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Assessment of the Shear Capacityof Existing RC Solid Slab Bridges Eva Lantsoght, Cor van der Veen, Joost Walraven, Ane de ...
Problem Bridges from 60s and 70s                                           Increased live loads                           ...
Highway network in the Netherlands• NL: 60% of bridges built before 1976• Assessment: shear critical in 600  slab bridges•...
Assessment practiceDevelopment of NEN 8700 series for existing structures⇒Load Levels: New, Repair, Unfit for UseRepair le...
Effective width in shear45° load spreading - Dutch practice          45° load spreading – French practice               As...
Goals•   Assess shear capacity of slabs    under concentrated loads•   Determine effective width in    shear      Assessme...
Experiments (1)Size: 5m x 2.5m (variable) x 0.3m = scale 1:2Continuous support, Line supportsConcentrated load: vary a/d a...
Experiments (2)• 2nd series experimental work:   • Slabs under combined loading   • Line load      • Preloading      • 50%...
Slabs vs. Beams • Transverse load redistribution • Geometry governing in slabs • Smaller influence a/d    • result of diff...
Explanation of recommendations (1)Choice of effective width 0   500      1000        1500         2000        2500        ...
Explanation of recommendations (2)Choice of effective width• Calculated from series vs. 45° load  spreading• minimum 4d• 4...
Explanation of recommendations (3)   Slab factor 1.25• Comparison between experiments  and EN 1992-1-1:2005   • based on n...
Explanation of recommendations (4)Hypothesis of Superposition      Assessment of the Shear Capacity of Existing RC Solid S...
Explanation of recommendations (5)Hypothesis of Superposition        f c,combi    3                     f   c , conc      ...
ResultsMost unfavorable position (1)                                                Detail of load spreading      Assessme...
ResultsUnity checks AASHTO / EC2 (1)• Checks required at indicated sections• 9 existing Dutch solid slab bridges + MBE exa...
Results     Unity checks AASHTO / EC2 (2)• Shear stresses similar  • BUT: AASHTO resistance factor on shear force  • load ...
Summary & Conclusions• Different requirements for reliability• Recommendations:   •   effective width from French method  ...
Contact:Eva LantsoghtE.O.L.Lantsoght@tudelft.nl+31(0)152787449                  Assessment of the Shear Capacity of Existi...
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Assessment of the Shear Capacity of Existing Reinforced Concrete Solid Slab Bridges

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Presentation for Transportation Research Board, Annual Meeting 2013

Presented in the session "Topics in Concrete Bridges"

Published in: Technology
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Transcript of "Assessment of the Shear Capacity of Existing Reinforced Concrete Solid Slab Bridges"

  1. 1. Assessment of the Shear Capacityof Existing RC Solid Slab Bridges Eva Lantsoght, Cor van der Veen, Joost Walraven, Ane de Boer Delft University of Technology Challenge the future
  2. 2. Problem Bridges from 60s and 70s Increased live loads common heavy and long truck (600 kN)The Hague in 1959 End of service life + larger loads Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 2
  3. 3. Highway network in the Netherlands• NL: 60% of bridges built before 1976• Assessment: shear critical in 600 slab bridges• Residual capacity? Highways in the Netherlands Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 3
  4. 4. Assessment 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) - ECcfr. design load at operating level, β = 2.5 - AASHTO Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 4
  5. 5. Effective width in shear45° load spreading - Dutch practice 45° load spreading – French practice Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 5
  6. 6. Goals• Assess shear capacity of slabs under concentrated loads• Determine effective width in shear Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 6
  7. 7. Experiments (1)Size: 5m x 2.5m (variable) x 0.3m = scale 1:2Continuous support, Line supportsConcentrated load: vary a/d and position along width Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 7
  8. 8. Experiments (2)• 2nd series experimental work: • Slabs under combined loading • Line load • Preloading • 50% of stress from slab strips • Concentrated load • loading until failure • Superposition hypothesis valid? Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 8
  9. 9. Slabs 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 Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 9
  10. 10. Explanation of recommendations (1)Choice of effective width 0 500 1000 1500 2000 2500 b (mm) Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 10
  11. 11. Explanation of recommendations (2)Choice of effective width• Calculated from series vs. 45° load spreading• minimum 4d• 4d average spreading of peak• Comparison between database (literature) + experiments and methods • French load spreading method underestimates less • Lower COV for French load spreading method • Database: 63% vs 42% • Delft experiments: 26% vs 22% Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 11
  12. 12. Explanation of recommendations (3) Slab factor 1.25• Comparison between experiments and EN 1992-1-1:2005 • based on normal distribution • characteristic value at least 1.25• Combination with β = av /2dl and enhancement factor 1.25⇒βnew = av /2.5dl⇒for 0.5dl ≤ av ≤ 2.5dl Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 12
  13. 13. Explanation of recommendations (4)Hypothesis of Superposition Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 13
  14. 14. Explanation of recommendations (5)Hypothesis of Superposition f c,combi 3 f c , conc τ combination = τ line + τ conc Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 14
  15. 15. ResultsMost unfavorable position (1) Detail of load spreading Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 15
  16. 16. ResultsUnity checks AASHTO / EC2 (1)• Checks required at indicated sections• 9 existing Dutch solid slab bridges + MBE example Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 16
  17. 17. Results Unity 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 S20T2• QS-EC2 more conservative for unity checks Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 17
  18. 18. Summary & Conclusions• Different requirements for reliability• Recommendations: • effective width from French method • minimum 4d • reduction factor βnew = av /2.5dl • superposition valid• Quick Scan: tool for first round of assessments Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 18
  19. 19. Contact:Eva LantsoghtE.O.L.Lantsoght@tudelft.nl+31(0)152787449 Assessment of the Shear Capacity of Existing RC Solid Slab Bridges 19
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