FACTORS AFFECTING THE DESIGN THICKNESS OF BRIDGE SLABS .
Technical Report Documentation Page1. Report No.2. Government Accession No.3. Recipient's Catalog No.FHWAlTX-94 1305-14. Title and Subtitle5. Report DateFACTORS AFFECTING THE DESIGN THICKNESS OFBRIDGE SLABS: DESIGN AND PRELIMINARYVERIFICATION OF TEST SETUPFebruary 19946. Performing Organization Code8. Performing Organization Report No.7. Author(s)J. H. Whitt, J. Kim, N. H. Bums, and R. E. KlingnerResearch Report 1305-110. Work Unit No. ITRAIS)9. Performing Organization Name and AddressCenter for Transportation ResearchThe University of Texas at Austin3208 Red River, Suite 200Austin, Texas 78705-265011. Contract or Grant No.Research Study 0-1305f - : - - - : - - - - : - - - : - : - - - - : - - : - 7 " - ; - - - - - - - - - - - - - - - - - - 1 13. Type of Report and Period Covered12. Sponsoring Agency Name and AddressTexas Department of TransportationResearch and Technology Transfer Officep. 0. Box 5051Austin, Texas 78763-5051Interim14. Sponsoring Agency Code15. Supplementary NotesStudy conducted in cooperation with the U.S. Department of Transportation, Federal Highway AdministrationResearch Study Title: "Factors Affecting Design Thickness of Bridge Slabs"16. AbstractThe punching shear behavior of concrete bridge decks under static, pulsating fatigue, and rolling fatigue loads wasstudied using both analytical and experimental models. The study of the analytical models also played a large role in thedesign of the experimental specimens, test setup, and test procedure.In this report, the development of the test setup is described, and preliminary test results are reported. Completestudy results will be discussed in future project reports.17. Key Words18. Distribution Statementconcrete bridge decks, bridge slabs, design thickness,punching shear behavior, static, pulsating fatigue,rolling fatigue, loads, analytical and experimentalmodels, specimens, test setup, test procedureNo restrictions. This document is available to the publicthrough the National Technical Information Service,Springfield, Virginia 22161.19. Security Classif. (of this report)UnclassifiedForm DOT F 1700.7 (8-72)20. Security Classif. (of this page)UnclassifiedReproduction of completed page authorized21 . No. of Pages4422. Price
FACTORS AFFECTING THE DESIGN TIDCKNESS OFBRIDGE SLABS: DESIGN AND PRELIMINARYVERIFICATION OF TEST SETlTPbyJ. H. Whitt, J. Kim, N. H. Burns, and R. E. KlingnerResearch Report Number 1305·1Research Project 0-1305Factors Affecting Design Thickness ofBridge Slabsconducted for theTEXAS DEPARTMENT OF TRANSPORTATIONin cooperation with theU.S. DEPARTMENT OF TRANSPORTATIONFEDERAL IDGHWAY ADMINISTRATIONby theCENTER FOR TRANSPORTATION RESEARCHBureau of Engineering ResearchTHE UNIVERSITY OF TEXAS AT AUSTINFebruary 1994
IMPLEMENTATIONThis report concerns the development of a testing program and test setup to evaluate the factorsaffecting the design thickness of bridge slabs. Results of this report have been incorporated into thetesting program. They are not intended for other implementation at this time. Implementation ofcomplete study results will be discussed in future project reports.Prepared in cooperation with the Texas Department of Transportation and the U.S. Departmentof Transportation, Federal Highway Administration.The contents of this report reflect the views of the authors, who are responsible for the facts andthe accuracy of the data presented herein. The contents do not necessarily reflect the view of the FederalHighway Administration or the Texas Department of Transportation. This report does not constitute astandard, specification, or regulation.NOT INTENDED FOR CONSTRUCTION,PERMIT, OR BIDDING PURPOSESNed H. Burns, Texas P.E. #20801Richard E. Klingner, Texas P.E. #42483Research Supervisorsiii
TABLE OF CONTENTSPageCHAPTER 1 - INTRODUCTION1.1General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . .1.2Scope and objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .,111CHAPTER2-BACKGROUND",,2,1Introduction. . . . , . . , . . . , . . , . . .2,2Arching action2.3Fatigue,2.4Other research , . . . . . . , . . . . . . . . .2.4.1 University of Texas at Austin.2.4.2 Case Western Reserve University.3334555CHAPTER 3 3.13.23.33.43.5, . ",,,. . . . . . . . . . . . . . . . , , . . . . . . .,,, . . ., . . . . . . . . . . . . . . . . ., . . . . . . . . , . , . . . . . . . . . . . . .,.,, . . . . .,.ANALYTICAL BASIS -- SLAB MODELS,,, . . . 7Introduction. . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "7Complete bridge model . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . " . . . 7Experimental specimen model . . . . . . . , . " . . . . . . . . . . . . . . . . . , . . . . 8Methods of analysis . . . . . . , . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . 93.4.1 Full-size bridge analysis.,," , . 103.4.2 Experimental specimen analysis.,,, . . . 11Relationship between analytical models11CHAPTER 4 - DEVELOPMENT OF TEST SETUP,, . . . . . . .4.1Introduction. . . , , . , , . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . .4.2Test specimens4.2.1 Scale and size.,,, . . . . . . . . . .4.2.2 Reinforcement., . . . . . . . . . . . . . . . . . . . . . . . . .4.3Testing frame,.4.4Instrumentation . ,, . ,, . , . . . . . . . . . . . . . . .4.5Loads. ,,,, . . . . . . . . . . . . . . . . . . .4,6Data acquisition, . . . . . . . . . . . . . . . . . . .151515151616171718CHAPTER 5 - TESTING PROCEDURE . , . ,, . . . . . . . . . . . .5.1Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , , . ,.5.2Static tests . . . . . . . . . . . . . . . . . . . , . . . . , . . . , . . . , . . . . . . . . . . .5.3Pulsating fatigue tests , . . . . . . , . . . . . , . . . . . . . . . . . . . . . . . . . . . . .5.4Rolling fatigue tests," . , . , . ,.1919192021v
CHAPTER 6 - SAMPLE TEST RESULTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.1Static test results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.1.1 Slab capacity -- analytical vs. experimental.6.2Pulsating fatigue test results6.3Rolling fatigue test results2323252929CHAPTER 7 - SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS.7.1Summary7.1.1 Analytical models.7.1.2 Experimental testing procedure. . . . . . . . . . . .7.2Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.3Recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .313131313232REFERENCES. . . . . . . . .,. . . . . . . . . . . . . . . . . . . . . . . . .33vi
LIST OF FIGURESPageFigure 2.1Figure 2.2Figure 2.3Figure 3.1Figure 63.73.8Figure 3.9Figure 4.1Figure 4.2Figure 5.1Figure 5.2Figure 5.3Figure 6.1Figure 6.2Figure 6.3Figure 6.4Figure 6.5Zone of compression balanced by surrounding zone of tension, archingactionLack of arching action in slab subjected to closely spaced axlesExample of an S-N curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Finite element model for full-size, 50-foot-span highway bridge. Onlyhalf of the bridge is modeled due to symmetry.Finite element model for experimental specimen tested in laboratory.Only half of the slab is modeled due to symmetry.Example of load-deflection curve using sequential linear analysisAASHTO design loads for standard HS20-44 truck . . . . . . . . . . . . .Plan view of loading pattern for full-size bridge model . . . . . . . . . . .Plan view of loading pattern for specimen modelAssumed failure surface of a general punching shear model . . . . . . . .Stress contours from finite element analysis of full-size bridge model,showing the effects of arching action (shaded regions denote areas oftensile stresses)Stress contours from finite element analysis of experimental specimenmodel, showing the effects of arching action (shaded regions denote areasof tensile stresses).Dimensions of full-scale slab modelSteel testing frame showing two pulsating fatigue test and one rollingfatigue testSetup for static tests of slab specimens . . . . . . . . . . . . . . . . . . . . .Schematic of hydraulic system for two simultaneous pulsating fatiguetestsSetup for rolling fatigue tests of slab specimensLoad-deflection curve of first statically loaded slab specimen. Graphshows two initial loading/unloading cycles. . . . . . . . . . . . . . . . . . .Plan view of top and bottom of slab, showing cracking patterns afterpunching shear failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Cross-section of static load test specimen showing observed punchingshear failureLoad vs. steel strain for both top and bottom layers of reinforcing steelduring static test of slab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Comparison between predicted and observed slab capacityvii. . . . . .3448. . . . . . . . . . . . .91011111212131415. . . . .1719,2021. . . . .23. . . . .2425. . . . .2628
SUMMARYThe punching shear behavior of concrete bridge decks under static, pulsating fatigue, and rollingfatigue loads was studied using both analytical and experimental models. The study of the analyticalmodels also played a large role in the design of the experimental specimens, test setup, and testprocedure.Two primary models were analyzed using the finite element method. The first model was a finiteelement mesh representing a full-size, realistic highway bridge. The prototype was a 50-foot-span(15.24 m), three-girder bridge with a 7 th-inch (191 mm) concrete deck. Solid elements, or 8-node brickelements, were used to model the concrete deck, while frame elements, or 2-node beam-column elements,were used to model the girders. This full-size bridge model was loaded in a typical AASHTO designtruck loading pattern.The second model represented the actual slab specimen to be tested in the laboratory. The fullscale specimen measured 6 feet (1.83 m) wide, 7 feet (2.13 m) long, and 7 th (191 mm) inches thick, andwas modeled using 8-node solid elements. Loading of the specimen model emulated the loading used inthe experiment, which, in turn, was representative of an actual truck tire footprint.When both models -- the full-size bridge model and the experimental specimen model -- wereanalyzed, it was observed that similar arching action behavior occurred in each, despite differentgeometries and load configurations. Also, it was possible to find out from the specimen model exactlyhow far a rolling load would have to move in order to obtain satisfactory fatigue behavior in the slab.The steel testing frame for this project was designed for three different types of test: staticloading, pulsating fatigue, and rolling fatigue. The static tests consisted of monotonically loading a fullscale slab until a punching shear failure occurred. The pulsating tests were very similar, but the loadvaried in magnitude, cycling until a punching shear failure occurred in the slab. The setup for the rollingtests was slightly different, allowing a constant load to be moved longitudinally across the slab, cyclinguntil failure. Both types of fatigue tests were controlled through closed-loop servo-controllers andhydraulic loading systems.As this report was being finalized, one complete static test had been completed. More static loadtests, as well as several fatigue tests, are scheduled to be performed and will be discussed and analyzedin future reports.IX
CHAPTERlINTRODUCTION1.1 GeneralExperimental research represents a vital concept in all engineering disciplines - the concept thattheoretical ideas can be explicitly proven to be applicable to the real, physical world. This concept isimportant to the academic world as well as the practical one. Therefore, a researcher must prove thatan experimental model directly relates to the real world situation that it is intended to represent. Thisis done by conducting thorough analyses and carefully designing an experimental testing scheme.An important area of research in the field of structural engineering is that of concrete slabbehavior. In recent years, the understanding of a phenomenon known as "arching action" has changedthe way designers think of concrete bridge decks. Arching action is the formation of compressive andtensile membrane forces after a slab has undergone flexural cracking. This structural action can bevisualized as similar to that found in a very flat dome, in which a compression ring forms in the loadedregion, and a tension ring forms in the surrounding structure. The principal effect of these membraneforces is to increase the flexural capacity of the cracked slab. This increase in flexural capacity has ledto changes in the way engineers design slabs, as exemplified by the "Ontario-type" bridge decks[1,2,3,4,5,6,7,8]. This subject is discussed extensively in Refs. 4 and 6.Since flexural capacity of a deck is increased by arching action, punching shear can then controlthe design. However, research pertaining to punching shear in bridge slabs is limited, and researchinvolving fatigue effects on punching shear is even more rare. Consequently, the Texas Department ofTransportation initiated a three-year investigation into the effects of fatigue deterioration on the punchingshear resistance of highway bridge slabs. A vital aspect of this research project was the development ofa relevant, working bridge deck model, and a testing procedure to validate the model analysis.1.2 Scope and objectivesThe general purpose of Texas Department of Transportation Project 3-15D-92/4-1305 is todevelop guidelines that will specify the required thickness of bridge decks as a function of variouscharacteristics, such as loading level, wheel spacing, and fatigue history. To determine these guidelines,the fatigue behavior of concrete slabs must be carefully analyzed. This consists mainly of testing slabsin different types of fatigue, and plotting "S-N curves," which display slabs' maximum stress rangesversus the number of fatigue cycles to failure.The objectives for Project 1305 are as follows:1)To review past research pertaining to the wheel load, axle width, and axle spacingcharacteristics of standard and nonstandard loads.1
22)To use structural analysis computer programs and engineering models to estimate thestress range experienced by a full-scale cracked bridge deck subjected to a conventionaltruck loading, and to predict the maximum principal tensile stress in the cracked deck.3)To design and construct a test setup that will allow for the static and dynamic testing offull-scale bridge decks, including both rolling and pulsating (constant location) loads.4)To develop S-N curves for both pulsating and rolling fatigue, and to use these curves todetermine the effects of rolling versus fixed load applications, and of arching action.5)To recommend guidelines for specifying the required thickness of bridge deck slabs asa function of traffic characteristics.The purpose of this report is to describe the development of the experimental program used toresearch the effects of fatigue on the punching shear capacity of a concrete bridge deck. Thisdevelopment involves the planning of a testing program, the design and construction of a testingapparatus, and the use of the apparatus for the proper testing of representative concrete bridge decks.This report will also include sample results to validate the testing program.The objectives of this report are as follows:1)To develop an experimental testing program that, within a reasonable time, adequatelyshows the effects of fatigue on the punching shear resistance of concrete bridge decks.2)To develop a testing apparatus on which concrete slabs can be tested in fatigue, bothpulsating and rolling.3)To design the aforementioned setup and slab specimens, construct both setup andspecimens, and use both in showing fatigue deterioration of the slabs' capacities.4)To present an initial sample of experimental test results.The complete investigation of bridge decks and recommended guidelines will be fully detailed infuture reports.
CHAPTER 2BACKGROUND2.1 IntroductionThis chapter will present an overview of arching action in concrete slabs, a discussion of fatigue,and a review of past research conducted concerning arching action, fatigue effects, and punching shearin concrete slabs. To fully understand the process of developing the experimental tests for this project,one must grasp the theories being tested and comprehend the expected behavior of the test specimens.2.2 Arching actionWhen an uncracked bridge deck undergoes loading, it acts primarily as a one-way system,resisting the load with transverse flexure. In-plane action remains insignificant in bridge decks beforeflexural cracking. However, once the deck cracks near the point of loading and above the supports, itacts as a flat dome. This subject is discussed extensively in Refs. 4 and 6.This "dome" is defined by a compression zone near the point of load, and a surrounding zoneof tension, as shown schematically in Figure 2.1. The compressive membrane forces surrounding theload increase the flexural capacity of the slab. This membrane action exists even if supports are notrestrained; the magnitude of such in-plane forces is higher for slabs whose edges are restrained.Recently, some have attempted to utilize the increased capacity of slabs due to arching action inthe design of highway bridge decks. In the mid-1970's, the Ontario Ministry of Transportation andCommunications adopted a code that allowedfor the empirical design of bridge decks. Thisempirical design, based on survey data fromGirderAxle Loadingactual bridge loadings, requires an isotropic(c--------- - --- - ,--, - - - - -- ---,reinforcinglayout that uses much less steel than!\Region ofRegion of!\current AASHTO design procedures. MuchSlab withSlab withresearchhas been conducted testing thisTensileTensileMembraneMembraneprocedure, and many actual bridges have beenForceForcebuilt using this design method, and havesubsequently performed satisfactorily.- - r ';(\I\!with CompressiveMembrane ForceFigure 2.1Zone of compression balanced bysurrounding zone of tension, archingaction3Another question about arching actionis how its behavior is affected when the load isapplied in more than one place. As mentionedbefore, a point load creates the effect of a flatdome in a concrete slab. However, little isknown about how a line load or a group ofclosely spaced loads might affect this dome-like
4Insufficient Area to Develop Significant Transverse Tension(Girder",\)JJJJIllllll1JLGirder /Little or No Arching ActionFigure 2.2Lack of arching action in slabsubjected to closely spaced axlesbehavior. This is a practical concern in bridgeswhen dealing with long, multi-axle trailerscarrying unusually large loads. In the point-loadscenario, the "dome" is created by a centralcompression zone, balanced by a surroundingtension ring. If this tension ring is also loaded, itwill go into compression, causing the tension zoneto spread toward the supports, as shown in Figure2.2. This" spreading" of the dome reduces theeffectiveness of the arching action.2.3 FatigueUnder cyclic stresses, a material's load-carrying capacity can deteriorate - the higher the numberof cycles, the greater the deterioration. If a material is subjected to a large number of loading cycles,its ultimate capacity can decrease, even if the level of load is fairly small relative to the ultimate value.This phenomenon, referred to as fatigue deterioration, is of particular concern in the design of highwaybridges and bridge decks. These structures are subjected to millions of loading cycles over their designlives, sometimes at very large loads relative to the loads assumed for design purposes.To predict the reduction in the capacity of afatigued structure, one must establish a relation
FACTORS AFFECTING THE DESIGN TIDCKNESS OF BRIDGE SLABS: DESIGN AND PRELIMINARY VERIFICATION OF TEST SETlTP by J. H. Whitt,J. Kim, N. H. Burns, andR. E. Klingner Research Report Number1305·1 Research Project 0-1305 Factors Affecting Design Thickness ofBridge Slabs conducted for the TEXAS DEPARTMENT OF TRANSPORTATION in cooperation with the
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