CONNECTOR DEVELOPMENT FOR HYBRID MASONRY SEISMIC STRUCTURAL SYSTEMS. Seth R. Goodnight Gaur P. Johnson and Ian N. Robertson

Transcription

1 CONNECTOR DEVELOPMENT FOR HYBRID MASONRY SEISMIC STRUCTURAL SYSTEMS Seth R. Goodnight Gaur P. Johnson and Ian N. Robertson Research Report UHM/CEE/11-03 May 2011

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3 ABSTRACT Hybrid masonry construction has recently been developed as a means to provide a more efficient use of masonry infill walls in steel frame structures by designing these walls to function as a part of a structure s lateral force resisting system. This system has current applications in low seismic regions (Seismic Design Categories A, B, and C). In regions of higher seismicity (Seismic Design Categories D and greater), there is a need for a clear understanding of the mechanics of the interaction between the steel frame and the masonry shear wall, as well as the development of specific detailing requirements to provide for a ductile and somewhat predictable response in a seismic event of significant magnitude. The scope of this report is the investigation of the connection between the steel beam and the top of the masonry wall for a Type I hybrid masonry system. The proposed steel connector plates are through-bolted to the masonry wall bond beam and welded to the bottom flange of the steel beam above. Preliminary guidelines and recommendations are provided for the development of energy dissipating hybrid masonry connector plates. The first portion of this study focused on the development of connector plate designs to determine which provided the most stable, ductile cyclic response. The second portion of this study investigated the strength and limit states of the through-bolted connection to the masonry wall bond beam under shear loading. Based on these experiments, recommendations are provided for the most suitable connector plate designs as well as a general evaluation of the connection to the masonry wall and potential limit states to consider in future design applications. For a rigid connection between the steel frame and CMU wall, link connectors with a thickness greater than 0.5 inches are recommended, whereas fuse Type T was proven to be superior for a ductile, energy dissipating connector plate. ACI design values for bolt shear yielding and masonry shear failure were determined to be the most appropriate limit states for determining an approximate design value for the throughbolted CMU wall connections. Page i

4 ACKNOWLEDGEMENTS This report is based on an MS thesis prepared by Seth Goodnight under the direction of Drs. Gaur Johnson and Ian Robertson. The authors would like to thank Drs. Ronald Riggs and David Ma for their contributions as part of the Thesis Committee for the project. Special thanks to Tileco Inc. and Bonded Materials Co. for their generous donation of materials used in this project, as well as to Mitch Pinkerton and Miles Wagner of the University of Hawai i at Mānoa s Structural Testing Laboratory for their assistance throughout the project. This research was supported by the National Science Foundation under Grant No. CMMI as part of the George E. Brown, Jr. Network for Earthquake Engineering Simulation. This support is gratefully acknowledged. Page ii

5 TABLE OF CONTENTS ABSTRACT... i ACKNOWLEDGEMENTS... ii 1 INTRODUCTION INTRODUCTION OBJECTIVE LITERATURE REVIEW HYBRID MASONRY LATERAL LOAD RESISTING SYSTEM CONNECTOR PLATES CMU THRU-BOLT PUSH-OUT TESTS APPROACH CONNECTOR PLATE TESTS Experimental Setup Test Specimens Procedure CMU THRU-BOLT PUSH-OUT TESTS Experimental Setup Test Specimens Procedure FULL-SCALE STEEL-MASONRY SUBASSEMBLIES RESULTS SHEAR CONNECTOR TESTS Test Results Summary Specimen Behavior Narratives CMU THRU-BOLT PUSH-OUT TESTS Specimen Behavior and Failure Mechanisms Test Results ANALYSIS COMPARISON OF CONNECTOR PLATES (LINK AND FUSE TYPES A, S, AND T) ATC-24 CONNECTOR PLATE ANALYSIS CMU THRU-BOLT PUSH-OUT TESTS Connection Failure Mechanisms Comparison of Wall Specimens (Partially vs. Fully Grouted) CONCLUSIONS / RECOMMENDATIONS REFERENCES APPENDICES (A, B, C, D) Page iii

6 TABLE OF FIGURES Figure 1. Three proposed types (Type I, Type II, and Type III, shown clockwise from top left) of hybrid masonry systems, classified according to types of loads transferred to masonry walls [Biggs, 2011] Figure 2. Current state of connector plate detailing requirements as provided by the International Masonry Institute Figure 3. Connector plate test setup with specimen highlighted. Lateral load is applied to the steel tube section at the top of the image Figure 4. Typical link and fuse connector details (in = 25.4 mm) Figure 5. Graphic representation of the proposed full-scale test structure to be constructed at UIUC Figure 6. Modified ATC-24 cyclic loading routine for steel connector plates, with three cycles at each level of lateral displacement Figure 7. CMU bolt push-out test concept Figure 8. CMU bolt push-out test setup Figure 9. Schematic drawing showing the dimensions and layout of the test assembly for loading of the CMU wall specimens Figure 10. (a) CMU block configuration "1", (b) CMU block configuration "2" Figure 11. (a) Non-Ductile Weld Rupture: P4_T4-01; (b) Rupture of Base Metal: P4_T Figure 12. (a) Yielding then buckling: P4_T2-01; (b) Yielding/Fatigue rupture: P4_T4_FT Figure 13. Bent plate behavior, ductile response followed by C-shaped weld rupture: P4_T4_FT3-B Figure 14. P4_T2-01, showing typical buckling failure Figure 15. P4_T4-02 showing weld failure and base plate rupture Figure 16. Specimens P4_T4_FA1-01, _FA2-01, and _FA3-01 showing typical fuse base rupture (shown from left to right) Figure 17. Fuse roughness and early rupture of P4_T4_FA2-P-01 due to cutting with a hand-held plasma torch Page iv

7 Figure 18. P4_T4-FS-01 showing significant buckling at ±2.00 displacement Figure 19. P4_T4-FT2-01 displaying a combination of lateral-torsional buckling and rupture due to fatigue Figure 20. P4_T4-FT3-01 displaying uniform distribution of yielding along entire fuse section Figure 21. Specimens P4_T4_FT2-01 and _FT3-01, showing buckling and tapered fuse base rupture (shown from left to right) Figure 22. P4_T4_FT3-B-01 showing rupture of C-shaped fillet weld on bent leg Figure 23. P4_T6_FA2-01 showing typical fuse base rupture Figure 24. (a) Final cracking patterns for specimen FG-1A; (b) Typical cracks around rod bearing area as seen in specimen FG-1A Figure 25. (a) Final cracking patterns for specimen FG-2A; (b) Typical threaded rod shear deformation as seen in specimen FG-2A. Load values shown on specimens were rounded to the nearest whole number Figure 26. Specimen PG-1B showing mortar joint separation along the entire height of the right side of the middle blocks, typical of partially grouted specimens Figure 27. Final cracking patterns of specimen PG-2A, with vertical mortar joint separation visible above the location of the threaded rod Figure 28. Load vs. for all CMU specimen "A" tests Figure 29. Load vs. for all CMU specimen "B" tests Figure 30. Assumed projected shear area for masonry breakout failure (in = 25.4 mm).47 Figure 31. Tapered fuse design dimensions Page v

8 TABLE OF TABLES Table 1. Seismic Design Values for Reinforced Masonry Shear Walls Table 2. Connector plate specimen naming convention (in = 25.4mm) Table 3. Actuator displacement summary Table 4. Critical Points of Hysteretic Response (in = 25.4 mm, kip = 4.45 kn, kip-in = 113 J) Table 5. ASTM E8 tension test results for connector plate steel bar (inch = 25.4mm, ksi = MPa) Table 6. CMU bolt push-out maximum load values and corresponding downward deflection (in = 25.4 mm, kip = 4.45 kn) Table 7. Summary of results from CMU prism tests Table 8. Specimen Cumulative and Total Energy Dissipation Values (in = 25.4 mm, kip-in = 113 J) Table 12. Summary of Applicable ACI Design Values and Measured Test Results (kip = 4.45 kn) Page vi

9 1.1 Introduction 1 Introduction There currently exist a wide variety of structural systems designed to resist lateral seismic and wind load, each system presenting its own unique set of advantages and disadvantages. Some of the most common systems in use today are steel moment frames, shear walls, and braced frames. In steel frame construction, architectural masonry infill walls are often present to enclose the building envelope but do not traditionally serve any structural purpose. Hybrid masonry, a relatively new concept in seismic load resisting building systems that has already been implemented in several projects in areas of low seismicity [Abrams et al., 2010], serves to incorporate the masonry infill walls, designed and reinforced as shear walls, as a specifically-designed structural component of the building s seismic force resisting system. A Type I hybrid masonry system uses steel connector plates to transfer only lateral forces from the steel frame to the top of the masonry wall. Type II hybrid masonry extends the purpose of the masonry wall to resisting both lateral forces and vertical compressive forces by eliminating the gap between the steel frame and the top of the wall and connecting the two components with a system of headed studs across the top of the masonry wall. Finally, Type III hybrid masonry contributes an additional load transfer mechanism by providing a similar headed stud connection along both sides of the masonry wall to resist vertical shear forces. The intent of this project is to investigate the incorporation of masonry infill walls into the lateral load resisting system, and more specifically, to develop a steel-masonry connector suitable for this purpose. Investigation will concentrate primarily on the development of a structural fuse to serve as a ductile link to dissipate seismic energy and enhance seismic performance of the lateral system. This project is part of a larger on-going NEESR-SG project under Principal Investigator Daniel Abrams of the University of Illinois (UIUC). Ductile fuses have been studied and tested by others for various applications, such as [Bruneau & El-Bahey, 2010] and [Aliaari & Memari, 2007]. 1.2 Objective The scope of this particular study is limited solely to the investigation of the Type I hybrid masonry system and will focus on the development of a steel-masonry connection using steel connector plates through-bolted to masonry walls to transfer horizontal shear forces from the steel frame into the masonry walls. Page 1

10 2 Literature Review 2.1 Hybrid Masonry Lateral Load Resisting System The hybrid masonry system, first proposed in 2006 [Biggs, 2006], incorporates the traditional, non-structural masonry infill wall into the lateral load resisting system of a structure through design of the infill wall as a masonry shear wall and application of a series of shear connector plates between the infill wall and the steel frame of the building. Hybrid masonry is classified into three categories, shown in Figure 1, based on the degree of confinement of load transfer between the steel frame and masonry wall [Biggs, 2011]. Figure 1. Three proposed types (Type I, Type II, and Type III, shown clockwise from top left) of hybrid masonry systems, classified according to types of loads transferred to masonry walls [Biggs, 2011]. For the Type I system, the masonry wall is designed only for in-plane and out-of-plane loads, with a gap between the top of the masonry panel and the bottom of the steel beam above to prevent transfer of gravity loads to the wall. In this case, connector plates have also been detailed with vertical slotted holes to eliminate any vertical load transfer through these connections. In the Type II system, the masonry wall is designed for the in-plane and out-of-plane loads of a Type I system, but the gap at the top of the Page 2

11 panel is not present, requiring the wall to serve additionally as a vertical loadbearing wall. In this case, hybrid masonry can serve to prevent progressive collapse as a means to increase redundancy in the structure. Finally, the Type III system, although still in the early stages of development, will provide for additional connectivity between the ends of the masonry panel and the wide flange steel columns, as a means to provide a greater degree of masonry confinement and more direct transfer of overturning moments. The International Building Code [IBC, 2006] and The Building Code Requirements and Specifications for Masonry Structures [MSJC, 2008] currently provide for three different classifications of masonry shear walls: ordinary reinforced, intermediate reinforced, and special reinforced. Each of these classifications is assigned different seismic factors that are used for the overall design of the lateral force resisting system. These factors, R (response modification coefficient), Ω 0 (system over-strength factor), and C d (deflection amplification factor), are given in Table 1 for each of the classifications of masonry shear walls. Current applications of hybrid masonry systems have been designed using the seismic forces developed according to the IBC and the design values for reinforced masonry shear walls. Table 1. Seismic Design Values for Reinforced Masonry Shear Walls. Wall Classification R Ω 0 C d Ordinary Intermediate Special To date, hybrid masonry systems have been implemented in Seismic Design Categories A, B, and C. Extension of hybrid masonry load resisting systems into higher SDCs is currently under investigation as the requirements of structural steel construction fall under the AISC Seismic Design Manual for SDC D and E [IMI, 2009]. Computer models have been developed for Type I hybrid masonry systems using Bentley RAM Elements and also with linear shell models to confirm the assumed behavior of the steel frame and masonry shear wall assembly [Abrams et al., 2010]. Based on the results from a comparison of these models with equations derived from statics, it was suggested that an appropriate design rule was to proportion steel columns to resist the axial forces resulting from total overturning moments and to proportion masonry walls to resist the total story shears. The total shear in the masonry wall and the column axial force can be represented by Equation [1] and Equation [2], respectively. [1] Page 3

12 [2] In these equations F j is the lateral force at level j, n is the total number of stories in the building under consideration, V k is the story shear in story k, h k is the individual story height, and L is the bay width. Results from the same study also demonstrated that current building codes would be appropriate for the structural design of both steel frames and masonry walls, but it was determined that there exists a lack of structural details for the connection between the two systems. 2.2 Connector Plates Design of the connector plates for hybrid masonry systems has been addressed in its simplest form but this design has focused solely on design for in-plane and out-ofplane masonry wall reactions [Biggs, 2011]. The preliminary design procedure was developed on the sole premise that the connector s only purpose is to transfer in-plane shear to the wall and also to brace the frame for out-of-plane loadings [Biggs, 2011]. Using this design approach the masonry wall is assumed to crack under high seismic loading, with the connectors resisting the load through flexure but providing little to no additional ductility to the overall system. Refer to Figure 2 for the current detailing requirements of the connector plates. There have been numerous investigations into the development of structural fuses, a building component that absorbs energy through yielding behavior, and even through failure, in order to prevent damage to more critical elements. In one study such structural fuses were proposed and tested as a component that initially engages the infill walls in seismic resistance of the frame, but ultimately isolates them [Aliaari & Memari, 2007]. Page 4

13 Figure 2. Current state of connector plate detailing requirements as provided by the International Masonry Institute. For the purposes of determining the required flexural strength of the connector plates, the plates have been idealized as a cantilever with a maximum moment equal to the total shear to each connector plate determined by computer analysis multiplied by the distance from the bottom of the beam flange to the center of the connector plate slotted hole. Alternatively, Biggs suggests that a second option is to detail the connector plate geometry in a manner that the plates may serve as a seismic energy-dissipating fuse in the system, minimizing damage to the masonry wall. 2.3 CMU Thru-Bolt Push-Out Tests The Building Code Requirements and Specifications for Masonry Structures (ACI ) [MSJC, 2008] provides guidelines and code requirements for the design of embedded anchor bolts in masonry, but through-bolted connections are never clearly addressed. In the commentary for ACI it states that the design equations provided in the Code stem from research conducted on cast-in-place headed anchor bolts and bent-bar anchors (J- and L-bolts) in grout. Therefore, the application of these provisions to post-installed anchors may be in question. ACI provides guidelines for determining the nominal bearing strength of masonry as well as the nominal shear strength of headed and bent-bar anchor bolts. For the purposes of determining the nominal shear strength, the Code addresses the following potential failure mechanisms: nominal shear strength governed by masonry breakout, nominal shear strength governed by masonry crushing, nominal shear strength governed by anchor bolt pryout, and nominal shear strength governed by steel yielding. Although, these provisions are not directly applicable to the through-bolted connection proposed for hybrid masonry systems, they can be used as a basis for an evaluation of the Page 5

14 connection performance. The applicability of the individual failure mechanisms will be addressed in more detail in the analysis portion of this report. ASTM E488 [ASTM, 2003] provides guidelines for determining the strength of anchors in concrete and masonry elements, loaded in single shear. Based on the procedure outlined in this guideline, a similar methodology has been developed for the testing of the post-installed through-bolted connections to be employed in this project. Page 6

15 3.1 Connector Plate Tests 3 Approach Experimental Setup The experimental test setup for this portion of the testing was developed to simulate the loading and restraints provided by the actual overall hybrid masonry assembly, while allowing for compliance with ATC-24 guidelines. Provision was also made for quick replacement of connector plates to facilitate the testing of multiple specimens with the only damage incurred by the test specimens themselves. The lateral load was applied to the connector plate by bearing of a ¾ diameter ASTM A325 bolt in a ¾ by 1 ¾ vertical slotted hole located from the top edge of the plate. The headed end of the bolt was welded to a 6 channel section, which provided adequate stiffness to simulate the condition of the connection to a CMU wall. The web of the channel was reinforced with a ½ cover plate at the location of the bolt for additional web stiffness. Lateral displacement of the channel section and attached bolt was provided by the extension and retraction of a hydraulic actuator connected to the 3 square tube section as shown in Figure 3. Each test specimen was individually welded to a 6 by 9 by ½ hot rolled steel base plate with four bolt holes symmetrically placed. During testing, the base plate was connected to a stiffened W12 wide flange section with four ¾ ASTM A325 bolts to provide a fixed reaction this setup isolates the behavior of the connector/fuse from the potential flexibility of the beam above the masonry wall in the hybrid system. Figure 3. Connector plate test setup with specimen highlighted. Lateral load is applied to the steel tube section at the top of the image. Page 7

16 The tube section was restrained from vertical translation using two load rods, with pinned connections at each end, that were bolted through the W12 base and into the laboratory s reinforced concrete strong floor. Additional braces were attached between three locations on the testing assembly and the laboratory wall located approximately 12 feet away to provide restraint against lateral twisting, rotation, and out-of-plane translation of the tube section. A load cell was used to measure the load applied by the hydraulic actuator while an internal LVDT measured displacement. Lateral deflection of the connector plates was measured at the centerline of the bolted connection relative to the specimen base using a string potentiometer as shown in the figure Test Specimens The connector plate specimens tested in this project were manufactured from ASTM A36 bar steel hot rolled to 4-inch widths and varying thicknesses, as identified by the actual thicknesses reported for the individual test specimens. For the purposes of this report, link connector plates will reference plates that have a uniform width throughout the length of the specimen, while fuse connector plates will refer to specimens manufactured with regions of constant or tapered width significantly less than the width of the rest of the plate. Bent plates refer to plates manufactured with a 90-degree bend near the bottom of the plate, simulating the bend as would be required for attachment to the beam flange above in the actual hybrid masonry assembly. All plates were cut to shape with a milling machine, except for specimen P4_T4_FA2-P-01, which was cut using a hand-held plasma torch. 17 connector plates were tested in this phase of the project; six link connectors and 11 fuse connectors. In order to identify the ideal fuse geometry for the purposes of this project, three unique fuse types were tested, identified as either type A, S, or T. Figure 4 shows the typical dimensions of a link connector plate as well as the three types of fuse connectors utilized. Fuse type A, for aspect ratio, was the first fuse to be designed and tested. This fuse type is characterized by a narrowed region of constant width machined into the bar with the intent to develop a plastic hinge and increase the deformation capacity of the connector plate. The narrowed region was designed to force full utilization of the non-linearity of the stress-strain curve within the fuse. Type A fuses were machined with an aspect ratio (length of narrowed region, L f, to reduced section width, w f ) of either one, two, or three and using plates of various thicknesses. The behavior of a type S fuse, for slotted, is governed by a 2-inch (50.8 mm) wide by 4-inch (101.6 mm) long slot removed from the 4-inch (101.6 mm) wide bar. The intent of this fuse was to develop plastic hinges within both one-inch wide legs adjacent to the slot to increase the deformation capacity of the connection, while providing greater flexural stiffness than fuse type A. Type S should allow an increase in the deformation capacity and ensure full utilization of the non-linearity of the stress-strain curve within the fuse. After observing the yielding behavior of the type A fuses, a modification was made to the design of the reduced width section to account for the linearly varying moment distribution in this region. Fuse type T, for tapered, was the result of this modification and was designed with a linearly varying reduced section width to facilitate first yielding simultaneously along the entire length of the narrowed region of the plate. For a detailed explanation of the methodology used to develop the tapered fuse section, refer to the Appendix. Fuse Page 8

17 type T was also machined with an aspect ratio of either two or three, similar to type A, and as identified in the specimen nomenclature. Figure 4. Typical link and fuse connector details (in = 25.4 mm). Table 2. Connector plate specimen naming convention (in = 25.4mm). PX _ TX _ FX - X - 0X Plate Thickness Fuse Specimen Specimen Misc. Width (in.) x 1/8 inch Type No. Designation [1] [2] [3] [4] [5] [6] P4_T A2 1 P4_T2_FA P4_T A2 1 P4_T3_FA P4_T P4_T B 1 P4_T4-B B 2 P4_T4-B A1 1 P4_T4_FA A2 1 P4_T4_FA A3 1 P4_T4_FA A2 P 1 P4_T4_FA2-P S 1 P4_T4_FS T2 1 P4_T4_FT T3 1 P4_T4_FT T3 B 1 P4_T4_FT3-B A2 1 P4_T6_FA2-01 In order to differentiate between the various connector plate properties utilized in each specimen test, a specimen naming convention was developed and is shown in Page 9

18 Table 2. Column 1 gives the width in inches of the bar, or plate, from which the connector was constructed, while Column 2 gives the thickness of the same bar in eighths of an inch. Column 3 identifies the fuse type, as well as the aspect ratio when applicable, utilized for the particular specimen. Column 4 identifies any miscellaneous information about the specimen such as whether the specimen was cut with a handheld plasma torch (P) or constructed as the bent plate to be used for attachment to the beam flange (B). Column 5 simply identifies the individual specimen number for such cases when a particular plate geometry required more than one test. Finally, the complete specimen name is assembled and listed in Column 6. All specimens are referenced using the names as shown in Column Procedure Of primary concern for the development of an effective steel-masonry connection is the detailing of the connector plates in order to facilitate a ductile response during seismic events. In order to investigate the response of various shaped and sized steel connector plates, a testing assembly was constructed to simulate the loading and deflection that will be applied to the plates in the full-scale tests, shown in Figure 5. This test assembly allowed for studying the behavior of a wide variety of connector plate designs under cyclic loading with minimum required labor to change test specimens. Figure 5. Graphic representation of the proposed full-scale test structure to be constructed at UIUC. Each plate was installed in the test assembly as shown in Figure 3 and loaded according to the displacement-controlled sequence shown in Figure 6, at a programmed strain rate of approximately 0.2 in./in. per minute according to specified loading rates in Page 10

19 ASTM A370 and E8 [ASTM, 2008]. Flexibility of the test setup resulted in an actual loading rate approximately 5% slower than the programmed value. Using the test assembly shown, a modification of the recommended ATC-24 single-specimen testing program was developed to investigate the hysteretic responses of each connector plate. According to this adaptation of the ATC-24 procedure, each specimen was cyclically loaded using a hydraulic actuator under displacement-based control. Each cycle began with the connector plate in the vertical position (origin) and proceeded with an outward extension of the actuator corresponding to the specified lateral displacement, followed by a reversal of direction back to the origin. The second half of the cycle consisted of the retraction of the actuator a distance corresponding to the specified lateral displacement and again followed by a reversal of direction back to the origin. The first half of each cycle, the extension and return to the origin, and the second half of each cycle, the retraction and return to the origin, have been termed as a positive excursion and a negative excursion, respectively. Each displacement level (±0.010, ±0.015,, ±2.75, ±3.00 ) consisted of three cycles, i, and each cycle (i = 1, 2, 3,, n-1, n) consisted of both a positive excursion, i +, and a negative excursion, i -. The deformation history used for testing of the connector plate specimens is shown in Table 3 and Figure 6. In determining the specific displacement levels for the testing routine, a value of the yield strain for a typical connector plate was approximated and used to calculate the corresponding lateral deflection. Taking this value, ±0.015 in., the first level of displacement was chosen to provide for the completion of at least three cycles prior to yielding. After assumed first yield had occurred, lateral deflections were increased stepwise according to the deformation history. Due the flexibility of the test setup, the specified displacement levels apply only to the programmed motion of the actuator. Actual plate displacements were determined to be approximately 10% less than these values. All data were plotted using the actual measured displacements of the specimens. The following general procedure was followed for each connector plate specimen: 1) Initiate hydraulics and data collection devices. 2) Attach connector plate Table 3. Actuator displacement summary. Deformation Step Number (inch = 25.4mm) Cumulative Cycles Completed specimen to the testing apparatus by bolting down the specimen base plate, tightening with an impact wrench for a rigid connection. Page 11

20 3) Attach nut and washers at location of the slotted hole, providing a finger-tight connection that will allow for plate rotation and vertical translation with respect to the bolt. 4) Adjust lateral displacement of the plate connection until the load cell registers an initial load near zero. 5) Begin cyclic displacement-controlled loading of the specimen according to the specified deformation history. Continue cyclic testing until plate failure or significant buckling failure occurs, indicated by a significant decrease in the load on the specimen. Figure 6. Modified ATC-24 cyclic loading routine for steel connector plates, with three cycles at each level of lateral displacement. 3.2 CMU Thru-Bolt Push-Out Tests Experimental Setup In order to determine the lateral capacity of a through-bolted connection to the bond beam of the hybrid masonry CMU wall, the experimental test setup was developed to load a single ¾ ASTM A307 threaded rod in double shear, bearing along the crosssection of the cell of a grouted concrete masonry block. In the hybrid masonry assembly, pairs of connector plates will be placed at specified locations along the top of the wall, one connector plate on each face of the wall. Figure 7 provides an illustration of the concept applied to the testing of these connections. In order to provide symmetric loading to the threaded rod extending from each side of the test specimen, the loading device shown in Figure 8 was constructed. This loading device, composed of a top piece and two legs, was constructed from a 4 channel section. The top piece was stiffened with a 0.5 steel plate welded to its flanges, providing for a contact surface with Page 12

21 the actuator platen. Each leg was connected to the top piece using two ½ diameter bolts, allowing for insertion of shims to level the device. The ¾ bolt holes were provided in each leg of the device for attachment to the test specimens. of the loading device relative to the test specimen was measured by attaching a linear potentiometer (LPOT) near the location of the bolted connection, on each face of the test specimen. A steel angle was welded to opposite flanges on each leg at the height of the bolt holes to support the LPOT pins. The base of each LPOT was connected to an aluminum block and epoxied to the face of the CMU assembly. A load cell on the actuator assembly measured the applied load on the specimens. During testing, the ends of the specimens were supported by thin steel plates and ¼ thick plywood pieces to provide a uniform bearing surface in contact with the reinforced concrete laboratory floor. The bearing plates extended 2 inward from the ends of the specimen. A threaded rod was installed into a pre-drilled ¾ hole at approximately 10.5 from each end of the wall as shown in Figure 9. Figure 7. CMU bolt push-out test concept. Page 13

22 Figure 8. CMU bolt push-out test setup. Figure 9. Schematic drawing showing the dimensions and layout of the test assembly for loading of the CMU wall specimens. Page 14

23 3.2.2 Test Specimens In order to determine the capacity of the through-bolted connection at the top of the CMU wall, small wall specimens were constructed to model the behavior of this connection. Since the critical bolt location of the small wall tests was determined to be at the second row of blocks from the top of the wall and at least one cell from the edge of the wall, the bolted connection capacity was tested using a specimen 3 blocks high by 2 blocks wide as shown in Figure 10. Each specimen was of running bond construction using standard 8x8x16 inch units obtained from Tileco on the island of Oahu. For a detailed test report of the CMU blocks, refer to the Appendix section of this report. The middle row of blocks was detailed as the bond beam with a centered #3 steel reinforcing bar (A s = 0.11 in. 2 ) with a 180 degree hook at each end. A single, centered vertical #5 steel reinforcing bar (A s = 0.31 in. 2 ) was provided at each end of the specimens. Identical reinforcement was provided for all the specimens. A ¾ hole was pre-drilled into each specimen at two mirrored locations, approximately 10.5 from the edge of the specimen and at the centerline of the second row. To minimize spalling of the test specimens, drilling of the holes for the threaded rod connection was performed by pre-drilling from both sides of the specimen with masonry drill bits of increasing diameter until the required ¾ hole size was achieved. Four specimens were constructed for testing, and each specimen was drilled to allow for two tests denoted as test A or test B in order of completion, for a total of eight push-out tests. Of the four specimens, two were partially grouted (PG) and two were fully grouted (FG). In order to address all possible block arrangements, the specimens were constructed with either two half blocks and a single whole block (Configuration 1) at the bond beam level or two whole blocks (Configuration 2) as shown in Figure 10(a) and Figure 10(b), respectively. For example, specimen FG-1B denotes the 2 nd test of a fully grouted specimen constructed according to block configuration 1. Figure 10. (a) CMU block configuration "1", (b) CMU block configuration "2". Page 15

24 3.2.3 Procedure Prior to testing, each CMU specimen was drilled at two locations as previously identified, to accommodate for test A and B loading. The specimen to be tested was rotated 90 degrees and placed under the four-post hydraulic frame and rested on the steel and plywood bearing supports, extending two inches from the edge of the specimen on each side. The loading device was placed over the specimen and attached to the threaded rod using nuts and washers. In order to insure a symmetrically applied load, shims were used as leveling devices at the connections of the legs to the top channel section. Once assembled, the loading device was centered and clamped to the raised actuator platen, to hold the apparatus in place. The actuator was then loaded downward at a displacement-controlled rate of in./sec. in 0.25-inch intervals. Loading was stopped periodically to make observations and record behavior of the test specimen. After completion of test A, the specimen was removed from the test assembly and rotated 180 degrees so that the damaged end of the specimen faced vertically upward. A new piece of threaded rod was inserted into the 2 nd hole and test B was completed just as the first test. It should be noted that there was often residual damage and cracking in the specimens from test A, which often propagated well into the region of the specimen that bolt B was bearing upon, potentially affecting the results of the second test on each specimen. 3.3 Full-Scale Steel-Masonry Subassemblies Three 8 thick CMU walls have been constructed for the purpose of testing the hybrid masonry assembly in its completed state, incorporating the results and designs from both the connector plate tests and CMU bolt push-out tests. These subassemblies will be tested under similar loading conditions to those proposed for the full scale tests at UIUC, including monotonic shear tests and cyclic shear tests. The masonry walls for these tests were previously constructed and consist of 4 rows of 8 blocks, each row 5 blocks long, in running bond assembly. Analysis of the results from both the steel connector plate tests and the masonry wall bolted connection tests will be used to determine the final plate connection details for the connection of the CMU walls to a steel frame, consisting of two wide flange columns and beam. Testing of these subassemblies will continue until an adequate system is finalized for implementation in the UIUC full-scale hybrid masonry panel tests. Page 16

25 4.1 Shear Connector Tests 4 Results Test Results Summary A plot of the hysteretic behavior (load vs. displacement) for each connector plate specimen was used to visually identify critical defining points (yield point, point of maximum load, and point of maximum displacement) in the behavior of the specimen. The displacement and corresponding load for each of these critical points was manually extracted from the plots for both the positive and negative excursions. Table 4 provides a summary of the identified points for each of the 17 specimens tested in this study. The load and corresponding displacement identified at the point of specimen yielding is listed in Column 2. The maximum load and corresponding displacement are listed in Column 3. Finally, Column 4 gives the maximum displacement and corresponding load for each specimen. Table 4. Critical Points of Hysteretic Response (in = 25.4 mm, kip = 4.45 kn, kip-in = 113 J). Specimen Designation [1] Yield Point Maximum Load Max. [2] [3] [4] Displ.(in) Load (kip) Displ.(in) Load (kip) Displ.(in) Load (kip) (+/-) (+/-) (+/-) (+/-) (+/-) (+/-) P4_T / / / / / /-2.3 P4_T2_FA / / / / / /-1.0 P4_T / / / / / /-5.1 P4_T3_FA / / / / / /-1.8 P4_T / / / / / /-8.0 P4_T / / / / / /-0.5 P4_T4-B / / / / / /-1.9 P4_T4-B / / / / / /-2.3 P4_T4_FA / / / / / /-3.5 P4_T4_FA / / / / / /-3.5 P4_T4_FA / / / / / /-3.4 P4_T4_FA2-P / / / / / /-2.5 P4_T4_FS / / / / / /-4.3 P4_T4_FT / / / / / /-3.2 P4_T4_FT / / / / / /-3.0 P4_T4_FT3-B / / / / / /-2.6 P4_T6_FA / / / / / /-1.9 In order to determine the actual material strengths of the ASTM A36 steel bar used for the connector plate specimens, tension tests were conducted according to ASTM E8 [ASTM, 2008c]. Table 5 provides a summary of the test results for the three thicknesses of steel bar tested. Page 17

26 Bar Thickness (in.) Table 5. ASTM E8 tension test results for connector plate steel bar (inch = 25.4mm, ksi = MPa). Yield Ultimate Young's Stress (ksi) Strain Stress (ksi) Strain Modulus, E (ksi) * * * * *Data not available due to testing error and/or insufficient load capacity of test frame. Figure 11. (a) Non-Ductile Weld Rupture: P4_T4-01; (b) Rupture of Base Metal: P4_T4-02. For all the specimens tested, five characteristic hysteretic behaviors were identified. Each of the 17 specimens displayed one of these five typical responses, with varying degrees of magnitude. The first of these, non-ductile weld rupture, is typified by the behavior of specimen P4_T4-01 in Figure 11(a). This hysteretic response represents the behavior of a specimen failure due to rupture of the weld at the base of the specimen. This weld joins the plate to the base plate that is bolted to, and considered part of, the testing frame. Figure 11(b) shows the hysteretic response of specimen P4_T4-02. This hysteretic response characterizes a specimen which first yields but then initiates rupture in the base plate and gradually separates itself from the testing frame with the base weld still intact. Page 18

27 Figure 12. (a) Yielding then buckling: P4_T2-01; (b) Yielding/Fatigue rupture: P4_T4_FT3-01. The hysteretic response of specimen P4_T2-01 shown in Figure 12(a) is representative of a specimen that begins to yield but then undergoes local buckling in the link, causing the load on the specimen to decrease at increasing displacement levels. Once buckling initiated in specimens displaying this behavior, the specimen would only begin to rupture due to fatigue from repeated cycling at large displacements. Figure 12(b) shows the hysteretic response of specimen P4_T4_FT3-01. This hysteretic response characterizes a specimen that first yields in the fuse region and then undergoes eventual fatigue rupture in this region due to increasing, or repeating, displacement cycles. The hysteretic response of specimen P4_T4_FT3-B-01, shown in Figure 13, shows the effect of a bent plate connection in combination with the yielding behavior displayed by a type T fuse. This response is characteristic of a specimen that first yields in the fuse region and continues to respond as a ductile connection until significant stress concentration at either leg of the C-shaped weld begins to initiate weld rupture. Figure 13. Bent plate behavior, ductile response followed by C-shaped weld rupture: P4_T4_FT3-B-01. Page 19

28 4.1.2 Specimen Behavior Narratives P4_T2-01 Plate test specimen P4_T2-01 was tested up to and through the ± 2.00 excursions, for a total of 39 complete loading cycles. Testing of this specimen did not continue beyond the ±2.00 level as significant buckling had already occurred and the load on the specimen had diminished significantly (Figure 14). Lateral-torsional buckling was determined to be the governing limit state for this specimen, with initiation of buckling observed around the ±0.5 cycles, at a load of 4.3 kips. This specimen reached a maximum load of 4.4 kips in the positive excursion direction and 4.3 kips in the negative excursion direction. P4_T2_FA2-01 Plate test specimen P4_T2_FA2-01 was tested up to and through the ± 2.00 excursions, for a total of 39 complete loading cycles. Testing of this specimen did not continue beyond the ±2.00 level as significant buckling had already occurred and the load on the specimen had diminished significantly. Lateral-torsional buckling was determined to be the governing limit state for this specimen, with initiation of buckling observed around the ±1.00 cycles, at a load of 1.3 kips. This specimen reached a maximum load of 1.4 kips in the positive excursion direction and -1.4 kips in the negative excursion direction. Figure 14. P4_T2-01, showing typical buckling failure. P4_T3-01 Plate test specimen P4_T3-01 was tested up to and through two complete cycles of the ± 2.00 excursions, for a total of 38 complete loading cycles. Prior to this test, an additional restraining brace was added to the test setup in order to minimize rotation of the loading hardware due to plate buckling. Due to the significant buckling induced in this plate, the additional restraint caused significant tensile forces to develop in the bolted connection. Tension in the bolted connection contributed to failure of the bolted connection prior to completion of testing. Testing of this specimen stopped due to the bolt failure. The test setup was then modified to eliminate flexural bending of the bolt that failed. The bolt is inserted through a tight fit clearance hole the hole was previously 1/16 oversized per typical AISC details. Lateral-torsional buckling was determined to be the governing limit state for this specimen, with initiation of buckling observed around the ±1.25 cycles, at a load of 7.1 kips. This specimen reached a maximum load of 7.25 kips in the positive excursion direction and -7.4 kips in the negative excursion direction, at a displacement of 0.9 inches. P4_T3_FA2-01 Plate test specimen P4_T3_FA2-01 was tested up to and through the ± 2.75 excursions, for a total of 48 complete loading cycles. The first signs of significant plate Page 20

29 rupture were detected at the base of the fuse at the beginning of the ±2.75 cycles, at a load of 2.5 kips. This rupture led to complete separation of the plate across the fuse base at the end of the ±2.75 cycles. Initial signs of lateral-torsional buckling were observed at the 3 rd cycle at the ±2.00 displacement level, but plate rupture was identified as the governing limit state. This specimen reached a maximum load of 2.5 kips in the positive excursion direction and -2.5 kips in the negative excursion direction. P4_T4-01 / P4_T4-02 Plate test specimen P4_T4-01 was tested up to and through the ±0.75 excursions, for a total of 24 complete cycles. Initial signs of rupture of the fillet weld joining the connector plate to the base plate were observed during the 0.50 cycles, at a load of 7.5 kips. Complete separation of the base fillet weld occurred by the end of the 0.75 cycles (Figure 15). This specimen reached a maximum load of 7.6 kips in the positive excursion direction and -8.0 kips in the negative excursion direction. In order to determine if insufficient weld thickness was the cause of premature failure, a second specimen (-02) was tested using a heavier weld. Plate test specimen P4_T4-02 was tested up to and through six complete cycles at the 1.25 displacement level. Initial signs of weld rupture were observed at the Figure 15. P4_T4-02 showing weld failure and base plate rupture. ±1.00 displacement level, at a load of 9.5 kips, followed by base plate rupture around the weld connection. This specimen reached a maximum load of 9.5 kips in the positive excursion direction and kips in the negative excursion direction. A combination of weld failure and base plate rupture was determined to be the governing limit state for this specimen. P4_T4-B-01 / P4_T4-B-02 Plate test specimen P4_T4-B-01 was tested up to and through the ±2.00 excursions followed by 12 cycles at ±2.25 and three cycles at ±2.50, for a total of 54 complete cycles. Initial signs of fillet weld rupture were identified during the ±1.00 cycles in the portion of the weld perpendicular to the wide face of the plate, at a load of 3.25 kips. After the specimen reached the ±2.25 displacement level one corner of the welded bent portion of the plate had separated completely, propagating the weld failure to the long weld parallel to the wide face of the plate. At the end of the 54 th cycle the load capacity dropped to 1.1 kips. The specimen was completely ruptured by manually controlled displacement with four additional cycles at undefined displacement levels until the weld had completely separated at all three sides. This specimen reached a maximum load of 3.25 kips in the positive excursion direction and -3.3 kips in the negative excursion direction. In order to determine if defects in the weld were the causes of premature failure, a second specimen (-02) was tested, with increased attention paid to weld application and thickness. Plate test specimen P4_T4-B-02 was Page 21

30 tested up to and including one cycle at the ±2.25 displacement level. During this testing, it was noted that initial yielding was occurring on the bent leg of the plate as early as the ±0.25 cycles. Weld failure began similarly to the previous bent plate, with one corner of the weld showing complete separation by the ±2.00 displacement level. This specimen reached a maximum load of 3.15 kips in the positive excursion direction and kips in the negative excursion direction. Weld failure was determined to be the governing limit state for these specimens. P4_T4_FA1-01 Plate test specimen P4_T4_FA1-01 was tested up to and through the ±2.25 excursions, for a total of 42 cycles. Yielding of the fuse section was first noticed through signs of flaking at the base of the fuse section during the ±0.25 displacement cycles, at a load of 2.1 kips. Initial rupture of the specimen was identified at the base of the fuse section at the ±2.00 displacement cycles, leading to complete separation at the fuse base at the end of the ±2.25 displacement cycles (Figure 16). This specimen reached a maximum load of 3.5 kips in the positive excursion direction and -3.5 kips in the negative excursion direction. Fuse base rupture was determined to be the governing limit state for this specimen. No significant buckling behavior was observed. P4_T4_FA2-01 Plate test specimen P4_T4_FA2-01 was tested up to and through the ±2.50 excursions with an additional cycle at ±2.50, for a total of 46 cycles. Yielding of the fuse section was first noticed through signs of flaking at the base of the Figure 16. Specimens P4_T4_FA1-01, _FA2-01, and _FA3-01 showing typical fuse base rupture (shown from left to right). fuse section at approximately the ±0.25 displacement cycles, at a load of 2.0 kips. Initial rupture of the specimen was identified at the base of the fuse section at approximately the ±2.00 displacement cycles, leading to complete separation at the fuse base at the end of four ±2.50 displacement cycles (Figure 16). This specimen reached a maximum load of 3.25 kips in the positive excursion direction and -3.5 kips in the negative excursion direction. Fuse base rupture was determined to be the governing limit state for this specimen. No significant buckling behavior was observed. P4_T4_FA3-01 Plate test specimen P4_T4_FA3-01 was tested up to and through the ±2.50 excursions with an additional cycle at ±2.50, for a total of 46 cycles. Yielding of the fuse section was first noticed through signs of flaking at the base of the fuse section at the ±0.25 displacement cycles, at load of 2.0 kips. Initial rupture of the specimen was identified at the base of the fuse section at the ±2.25 displacement cycles, leading to Page 22

31 complete separation at the fuse base at the end of four ±2.50 displacement cycles (Figure 16). This specimen reached a maximum load of 3.4 kips in the positive excursion direction and -3.4 kips in the negative excursion direction. Fuse base rupture was determined to be the governing limit state for this specimen. No significant buckling behavior was observed. A machining error was noted to have caused a slightly over-sized slotted hole in this specimen, leading to approximately 0.10 of slip in the connection at the top of the plate. Surface flaking was not observed over the entire fuse region but stopped at approximately 4/5 th of the distance from the base to the top of the fuse. P4_T4_FA2-P-01 Plate test specimen P4_T4_FA2-P-01 was tested up to and through the ±1.50 excursions with an additional cycle at ±1.50, for a total of 34 cycles. Yielding of the fuse section was first noticed through signs of flaking at the base of the fuse section at approximately the ±0.25 displacement cycles, at a load of 1.7 kips. Initial rupture of the specimen was identified at the base of the fuse section at the ±1.25 displacement cycles, at a load of 2.4 kips. This led to complete separation at the fuse base at the end of four ±1.50 displacement cycles (Figure 17). This specimen reached a maximum load of 2.45 kips in the positive excursion direction and -3.5 kips in the negative excursion direction. Fuse base rupture was determined to be the governing limit state for this specimen. No significant buckling behavior was observed. P4_T4_FS-01 Plate test specimen P4_T4_FS-01 was tested up to and through the ± 2.25 excursions, for a total of 42 complete loading cycles. Testing of this specimen did not continue beyond the ±2.25 level as significant buckling had already occurred and the load on the specimen had diminished significantly to 2.9 kips (Figure 18). Out-of-plane buckling was determined to be the governing limit state for this specimen, with initiation of significant buckling observed around the ±1.00 cycles, at a load of 5.9 kips. This specimen reached a maximum load of 5.85 kips in the positive excursion direction and -5.8 kips in the negative excursion direction. Figure 17. Fuse roughness and early rupture of P4_T4_FA2-P-01 due to cutting with a hand-held plasma torch. Figure 18. P4_T4-FS-01 showing significant buckling at ±2.00 displacement. Page 23

32 P4_T4_FT2-01 Plate test specimen P4_T4_FT2-01 was tested up to and through the ±3.00 excursions with an additional 13 cycles at this displacement level, for a total of 64 complete loading cycles. Uniform flaking of the tapered fuse region was observed as early as the ±0.25 displacement level, at a load of 1.76 kips, and initial signs of lateral torsional buckling behavior were identified at the ±2.25 displacement level, at a load of 2.8 kips. Although buckling behavior became significant, no decrease in load was observed so testing was continued until rupture of the plate at the 64 th cycle (Figure 19). A combination of lateral-torsional buckling and plate fatigue were identified as the governing limit state for the specimen. This specimen reached a maximum load of 3.4 kips in the positive excursion direction and kips in the negative excursion direction. P4_T4_FT3-01 Plate test specimen P4_T4_FT3-01 was tested up to and through the ±3.00 excursions with an additional 28 cycles at this displacement level, for a total of 79 complete loading cycles. Loading of this specimen was stopped after the 57 th cycle. The specimen was uninstalled from the test setup and reinstalled when testing was later resumed until failure occurred at the end of the 79 th cycle. Uniform flaking of the tapered fuse region was observed as early as the ±0.25 displacement level, at a load of 1.6 kips, and initial signs of lateral torsional buckling behavior were identified at the ±2.25 displacement level, at a load of 2.6 kips (Figure 20). Although buckling behavior became significant, no decrease in load was observed so testing was continued until failure. A combination of lateral-torsional buckling and eventual plate fatigue were identified as the governing limit state for the specimen. This specimen reached a maximum load of 3.2 kips in the positive excursion direction and -3.3 kips in the negative excursion direction. Figure 21 shows the final failed state of both tapered fuse specimens. Figure 19. P4_T4-FT2-01 displaying a combination of lateral-torsional buckling and rupture due to fatigue. Figure 20. P4_T4-FT3-01 displaying uniform distribution of yielding along entire fuse section. Page 24

33 Figure 21. Specimens P4_T4_FT2-01 and _FT3-01, showing buckling and tapered fuse base rupture (shown from left to right). P4_T4_FT3-B-01 Plate test specimen P4_T4_FT3-B-01 was tested up to and through the ±3.00 excursions with an additional 15 cycles at this displacement level, for a total of 66 complete cycles. Uniform flaking of the tapered fuse region was observed as early as the ±0.25 displacement level, at a load of 1.2 kips. Yielding of the plate specimen in the region welded to the base plate was also observed at approximately the 0.50 displacement level, at a load of 1.8 kips. Initial signs of fillet weld rupture were identified during the ±2.00 cycles in the portion of the weld perpendicular to the wide face of the plate, at a load of 2.4 kips. After the specimen had completed several cycles at the ±3.00 displacement level one corner of the welded bent portion of the plate had separated completely, propagating the weld failure to the long weld parallel to the wide face of the plate. Loading was continued until the weld had completely separated at all three sides (Figure 22). This specimen reached a maximum load of 2.55 kips in the positive excursion direction and -2.6 kips in the negative excursion direction. Weld failure was determined to be the governing limit state for this specimen. Figure 22. P4_T4_FT3-B-01 showing rupture of C-shaped fillet weld on bent leg. Page 25

34 P4_T6_FA2-01 Plate test specimen P4_T6_FA2-01 was tested up to and through the ±2.25 excursions with an additional two cycles at this displacement level, for a total of 44 complete loading cycles. Yielding of the fuse section was first noticed through signs of flaking at the base of the fuse section at approximately the ±0.25 displacement cycles, at a load of 2.9 kips. Initial rupture of the specimen was identified at the base of the fuse section at approximately the ±2.00 displacement cycles, at a load of 5.0 kips, leading to complete separation at the fuse base at the end of five ±2.25 displacement cycles (Figure 23). This specimen reached a maximum load of 5.1 kips in the positive excursion direction and -5.1 kips in the negative excursion direction. Fuse base rupture was determined to be the governing limit state for this specimen. No significant buckling behavior was observed. Figure 23. P4_T6_FA2-01 showing typical fuse base rupture. Page 26