let load point (Figure 8-12). Vertical oset in the soit o the beam on either side o this crack may have contributed to the initiation o delamination. In addition, large strain dierential between the CFRP strips and the lexurally cracked concrete would also have contributed to deterioration o the bond between CFRP and concrete. Figure 8-12 Flexure-shear crack ormed outside o the let load point (T-Beam 2). 157

178 For the irst 18 inches rom the delamination initiation point, the ailure occurred in the surace concrete, with a thin layer o concrete remaining attached to the CFRP strips (Figure 8-13). Beyond this point, the CFRP strips separated rom the epoxy, likely because o the increased angle o peeling as the CFRP stripped away rom the beam soit. The delamination occurred rapidly and extended rom the lexure-shear crack to the end o the CFRP strips, which pulled hal way out o the CFRP abric wrap anchors (Figure 8-14). There was no tendency or delamination to initiate at the end o the carbodur strips as had been reported in some laboratory studies, however the anchor wraps were not suicient to prevent pull-out once delamination had initiated elsewhere. Figure 8-12 and Figure 8-13 show the bottom o the CFRP shear stirrups adjacent to the ailure crack. The stirrups were not continuous around the soit o the beam so as not to add anchorage to the carbodur strips that was not present in the ield application being evaluated. However, it was evident that the bottom bulb o the T-Beam has split open with the ledge sections rotating outwards with the CFRP stirrups still attached. The bottom o the bulb, with carbodur strips, was then ree to move downward, causing delamination o the lexural CFRP. Had the CFRP shear stirrups been continuous around the soit o the beam, they may have prevented this splitting o the bottom bulb and delayed the delamination o the carbodur strips. In some o the subsequent shear test on the beam halves with CFRP shear retroit, continuity o the stirrups and sheets was instated by splicing additional wraps around the soit o the beam. 158

179 Front side o beam Back side o beam Figure 8-13 Delamination o carbodur strips initiating at the lexure-shear crack Figure 8-14 Carbodur strips delaminated rom beam and pulling out o CFRP wrap anchor 159

180 8.2.2 Slab Reinorcement Strain Gage Readings A total o six strain gages were attached to the longitudinal reinorcement in the top slab o T-Beam 2. The strain gage locations are described in Chapter 5, and were relatively close to those used in T-beam1. Strain readings rom these strain gages are plotted in Figure The maximum strain is around 900 microstrain, which is similar to the maximum observed in T-Beam 1. This suggests that the concrete in the compression block is well below the assumed ailure strain o 3000 microstrain and that tension ailure, and not concrete crushing, should govern beam ailure. This conirms the ductile lexural ailure observed or T-Beam 2. These top slab strain readings were plotted across the mid-span section and along the length o the beam to illustrate the strain distribution in the top slab. Proiles are plotted or each o the six stages identiied in the moment-displacement curve (Figure 8-10). Figure 8-16 shows the strain distribution across the slab at the mid-span section based on strain readings rom strain gage 4-6. The shape o the distribution is similar to that observed in T-Beam 1. Strain gage 4 is set lower in the slab than gages 5 and 6, resulting in lower strain readings. However the gages illustrate the nearly uniorm distribution o stress across the ull width o the slab. This conirms that the ull width o the lange was eective in compression. Figure 8-17 shows the distribution o strain along the let hal o the beam based on strain readings rom gages 1-4. Strain gage 2 was damaged during the concrete pour and did not provide reliable strain readings. The remaining gages show the expected decrease in strain rom a maximum at the load point to zero at the supports. The strains at gage 4 were low because its location was lower in the slab than the other gages. 160

181 8.2.3 Vertical Displacement rom LVDT Readings Three LVDTs were used to record vertical delections o the top o the concrete slab during testing. Since no support settlement was observed in the test o T-beam1, dial gages were not placed at the supports or T-Beam 2. Figure 8-18 shows the beam delection at each o the previously identiied load stages using the three LVDT readings and their mirror image on the other hal o the beam. 161

182 Slab Reinorcement Readings 5'-4" 1 1'-11" 3' " 3" wide crp stirrups (typ) 1'-11" 3 1' 1' ' TYP 162 Strain 1 (End-Center o Slab) Strain 2 (Next to End)-Damaged Strain 3 (Next to MidSpan) Strain 4 (Midspan) Strain 5 (O Center) Strain 6 (O-Center Edge) 24'-10" Strain (10^-6) 7" TYP Moment (kip-t) Figure 8-15 Strain readings or slab reinorcement strain gage (T-Beam 2)

183 Slab Reinorcement Strain Gage Readings or " 1' 1' 2" 163 Strain (10^-6) (Center Line) 5 6 A - Cracking B - "Yielding" C - Ductility 2.42 D - Ductility 4.98 E - Ductility 6.74 FAILURE (Max Load) Right Hal Span o T-Beam 2 cross section (in) Figure 8-16 Strain readings or strain gages 4-6 (T-Beam 2)

184 Slab Reinorcement Strain Gage Readings or 1-4 P P existing shear stirrups (typ) 4'-3" " 2" " 2 1 2" " CL 4 2' 25' " 5'-4" 1'-11" 1 3' " 2 (Damaged) 1'-11" '-10" 3 Strain (10^-6) Slab A - Cracking 1 B - "Yielding" C - Ductility 2.42 D - Ductility 4.98 E - Ductility 6.74 FAILURE (Max Load) Support Slab Let Hal Span o T-Beam 2 (in) Figure 8-17 Strain readings or strain gages 1-4 (T-Beam 2) 4 (Center Line)

185 Vertical Displacement rom LVDTs existing shear stirrups (typ) P CL 4'-3" LVDT 1 P LVDT 2 12'-5" 6'-9" LVDT 3 3'-9" " 2' 25' " 165 Vertical Displacement (in) Beam Span Length (in) Support Mirror Image Mirror Image LVDT 1 LVDT 2 Figure 8-18 Representation o the vertical delection o T-Beam 2 rom LVDT readings LVDT 3 A - Cracking B - "Yielding" C - Ductility 2.42 D - Ductility 4.98 E - Ductility 6.74 FAILURE (Max Load) Support

186 8.2.4 Carbodur Strip Strain Gages T-Beam 2 was retroitted in lexure with three carbodur strips. Strain gages were attached to each o these strips to monitor the longitudinal strains during lexural testing. The gages were installed on each strip at the locations shown in Figure CL Third Strip Second Strip First Strip ' " 3' 3' 3' 2' " 8' " 3' Figure 8-19 T-Beam 2 beam soit showing location o strain gages These strain gages all provided reliable readings throughout the test. Strain gages 7-9 and registered very small strains because they were ar rom mid-span and close to the supports (Figure 8-20 and Figure 8-21). Strain gages and were virtually symmetric about mid-span (Figure 8-22 and Figure 8-23). They recorded small strains up to a mid-span bending moment o 520 kip-t, ater which the strains increased linearly to a maximum o 2800 microstrain. Strain gages also recorded small strains until the mid-span bending moment reached 340 kip-t. At this point the strains increased linearly to a maximum o 8500 microstrain (Figure 8-24). This high strain relects their position close to the let load point. Note that no corresponding strain gages were installed on the right hal o the beam because o the transverse wrap covering the carbodur strips. Although this wrap had been removed rom the sides o the beam to avoid restraining the carbodur strips, it was not removed rom the strips themselves so as to avoid damaging the carbodur material. Strain gages and show almost identical behavior because they are below or between the load points and thereore represent sections subjected to the same bending 166

187 moment (Figure 8-25 and Figure 8-26). Strain gages recorded small strains up to a mid-span bending moment o 220 kip-t, which corresponds to the irst lexural cracks observed in the mid-span region. The slope then decreased signiicantly but remained constant until the maximum strains o around microstrain were recorded immediately prior to beam ailure. Gages experienced similar response except that the change in slope was delayed until lexural cracks developed under the point load at 250 kip-t mid-span moment. The six stages identiied in the moment-displacement curve are also plotted on the moment-strain relationships. In all cases the change in slope o the strain diagrams was the result o ormation o cracks in the beam soit at or near the strain gage locations. This cracking initiated at mid-span and under the point loads, but slowly spread towards the supports as the load increased (Figure 8-27). Figure 8-28 to Figure 8-30 show the strains in all gages attached to a particular carbodur strip. Figure 8-31 to Figure 8-33 show the proile o strain along the length o each carbodur strip corresponding to the six stages identiied earlier. As noted above, the strains were highest within the point loads and decreased towards the supports. 167

188 168 Moment (kip-t) 1' " E D C B A 3' FAILURE 3' Carbodur Strip Strain Gages First Strip 10 3' 2'-1 1 8' " 2 " 3' Strain (10^-6) Third Strip Second Strip Figure 8-20 Strain readings o strain gages 7-9 Strain Gage 7 Strain Gage 8 Strain Gage 9 A B C D E FAILURE

189 169 Moment (kip-t) 1' " C B A E D 3' FAILURE 3' Carbodur Strip Strain Gages First Strip 10 3' 2'-1 1 8' " 2 " 3' Strain (10^-6) Third Strip Second Strip Figure 8-21 Strain readings o strain gages Strain Gage 25 Strain Gage 26 Strain Gage 27 A B C D E FAILURE

190 170 Moment (kip-t) 1' " C B A 3' D E 3' FAILURE Carbodur Strip Strain Gages First Strip 10 3' 2'-1 1 8' " 2 " 3' Strain (10^-6) Third Strip Second Strip Figure 8-22 Strain readings o strain gages Strain Gage 10 Strain Gage 11 Strain Gage 12 A B C D E FAILURE

191 Carbodur Strip Strain Gages Moment (kip-t) 1' " C B A 3' D E 3' First Strip 10 3' 2'-1 1 8' " 2 " 3' FAILURE Third Strip Second Strip Strain Gage 22 Strain Gage 23 Strain Gage 24 A B C D E FAILURE Strain (10^-6) Figure 8-23 Strain readings o strain gages 22-24

192 Carbodur Strip Strain Gages Moment (kip-t) 1' " B A 3' C 3' First Strip 10 3' 2'-1 1 8' " 2 " 3' D E Third Strip Second Strip FAILURE Strain Gage 19 Strain Gage 20 Strain Gage 21 A B C D E FAILURE Strain (10^-6) Figure 8-24 Strain readings o strain gages 19-21

193 Carbodur Strip Strain Gages Moment (kip-t) 1' " ' B A 3' C First Strip 10 3' 2'-1 1 8' " 2 " 3' D Third Strip Second Strip E FAILURE Strain Gage 16 Strain Gage 17 Strain Gage 18 A B C D E FAILURE Strain (10^-6) Figure 8-25 Strain readings o strain gages 16-18

194 174 Moment (kip-t) 1' " ' A B 3' C Carbodur Strip Strain Gages First Strip 10 3' 2'-1 1 8' " 2 " 3' D E FAILURE Strain (10^-6) Third Strip Second Strip Strain Gage 13 Strain Gage 14 Strain Gage 15 A B C D E FAILURE Figure 8-26 Strain readings o strain gages 13-15

195 175 Web-shear racks that ormed on let span Web-shear cracks that ormed on right span Flexure-shear cracks started under the point load. At higher loading, web-shear cracks ormed away rom the mid-span. Figure 8-27 Web-shear cracks orming away rom the mid-span o beam as conirmed by carbodur strain readings

196 176 Moment (kip-t) 1' " ' 3' Carbodur Strip Strain Gages on the First Strip Third Strip Second Strip First Strip 10 3' 2'-1 1 8' " 2 " 3' Strain Gage 25 Strain Gage 22 Strain Gage 19 Strain Gage 16 Strain Gage 13 Strain Gage 10 Strain Gage Strain (10^-6) Figure 8-28 Strain readings or gages on the irst carbodur strip

197 177 Moment (kip-t) 1' " ' 3' Carbodur Strip Strain Gages on the Second Strip Third Strip Second Strip First Strip 10 3' 2'-1 1 8' " 2 " 3' Strain Gage 26 Strain Gage 23 Strain Gage 20 Strain Gage 17 Strain Gage 14 Strain Gage 11 Strain Gage Strain (10^-6) Figure 8-29 Strain readings or gages on the second carbodur strip

198 178 Moment (kip-t) 1' " ' 3' Carbodur Strip Strain Gages on the Third Strip Third Strip Second Strip First Strip 10 3' 2'-1 1 8' " 2 " 3' Strain Gage 27 Strain Gage 24 Strain Gage 21 Strain Gage 18 Strain Gage 15 Strain Gage 12 Strain Gage Strain (10^-6) Figure 8-30 Strain readings or gages on the third carbodur strip

199 Gages on First Strip 179 Strain (10^-6) 1' " 25 0 Support Gage ' 3' Gage First Strip 10 3' 2'-1 1 8' " 2 " 3' Gage Gage Beam Span (in) Gage 13 Third Strip Second Strip Gage 10 Gage 7 Support A - Cracking B - "Yielding" C - Ductility 2.42 D - Ductility 4.98 E - Ductility 6.74 FAILURE (Max Load) Figure 8-31 Strain readings on the irst carbodur strip corresponding to the six ductility levels

200 180 Strain (10^-6) 1' " 25 0 Support Gage ' 3' Gage 23 Gage 20 Gages on Second Strip First Strip 10 3' 2'-1 1 8' " 2 " 3' Gage Beam Span (in) Gage 14 Third Strip Second Strip Gage 11 Gage 8 Support A - Cracking B - "Yielding" C - Ductility 2.42 D - Ductility 4.98 E - Ductility 6.74 FAILURE (Max Load) Figure 8-32 Strain readings on the second carbodur strip corresponding to the six ductility levels

201 1' " 25 0 Support Gage ' 3' Gages on Third Strip First Strip 10 3' 2'-1 1 8' " 2 " 3' Beam Span (in) Third Strip Second Strip Gage 9 Support Gage 24 Gage 12 Strain (10^-6) Gage 21 Gage 18 A - Cracking B - "Yielding" C - Ductility 2.42 D - Ductility 4.98 E - Ductility 6.74 FAILURE (Max Load) Gage 15 Figure 8-33 Strain readings on the third carbodur strip corresponding to the six ductility levels

202 8.3 ACI 440 Versus Experimental Moment Capacity The moment capacity o T-Beam 2 was compared with the ACI 440R-02 prediction using the same approach as Lyle Nakashima in his Masters Report 21. Figure 8-34 rom his report shows the normalized nominal moment capacities o previous tests on FRP retroitted concrete beams compared with the ACI 440 report predictions. The nominal moment values are normalized with respect to the beam cross-section dimensions. The 45-degree datum represents a one-to-one agreement between the predicted and experimental results. For all specimens the experimental results exceed the ACI 440 predictions. The ailure moment capacity o T-Beam 2 with CFRP carbodur strips is also plotted in Figure Because o the large lange width, the normalized moment capacity is considerably lower than the tests perormed on rectangular sections. The experimental bending capacity exceeded the ACI 440R-02 prediction as indicated by the point alling below the 45 degree datum. 182

203 1.80 ACI 440 Vs. Experimental Moment Capacities ACI 440 Mn/bdp 2 (ksi) Experimental M n /b d p 2 (ksi) Spaeda Shahawy Fanning Bonacci Swamy T-Beam 2 GangaRao White Design Datum Figure 8-34 Plot o Normalized ACI 440 prediction and experimental moment capacities

204 8.4 Shear Strength o T-Beam 2R1 (plain concrete) T-Beam 2R1 represents a shear test o the right hand portion o T-Beam 2 with internal steel stirrups but no externally applied CFRP shear reinorcement. It was loaded so as to induce a shear ailure in the area without CFRP shear stirrups or sheets shown in Figure The test section had a span to depth ratio o about 1.5. A detailed description o the test setup and instrumentation is provided in Chapter 5. Figure 8-35 Test setup and shear span o T-Beam 2R1 The shear orce applied to the test shear span is plotted against the vertical displacement at the applied load in Figure The ACI predicted shear strengths provided by concrete, V c, and concrete plus internal steel stirrups, V c +V s, are also plotted or comparison with the test result. Three stages were selected in the response and identiied in Figure The beam condition at each o these stages is shown in Figure The irst diagonal tension crack ormed in the test span under an applied shear orce o 58 kips (Figure 8-37, Initial Crack). It initiated in the web as a web-shear crack. As the load increased, additional diagonal cracks ormed adjacent to the original crack. This zone o diagonal cracking extended downwards toward the let support and up to the 184

205 soit o the concrete slab. By the time the applied shear reached 86 kips, the diagonal crack zone extended rom the support to the soit o the top slab (Figure 8-37, Applied Load o 130 kips). The width o the cracks continued to open until the beam reached its maximum load capacity at an applied shear o 122 kips which is 34% greater than the predicted ACI nominal shear capacity (Figure 8-37, FAILURE). Figure 8-38 and Figure 8-39 show the ailure shear zone ater removal o the loose concrete. The shear ailure crossed three o the internal steel stirrups. Only the center stirrup reached its ull capacity and ailed in tension at the shear zone (Figure 8-38). The stirrup that crossed the shear zone close to the bottom o the web ailed due to anchorage pull-out because o the lack o hook anchorage at the bottom o the web (Figure 8-39). Better anchorage o this vertical stirrup in the original construction may have increased the shear capacity. The shear stirrup that crossed the shear zone at the top o the web did not ail, but was unable to prevent propagation o the shear crack through the top slab (Figure 8-38). The tension reinorcement consisting o internal prestressing strands and externally applied carbodur strips were deormed when shear ailure occurred but did not ail (Figure 8-38 and Figure 8-39). In spite o inadequate anchorage o the shear stirrups at the bottom o the web, the shear capacity o the original prestressed concrete beam well exceeded that predicted by the ACI code. This may be attributed to the relatively high concrete strength and general conservatism in the ACI shear estimate. In addition, the shear span to depth ratio o around 1.5 restricted the shear ailure to a limit portion o the beam. 185

206 160 T-Beam 2R1 Shear-Displacement Curve FAILURE 186 Shear (kips) Initial Crack Applied 130 kips Vc + Vs (ACI ) Vc (ACI ) Vertical Applied Load (in) Figure 8-36 Shear-Displacement relationship or T-Beam 2R1

207 Front Side Initial Shear Crack Back Side Front Side Applied load o 130 kips Back Side Front Side Back Side FAILURE Figure 8-37 T-Beam 2R1 condition at critical stages during the test 187

208 Figure 8-38 Failure o steel shear reinorcement at ailure shear crack Figure 8-39 Shear reinorcement anchorage ailure at base o web 188

209 8.5 Shear Strength o T-Beam 1L (CFRP Stirrups) T-Beam 1L was retroitted in shear with CFRP stirrups. The test setup and layout o T-Beam 1L are shown in Figure The beam was supported on pinned supports at both ends o the span. During testing, it was noted that the supports were resisting longitudinal movement o the bottom o the beam, thereby introducing a net compression in the beam. The beam was unloaded and a roller support installed at the right support. The beam was reloaded with the second test supported on pinned and roller supports at the two ends. A more detailed description o the test setup is given in Chapter 5. Both results rom the irst and second loadings are presented below. Although the beam experienced signiicant shear cracking, the shear capacity o the section was not reached beore lexural ailure o the beam at mid-span. Subsequent shear test specimens were retroitted in lexure with carbodur strips to prevent premature lexural ailure. Figure 8-40 Test setup o T-Beam 1L (CFRP stirrups) 189

210 The shear-displacement relationships or each loading are plotted in Figure Six signiicant stages are noted on the response. The predicted shear capacities rom ACI and ACI 440R-02 are also shown. The beam condition at each o the highlighted stages is shown in Figure 8-42 through Figure On the ront o the beam, the black lines reer to the cracks observed during the lexural test o T-Beam 1. The red lines indicate the shear cracks resulting during T-Beam 1L testing. On the back o the beam, the opposite color scheme applies with the shear cracks indicated in black. The irst visible diagonal tension crack occurred at a shear orce o about 50 kips (Figure 8-42, Initial Crack). Existing cracks rom prior lexural testing o T-Beam 1 also increased in size as the load increased. With increasing load, lexural cracks ormed at mid-span while additional shear cracks ormed parallel to the irst diagonal tension crack (Figure 8-42, Applied Load o 148 kips). The beam reached a maximum shear orce o 85 kips (Figure 8-42, Applied Load o 170 kips) beore ailing in lexure at mid-span (Figure 8-43). Although the ull shear capacity o the beam was not achieved, a number o observations were made regarding the perormance o the CFRP shear stirrup retroit. At a shear load o 64 kips, portion o a CFRP stirrup delaminated rom the concrete surace (Figure 8-44, D-0.45). The delamination extended as the load increased. A second CFRP stirrup started delaminating at an applied shear o 78 kips (Figure 8-44, D-0.60). The eect o this delamination on the strains in the CFRP stirrups is discussed in Section Delamination initiated at uneven sections o the concrete web. Because o deviations in the stirrup alignment, tension developing in the CFRP stirrup resulted in out-o-plane 190

211 loads on the bond between the CFRP and concrete surace. Better preparation o the concrete surace may have reduced this tendency, however, deviations in the CFRP alignment are to be expected during typical installation. This delamination would probably have resulted in the complete debonding o the shear stirrups had it not been or the continuity provided at the top o the stirrups by wrapping the CFRP through the top slab. In addition, the steel tube anchorage at the bottom o the web prevented pealing o the stirrups at the re-entrant corner. Since this delamination occurred beore reaching even the nominal capacity o the un-retroitted beam, it is likely that without adequate anchorage, the CFRP stirrups would not have contributed to the shear capacity o the beam. 191

212 160 T-Beam 1L Shear-Displacement Curve Vc + Vs + ψv (ACI 440R-02) 192 Shear (kips) Vc + Vs (ACI ) Vc (ACI ) Applied 170 kips 2nd Delam Applied 148 kips FAILURE Initial Crack 1st Delam TBeam1L TBeam1L Midspan Vertical Displacement (in) Figure 8-41 Shear-Displacement relationship or T-Beam 1L

213 Front Side Right Initial Shear Crack Back Side Let Front Side Right Applied Load o 148 kips Back Side Let Front Side Right Applied Load o 170 kips Back Side Let Figure 8-42 T-Beam 1L condition at various stages in the shear-displacement response 193

214 FAILURE Figure 8-43 Flexural ailure o T-Beam 1L Delamination points Figure 8-44 Delamination o CFRP stirrups rom T-Beam 1L 194

215 8.5.1 Measured strain in the CFRP stirrups A total o seven strain gages were installed on the CFRP stirrups on the ront side o the beam. The strain gage readings were plotted against the applied shear in Figure 8-45 through Figure Because o the additional shear capacity provided by the inclined prestress strands in the let shear span, shear cracks only occurred in the right shear span o T-Beam 1L. The strains recorded in the CFRP stirrups on the let shear span were thereore very small throughout the test (Figure 8-45 to Figure 8-48), while those on the right shear span recorded signiicant strains in the CFRP stirrups (Figure 8-49 to Figure 8-51). Figure 8-52 shows the strains recorded during the irst test o T-Beam 1L in the three strain gages located on the CFRP stirrups in the ailure shear span. The ormation o the irst diagonal tension crack at a shear o 20 kips corresponds with the rapid increase in strain recorded by strain gage 30. As the shear load increased to 40 kips, the crack propagated through the next stirrup causing increased strains in strain gage 29. Strain gage 28 also indicates increased strain ater 40 kips, but increases more rapidly ater 60 kips load when additional shear cracks ormed in the web. As the load increased, the strain gages recorded increasing strains to a maximum o 3250 microstrain. At a shear orce o 78 kips, the irst two CFRP stirrups rom the right support delaminated rom the concrete surace. The strains recorded by gages 29 and 30 dropped slightly as the reduction in stiness o the stirrups transerred some o the shear orce to the concrete and internal stirrup mechanism. Strain gage 28 continued to measure higher strains until lexural ailure o the beam because delamination did not occur on this stirrup. 195

216 The strain measurements recorded during the second loading o T-Beam 1L indicate that the CFRP stirrups supported load throughout the test because the beam was already cracked and the end two stirrups had already delaminated during the irst loading (Figure 8-53). 196

217 Strain '-2" 80 CL 197 Shear (kips) TBeam1L TBeam1L Strain (10^-6) Figure 8-45 Strain readings rom strain gage 25

218 Strain '-2" 80 CL 198 Shear (kips) TBeam1L TBeam1L Strain (10^-6) Figure 8-46 Strain readings rom strain gage 24

219 100 Strain 26 1'-2" 80 CL 199 Shear (kips) TBeam1L TBeam1L Strain (10^-6) Figure 8-47 Strain readings rom strain gage 26

220 100 Strain 27 1'-2" 80 CL 200 Shear (kips) TBeam1L TBeam1L Strain (10^-6) Figure 8-48 Strain readings rom strain gage 27

221 100 Strain TBeam1L TBeam1L Shear (kips) '-2" CL Strain (10^-6) Figure 8-49 Strain readings rom strain gage 28

222 100 Strain Shear (kips) '-2" CL TBeam1L TBeam1L Strain (10^-6) Figure 8-50 Strain readings rom strain gage 29

223 100 Strain Shear (kips) '-2" CL 20 TBeam1L TBeam1L Strain (10^-6) Figure 8-51 Strain readings on strain gage 30

224 100 CFRP Readings on Strain Gages Right Side (T-Beam 1L 72202) Shear (kips) '-2" CL 20 Strain Gage 28 Strain Gage Strain Gage Strain (10^-6) Figure 8-52 Strain readings rom strain gages rom the irst test o T-Beam 1L

225 100 CFRP Readings on Strain Gages Right Side (T-Beam 1L 72302) 80 Strain Gage 28 Strain Gage 29 Strain Gage Shear (kips) '-2" CL Strain (10^-6) Figure 8-53 Strain readings rom strain gages rom the second test o T-Beam 1L

226 8.6 Shear Strength o T-Beam 2L (CFRP Stirrups) T-Beam 2L was the let shear span o the lexural test o T-Beam 2, recovered or evaluation o the CFRP stirrups. Because the ailure o T-Beam 2 resulted rom a lexure-shear crack just outside the let load point, the remaining section o beam to be tested as T-Beam 2L was only one third o the original beam length. This complicated the shear testing o this section since mid-span loading would have resulted in a shear span to depth ratio less than 1.5. In addition, lexural cracking had already lead to debonding o the prestressing strands at the right end o T-Beam 2L. The beam was loaded o center to produce a 1.5 shear span to depth ratio and induce a shear crack in the right side o the beam. The beam was also retroitted with carbodur strips or additional lexural reinorcement. This beam was considered completely wrapped because the bottom end o the stirrups was continued under the beam soit with additional CFRP wraps. During loading o the beam, a crack developed between the let support and the end o the carbodur strips added or lexural strengthening. In order to avoid a premature ailure at this location, the beam was unloaded and the let reaction moved inward to bear directly below the end o the carbodur strips. Figure 8-54 shows the test setup or T-Beam 2L. A more detailed description is covered in Chapter 5. The initial condition o the beam beore testing is shown in Figure The existing cracks are the result o the original T-Beam 2 lexural test. 206

227 Figure 8-54 T-Beam 2L test setup Front Side Back Side Figure 8-55 Initial condition o T-Beam 2L beore testing 207

228 The shear-displacement response is plotted in Figure The predicted shear capacities rom ACI and ACI 440R-02 are also plotted. Three signiicant stages during the test were identiied and are indicated on the response curve. The beam condition at each o these stages is shown in Figure The igure shows both ront and back sides o the beam. Stirrup delamination was observed at an applied load o 149 kips which corresponds to a shear o 70 kips (Figure 8-57, Applied Load o 149 kips). At an applied load o 191 kips, which corresponds to a shear o 90 kips, shear cracks had extended and additional stirrup delamination was noted (Figure 8-57, Applied Load o 191 kips). The beam reached an ultimate shear capacity o 120 kips and ailed as the shear cracks opened near the support (Figure 8-57, FAILURE). The beam never reached the ACI 440R-02 predicted shear capacity o 130 kips. This premature ailure was attributed to anchorage slip o the prestress tendons at the right end o the beam (Figure 8-58). The CFRP angles ruptured at the thru-bolts during shear ailure (Figure 8-59). A close up view o the delamination o the CFRP stirrups at ailure is shown in Figure 8-60 and Figure

229 160 T-Beam 2L Shear-Displacement Curve 140 Vc + Vs + ψv (ACI 440R-02) Shear (kips) Applied 191 kips Applied 149 kips FAILURE Vc + Vs (ACI ) Vc (ACI ) First Loading Second Loading Vertical Applied Load (in) Figure 8-56 Shear Displacement curve or T-Beam 2L

230 Front Side Back Side Applied Load o 149 kips Front Side Back Side Applied Load o 191 kips Front Side Back Side FAILURE Figure 8-57 T-Beam 2L condition at various stages during testing 210

231 Figure 8-58 Shear ailure and tendon end anchorage slip Figure 8-59 Rupture o GFRP angle at thru-bolts 211

232 Figure 8-60 Areas o CFRP delamination on T-Beam 2L Figure 8-61 Buckling o CFRP stirrups at FAILURE 212

233 8.6.1 Strain Gage Readings or CFRP Stirrups There were two groups o readings taken rom the strain gages because the beam was loaded twice. The two readings were combined to produce a single strain response. A total o twelve strain gages were installed on the CFRP stirrups. Six were installed on the ront o the beam and the other six were installed on the back. The strain gage readings were plotted against the applied shear in Figure 8-62 to Figure The strain results indicate that shear cracks occurred close to strain gages 1, 8, 3 and 9, and 6 and 12. This can be veriied by the pictures shown in Figure 8-58 and Figure The other gages recorded small strains throughout the test until immediately prior to ailure. Delamination o the CFRP is evident rom the sudden decrease in strain readings in gages 1, 8, 9, 6, and

234 Strain Gages 1 & Shear (kips) First Loading Second Loading 2'-10" P & LVDT 7'-5" 6'-9" '-3" Strain Gages 1-6 Front Side Strain Gages 7-12 Back Side 2'-3" Strain Gage 1 - First Loading Strain Gage 1 - Second Loading Strain Gage 7 - First Loading Strain Gage 7 - Second Loading Strain (10^-6) Figure 8-62 Strain readings rom strain gages 1 and 7

235 Strain Gages 2 & Shear (kips) 2'-10" P & LVDT 3'-3" 2'-3" First Loading Second Loading 7'-5" 6'-9" Strain Gages 1-6 Front Side Strain Gages 7-12 Back Side Strain (10^-6) Figure 8-63 Strain readings rom strain gages 2 and Strain Gage 2 - First Loading Strain Gage 2 - Second Loading Strain Gage 8 - First Loading Strain Gage 8 - Second Loading

236 Strain Gages 3 & Shear (kips) First Loading Second Loading 2'-10" P & LVDT 7'-5" 6'-9" '-3" Strain Gages 1-6 Front Side Strain Gages 7-12 Back Side 2'-3" Strain Gage 3 - First Loading Strain Gage 3 - Second Loading Strain Gage 9 - First Loading Strain Gage 9 - Second Loading Strain (10^-6) Figure 8-64 Strain readings rom strain gages 3 and 9

237 Strain Gages 4 & Shear (kips) P & LVDT Strain Gage 4 - First Loading 2'-10" 3'-3" '-3" Strain Gage 4 - Second Loading Strain Gage 10 - First Loading Strain Gage 10 - Second Loading First Loading Second Loading 7'-5" 6'-9" Strain Gages 1-6 Front Side Strain Gages 7-12 Back Side Strain (10^-6) 20 0 Figure 8-65 Strain readings rom strain gages 4 and 10

238 Strain Gages 5 & Shear (kips) P & LVDT First Loading Second Loading 2'-10" 7'-5" 6'-9" '-3" Strain Gages 1-6 Front Side Strain Gages 7-12 Back Side 2'-3" Strain (10^-6) Figure 8-66 Strain readings rom strain gages 5 and 11 0 Strain Gage 5 - First Loading Strain Gage 5 - Second Loading Strain Gage 11 - First Loading Strain Gage 11 - Second Loading

239 Strain Gages 6 & Shear (kips) '-10" P & LVDT 3'-3" 2'-3" 60 First Loading Second Loading 7'-5" 6'-9" Strain Gages 1-6 Front Side Strain Gages 7-12 Back Side Strain Gage 6 - First Loading Strain Gage 6 - Second Loading Strain Gage 12 - First Loading Strain Gage 12 - Second Loading Strain (10^-6) Figure 8-67 Strain readings rom strain gages 6 and 12

240 8.7 Shear Strength o T-Beam 1R (CFRP Sheets) T-Beam 1R was the right hal o T-Beam 1 which was strengthened in shear with CFRP sheets. To evaluate the shear capacity o the CFRP sheet retroit, the beam was subjected to two point loads as described in Chapter 5. In order to prevent the premature lexural ailure observed in T-Beam 1L, this section o beam was retroitted with carbodur strips as additional lexural reinorcement. The shear sheets were not continued around the soit o the beam, so the shear retroit was considered to be a two-sided application. Figure 8-68 shows the test setup or T-Beam 1R. A more detailed description is provided in Chapter 5. Figure 8-68 T-Beam 1R test setup 220

241 The shear-displacement response is plotted in Figure 8-69 along with the predicted shear capacities rom ACI and ACI 440R-02. Six signiicant stages are identiied on the response curve and the beam condition at each o these stages is shown in Figure 8-70 to Figure The initial shear cracks developed at a shear o 68 kips (Figure 8-70, Actuator Disp o 0.35 ) which was close to the ACI predicted shear capacity o the concrete, V c. No CFRP delamination was observed on this stage. As the load increased, more shear cracks ormed and extended (Figure 8-70, Actuator Disp o 0.55 ). The ACI predicted nominal shear capacity o the beam was reached at the same shear o 91 kips. CFRP sheet delamination was observed at a shear o 104 kips (Figure 8-70, Actuator Disp o 0.70 ). At a shear o 116 kips, the tube steel anchors lited o the epoxy bedding (Figure 8-71, Actuator Disp o 0.85 ). The CFRP sheet delamination increased at a shear o 124 kips (Figure 8-71, Actuator Disp o 1.00 ), below the ACI 440R-02 predicted nominal shear capacity. Without the steel tube anchors, the CFRP sheet may have delaminated completely resulting in premature ailure. However, because o the anchorage, the beam was able to exceed the ACI 440R-02 predicted capacity. The beam reached an ultimate shear o 131 kips which was 2% greater than the ACI 440R-02 nominal shear capacity and 44% greater than the ACI nominal shear capacity (Figure 8-72, FAILURE). The ailure o the beam caused a large shear crack extending rom the support through the concrete top slab. Although the steel tube anchors were deormed during ailure, no bolt ailures or steel rupture occurred. 221

242 160 T-Beam 1R Shear-Displacement Curve Vc + Vs + ψv (ACI 440R-02) Actuator 1.0" Actuatro 0.85" 222 Shear (kips) Actuator 0.70" Vc + Vs (ACI ) Actuator 0.55" Vc (ACI ) Actuator 0.35" FAILURE Midspan Vertical Displacement (in) Figure 8-69 Shear-Displacement curve or T-Beam 1R

243 Let side Front view Actuator Disp o 0.35 Right side - Back view Let side Front view Actuator Disp o 0.55 Right side - Back view Let side Delaminate - Let side Delaminate - Back side Actuator Disp o 0.70 Figure 8-70 T-Beam 1R condition at various stages during shear testing 223

244 Tube Lit Actuator 0.85 CFRP Delaminate Actuator 1.00 Figure 8-71 T-Beam 1R condition at CFRP delamination Let side Front view Right side - Back view FAILURE Figure 8-72 T-Beam 1R condition at ailure 224

245 8.7.1 Strain Gage Readings or CFRP Sheets There were a total o 14 strain gages on the CFRP sheets. Seven strain gages were installed on each side o the beam. Figure 8-73 through Figure 8-76 plots these strain readings against the applied shear. Strain gages recorded smaller strains than gages because the shear cracks passed through the bottom o the irst CFRP sheet and urther up through the second sheet. Strain gage 18 indicates increasing strain due to a shear crack. At a shear o approximately 65 kips, strain gage 17 shows a rapid increase in strain to match the strains recorded by gage 18. This indicates delamination o the CFRP sheet between gages 17 and 18. The same occurs to gage 19 at a shear o approximately 105 kips. Ater this load, the CFRP is completely delaminated and its perormance relies entirely on the anchorage provided by the steel tubes at the top and bottom o the web. Flexibility in this anchorage system resulted in a drop in the sheet strains Carbodur strip strain gages Three strain gages were installed on the carbodur strip at mid-span. Figure 8-77 shows a plot o these strains against the applied shear. The strain readings are very similar to those recorded at mid-span o T-Beam 2 during lexural testing. The signiicant change o slope corresponds to ormation o a mid-span lexural crack at a mid-span moment o 260 kip-t, which is similar to that observed or T-Beam

246 First Let Side FRP Shear (kips) '-2" CL Strain Gage 13-Top Strain Gage 14 - Middle Strain Gage 15-Bottom Strain Gage 16-Slope 10'-2 1 " Strain(10^-6) Figure 8-73 Strain readings rom strain gages

247 Second Let Side FRP Shear (kips) 1'-2" CL '-2 1 " Strain Gage 17-Top Strain Gage 18 - Middle Strain Gage 19-Bottom Strain(10^-6) Figure 8-74 Strain readings rom strain gages 17-19

248 Second Right Side FRP Shear (kips) 1'-2" CL Strain Gage 20-Top Strain Gage 21 - Middle Strain Gage 22-Bottom 10'-2 1 " Strain(10^-6) Figure 8-75 Strain readings rom strain gages

249 First Right Side FRP Shear (kips) 1'-2" CL Strain Gage 23-Top Strain Gage 24 - Middle Strain Gage 25-Bottom Strain Gage 26-Slope 10'-2 1 " Strain(10^-6) Figure 8-76 Strain readings rom strain gages

250 Carbodur Strip Strains CL Third Strip 31 Second Strip 32 First Strip Actuator 1.0" 120 Actuator 0.70" 230 Shear (kips) Actuator 0.35" Actuator 0.55" Actuator 0.85" Strain 30-Third Strip Strain 31-Second Strip Strain 32-First Strip FAILURE Strain(10^-6) Figure 8-77 Strain readings on the carbodur strips rom strain gages 30-32

251 8.8 Shear Strength o T-Beam 2R2 (CFRP Sheets) T-Beam 2R2 was the second test o the right hand portion o T-Beam 2 recovered ater lexural testing. The let end o this beam had already been tested to determine the shear capacity o the prestressed beam without CFRP shear retroit. T-Beam 2R2 was tested to evaluate the CFRP shear sheet with ull continuity around the beam soit. It was loaded by a line load applied at mid-span. The beam was retroitted with carbodur strips or additional lexural reinorcement. Wedge anchors were placed on the ends o the prestressed tendons to prevent tendon slip. CFRP wraps were used to extend the previous shear sheets around the soit o the beam. According to ACI 440R-02, this represents a three-sided retroit. Figure 8-78 shows T-Beam 2R2 in the test rame. A detailed description is provided in Chapter 5. Figure 8-78 T-Beam 2R2 test setup 231

252 The shear-displacement response is plotted in Figure 8-79 along with the predicted shear capacities rom ACI and ACI 440R-02. Seven signiicant stages during the test are identiied and the condition o the beam at each o these stages is shown in Figure The initial shear cracks occurred at a shear o 59 kips (Figure 8-80, Applied Load o 119 kips). This is also when the irst delamination o the CFRP sheets was observed. As the load increased, the shear crack opened and extended up to the soit o the top slab. Delamination o the CFRP sheets also extended as the load increased. The majority o the shear cracks ormed in the let span o the beam. The beam reached an ultimate shear o 142 kips (Figure 8-80, Ultimate Shear Back Side). This represented an increase o 16% over the capacity o T-Beam 2R1 tested without CFRP shear strengthening. This is signiicantly less than the 42% increase predicted by the ACI 440R-02 procedure. However, the ailure shear capacity still represents a 10% increase over the ACI 440R-02 predicted nominal shear capacity. Delamination o the CFRP sheets occurred soon ater development o shear cracks below the CFRP as shown in Figure Without the GFRP angle anchorage at the top and bottom o the web, it is possible that the sheets would have lost their capacity. Ater extensive delamination, the GFRP angles deormed and eventually ruptured at the thrubolts (Figure 8-82). 232

253 160 T-Beam 2R2 Shear-Displacement Curve 140 Vc + Vs + ψv (ACI 440R-02) Ultimate Shear FAILURE Vc + Vs (ACI318-02) Applied 247 kips Applied 239 kips Applied 235 kips Applied 227 kips 233 Shear (kips) Vc (ACI318-02) Applied 119 kips Midspan Vertical Displacement (in) Figure 8-79 Shear-Displacement curve or T-Beam 2R2

254 Applied Load o 119 kips Applied Load o 227 kips Applied Load o 235 kips 234 Applied Load o 239 kips Applied Load o 247 kips Ultimate Shear Back Side FAILURE Figure 8-80 T-Beam 2R2 condition at seven stages

255 Figure 8-81 Delamination o the CFRP sheet 235 Figure 8-82 Rupture o GFRP angles at thru-bolts

256 8.8.1 Strain Gage Readings attached on CFRP Sheets There were a total o 9 strain gages on the CFRP sheets on the right side o the beam because shear ailure was anticipated in this shear span. Figure 8-83 through Figure 8-85 show plots o the measured strains against the applied shear. Strain gages 4-9 recorded the highest strains because o shear cracks passing below the second CFRP shear sheet. Initial shear cracks ormed at 59 kips and additional shear cracks ormed in the same area as the load increased. The strain readings highlight the delamination o the CFRP sheets. Gages 5 and 6 record increasing strains due to a shear crack below the CFRP. Further rom the crack, gage 4 records very small strains until a shear load o 110 kips. At this point the strain in gage 4 suddenly increases to match that in gages 5, indicating delamination o the CFRP sheet between gages 4 and 5. The sudden decrease in strain in the CFRP sheets ater delamination is due to the lexibility o the GFRP angles allowing relaxation o the sheets. More o the shear load is thereore transerred to the concrete and internal stirrups system leading to ailure o the beam. 236

257 Load vs. Strains on First FRP Stirrup Shear (kips) Strain Gage 1 - First FRP, top Strain Gage 2 - First FRP, middle Strain Gage 3 - First FRP, bottom Strains (10^-6) P & MIDSPAN ' Figure 8-83 Strain readings rom strain gages 1-3

258 Load vs. Strains on Second FRP Stirrup Strain Gage 4 - Second FRP, let side, top Strain Gage 5 - Second FRP, let side, middle Strain Gage 6 - Second FRP, let side, bottom Shear (kips) P & MIDSPAN Strains (10^-6) Figure 8-84 Strain readings rom strain gages 4-6 9'

259 Load vs. Strains on Second FRP Stirrup Shear (kips) P & MIDSPAN Strain Gage 7 - Second FRP, right side, top Strain Gage 8 - Second FRP, right side, middle Strain Gage 9 - Second FRP, right side, bottom Strains (10^-6) Figure 8-85 Strain readings rom strain gages 7-9 9'

260 8.9 Comparison o the Shear Strengths o the T-Beams Tested in Shear Figure 8-86 shows the shear-displacement response or all o the shear test beams. T- Beam 2R1 was a shear test o the prestressed concrete beam without CFRP shear strengthening. This provided a control shear strength, which exceeded the ACI predicted strength by 34%. T-Beams 1L and 2L were strengthened in shear with CFRP stirrups. Due to lexural ailure, T-Beam 1L did not reach its shear capacity. To prevent premature lexural ailure all other shear test specimens were strengthened in lexure using CFRP carbodur strips bonded to the soit o the beam. T-Beam 2L ailed in shear but did not achieve the strength predicted by the ACI 440R-02 approach. This was attributed in part to debonding and slip o the prestressing tendons at the end o this portion o T-Beam 2. To avoid this tendon slip in subsequent tests, wedge anchors were installed on the strand extensions. T-Beam 1R and T-Beam 2R2 with CFRP sheets or shear strengthening exceeded the ACI 440R-02 predicted nominal shear capacity. T-Beam 1R represented a 2% increase over the ACI 440R-02 predicted nominal shear capacity while T-Beam 2R2 represented an increase o 10%. The expected increase rom the ACI predicted nominal shear capacity to the ACI 440R-02 predicted nominal shear capacity was 42%. In these shear tests, the majority o the increased strength is the result o conservatism in the ACI strength predictions and only part o the increase results rom the addition o the CFRP sheets. 240

261 160 Shear-Displacement Curve Vc + Vs + V (ACI 440R-02) For T-Beam 1L Two Sided Vc + Vs + ψv (ACI 440R-02) For Sheets and T-Beam 2L 241 Shear (kips) Vc + Vs (ACI ) For Stirrups and Sheets Vc (ACI ) For Stirrups and Sheets T-Beam 2R1 T-Beam 1L T-Beam 2L - Second Loading T-Beam 1R T-Beam 2R Vertical Applied Load (in) Figure 8-86 Shear-Displacement curves or all shear tests

262 8.10 ACI 440 Versus Experimental Shear Capacities The shear capacities o the shear tests were normalized with respect to the section dimensions and plotted in Figure The igure also includes the results o prior research compiled by Lyle Nakashima in his Masters Report 21. The 45-degree datum represents a one-to-one agreement between the predicted and experimental results. For all specimens except T-Beam 2L, the experimental results exceeded the ACI 440R-02 predictions. As noted earlier, tendon slip in T-Beam 2L during testing resulted in a reduction in the shear capacity. The shear capacities o both T-Beam 1R and T-Beam 2R2 with CFRP sheets as shear reinorcement exceeded the ACI 440R-02 predicted values. 242

263 1.80 ACI 440 Vs. Experimental Shear Capacities ACI 440 Vn/bwdp (ksi) Experimental V n /b w d p (ksi) Chaallal Xiao Czaderski Triantaillou Chajes Al-Sulaimani T-Beam 1R (Sheets) T-Beam 2R2 (Sheets) T-Beam 2L (Stirrups) Design Datum Figure 8-87 Normalized ACI 440 predictions versus experimental shear capacities

264 244

265 CHAPTER 9 9 SUMMARY AND CONCLUSION 9.1 Summary This research study involved lexural and shear testing o two precast prestressed T- Beams salvaged rom the Ala Moana Parking Garage. One un-strengthened beam was used as the control specimen reerred to as T-Beam 1. The second beam was the strengthened beam reerred to as T-Beam 2. This beam had been strengthened in 1997 using CFRP carbodur strips epoxy bonded to the soit o the beam because o a number o lexural cracks and severe spalling to the beam ledges. Initial theoretical strength calculations or T-Beam 1 and T-Beam 2 indicated that the addition o CFRP to increase the lexural capacity o T-Beam 2 resulted in a shear critical ailure mode i the beam were tested under the proposed laboratory conditions. To reduce the potential or a shear ailure and ensure the desired lexural ailure o T-Beam 2, the shear spans o both beams were increased or the laboratory loading and CFRP shear retroit was applied prior to lexural testing. Two shear retroit techniques were employed on each beam, namely external CFRP shear stirrups on the let hal o the beam and CFRP sheets on the right hal o the beam. In order to prevent premature delamination o the CFRP shear retroits at the re-entrant corners at the top and bottom o the beam web, mechanical anchorage was provided in the orm o steel tubes and GFRP angles with steel bolts through the beam web. Subsequent to lexural testing, each o the beam shear spans was tested in shear to evaluate the perormance o the CFRP shear retroit and mechanical anchorage. 245

266 9.2 Conclusions Flexure Tests Sika CFRP pre-cured carbodur strips epoxy bonded to the soit o the strengthened beam signiicantly increased the lexural strength over that o the control beam without reducing the beam ductility. There was no apparent degradation o the CFRP strips, CFRP abric wrap anchors or epoxy bonding agent during the ive years o ield exposure between application in 1997 and testing in The ACI 440R-02 strain compatibility procedure or estimating the lexural strength o concrete beams with externally bonded CFRP is conservative or the condition tested here. The ailure bending strength o the retroit beam was 21% greater than that predicted by the ACI 440R-02 report procedure. The ailure bending strength represented a 71% increase compared with the control specimen, while the ACI 440R-02 predicted a 37% increase when compared with the ACI predicted lexural capacity o the control specimen. 246

267 9.2.2 Shear Tests o The shear capacity o the prestressed T-Beam without CFRP shear strengthening exceeded the ACI predicted strength by 33%. o The two T-Beam tests with CFRP sheets produced 7% and 16% increases in the shear capacity when compared with the beam without CFRP shear strengthening. These increases are below the 42% increase predicted by ACI 440R-02. o The ailure shear strength o the beams retroitted with CFRP sheets was slightly greater than the ACI440R-02 prediction. o In all shear tests, delamination o the CFRP stirrups and sheets occurred prior to the maximum shear load. Without adequate anchorage at the top and bottom o the beam web, the CFRP would have been ineective. o The steel tubes provided better anchorage than the GFRP angles. o Future research studies in anchorage system design are necessary to maximize the eectiveness o CFRP shear retroit systems, particularly when applied to prestressed concrete beams with existing internal shear reinorcement. 247

268 248

269 10 APPENDIX A Field Retroit o Prestressed Concrete T-Beam Using CFRP by I. N. Robertson, A. A. Agapay, and L. M. Nakashima Technical Paper presented at the ACI Fall Convention, September 2003 in Boston, Massachusetts and published in Field Applications o FRP Reinorcement: Case Studies Editors: Sami Rizkalla and Antonio Nanni, SP-215, ACI,

270 250

271 Field Retroit O Prestressed Concrete T-Beam Using CFRP Ian N. Robertson, Alison A. Agapay, Lyle M. Nakashima Synopsis In 1997, a precast, prestressed T-beam in the Ala Moana Shopping Center parking garage, in Honolulu, Hawaii, was strengthened in lexure using carbon iber reinorced polymer (CFRP) strips epoxy bonded to the soit o the beam. When the parking garage was demolished in June 2000, this beam and two control beams were salvaged and brought to the University o Hawaii or testing. This paper presents the retroit procedures used during ield application o the CFRP strips. It also describes the beam recovery and preparation or laboratory testing. The test program and results o the lexural testing o both unstrengthened and strengthened beams under our-point loading are presented in detail. The CFRP retroit signiicantly increased the lexural capacity o the beam while also increasing its lexural ductility. The ailure moment was well in excess o the nominal moment capacity predicted using the strain-compatibility procedure described in the ACI 440R-02 report. Keywords: T-beam, strengthening, prestressed concrete, carbon iber, iber reinorced polymers, ield application 251

272 Ian Robertson, teaches structural engineering design courses and perorms experimental research investigating the perormance o concrete and steel structures under dynamic, cyclic and long-term loading conditions. He is a registered proessional structural engineer in the State o Hawaii and has been involved in structural engineering design and research or over 20 years. Alison Agapay, is a Graduate Research Assistant in the Structural Engineering Laboratory at the University o Hawaii. The project reported here constitutes the research component o his Masters Thesis. He constructed the 4-post load rame used to test the T-beams and perormed all testing and result analysis or this study. Lyle Nakashima, is a design engineer with Mitsunaga and Associates, a structural engineering consulting company in Honolulu, Hawaii. He perormed an extensive literature review on FRP strengthening, assisted in the beam recovery operation, and computed the theoretical beam strengths reported in this paper as part o his Masters program in structural engineering at the University o Hawaii. INTRODUCTION During a routine structural inspection o the Ala Moana Shopping Center Parking Garage in Honolulu, Hawaii, it was noted that one o the prestressed T-beams had substantial spalling damage to the beam ledges and a large lexural crack across the bottom lange o the beam. The beam is a precast prestressed inverted T-beam supporting joists and a slab, which acts as the top lange or the T-beam (Figure 1). The beam was repaired in 1997 using CFRP pre-cured strips bonded to the beam soit to augment the lexural capacity (Figure 2). This was the irst use o FRP materials or structural retroit in the State o Hawaii. CFRP wet lay-up wrap and epoxy mortar were used to repair the damaged beam ledges. CFRP wraps were also provided at the ends o the span to restrain the end o the CFRP tension strips. The repairs were perormed by Concrete Coring o Hawaii using Sika Carbodur precured CFRP strips epoxied to the bottom lange o the beam. The repairs were perormed ollowing standard manuacturer s instructions, with no thought that the beam would be tested at some uture date. In additional to the retroit beam, an identical unstrengthened beam was tested as a control specimen. This is one o the irst tests o a ield installed FRP retroit ater an extended ield service period. The Hawaii Department o Transportation (HDOT) unded this research program in order to evaluate the potential or FRP retroit o deicient bridge structures in the state. 252

273 RESEARCH SIGNIFICANCE Field application o FRP materials or strengthening o concrete members has increased signiicantly subsequent to extensive laboratory testing o retroit techniques (GangoRao and Vijay, 1998; Fanning and Kelly, 2001; Shahawy et al, 2001; Spadea et al, 2002 and many others). Very ew o these ield applications are available or testing ater exposure to service conditions. This paper presents the results o lexural testing o a prestressed concrete T-beam strengthened in the ield with CFRP pre-cured strips and CFRP wet layup. The results are an important link between traditional laboratory testing and the perormance o ield installed FRP strengthening. FIELD APPLICATION OF CFRP PRE-CURED STRIPS The CFRP retroit was designed in 1997 by Martin and Bravo Structural Engineers, Honolulu, Hawaii, ollowing design procedures presented in the literature at the time. No standard was available at that time or surace application o FRP to concrete members. The surace o the concrete was prepared by grinding to remove paint and weak surace paste. This resulted in a relatively smooth surace preparation similar to ICRI-CSP surace proile 2 (ICRI, 2002). Current FRP application speciications would generally require a slightly rougher surace proile such as ICRI-CSP 3-4. The CFRP strips were cleaned prior to installation and a layer o Sikadur 30 Hi-Mod Gel epoxy was placed on the soit o the beam. The strips were then pressed onto the epoxy using a roller as shown in Figure mm wide strips o SikaWrap Hex 103C unidirection carbon abric were saturated with Sikadur Hex 300 epoxy and applied to the ends o the beam to restrain the ends o the lexural strips (Figure 4). Additional CFRP abric sheets were used to wrap the epoxy mortar patches at the ledge spalls at third points along the span. Since these additional wraps are not typical o lexural strengthening, they were removed prior to testing the beam. The end anchorage wraps were however let in place as they are commonly installed as part o the lexural strengthening. BEAM RECOVERY AND REPAIR During demolition o the parking structure in June 2000, the precast prestressed beam with CFRP strengthening was salvaged along with two nominally identical beams (Figure 5). In the recovery process, the top slab orming the beam lange was removed to acilitate shipping. In addition, portions o the beam web suered minor damage in the orm o concrete spalls and negative bending cracks. This damage was repaired by personnel rom PlasTech Inc., Hawaii, using Sika epoxy injection and epoxy mortar 253

274 patch materials (Figure 6). It is assumed that none o these repairs aected the lexural perormance o the beams during testing. The top lange o the beam was reinstated in the Structural Laboratory at UH with the same reinorcement layout as the original slab (Figure 7). The dimensions o the ourpost test rame limited the lange width to 1500 mm, which corresponds to one ith o the beam span and a slab overhang o six times the slab thickness on either side o the web. The ACI 318 building code eective lange width or this beam would be 1800 mm (ACI 2002a). Beam ailures were initiated by tension reinorcement ailure and not compression ailure o the top lange. It is thereore assumed that the reduced lange width did not signiicantly aect the beam lexural perormance. The cross-sectional dimensions o the beams are shown in Figure 8. MATERIAL PROPERTIES Table 1 lists the concrete material properties or the two T-beams tested in this study. Ater beam testing, concrete cores were taken rom the web and anchorage blocks o each beam to determine compressive strength. Core recovery and testing were perormed according to ASTM C42-99 (ASTM C42, 1999). The cores were all 100 mm diameter by 140 mm long. The compressive strength determined rom each core was adjusted because the length to diameter ratio was below 1.75 (ASTM C42, 1999). The resulting concrete compressive strengths are listed in Table 1. Standard 150 mm diameter by 300 mm concrete cylinders were made while pouring the top slabs o each T-beam. These cylinders were tested in compression on the same day as the corresponding T-beam test producing the average compressive strengths listed in Table 1. Table 2 lists the material properties o the reinorcing and prestressing steel used in the test beams. Web shear reinorcing bars were recovered during beam demolition and tested in tension. The average tensile strength or shear reinorcing in each T-beam is listed in Table 2. Coupons o the 10 mm nominal diameter prestress strands were also recovered rom the test beams and tested in tension producing the ultimate tensile strengths listed in Table 2. Table 3 lists the material properties or the FRP materials used in the lexural strengthening o T-beam 2. These properties are based on the manuacturer s test inormation since no material coupons were available rom the original repair work. Because o damage to the FRP materials during destructive testing o the T-beam, it was not possible to recover representative samples or testing. Pull-o tests on the CFRP strips would also not be representative o the installed condition because o damage caused to the epoxy bond during the beam test. 254

275 FLEXURAL TESTING PROGRAM Both control and strengthened T-beams were tested under our-point loading as shown schematically in Figure 9. T-beam 1, the control specimen, was tested over a span o 7.24 meters with a pinned support at one end and roller support at the other. The load was applied through two line loads each 610 mm rom midspan. For T-beam 2, the strengthened beam, the support locations used or T-beam 1 would have been directly under the ends o the CFRP strips. These reactions would thereore have enhanced the restraint provided by the CFRP wrap at the ends o the strips. To avoid this additional restraint, steel support brackets were bolted to the ends o the beam so that the supports could be located beyond the ends o the beam. The span or T-beam 2 was 7.76 meters as shown in Figure 9. Figure 10 shows T-beam 2 in the test rame prior to testing. Because o the enhanced lexural capacity provided by the CFRP strengthening, the lexural capacity o T-beam 2 now exceeded the theoretical shear capacity. In order to prevent a premature shear ailure, shear reinorcement was installed on both beams in the orm o CFRP wet lay-up stirrups bonded to the web in the let hal o the beam and CFRP wet lay-up sheets bonded to the surace o the web on the right hal o the beam as seen in Figure 10. Two dierent conigurations o shear retroit were used so as to investigate their perormance through shear testing o each hal o the beam ater lexural ailure. Ideally this shear reinorcement would be continuous around the soit o the beam, however, in order not to alter the CFRP lexural strips by providing additional restraint, the shear reinorcement was terminated at the bottom o the web. Anchorage o the CFRP shear reinorcement was provided at the re-entrant corners at top and bottom o the web by means o steel tubes and FRP angles secured by steel bolts through the beam web. The load was applied under displacement control in increments o 0.25 mm up to a midspan delection o 12.5 mm, then in increments o mm to a displacement o 50 mm, and then at increments o 1.25 mm till ailure. At each displacement increment, all strain and displacement readings were recorded and the extent o beam cracking was noted. T-beam 1 response FLEXURAL TEST RESULTS The bending moment at midspan o T-beam 1 (control specimen) is plotted against the midspan delection in Figure 11. The irst lexural cracks were observed at midspan at the bottom o the beam at a bending moment o 300 kn-m. As the load increased, these cracks extended up into the web and new lexural cracks ormed below the load points. The theoretical moment capacity o the beam as predicted by the ACI code, and using measured strengths o concrete and prestress steel, was 588 kn-m. The test beam was unable to reach this moment capacity. The midspan lexural crack continued to open as the load was increased, with inal lexural ailure occurring at a bending moment o 574 kn-m and midspan delection o 78 mm when the ten prestress strands ruptured at this center crack (Figure 12). This ailure strength was 2% below the ACI code nominal capacity. 255

276 T-beam 2 response T-beam 2 (strengthened beam) was tested under the same loading conditions as the control T-beam 1. However, in order to prevent the support condition rom providing additional restraint to the end o the Carbodur strips on the beam soit, steel extensions were abricated and bolted to the ends o the beam. This resulted in a longer span or T- beam 2 compared with T-beam 1 (Figure 9). During the lexural test o T-beam 2, the response was similar to that or the control specimen until lexural cracking o the beam. The post-cracking stiness or T-beam 2 was greater than that or T-beam 1, and did not degrade as rapidly. Figure 13 shows the moment-delection response o T-beam 2 compared with that or the control beam. ACI committee 440 recently published a report on the strengthening o concrete members using externally bonded FRP (ACI, 2002b). This ACI440R-02 report was used to predict the ailure bending moment or T-beam 2. The anticipated nominal moment capacity o 846 kn-m was easily exceeded by the strengthened beam, which supported a maximum moment o 984 kn-m prior to ailure, 16% greater than the predicted value. This represents a 71% increase in lexural strength compared with the control specimen, while the ACI 440R-02 suggests the increase to be 44% compared with the ACI 318 nominal capacity. The apparent conservative prediction using the ACI 440R-02 procedure is attributed to the debonding coeicient which limits the strain capacity o the CFRP strips to simulate premature debonding. Because o the unpredictable nature o a debonding ailure, reasonable conservatism is warranted. The maximum midspan delection or T-beam 2 was 100 mm compared with the 75 mm delection or the control specimen. The addition o CFRP lexural strengthening increased the ductility o the beam. Failure occurred when the CFRP strips delaminated rom the bottom o the beam. This delamination appeared to initiate at the base o a lexure-shear crack that had ormed just outside the let load point. Vertical oset in the soit o the beam on either side o this crack may have contributed to the initiation o delamination. In addition, large strain dierential between the CFRP strips and the lexurally cracked concrete may also have contributed to deterioration o the bond between CFRP and concrete. I the CFRP shear reinorcement had extended around the soit o the beam, it may have provided additional restraint to the CFRP strips and delayed the delamination, thus urther increasing the lexural strength. For the irst 500 mm rom the delamination initiation point, the ailure occurred in the surace concrete, with a thin layer o concrete remaining attached to the CFRP strips. Beyond this point, the CFRP strips separated rom the epoxy, likely because o the increased angle o peeling as the CFRP stripped away rom the beam soit. The delamination occurred rapidly and extended rom the shear-lexure crack to the end o the CFRP strips, which pulled part way out o the CFRP abric wrap anchor. The anchor was not suicient to prevent pull-out once delamination had occurred, but there was no tendency or delamination to initiate at the end o the strips as had been reported in some laboratory studies. 256

277 SUMMARY AND CONCLUSIONS Two precast prestressed concrete T-beams were recovered rom a Honolulu shopping center parking garage and tested in lexure in the University o Hawaii Structural Engineering Laboratory. One o the beams had been strengthened in 1997 using CFRP carbodur strips epoxy bonded to the soit o the beam. The other was used as a control specimen. The ollowing conclusions were made based on the results o these tests. Sika Carbodur CFRP pre-cured strips epoxy bonded to the soit o the strengthened beam signiicantly increased the lexural strength over that o the control beam without reducing the beam ductility. There was no visually noticeable degradation o the CFRP strips, CFRP abric wraps or epoxy bonding agents during the 5 years o ield exposure between application in 1997 and testing in The ACI 440R-02 strain-compatibility procedure or estimating the lexural strength o concrete beams with externally bonded CFRP appears to be conservative or the condition tested here. The ailure bending strength o the retroit beam was 16% greater than that predicted by the ACI 440R-02 report procedure. ACKNOWLEDGEMENTS The authors are extremely grateul to Adriano A. B. Bortolin o Sika Products, USA, or providing valuable inormation concerning the original FRP application, at which he was the Sika representative. Sika Products also donated all additional FRP and epoxy materials required to repair the recovered beams and retroit them in shear so as to avoid a premature shear ailure. The authors are also indebted to Brian Ide, the structural engineer responsible or the original FRP strengthening design. Brian provided construction drawings, design calculations and photographic records o the original retroit. Chandler Rowe and his colleagues at PlasTech Inc., Honolulu, Hawaii, are thanked or donating their labor and expertise in the repair o the recovered beams and or installation o the shear retroit materials at the UH Structural Engineering laboratory. This project was unded through research grant No rom the Hawaii Department o Transportation Research Board. This inancial support is grateully acknowledged. The opinions and observations made in this paper are those o the authors and do not necessarily relect the opinion o any o the project sponsors. REFERENCES ACI 2002a, ACI /318R-02, Building Code Requirements or Structural Concrete and Commentary, American Concrete Institute, Farmington Hills, Michigan, 443 pp. ACI 2002b, ACI 440R-02, Guide or the Design and Construction o Externally Bonded FRP Systems or Strengthening Concrete Structures, American Concrete Institute, Farmington Hills, Michigan, 45 pp. 257

278 ASTM C42, 1999, Standard Test Method or Obtaining and Testing Drilled Cores and Sawed Beams o Concrete, American Society or Testing and Materials, West Conshohocken, PA, 4. Fanning, P. J., and Kelly, O., 2001, Ultimate Response o RC Beams Strengthened with CFRP Plates, Journal o Composites or Construction, Vol. 5, No. 2, pp GangaRao, V. S., and Vijay, P. V., 1998, Bending Behavior o Concrete Beams Wrapped With Carbon Fabric, Journal o Structural Engineering, Vol. 124, No. 1, pp ICRI 2002, Selecting and Speciying Concrete Surace Preparation or Coatings, Sealers, and Polymer Overlays, International Concrete Repair Institute Technical Guideline No Shahawy, M., Chaallal, O., Beitelman, T. E., and El-Saad, A., 2001, Flexural Strengthening with Carbon Fiber-Reinorced Polymer Composites o Preloaded Full- Scale Girders, ACI Structural Journal, Vol. 98, No. 5, pp Spadea, G., Mencardino, F., and Swamy, R. N., 2002, Strength and Ductility o Reinorced Concrete Beams Externally Reinorced with Carbon Fiber Fabric, ACI Structural Journal, Vol. 99, No. 2, pp

279 Table 1: Concrete material properties Beam Location Compressive Strength, c (MPa) T-beam 1 Control T-beam 2 With CFRP Description Precast Beam 58 (8413 psi) Average o 4 core tests 37 (5396 psi) Average o 3 cylinder Top Slab tests Precast Beam 58 (8400 psi) Average o 3 core tests Top Slab 62 (9025 psi) Average o 3 cylinder tests Table 2: Steel material properties Beam T-beam 1 Control T-beam 2 With CFRP Average Tensile Yield Stress, F y Average Tensile Strength Sample (F pu or Prestress) (F u or Reinorcement) (MPa) (MPa) Prestress Strands (272 Ksi) Web Shear Reinorcement 350 (50.9 Ksi) 503 (73.1 Ksi) Prestress Strands (272 Ksi) Web Shear Reinorcement 350 (50.9 Ksi) 503 (73.1 Ksi) Table 3: CFRP material properties FRP material Description Tensile Strength, FRP (MPa) Tensile Modulus, E FRP (Gpa) Carbodur Strips 102 mm x 1.2 mm 2790 (406 Ksi) 164 (23,900 Ksi) Sika Wrap Hex 103C Uni- Directional Single Ply 1010 (147 Ksi) 73 (10,600 Ksi) 259

280 Figure 1: Precast Prestressed T-beam repaired using CFRP strips and wrap Figure 2: Beam cross-section showing three CFRP strips or lexural strengthening 260

281 Figure 3: Field application o CFRP strips Figure 4: CFRP abric wrap at end o lexural strips 261

282 Figure 5: Removal o T-beams during parking garage demolition Figure 6: Repair o spalling damage to web 262

283 Figure 7: Reconstruction o top lange in UH laboratory 1500mm Slab Reinorcement 2-leg 10mm Ø Stirrups at 300mm o.c. 140mm 115mm 470mm (10) 10mm Ø Stress-relieved prestress strands 3 Carbodur CFRP Strips 420mm MIDSPAN BEAM SECTION 140mm Figure 8: T-Beam Cross-section 263

284 4-post Load Frame 1300 kn Actuator Load Cell Spreader Beam Test Beam 1220mm 7240mm or T-Beam mm or T-Beam 2 A TEST SETUP ELEVATION SECTION "A-A" Figure 9: T-Beam test setup Figure 10: T-beam 2 in test rame 264

285 1000 Moment Capacity Applied Moment (kn-m) M n Midspan Vertical Displacement (mm) T-beam 1, control Figure 11: T-beam 1, control specimen, lexural response (T-beam 1: Shear retroit but no lexural strengthening) Figure 12: Flexural ailure o control T-beam. 265

286 1200 Moment Capacity 1000 Applied Moment (kn-m) M nfrp M n Midspan Vertical Displacement (mm) T-beam 1, control T-beam 2, with CFRP Figure 13: Flexural perormance o control and strengthened T-beams (T-beam 2: Shear retroit and lexural strengthening) Figure 14: Failure o strengthened T-beam showing CFRP tension strip delamination 266