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IABSE presentation on Shear Capacity of Concrete Bridges

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Shear capacity of concrete beams under sustained long-term loading is investigated.

Shear capacity of concrete beams under sustained long-term loading is investigated.

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    IABSE presentation on Shear Capacity of Concrete Bridges IABSE presentation on Shear Capacity of Concrete Bridges Presentation Transcript

    • Assessment, Upgrading and Refurbishment of InfrastructuresIABSE Conference, Rotterdam, May 6 - 8, 2013Shear Capacity of Concrete Beamsunder Sustained LoadingR. Sarkhosh, PhD Researcher, TU DelftJ.C. Walraven, Professor, TU DelftJ.A. den Uijl, Associate Professor, TU DelftC.R. Braam, Associate Professor, TU DelftDelft University of Technology, the Netherlands
    • 2TABLE OF CONTENTSShear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of Technology Introduction Aim of research Experiments on concrete beams Short-term static loading Long-term sustained loading Conclusions and outlook
    • 3INTRODUCTIONShear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of TechnologyMillions of concrete structures in the world…Q: What happens to concrete under loading in ages?A known phenomenon is creep/relaxation…… which is time dependent strain under applied stressQ: What is the effect on concrete beams?Appearance of flexural and shear cracksPropagation of existing cracks
    • 4SHEAR!Shear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of Technology• Aug 2004: The $21.3 million MLK Drive Bridge opens to traffic. Bridge carries about4,500 vehicles a day.• Mar 2009: Shear cracks in concrete bridge beams found during INDOT inspection.• April 2010: A research team is hired by INDOT to inspect the bridge. Early findingslead INDOT to restrict traffic on bridge to cars only.• May 2010: INDOT closes Martin Luther King Drive Bridge indefinitely.• July 2010: Inspectors say 3 more bridges all built by the same firm in same time-frame as MLK Bridge — are safe.• Jan 2011: Further inspections find MLK Bridge is too damaged to be repaired.INDOT decides bridge will be demolished and rebuilt.• Feb 2012: Demolition begins. Superior Construction Company, its designer and itsprimary material supplier have agreed to pay INDOT a total of $1.35 million.• Oct 2012: The new bridge opened to traffic.Appearance of Shear cracks after 5 years inMartin Luther King Drive Bridge, IndianapolisKarl Zimmerman, Ph.D., P.E.Former Assistant Professorof Civil Engineering,Valparaiso University,Indiana
    • 5SUSTAINED LOADING EFFECT?Shear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of TechnologySustained loading tests on plain concreteBy: Zhang, Phillips and Green , 1998Formulation of sustainedloading effect in EC-2cckcccdffγα=cctkctctdffγα=For concrete in compressionFor concrete in tensionValues for αcc and αct are mostly chosen between 0,8 and 1,0
    • 6AIMS OF THE RESEARCHShear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of Technology• To investigate the sustained loading effect inconcrete beams without shear reinforcement.• To Investigate the behavior of a cracked beam inTime.
    • 7TEST SCHEMEShear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of TechnologyGroup fcm,cube [MPa] Type of test Pmax, mean [kN] Load ratio Sustained loading duration1 30.3 6 short-term 184.7 (COV = 4.6%) - -2 32.1 3 short-term3 long-term188.9 (COV = 3.2%)--0.87-3 months3 47.0 3 short-term3 long-term204.9 (COV = 1.4%)--0.95-38 months4 42.0 3 short-term3 long-term194.7 (COV = 4.9%)--0.95-12 months5 44.2 3 short-term3 long-term203.2 (COV = 3.1%)--0.89-14 months6 73.4 3 short-term3 long-term250.1 (COV = 2.7%)--0.90-24 months7 78.0 3 short-term3 long-term229.9 (COV = 6.7%)--0.92-18 months
    • 8TEST RESULTS: BEAMS GROUP 1Shear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of Technology6 short-term static tests:fcm = 38,1 MPaPultimate,mean = 184,7 kN (COV = 4,6%)3 Ф 20 *LoadSupport Support300 1200 mm 3001200 mmShort-term static loading
    • 9LONG-TERM SUSTAINED LOADINGShear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of TechnologyTest setup and measuring devicesRollerSupport RollerSupportLoad CellLoading plateMeasuringGrid 
    • 10DEVELOPMENT OF CRACK LENGTHShear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of Technology
    • 11DEVELOPMENT OF CRACK WIDTHShear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of Technology
    • 12FAILURE IN EARLY AGESShear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of TechnologyFracture of two specimens shortly after application ofsustained loadingIn these cases, however, thesustained load was beyond the 95%confidence interval of the short-termshear capacity.
    • 13CONCLUSIONSShear Capacity of Concrete Beams under Sustained LoadingR. Sarkhosh, PhD Researcher, Delft University of Technology• Under sustained loading equal to 87% ~ 95% of thestatic strength no significant sustained loading effect isobserved;• Crack width and length are monitored periodically:•slight propagation of shear cracks is observed and found to bemore pronounced in the first six months of loading;•the crack width increase in the first week of loading, butafterwards the cracks stabilize and become dormant;•most of the new cracks that appeared on the surface of the beamsare likely shrinkage cracks.