Quick Scan Method


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Presentation given at the International Bridge Conference 2013

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Quick Scan Method

  1. 1. Challenge the futureDelftUniversity ofTechnologyQuick Scan MethodDutch Approach for the Shear Assessment of Reinforced ConcreteSlabs BridgesEva Lantsoght, Cor van der Veen, Joost Walraven, Ane de Boer
  2. 2. 2Quick Scan MethodProblemBridges from 60s and 70sThe Hague in 1959Increased live loadscommon heavy and long truck (600 kN)End of service life + larger loads
  3. 3. 3Quick Scan MethodHighway network in the Netherlands• NL: 60% of bridges built before 1976• Assessment: shear critical in 600slab bridges• Residual capacity?Highways in the Netherlands
  4. 4. 4Quick Scan MethodLive Loads in EN 1991-2:2003
  5. 5. 5Quick Scan MethodAssessment practiceDevelopment of NEN 8700 series for existing structures⇒Load Levels: New, Repair, Unfit for UseRepair level: β < 3.8 (3.6 for bridges built before 2012) - ECvs. design load at operating level, β = 2.5 - AASHTO
  6. 6. 6Quick Scan MethodEffective width in shear45° load spreading - Dutch practice 45° load spreading – French practice
  7. 7. 7Quick Scan MethodGoals• Assess shear capacity of slabsunder concentrated loads• Determine effective width inshear
  8. 8. 8Quick Scan MethodExperiments (1)Size: 5m x 2.5m (variable) x 0.3m = scale 1:2Continuous support, Line supportsConcentrated load: vary a/d and position along width
  9. 9. 9Quick Scan MethodExperiments (2)• 2ndseries experimental work:• Slabs under combined loading• Line load• Preloading• 50% of strength from slab strips• Concentrated load• loading until failure• Superposition hypothesis valid?
  10. 10. 10Quick Scan MethodSlabs vs. Beams• Transverse load redistribution• Geometry governing in slabs• Smaller influence a/d• result of different load-carrying paths• Smaller influence of moment at continuous support:• influence of transverse moment• Larger influence size of loading plate• more 3D action
  11. 11. 11Quick Scan MethodExplanation of recommendations (1)Choice of effective width5000 1000 1500 2000 2500b (mm)
  12. 12. 12Quick Scan MethodExplanation of recommendations (2)Choice of effective width• Calculated from series vs. 45° loadspreading• minimum 4d• 4d average spreading of peak• Comparison between database(literature) + experiments and methods• French load spreading methodunderestimates less• Lower COV for French load spreadingmethod• Database: 63% vs 42%• Delft experiments: 26% vs 22%
  13. 13. 13Quick Scan MethodExplanation of recommendations (3)Slab factor 1.25• Comparison between experimentsand EN 1992-1-1:2005• based on normal distribution• characteristic value at least 1.25• Combination with β = av /2dl andenhancement factor 1.25⇒βnew = av /2.5dl⇒for 0.5dl ≤ av ≤ 2.5dl
  14. 14. 14Quick Scan MethodExplanation of recommendations (4)Hypothesis of Superposition
  15. 15. 15Quick Scan MethodExplanation of recommendations (5)Hypothesis of Superpositioncombination line concτ τ τ= +,3,c combic concff
  16. 16. 16Quick Scan MethodResultsMost unfavorable position (1)Detail of load spreading
  17. 17. 17Quick Scan MethodResultsUnity checks AASHTO / EC2 (1)• Checks required at indicated sections• 9 existing Dutch solid slab bridges + MBE example
  18. 18. 18Quick Scan MethodResultsUnity checks AASHTO / EC2 (2)• Shear stresses similar• BUT: AASHTO resistance factor on shear force• load factors ≈ different target reliability• NEN 8700: γDL=1.15 & γLL=1.30• AASHTO LRFR: γDL=1.25 & γDC=1.50 & γLL=1.35• Shear capacity: Eurocode more conservative• QS-EC2 more conservative for unity checks• QS-EC2 vs QS-DutchCode: reduction in loadsby 18%S20T2
  19. 19. 19Quick Scan MethodSummary & Conclusions• Quick Scan: tool for first round ofassessments• Recommendations:• effective width from French method• minimum 4d• reduction factor βnew = av /2.5dl• superposition valid
  20. 20. 20Quick Scan MethodContact:Eva LantsoghtE.O.L.Lantsoght@tudelft.nl+31(0)152787449