TECHNICAL SESSION 3. Strengthening, Repair & Rehabilitation

Transcription

1 TECHNICAL SESSION 3 Strengthening, Repair & Rehabilitation

2 2004 PTI Technical Session 3 T. Theryo, P. Garcia - Repair of Sunshine Skyway Bridge The Post-Tensioning Column Repair of High Level Approaches of Sunshine Skyway Bridge in Florida Teddy Theryo, P.E. Pepe Garcia, P.E. Technical Manager District Structures & Facilities Eng. Parsons Brinckerhoff Florida Dep. Of Transportation 5405 West Cypress St.,Ste Leslie Road MS Tampa, Florida Tampa, Florida ABSTRACT The Sunshine Skyway Bridge located over Tampa Bay on the west coast of Florida, U.S.A., has a total bridge length of 4.1miles, including approaches structure. The bridge is on Interstate 275 Highway, and links the major metropolitan areas of Tampa/St.Petersburg on the north and Bradenton/Sarasota on the south of Tampa Bay. The bridge consists of three major portions namely 4000 foot main cable stayed bridge span, 4860 foot high-level approach spans, and 13,000 foot low-level approach spans. The bridge was constructed with precast segmental construction method, including high level approach columns. This paper focuses on the repair of the high-level approach piers. The north and south high-level approaches consist of twin trapezoidal pre-cast post-tensioned (PT) box girder superstructures on pier columns supported on piles at 135 foot from center to center. The pier columns are post-tensioned and consist of pre-cast caps and elliptical shaped pre-cast segments with match-cast epoxy joints. The lower sections of the columns have a 2 foot thick wall and the upper sections have a 10 inches thick wall. The vertical tendons that hold the column segments together were internally bonded in the lower sections and are external in the upper sections of the columns. The tendons comprised of U loop tendons with 12, 17, and 18 strands of 0.5 inches diameter encased in 3 inches diameter smooth polyethylene (PE) primary duct. In the thick wall section of the columns, the primary duct was placed within a 5 inches diameter corrugated secondary PE duct, which was cast in the pre-cast segment. The U-loop tendons were looped in the footing (pile cap) and anchored in the pier cap. During a special inspection of the high-level approach columns in August 2000, severe tendon corrosion was discovered in one of 72 pier columns, namely 133 NB (northbound structure). Eleven of seventeen 0.5 inches strands in one of the four tendon legs, specifically the SE (southeast) tendon leg, had corroded fully in the external tendon region immediately below the column cap. The NE (northeast) tendon leg exhibited significant pitting corrosion, but no strand failure was identified. Both tendon legs had cracked PE ducts in the corroded areas. The rehabilitation of column 133 NB was completed on June 1, The detection of this severe corrosion failure prompted the Florida Department of Transportation (FDOT) to contract the services of Parsons Brinckerhoff Quade and Douglas, Inc. (PBQ&D) to perform comprehensive tendon corrosion investigation and repair of deficient structural members. As a result of the above investigation, a major rehabilitation of the 71 post-tensioned columns was recommended. The columns were repaired by filling the column shaft with reinforced concrete (Type 1 repair) or in combination with vertical PT bars in the upper part of the columns (Type 2 repair). For type 2 repair, the concrete was filled up to about 20 feet above the mean high water level. For both repair option, the existing vertical tendons were not utilized, however the tendons were left in place. Structurally, the repair method was designed based on composite action between the infill concrete and the existing column in resisting live loads, wind loads, temperature loads and ship impact loads. Vertical reinforcing bars were anchored in the footing by means of coring the footing and anchoring the bars with cementitious grout. The existing foundation capacity was also checked and it was determined that its support capacity is sufficient in supporting additional loads of infill concrete. The new PT bars were embedded in the infill concrete and anchored in the column cap by coring hole. A full scale vertical tendon mock-up grouting test was required in the repair contract. A new approved prepackaged grout material was utilized for the new vertical tendons. The pier caps were coated with elastomeric coating membrane to protect the PT system from future intrusion of contaminants. The columns rehabilitation was completed in February Copyright - Post-Tensioning Institute 19 All rights reserved

3 Engineering for Post-Tensioning Strengthening of Preheater Tower Dr. Ralph G. Oesterle, P.E., S.E. Senior Principal Structural Engineer Construction Technology Laboratories, Inc Old Orchard Road Skokie, IL (P) (F) Inspection by plant personnel revealed cracking in the concrete frame of a 326-ft-tall, 7-level preheater tower. On-site plant engineers deemed the cracking significant, especially since the structure supports critical manufacturing process equipment. A structural engineering consulting firm was retained to evaluate the extent of the problem and formulate a repair plan on a fast-track basis. The firm mobilized at the site in less than 24 hours and performed an initial structural safety assessment. A comprehensive condition survey and structural evaluation indicated that all levels of the structure required strengthening. Restoration consultants were engaged to assist locally with engineering and construction administration. A specialty repair contractor also was engaged to review the constructibility of several alternate repair schemes and maintain the fast-track schedule. After considering structural capacity and serviceability requirements, durability issues, the high-temperature operating environment, constructibility, and an aggressive construction schedule, the team recommended a retrofit consisting of bonded post-tensioning within internal holes drilled in the beams. This solution was quite extraordinary, as it required precision-drilling horizontal holes up to 87 ft long in the beams of the elevated frame structure, without cutting existing embedded reinforcement. Nondestructive impulse radar testing was used to locate existing embedded reinforcing steel, as well as to monitor the drilled holes trajectory. This process helped ensure proper tendon alignment and prevent damage to embedded steel. The cored holes served as post-tensioning ducts. The repairs were executed on a fast track and under challenging circumstances, which included working high on the exposed structure through a cold winter with severe wind conditions. The unique retrofit resulted in a structure that is stronger, more serviceable, and more durable than the original tower. The project represented an exceptional team effort, and its success is attributable to the leadership of the owner and client, the ingenuity of the engineering team, and the resourcefulness of the contractor. This presentation describes the engineering effort required for the strengthening work including the condition survey, structural evaluation, retrofit concept evaluations, retrofit design, and engineering support for the retrofit work. This presentation is intended to be given in conjunction with a presentation by Structural Preservations Systems, Inc. regarding the retrofit construction. Copyright - Post-Tensioning Institute 20 All rights reserved

4 Engineering for Post-Tensioning Strengthening of Preheater Tower Level 7 Level 6 Level 7 Level 6 N 1 2 Level 5 Level 5 B 8.2 FT. 9.5 FT. B X01 Level 4 Level 4 Level 3 320FT. Level 3 B X03 B X04 47 FT. Level 2 Level 2 Level 1 Level 1 A B X02 87 FT. Top/Grade Top/Grade 87 FT. 47 FT. Copyright - Post-Tensioning Institute 21 All rights reserved

5 Condition Survey Scope: Extensive Crack Survey Concrete Cores Ground Penetrating Radar (GPR) Ultrasonic Pulse Velocity (UPV) and Impulse Response (IR) Condition Survey Results: 4 Beams With Extensive Cracking at End Anchorage Regions Equivalent f ' c = 6,000 psi Cold Joint at Level 4 Adequate Reinforcement Was Consistent With Design Drawings #8 EF NDT Indicated Either Poor Concrete Consolidation Or Possible Splitting Cracks Copyright - Post-Tensioning Institute 22 All rights reserved

6 Structural Evaluation Scope: Reviewed Design Criteria Wind Load/Seismic Load Thermal Load Load Combinations Reviewed Original Computer Model Checked Reinforcement Details Structural Evaluation Scope: Analyses for Gravity, Thermal and Lateral Loads Beams Columns Diaphragms Foundations Structural Evaluation End Anchorage Requirements for Flexural Reinforcement Local or Global Problem? Structural Evaluation Results: All End Regions of All Beams at All Levels Required Strengthening Structural Evaluation Wind Load Results Beams Flexure and Shear Columns Flexure and Axial Shear Beam/Column Joint Shear Diaphragms Connection to Frame Foundation Pile Capacity 47 FT. Copyright - Post-Tensioning Institute 23 All rights reserved

7 Retrofit Concept Evaluation Beam/Joint Flexural Strengthening Requirements: Control of Cracking Sense of Safety Long Term Confidence High Temperature Environment Constructibility Aggressive Construction Schedule Retrofit Concrete Evaluation Early Concepts: Unbonded External Post-Tensioning Local Post-Tensioning Across Column Above and Below Beams King Post Truss System Bonded External Post-Tensioning External Plates Retrofit Concept Evaluation Unbonded External Post-tensioning tensioning Constructibility and Time to Install Required Post-Tensioning Crack Control Temperature Protection Retrofit Concepts Evaluation Bonded External Post-Tensioning Copyright - Post-Tensioning Institute 24 All rights reserved

8 Retrofit Design Requirements for Internal Post-Tensioning Design for Full Strength Utilize Existing Rebar for Crack Control Thermal Analyses Strength Reductions for Long Term Temperature Effects Increased Creep and Shrinkage Other Retrofit Issues Beam/Column Joint Shear Column Shear Column Axial Load Beam B302 Epoxy Injection Diaphragms Foundations Copyright - Post-Tensioning Institute 25 All rights reserved

9 Other Retrofit Issues Beam/Column Joint Shear Column Shear Column Axial Load Beam B302 Epoxy Injection Diaphragms Foundations Other Retrofit Issues Beam/Column Joint Shear Column Shear Column Axial Load Beam B302 Epoxy Injection Diaphragms Foundations Other Retrofit Issues Beam/Column Joint Shear Column Shear Column Axial Load Beam B302 Epoxy Injection Diaphragms Foundations Copyright - Post-Tensioning Institute 26 All rights reserved

10 Engineering Support of Retrofit Work Scope Continuous Site Engineering Presence Review/Respond to Submittals RFI s Field Clarification Engineering Support of Retrofit Work Structural Safety Crack Monitoring Elevation Survey Wind Monitoring Wind Monitoring Initial 35 mph Evacuation Criteria (15% of Design Wind) Seasonal Winds Increased Evacuation Decreased Productivity Wind Monitoring Reviewed Site Records Wind Consultant to Refine Loading Meteorological Consultant to Forecast Winds Refine Post-Tensioning Sequence to Strengthen Critical Members Earlier in Schedule Coring Support Pre-coring Surveys Individual Layouts With Anticipated Steel Use of GPR to Monitor Core Barrel Reviewed Each Core for Embedded Steel Analyses/Resolution of the Effects of Cut Steel Copyright - Post-Tensioning Institute 27 All rights reserved

11 Engineering for Post-Tensioning Strengthening of Preheater Tower Copyright - Post-Tensioning Institute 28 All rights reserved

12 2004 PTI Technical Session 3 S. Greenhaus - Strengthening the Holcim Preheater Tower Construction Strengthening the Holcim Preheater Tower Repair Work Items Epoxy injection Internal Post tensioning Multistrand tendons Grouted anchor bars Column enlargement Column strengthening Local zone reinforcement Mechanical relocations Beam enlargements Steel frame modifications Access and Logistics Tower completely scaffolded Interior and exterior access Hanging work platforms Service elevator and material hoists Access and Logistics Safety Issues Vertical work area Falling object protection Access and Logistics 24/7 operation 200 people Engineering communication Access and Logistics Winter Construction Core drilling operations -20 deg wind chill Heating Copyright - Post-Tensioning Institute 29 All Rights Reserved

13 2004 PTI Technical Session 3 S. Greenhaus - Strengthening the Holcim Preheater Tower Mock Ups Drilling, grouting and bearing plate installation were performed on decommissioned pier Internal Post-Tensioning Internal Post-tensioning scheme required accurate core drilling Pre-heat tower was constructed by slipform methods Reinforcement placement? Jackrod locations? Environmental concerns Winter construction Waste water Core Drilling Drilling mock up Decommissioned kiln pier Holes drilled to ensure accuracy 4.75 cores- 39 ft in length Trial drilling successful Deviation 3/8 horizontal, 5/8 vertical Production Core Drilling Predrilling process GPR survey to locates rebar Set up string line to establish entry/exit points Erect drill frame to proper orientation Establish horizontal and vertical ref. Points Review GPR survey for rebar interferences Production Core Drilling Water Feed Insulated water tank Waste water handling Water collection system Production Core Drilling (8 crews) Drill 3-5 to first rebar location, remove core Continue drilling to the next rebar, break core, remove for logging Follow sighting procedures at each core removal Continue drilling every 4,6,10 intervals inside the column, break cores and remove for logging Copyright - Post-Tensioning Institute 30 All Rights Reserved

14 2004 PTI Technical Session 3 S. Greenhaus - Strengthening the Holcim Preheater Tower Production Core Drilling Continue drilling every 4,6,&10 max. intervals inside the column Stop drilling if steel is encountered or deviation exceeds 1 in either horizontal or vertical direction. Perform radar survey to locate the core bit inside the beam at quarter points for long span beams Corrective actions Trajectory wedge/shoe Back drilling Production Core Drilling Core logging Cores reviewed for rebar Accurate logs retained Hole Preparation Bonded P-T Spec-ICRI CSP-6 required rough hole surface roughness Hole prepared with QC- Flexible high pressure water boroscope monitoring Flushing and air drying Internal Post-Tensioning 114 Internal tendons 19, 31 and 37 strand,.5 dia. 270 ksi tendons 265,000 lf strand 4 tendons per location Tendon Installation Strands precut to length Strands push through entry and exit anchor heads Wedges installed Tendon stressing Staged stressing Steel diaphragm modified to allow for frame shortening Monostrand stressing Copyright - Post-Tensioning Institute 31 All Rights Reserved

15 2004 PTI Technical Session 3 S. Greenhaus - Strengthening the Holcim Preheater Tower Tendon Stressing 2 monostrand rams/corner top & bottom 4 strands stressed per tendon Stressed to 20%, then 50% to 100% Permanent anchor cap installed Tendon Grouting Raw mill operations to start prior to grouting Thermal protection installed Jack rods grouted Low points established Low bleed prepackaged grout 2 pumps- ground level and 7th floor Tendon Grouting PTI grouting manual Mud balance Colloidal mixer Flow cone Anchor bar installation Shear reinforcement in column buildouts Full length embedment (6-8 ) Spacing Stressed and grouted Anchor Bar Installation Procedure 2 dia. core drill Roughen the surface of the hole using a high-pressure water jet to obtain CSP 6 Flush out the hole with water and then with air to obtain a clean dry hole. Anchor Bar Installation Procedure Install anchor bar & apply torque of 200 ft-lb. Install the washer and nut and apply torque of ft-lb. After installation of the anchor bars, grout holes through anchor bar. Copyright - Post-Tensioning Institute 32 All Rights Reserved

16 2004 PTI Technical Session 3 S. Greenhaus - Strengthening the Holcim Preheater Tower Concrete Enlargement Column enlargement-levels 2-5 Column build outs at anchorage zones Beam enlargement-level 3 Concrete Enlargement Completed Repairs Thank You Copyright - Post-Tensioning Institute 33 All Rights Reserved