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Quick Scan Method


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Presentation given at the International Bridge Conference 2013

Presentation given at the International Bridge Conference 2013

Published in: Design

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  • 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. 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. 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. 4Quick Scan MethodLive Loads in EN 1991-2:2003
  • 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. 6Quick Scan MethodEffective width in shear45° load spreading - Dutch practice 45° load spreading – French practice
  • 7. 7Quick Scan MethodGoals• Assess shear capacity of slabsunder concentrated loads• Determine effective width inshear
  • 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. 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. 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. 11Quick Scan MethodExplanation of recommendations (1)Choice of effective width5000 1000 1500 2000 2500b (mm)
  • 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. 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. 14Quick Scan MethodExplanation of recommendations (4)Hypothesis of Superposition
  • 15. 15Quick Scan MethodExplanation of recommendations (5)Hypothesis of Superpositioncombination line concτ τ τ= +,3,c combic concff
  • 16. 16Quick Scan MethodResultsMost unfavorable position (1)Detail of load spreading
  • 17. 17Quick Scan MethodResultsUnity checks AASHTO / EC2 (1)• Checks required at indicated sections• 9 existing Dutch solid slab bridges + MBE example
  • 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. 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. 20Quick Scan MethodContact:Eva