The structural strengthening of bridges by post-tensioning

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permission UMI Number 1397436 _ ® UMI UMI Microform 1397436 Copyright 2000 by Bell & Howell Information and Learning Company All rights reserved This microform edition is protected against unauthorized copying under Title 17, United States Code Bell & Howell Information and Learning Company 300 North Zeeb Road P.O Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner Further reproduction prohibited without permission The Cooper Union For The Advancement Of Science And Art Albert Nerken School O f Engineering This thesis was prepared under the direction o f the Candidate's Thesis Advisor and has received approval It was submitted to the Dean of the School o f Engineering and the hill Faculty, and was approved as partial fulfillment o f the requirements for the degree o f Master o f Engineering & Dean o f the School o f Engineering December 1999 December 1999 Reproduced with permission of the copyright owner Further reproduction prohibited without permission to myfather who gave me the inspiration and means to this and to my mother whoju st gave without questioning i Reproduced with permission of the copyright owner Further reproduction prohibited without permission ABSTRACT Since the erection o f the earliest structures there has been the need for structural strengthening The necessity for strengthening originates primarily from insufficient load capacities, structural deterioration by environmental and service effects, design and construction inadequacies, or inadequate performance In the case o f bridges, the need has never before been so noticeable The performance o f our aging bridges is falling significantly short o f our needs As of June 30, 1996, 19.6 percent of our nations bridges are or should be load posted because o f structural deficiencies or functional obsolescence The challenge is to address these bridge deficiencies with limited funds A feasible and economic method to strengthen bridges is by post­ tensioning Post-tensioning is applicable to nearly all structural and material types However, bridge post-tensioning is wrongly often not regarded as the preferred alternative for structural upgrades Other strengthening schemes, partial structural replacement or total structural replacement are often uneconomically chosen over p o st-te nsioning With the advent o f advanced structural analysis tools and field assessment instrumentation has come greater acceptance o f strengthening by post-tensioning As well, future technology should greatly increase its acceptability The future will bring forth advanced materials with greater environmental and service durability and more predictable mechanical characteristics as well as advanced health monitoring techniques that may more accurately assess the condition and Reproduced with permission of the copyright owner Further reproduction prohibited without permission capacity o f our bridges These technologies will enable more confident and economical decisions aimed at extending the service life o f structures In the near future, these two technologies will be applied in conjunction as smart fiber reinforced polymer composite tensioning systems This thesis addresses the situations where bridge strengthening may be needed, why and when strengthening by post-tensioning should be included in the alternatives for upgrading bridges which are structurally deficient and, if chosen, how to go about designing and constructing the strengthening system The argument is approached from multiple perspectives o f which economics, safety and mobility are always o f primary importance Reproduced with permission of the copyright owner Further reproduction prohibited without permission The Structural Strengthening O f Bridges By Post-Tensioning TABLE OF CONTENTS List o f Figures List o f Tables Introduction p The History O f Strengthening By Post-Tensioning p P -19 The Need For The Structural Strengthening O f Bridges 3.1 Increase Bridge Load Rating 3.2 Correct Inadequate Design And Construction 3.2.1 Inadequate Steel Reinforcement 3.2.2 Excessive Deflections 3.2.3 Seismic Retrofits 3.2.4 Other Performance Improvements 3.3 Emergency Repair 3.4 Strengthening For Construction 3.5 Historically And Culturally Significant Bridges 3.6 Cited References The Theory, Design And Construction Concepts O f Bridge Strengthening By PostTensioning p 62 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 Post-Tensioning Construction Operations And Stages The Principle O f Prestressing Active Versus Passive Strengthening Systems The Difference Between Post-Tensioned Concrete And Post-Tensioned S tren gthening Systems The Mechanics O f A Post-Tensioned Axial Load Carrying Member The Mechanics O f A Post-Tensioned Beam Prestressing Steel Mechanical Properties Anchorages Post-Tension Force Losses 4.9.1 Friction Loss 4.9.2 Anchorage Slip 4.9.3 The Relaxation O f Steel Tendons 4.9.4 Controlling The Post-Tensioning Force Protection O f Tendons And Anchorages From The Environment IV Reproduced with permission of the copyright owner Further reproduction prohibited without permission 4.11 Design And Construction Standards And Specifications 4.11.1 AASHTO LFD And LRFD Standard Specifications For Highway Bridges 4.11.2 Federal Procedures-96: Standard Specifications For Construction O f Roads And Bridges On Federal Highway Projects 4.11.3 A S ™ Volume 1.04, Steel 4.11.4 Discussion On Specifications 4.12 Design And Construction Considerations When To Use Strengthening - WhenNot To Use Strengthening 5.1 5.2 5.3 5.4 5.5 p 162 Selection O f Post-Tensioned Strengthening Option Strength Evaluation By An Integral Field And Analytical Investigation Life-Cycle Cost Build Then Forget? Cited References Case Studies p 176 6.1 Case Study One: Strengthening Simple Span Composite Steel Beam Bridges By PostTensioning p 176 6.1.1 Summary 6.1.2 Background And Need 6.1.3 The Investigations' Considerations And Findings 6.1.4 Recommended Design Procedure For The Strengthening Of Simply Supported Exterior Beams 6.1.5 Analytic Ultimate Strength Model O f An Isolated Post-Tensioned Beam 6.1.6 Ultimate Strength O f An Isolated Post-Tensioned Beam Compared To The Ultimate Strength O f A Bridge System 6.1.7 Conclusions And Recommendations 6.1.8 Cited References 6.2 Case Study Two: Strengthening Continuous Span Composite Steel Beam Bridges By Post-Tensioning p 205 6.2.1 Summary 6.2.2 Background And Need 6.2.3 The Dual Strengthening System 6.2.4 Experimental And Analytical Investigation 6.2.5 Design Methodology For Strengthening 6.2.6 Cited References 6.3 Case Study Three: Strengthening Bridge Pier Caps By Post-Tensioning 6.3.1 Background And Need 6.3.2 The Remediation Plan 6.3.3 Strengthening O f The Pier Caps Reproduced with permission of the copyright owner Further reproduction prohibited without permission p 229 post-tensioning tendon (typ-) concrete diaphragms (^P-) integral substructure polyethylene pipe with grout tendon backwall tendon diaphragm saddle pipe Figure 7.5: Post-Tensioned Plate Girder Schematic (courtesy of Leo Spaans) The Future O f Strengthening By Post-Tensioning Reproduced with permission of the copyright owner Further reproduction prohibited without permission 276 7.4 Cited References American Association o f State Highway Officials (AASHTO), Standard Specifications For Highway Bridges: Sixteenth Edition, Washington D.C., 1996 Ansari, Farhad, editor, Fiber Optic Sensors For Construction Materials And Bridges, Technomic Publishing Co., Lancaster, PA, 1998 Hollaway, L., editor, Polymers And Polymer Composites In Construction, Thomas Telford Ltd., London, 1990 Livingston, Richard, Federal Highway Administration Research Program in Fiber Opticsfo r the Infrastructure, FHWA Turner Fairbank Highway Research Center, McLean, VA, 1998 The National Seminar On Advanced Composite Material Bridges, Sponsored By The Federal Highway Administration, Arlington, VA, May 5-7, 1997 Spaans, Leo, Janseen & Spaans Engineering, “Innovative Post-Tensioned Steel Bridge On Indiana E-W Toll Road”, presentation and paper for Transportation Research Board 7&hAnnual Meeting, Washington D.C., January 10-14,1999 Tang, Benjamin, Fiber Reinforced Polymer Composites Applications In USA: USDOT Federal The Future O f Strengthening By Post-Tensioning Reproduced with permission of the copyright owner Further reproduction prohibited without permission 277 H ig h w a y A d m in is tr a tio n , FHWA Bridge Specialist Group, Washington, D.C., January, 1997 USDOT Federal Highway Administration, FHWA Study Tour For Advanced Composites In Bridges In Europe And Japan, FHWA’s Scanning Program, Government Printing Office, Washington, D.C., December 1997 VSL International Ltd., Wenger, T., editor, “Non-Metallic Tendons”, VSL News: Number One, 1993, VSL International Ltd., Bernstrasse, Switzerland, 1993 The Future O f Strengthening By Post-Tensioning Reproduced with permission of the copyright owner Further reproduction prohibited without permission 278 CONCLUSIONS AND RECOMMENDATIONS 8.1 Design Conclusions There is the need for more efficient alternatives for upgrading deficient bridges Post-tensioning should be included among proposed alternatives Post-tensioning is more economical than most rehabilitation and strengthening procedures because; • It utilizes high-strength materials • The post-tensioning material carries load axially • It is an active strengthening procedure that utilizes the existing material’s tensile and compressive strength and the structural section geometry more efficiently • It can relieve both dead and live load effects including stresses and deflections • Most other strengthening systems can only relieve dead load stresses by jacking the structure, affixing the strengthening members, then releasing the structure Post­ tensioning obtains the same results by simply jacking the tendons which is a less costly and easier proposition Post-tensioned strengthening o f simple and continuous span steel girders, although seldom used nationwide, is a feasible and economical strengthening procedure This has been proven by its Conclusions And Recommendations Reproduced with permission of the copyright owner Further reproduction prohibited without permission 279 occasional utilization over the past 50 years as well as recent research by Iowa State University Post-tensioned strengthening has the ability to; • Decrease elastic stresses to satisfy inventory and operating loads • Raise the ultimate strength o f a structure • Stiffen a structure to decrease dead and live load deflections • Improve other performance characteristics Post-tensioning is a more attractive strengthening procedure by the Service Load Design method than the Load Factor Design method because ultimate strength increases are less in percentage terms than allowable load increases Finite element models are capable o f accurately modeling the behavior o f a post-tensioned bridge as long as features that affect the longitudinal and transverse bridge stiffness are included These features may include sidewalks, parapets, diaphragms, bearing restraint and skew Regarding post-tensioning applied to steel bridge beams; • The primary difficulty in designing a post-tensioned strengthening system for a composite bridge is the unknown distribution of post-tension forces to the various beams • Researchers have found that post-tension force distribution fractions (synonymous with AASHTO’s load fractions) can accurately represent post-tension force distributions Conclusions And Recommendations Reproduced with permission of the copyright owner Further reproduction prohibited without permission 280 among beam s o f simple and continuous span bridges • Researchers at Iowa State University have shown that the distribution o f post-tensioning throughout a steel beam composite bridge is largely affected by the aspect ratio o f the post-tensioned region, deck thickness, transverse spacing between beams, relative stiffness o f the beams, and the orthotropic plate flexural parameter for the bridge • Because the axial force and moment components o f post-tensioning are distributed differently among a bridge section, the effect o f each should be separated during analysis, and different distribution fractions applied for each Special considerations for anchorages include: • Conventional prestressed concrete tendons are bonded systems while post-tensioned strengthening systems are usually unbonded systems This primary difference must be accounted for in the design and construction of the anchorages • Unbonded tendon anchorages see larger stress and larger stress ranges than bonded tendon anchorages It is recommended that they be designed for at least 100 percent o f the tendon ultimate capacity and the same stress range and fatigue cycles as the members they are required to strengthen • Bolted rather than welded anchorage connections should be used to avoiding fatigue cracking initiated at welds • Connections between anchorages and steel beams should be designed to transmit out of plane forces to the flanges rather than to the webs Out o f plane forces may result from eccentric post-tensioning forces, temperature differentials between tendons on either side Conclusions And Recommendations Reproduced with permission of the copyright owner Further reproduction prohibited without permission 281 o f the web, accidental impact, etc., and cause web fatigue cracking and warping Corrosion protection is essential to long-term performance and safety Tendons and anchorages, particularly for strand systems, should be encased in seamless protection and, if at all possible, located away from the elements To determine post-tensioning candidates from a bridge inventory, bridge management systems can be used to query bridges with low load ratings due to under-strength superstructure elements Generally, post-tensioned strengthening should be chosen over other improvement options ifr • Post-tensioning can correct the problem • The post-tensioning system can be designed, constructed and maintained with confidence • Post-tensioning was proven as the least costly option by a lifecycle cost analysis Generally, post-tensioned strengthening should not be chosen if: • There is insufficient information about a bridge’s behavior and environment to accurately access the stress relief needed and to accurately design, construct and maintain the post­ tensioning • There is severe section loss throughout structural members that may lead to crippling and buckling under post-tensioning For only local section loss, it may be feasible to build-up the section at local locations and then post-tension Conclusions And Recommendations Reproduced with permission of the copyright owner Further reproduction prohibited without permission 282 • The post-tensioning system is subjected to large force fluctuations from dynamic or live load impact forces • The post-tensioning system is susceptible to impact by surface or water vehicles • When factors other than flexural behavior (shear, stability, etc.) are the cause o f low load capacities, post-tensioning may not be correct choice The accurately determine the required post-tension force it is beneficial to a field investigation where, at the very least, the member stresses are assessed 8.2 Construction Conclusions At construction, the following should be considered: • Choice o f tendon type, size, and number depends not only on the required tensioning force, but also on the means o f corrosion protection and tendon path obstructions • There are particular advantages to either threaded bars or cables that must be considered in the final design choice • If the tendon does not have a straight or nearly straight profile, double-end tensioning should be specified in the contract documents • The strands in a multiple strand tendon should be tensioned simultaneously to avoid losses from elastic shortening • The strands in a multiple strand tendon should preferably not be intertwined If they are Conclusions And Recommendations Reproduced with permission of the copyright owner Further reproduction prohibited without permission 283 intertwined and a strand breaks during tensioning, the whole tendon must be de-stressed to free up and replace the broken strand unless extra strands were placed in the tendon • When tensioning beams with tendons located on both sides o f the web, the tendons should be tensioned simultaneously, and if not, the eccentric forces must be analyzed • Post-tensioning will induce some tensile stresses and camber that may cause some cracking o f the deck and curbs • Tendons should only be grouted after tensioning Otherwise, the grout may crack and delaminate from the steel providing avenues for moisture penetration A post-tensioning force loss that can be substantial and is seldom considered in design is the loss that occurs when the bridge deck, integral curbs, and integral parapets are replaced or modified 8.3 Recommended Continued Studies Nationally recognized standards and specifications specific to the design and construction of unbonded external post-tensioned strengthening systems are not available and should be developed The emergence o f prestressed steel for newly designed steel bridges will further the acceptance of post-tensioned strengthening The competiveness o f prestressed steel with prestressed concrete Conclusions And Recommendations Reproduced with permission of the copyright owner Further reproduction prohibited without permission 284 requires continued study and development, particularly in the area o f standards and specifications for design and construction While the ultimate strength o f an isolated beam can be reasonably determined by theoretical analysis, the distribution of post-tensioning force among bridge beams at ultimate load remains to be determined Fiber reinforced polymer (FRP) tendons will see significant use in the future due to their design flexibility, greater corrosion resistance, lower maintenance, extended service lives and minimal force losses The primary constraint on the use o f FRP tendons is the lack of nationally recognized standards and specifications Because of the multitude o f FRP types, strict performance specifications as opposed to material specifications (as is conventional to high-strength steel) must be developed to ensure designers that the material will have sufficient durability and long-term performance to meet the intended use Because the most significant difference between steel and FRPs is their behavior at ultimate load, FRPs’ ultimate load behavior requires further study from which specifications for their ultimate load design can be developed Conclusions And Recommendations Reproduced with permission of the copyright owner Further reproduction prohibited without permission 285 APPENDIX B ib lio g r a p h y American Association O f State Highway And Transportation Officials (AASHTO), Guide Specifications For Strength Evaluation O fExisting Steel And Concrete Bridges, Washington D.C., 1989 American Association o f State Highway Officials (AASHO), Standard Specifications For Highway Bridges: Seventh Edition, Washington D.C., 1957 American Association O f State Highway And Transportation Officials (AASHTO), Standard Specifications For Highway Bridges: Thirteenth Edition, Washington D.C., 1983 American Association o f State Highway Officials (AASHTO), LRFD Bridge Design Specifications: Second Edition, Washington D.C., 1996 American Association of State Highway Officials (AASHTO), Standard Specifications For Highway Bridges: Sixteenth Edition, Washington D.C., 1996 American Association Of State Highway And Transportation Officials (AASHTO), Standard Specifications For Transportation Materials And Methods O fSampling And Testing, Seventeenth Edition, 1995, P arti, Specifications, Washington, D.C., 1995 American Society O f Testing And Materials (ASTM), 1998 Annual Book o f ASTM Standards, Section 1, Iron and Steel Products, Volume 01.04, Steel—Structural, Reinforcing Pressure Vessel, Railway, West Conshohocken, PA, 1998 Ansari, Farhad, editor, Fiber Optic Sensors For Construction Materials And Bridges, Technomic Publishing Co., Lancaster, PA, 1998 Barker, M.G., ImhofF, C.M., McDaniel, W.T., Frederick, T.L., “Steel Girder Bridge Field Test Procedures”, presentation and paper for Transportation Research Board 78lh Annual Meeting, Washington D.C., January 10-14, 1999 Beck, B.L., Klaiber, F.W and Sanders, W.W Jr., Field Testing O f County Road 54 Bridge Over Anclote River, Pasco County, Florida, ERI Project 1730, ISU-ERI-Ames-85417, Engineering Research Institute, Iowa State University, Ames, Iowa, 1984 Burren, W.H and Day, H.B., "King's Bridge, Melbourne; Restoration Works", The Journal O f The Institution O fEngineers, Australia, Volume 40, December 1968 Appendix Reproduced with permission of the copyright owner Further reproduction prohibited without permission 286 Dunker, K.F., Klaiber, F.W., Becker, BX and Sanders, W.W Jr., Strengthening O fExisting Single-Span Steel-Beam And Concrete-Deck Bridges, Final Report - Part n, ISU-ERI-Ames85231, Engineering Research Institute, Iowa State University, Ames, Iowa, 1985a Dunker, K.F., Klaiber, F.W., and Sanders, W.W Jr., Design Manual For Strengthening SingleSpan Composite Bridges By Post-Tensioning Final Report - Part HI, ISU-ERI-Ames-85229, Engineering Research Institute, Iowa State University, Ames, Iowa, 1985b DWIDAG-Systems International, DWIDAG Bar Post-Tensioning System, DWIDAG-Systems International, Bolingbrook, Illinois, 1998 DWIDAG-Systems International, DWIDAG Multi-Strand Post-Tensioning System, DWIDAGSystems International, Bolingbrook, Illinois, 1999 El-Arabaty, H.A., Strengthening O f Continuous Span Composite Bridges Using Post-Tensioning And Superimposed Trusses, Ph.D Dissertation, Iowa State University, Ames, Iowa, 1993 El-Arabaty, H A., Klaiber, F W., Fanous, F S and Wipf T J., “Design Methodology For Strengthening O f Continuous Span Composite Bridges”, Journal o f Bridge Engineering, August 1996 El-RemaQy, A., Krause, G., Tadros, M.K., Yamane, T., “Transverse Design O f Adjacent Precast Prestressed Concrete Box Girder Bridges”, PCI Journal, July-August, 1996 Federal Highway Administration, The Status O f The Nation's Highway Bridges: Highway Bridge Replacement And Rehabilitation Program And National Bridge Inventory, Thirteenth Report to the United States Congress, Government Printing Office, Washington, D.C., May 1997 Heins, C.P and Kuo, J.T.C., "Ultimate Live Load Distribution Factor For Bridges”, Journal o f the Structural Division, Volume 101, Number ST7, July 1975 Hollaway, L., editor, Polymers And Polymer Composites In Construction, Thomas Telford Ltd., London, 1990 Iowa Department o f Transportation Highway Division, Standard Design, 30 Foot Roadway, Simple Span I-Beam Bridges, H 20-44 Loading Highway Division, Iowa Department of Transportation, Ames, Iowa, 1975 Iowa State Highway Commission, Standard Design, Continuous Three Span I-Beam Bridges, 24 Foot Roadway, Concrete Floor, Steel Rail, H -I5 Loadings, Iowa State Highway Commission, Ames, Iowa, 1957 Iowa State Highway Commission, Standard Design, 28 Foot Roadway, Continuous I-Beam Bridges, Concrete Floor, Steel Rail, H-20 Loadings, Iowa State Highway Commission, Ames, Appendix Reproduced with permission of the copyright owner Further reproduction prohibited without permission 287 Iowa, 1960 Iowa State Highway Commission, Standard Design, Simple Span I-Beam Bridges, 20 Foot Roadway, Concrete Floor, Steel Rail, H IS Loading Iowa State Highway Commission, Ames, Iowa, 1964 Iowa State Highway Commission, Standard Design, Simple Span I-Beam Bridges, 24 Foot Roadway, Concrete Floor, H 15 Loading, Iowa State Highway Commission, Ames, Iowa, 1964 Iowa State Highway Commission, Standard Design, Simple Span I-Beam Bridges, 28 Foot Roadway, Concrete Floor, H 20 Loading Iowa State Highway Commission, Ames, Iowa, 1964 Klaiber, F.W., Dedic, D.J., Dunker, K.F., and Sanders, W.W Jr., Strengthening O fExisting Single Span Steel Beam And Concrete Deck Bridges, Final Report - Part I, ISU-ERI-Ames83185, Engineering Research Institute, Iowa State University, Ames, Iowa, 1983 Klaiber, F.W., Dunker, K.F., and Sanders, W.W Jr., Feasibility Study O fStrengthening Existing Single Span Steel Beam Concrete Deck Bridges, Final Report, ISU-ERI-Ames-81251, Engineering Research Institute, Iowa State University, Ames, Iowa, 1981 Klaiber, F.W., Fanous, F.S., Wipth, T.J., and El-Arabaty, H.A., Design Manual For Strengthening O fA Continuous Span Composite Bridge, ISU-ERI-AMES-94403, Engineering Research Institute, Iowa State University, 1993b Klaiber, F.W., Wip£ T.J., Fanous, F.S., Bosch, T.E., and El-Arabaty, H.A., Strengthening O fAn Existing Continuous Span, Steel Beam, Concrete Deck Bridge, Final Report, ISU-ERI-Ames94403, Engineering Research Institute, Iowa State University, Ames, Iowa, 1993a Lamberson, E.A Post-Tensioning Concepts For Strengthening And Rehabilitation O fBridges, Structures Congress American Society of Civil Engineers (ASCE), Houston, Texas, Reprint SC10, October 17-19, 1983 Libby, James R., Modem Prestressed Concrete: Design Principles And Construction Methods, Third Edition, Van Nostrand Reinhold Company, New York, 1984 Livingston, Richard, Federal Highway Administration Research Program in Fiber Opticsfo r the Infrastructure, FHWA Turner Fairbanks Highway Research Center, McLean, VA, 1998 Mancarti, Guy D., "Strengthening California's Bridges By Prestressing", TRB Research Record 950, Second Bridge Engineering Conference, Volume 1, Washington D.C., 1984 Mancarti, Guy D., "Strengthening Short Span Bridges For Increased Live Loads”, Proceedings o f the Third International Corference on Short and Medium Span Bridges, Toronto, Ontario, Canada, 1990 Appendix Reproduced with permission of the copyright owner Further reproduction prohibited without permission 288 Maryland Department O f Transportation State Highway Administration, The Task Force Report On Closure O f The Governor Thomas Johnson Memorial Bridge, Bridge No 4019 Carrying Maryland Route 24 Over Lower Patuxent River At Solomon's Island, Final Report, Summer 1989 Massachusetts Highway Department, Central Artery (I-93)/Tunnel (1-90) Project, Contract Drawings for Contract C09A41-93/I-90 Interchange, 1-93 Northbound, 06/02/97 The National Seminar On Advanced Composite Material Bridges, Sponsored By The Federal Highway Administration, Arlington, VA, May 5-7,1997 Nilson, Arthur H., Design O fPrestressed Concrete, Second Edition, John Wiley And Sons Inc., New York, 1987 Parsons Brinckerhoff Silano, L., editor, Bridge Inspection And Rehabilitation: A Practical Guide, John Wiley And Sons, Inc., New York, 1993 Podolny, Walter, Federal Highway Administration Senior Structural Engineer, Introduction to Prestressed Steel Bridges Theory And Design, Troitsky, M.S., New York, Van Nostrand Reinhold Company, 1990 Post-Tensioning Institute, Post-Tensioning Manual: Second Edition, Post-Tensioning Institute, Glenview, Illinois, 1976 Precast / Prestressed Concrete Institute, Prestressed Precast Concrete PCI Bridge Design Manual: Volume One, October 1997, Chicago, 1997 Rand McNally & Company, 1994 Motor Carriers' Road Atlas, 1994 Sandoval, Luis, Federal Highway Administration Puerto Rico Division Bridge Engineer, interview, November 18, 1998 Spaans, Leo, Janseen & Spaans Engineering, “Innovative Post-Tensioned Steel Bridge On Indiana E-W Toll Road”, presentation and paper for Transportation Research Board 7tfh Annual Meeting, Washington D.C., January 10-14, 1999 Subcommittee Three On Prestressed Steel O f Joint ASCE-AASHO Committee, "Development And Use O f Prestressed Steel Flexural Members", Proceedings ASCE Structural Division, Volume 49, Number ST9,1968 Tang, Benjamin, Fiber Reinforced Polymer Composites Applications In USA: USDOT Federal Highway Administration, FHWA Bridge Specialist Group, Washington, D.C., January, 1997 Transportation Research Board, National Research Council, NCHRP Report 280: Guidelines Appendix Reproduced with permission of the copyright owner Further reproduction prohibited without permission 289 For Evaluation And Repair OfDamaged Prestressed Concrete Members Washington D.C., 1985 Troitsky, M.S., Prestressed Steel Bridges Theory And Design, New York, Van Nostrand Reinhold Company, 1990 United States Department Of Transportation, Federal Highway Administration, Federal Procedures-96, Standard Specifications For Construction O fRoads And Bridges On Federal Highway Projects, U.S Government Printing Office, Washington D.C., 1996 USDOT Federal Highway Administration, FHWA Study Tour For Advanced Composites In Bridges In Europe And Japan, FHWA’s Scanning Program, Government Printing Office, Washington D.C., December 1997 VSL International Ltd., Wenger, T., editor, “Parrots Ferry Bridge Retrofit”, VSL News: Number One 1994, VSL International Ltd., Berastrasse, Switzerland, 1994 VSL International Ltd., VSL Post-Tensioning Systems, VSL International Ltd., Raleigh, North Carolina, 1996 VSL International Ltd., Wenger, T., editor, “Non-Metallic Tendons”, VSL News: Number One, 1993, VSL International Ltd., Bernstrasse, Switzerland, 1993 Appendix Reproduced with permission of the copyright owner Further reproduction prohibited without permission 290 ... post-tension strengthening has been used to date Next, the section The Need For The Structural Strengthening O fBridges will present and assess the reasons why strengthening is needed Then the discussion... permission of the copyright owner Further reproduction prohibited without permission The Cooper Union Albert Nerken School O f Engineering THE STRUCTURAL STRENGTHENING OF BRIDGES BY POST-TENSIONING by. .. are leading the way in post-tension strengthening England holds annual conferences on strengthening and The History O f Strengthening By Post-Tensioning Reproduced with permission of the copyright