Tài liệu The structural strengthening of bridges by post tensioning

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Tzavelis A thesis submitted in partial fulfillment o f the requirements for the degree o f Master o f Engineering December 16, 1999 The Cooper Union For The Advancement O f Science And Art Reproduced with permission of the copyright owner. Further reproduction prohibited without 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 do 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 1. Introduction. p. 1 2. The History O f Strengthening By Post-Tensioning. p. 6 3. 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 4. 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 5. 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 6. 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 6.3.4 Conclusions And Recommendations 7. The Future O f Strengthening By Post-Tensioning....................................... p. 244 7.1. Fiber Reinforced Polymer Prestressing Systems 7.1.1 The Benefits O f Fiber Reinforced Polymer Prestressing Systems 7.1.2 Fiber Reinforced Polymer Material Properties And Their Comparison To Prestressing Steel 7.1.3 Research And Development Needs 7.2. Health Monitoring And Assessment Utilizing Smart FRP Prestressing Systems 7.3. Post-Tensioned Steel Plate Girders For New Construction 7.4. Cited References 8. Conclusions And Recommendations p. 279 8.1. Design Conclusions 8.2. Construction Conclusions 8.3. Recommended Continued Studies 9. Appendix 9.1. Bibliography Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. p. 286 The Structural Strengthening O f Bridges By Post-Tensioning LIST OF FIGURES Description Figure 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Prestressed Truss By H. Rider, 1850 Elbe Bridge, Prestressing By An. Artificial Load, 1878 Prestressing By Ballast Load, Railway Bridge Over The Elbe River Prestressed Arch Bridge By Force Regulation Aare Bridge, Trusses Strengthened By Polygonal Cable Configurations, 1969 Aare Bridge, Details O f Cable Support At Midspan, 1969 Aare Bridge, Detail O f Cable Anchorage, 1969 Post-Tensioned Bridge Beam, 1984 3.1 Status O f Bridges Approved For The Highway Bridge Replacement And Rehabilitation Program California’s Maximum Permit Load Pier Cap Strengthened By Post-Tensioning, Interstate 495, Maryland Pier Cap Post-Tensioning Anchorage Bearing Plate, Interstate 495, Maryland Pier Cap Post-Tensioning Tendons And Deviation Saddle, Interstate 495, Maryland Pier Cap Post-Tensioning Anchorage Bearing Plate And Wiring For Strand Monitoring, Interstate 495, Maryland Post-Tensioned Earth-Filled Arch, Bridge Number 3094, Maryland Route 147 Over Gunpowder Falls Earth Filled Arch Tie Rods, Bridge Number 3094, Maryland Route 147 Over Gunpowder Falls Typical Voided Slab Plan And Section Prestressed Concrete Girder Damage Repair By Post-Tensioning Prestressed Concrete Box Girder Damage Repair By Post-Tensioning Thrust Pit Bracing Plan Thrust Pit Section Post-Tensioned Slurry Wall Typical Elevation And Section Post-Tensioned Slurry Wall Horizontal Section Post-Tensioned Slurry Wall Anchorage Details Truss Strengthened By Superimposed Arch, Baltimore County Bridge Number 18, Sparks Road Over Gunpowder Falls, Maryland Superimposed Arch Splice To Truss Vertical Member, Baltimore County Bridge Number 18, Sparks Road Over Gunpowder Falls, Maryland 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 vii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.19 Superim posed Arch Bearing End, Baltimore County Bridge Number 18, Spades Road Over Gunpowder Falls, Maryland 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27 4.28 Active Versus Passive Strengthening System External Post-Tensioned Concrete Tendon System Prestressed Beam Equivalent Loads Prestressed Beam Stress Distribution Prestressed Beam Tendon Deformation Under Additional Load Stress-Strain Diagrams O f Prestressing Versus Mild Steels Typical Stress-Strain Curves For Prestressing Steels Magnel Sandwich Plate Wire Anchorage (courtesy o f Troitsky, 1990) Strand Wedges Strand Anchorages And Couplers Mono-Strand Anchorage Strand Chuck Multi-Strand Tensioning Jack Mono-Strand Tensioning Jack Threaded Bar Anchorage Shell-And-Bar Strand Anchorage Shell-And-Bar Strand Anchorage, Interstate 495, Maryland, Pier Cap Strengthening Threadbar Tensioning Jack Smooth Bar Anchorage Systems Tendon Deviation Support Friction Loss Along A Tendon Derivation Of Formulas For Calculation O f The Effects O f Anchor Set Percent O f Initial Prestress Force Loss Due To Anchor Slip Comparison O f Strand Relaxation Losses Stress Relaxation Curves Final Stress Ratio Versus Initial Stress Ratio Typical Tendon Stressing Log Prorated Graph Of Jacking Force Versus Elongation 5.1 5.2 Bridge Field Inspection Report Methodology For Selection O f Bridge Improvement Option 6.1.1 Bridges Included In Regression Analysis For Distribution Fractions 6.1.2 Regression Formula Variables 6.1.3 Regression Formulas For Force And Moment Fractions, Post-Tensioned Exterior Beams, Skew o f 0 To 45 Degrees 6.1.4 Post-Tensioned Beams And Moment Diagrams vii! 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Further reproduction prohibited without permission. 6.1.5 R ecommended Interpolation For Distribution Fractions At Locations Other Than Mid-Span 6.1.6 Idealized Composite Post-Tensioned Beam Failure Mechanism 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 Strengthening Method For Continuous Span Beams Strengthening Schemes Effect O f Strengthening Scheme (a) Post-Tensioned End Span Exterior Beams Parameters Considered In Analysis O f Distribution Factors Regression Formula Variables 6.3.1 6.3.2 6.3.3 6.3.4 6.3.5 6.3.6 Governor Thomas Johnson Memorial Bridge Deep Water Pier Cap Dimensions Thomas Johnson Memorial Bridge Post-Tensioned Pier Cap Pier Cap Post-Tensioning System Pier Cap Post-Tensioning System Costs Associated With Repair O f Bridge 7.1 7.2 7.3 7.4 7.5 PARAFTL Strand, Coupler And Spike Wedge FRP Reinforcing Fibers Stress-Strain Curves Testing O f Concrete Beam Post-Tensioned With PARAFIL Tendons Fiber Optic Wires To Be Placed Within A Laminate Composite Post-Tensioned Plate Girder Schematic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Structural Strengthening O f Bridges By Post-Tensioning LIST OF TABLES Table Description 4.1 4.2 Properties O f Uncoated Seven-Wire Steel Strand Properties Of-High Strength Steel Bars 7.1 7.2 7.3 Mechanical Properties O f Prevalent Reinforcing Fibers Comparison O f Fibers And Prestressing Steel Allowable Strains At Service Load Cost Comparison Of Materials And Fabrication For Indiana E/W Toll Road Bridge Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1. INTRODUCTION The United States’ transportation providers are faced with the enormous problem that many o f their bridges are structurally deficient or functionally obsolete. This problem is currently an economic burden o f incredible proportions and, unless counteractive measures are taken, will become an even larger burden. According to the 1997 report to the United States Congress, “The Status O f The Nation’s Highway Bridges: Highway Bridge Replacement And Rehabilitation Program And National Bridge Inventory”, 31.4 percent o f our bridges are structurally deficient or functionally obsolete. Since the net material worth o f our nation's bridges is roughly estimated at 300 billion dollars, and one-third of our bridges require replacement or rehabilitation, this equates to upwards o f 75 billion dollars o f replacement or rehabilitation costs. But, more important than the net material worth o f our bridges is their net worth to our economy, which is even larger and not quantifiable. While structural strengthening may benefit many o f these deficient bridges, the most accurate representation o f those bridges that may benefit from stren g th en in g are those which require load posting. The 1997 report indicates that o f all the nation’s bridges (581,862), 19.6 percent (182,726) are or should be load posted because o f inadequate load capacities. Load posting requirements are indicative o f the inability o f bridges to serve their intended use. This condition has resulted primarily from environmental and service deterioration, increases in legal trucking loads, changes in specifications and standards, and increased dead weight from either resurfacing Introduction Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I or the addition o f bridge features. Load posting has incurred sizeable costs to the freight industry as motor carriers are required to take alternate routes over greater distances to avoid posted bridges. Bridges that require load posting fell into two groups. The first group includes structurally deficient bridges that have deteriorated to the extent that they cannot carry the load for which they were designed. The second group includes functionally obsolete bridges that are in good condition but whose current State legal load exceeds the originaL design load and therefore require posting. (Federal Highway Administration, 1997) There are three possible solutions to this problem. The first solution is bridge replacement, an extremely expensive solution not only because o f the tangible costs of reconstruction, but also because o f the intangible costs o f inconvenience to the traveling public in the form o f additional times and distances traveled as a result o f detours and increased fuel consumption (collectively termed road user costs). The second solution is posting load restrictions where trucks with loads exceeding the posted load limits would be required to take alternative routes attending intangible costs as indicated in the first solution. The third solution is to strengthen these bridges. (Podolny, 1990) Today's challenge is to address these deficiencies with limited funds. A feasible and extremely cost-effective method to strengthen bridges is by post-tensioning. Bridge p o st-te nsioning dates back to the late 1800's and early 1900's and has been used steadily since, but wrongly, is often not Introduction Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 regarded as the preferred alternative. Other strengthening schemes, partial structural replacement, or total structural replacement are often uneconomically chosen over post-tensioning. The basic principle o f post-tensioning is “the introduction o f internal stresses o f such magnitude and distribution that the stresses resulting from additional loadings are counteracted to a desired degree”. While most associate post-tensioning with only concrete, almost any material is conducive to post-tensioning whether steel, masonry, timber, composites or synthetics. The state of the art o f post-tensioning has changed little since its inception. However, with the advent o f advanced structural analysis tools including finite element modeling and various fieldtesting and response data acquisition systems, there has come an increased understanding o f the responses o f various structural systems to post-tensioning. Future technologies should greatly increase the acceptability o f post-tension strengthening. The current focus o f bridge research and development is for more advanced materials and the health monitoring and assessment o f in-place structural systems. With the introduction o f advanced materials will come materials with greater durability under environmental and service effects and more predictable performance characteristics with respect to time, stress levels, etc. With the introduction o f advanced health monitoring instrumentation and response data acquisition systems will come the ability to more accurately assess the condition and capacity o f our existing bridges from which more confident and economical decisions can be made to extend their service lives. In the near future, these two technologies will merge and be applied in the form o f smart fiber reinforced polymer (FRP) composite tensioning systems. Introduction Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 This thesis’ first section, The History O fStrengthening By Post-Tensioning will give a brief background on how 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 will turn to the heart o f the subject where the section The Theory, Design And Construction Concepts o f Bridge Strengthening By PostTensioning will present the principles o f post-tensioning, the mechanics o f post-tensioned structural members, the materials used for post-tensioning, and design and construction specifications and considerations. From there, the all important question When To Use Strengthening - When Not To Use Strengthening will be addressed with a discussion on the required steps to be taken to make an informed engineering decision. Then, various case studies will be presented which will demonstrate current findings and the attending design and construction standards. The section The Future O fStrengthening By Post-Tensioning will assess future technologies and needs. Lastly, the thesis findings will be presented in the section Conclusions And Recommendations. Introduction Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cited References 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. Podolny, Waiter, Federal Highway Administration Senior Structural Engineer, Introduction to Prestressed Steel Bridges Theory And Design by M.S. Troitsky, New York, Van Nostrand Reinhold Company, 1990. Introduction Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.