Shear Assessment of Slab Bridges

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Presentation given at IABSE 2013

Presentation given at IABSE 2013

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  • 1. Challenge the futureSHEAR ASSESSMENT OFREINFORCED CONCRETE SLABBRIDGESEva O.L. Lantsoght*, Cor van der Veen*Joost C. Walraven*, Ane de Boer^*Delft University of Technology^Ministry of Infrastructure and the Environment
  • 2. 2Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyINTRODUCTIONPROBLEM STATEMENTBridges from 60s and 70sThe Hague in 1959Increased live loadscommon heavy and long truck (600 kN)End of service life + larger loads
  • 3. 3Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyINTRODUCTIONCURRENT SITUATION• NL: 60% of bridges built before1976• Assessment: shear critical in 600slab bridges• Quick Scan• spreadsheet-based• since mid-2000s• conservative, first-order method• result = unity check Highways in the Netherlands
  • 4. 4Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyRECOMMENDATIONSEFFECTIVE WIDTH• Experiments different specimen widths• Statistical analysis of Vexp/VEC with beff1 andbeff2• NLFEA: shear stress distribution at thesupport• Lower bound: 4dl
  • 5. 5Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyRECOMMENDATIONSSLAB FACTOR 1,25• Comparison betweenexperiments and EN 1992-1-1:2005• based on normal distribution• characteristic value at least1,25• Combination with β = av /2dland enhancement factor 1,25βnew = av /2,5dlfor 0,5dl ≤ av ≤ 2,5dl
  • 6. 6Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyRECOMMENDATIONSHYPOTHESIS OF SUPERPOSITION• Experiments on slabs under line load +concentrated load• Superposition is safe assumption• Concentrated loads over effective width• Distributed loads over full width
  • 7. 7Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyRECOMMENDATIONSLOWER BOUND FOR SHEAR• Before 1962: QR24 type steel• fyk = 240 MPa• EC vmin based on fyk = 500 MPa3/2 1/2 1/2min 0,772 ck ykv k f f
  • 8. 8Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyIMPROVED QUICK SCAN METHODLIVE LOADSDetail of load spreadingLane load of first lane
  • 9. 9Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyIMPROVED QUICK SCAN METHODSECTIONS• Checks required at indicated sections• Selected cases: 9 existing Dutch solid slab bridges
  • 10. 10Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyRESULTSUNITY CHECKS QS-EC2 VS QS-VBC• Shear stresses: influence of recommendations• QS-EC2: wheel loads at av = 2,5dl• QS-VBC: wheel loads at av = dl• QS-EC2 18% reduction in loads• Shear capacity:• QS-EC2: vRd,c ~ ρ, d• low reinforcement + deep section = small shearcapacity• QS-VBC: τ1 ~ fck only• QS-EC2 improved selection ability
  • 11. 11Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologySUMMARY & CONCLUSIONS• Quick Scan: tool for first roundof assessments• Recommendations:• effective width from Frenchmethod• minimum 4dl• reduction factor βnew = av /2,5dl• superposition valid• vmin expression fyk
  • 12. 12Shear Assessment of Reinforced Concrete Slab BridgesEva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnologyContact:Eva LantsoghtE.O.L.Lantsoght@tudelft.nl+31(0)15278744914/06/2013 – 12h: PhD Defence at Aula TU Delft