Experimental study of shear capacity of reinforced concrete slabs

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Presentation held at the ASCE Structures Congress 2011

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Experimental study of shear capacity of reinforced concrete slabs

  1. 1. Shear capacity of Reinforced Concrete Slabs experimental study Eva Lantsoght
  2. 2. Overview <ul><li>Background </li></ul><ul><ul><li>Project description </li></ul></ul><ul><ul><li>Current practice </li></ul></ul><ul><li>Experiments </li></ul><ul><li>Results and discussion </li></ul><ul><ul><li>Loading history </li></ul></ul><ul><ul><li>Distance to support </li></ul></ul><ul><ul><li>Concrete compressive strength </li></ul></ul><ul><li>Preliminary conclusions </li></ul>
  3. 3. Key message Slabs under wheel loads behave differently in shear than beams
  4. 4. Background Project description (1) <ul><li>Capacity of existing bridges in NL </li></ul><ul><ul><li>TU Delft </li></ul></ul><ul><ul><ul><li>Concrete Structures </li></ul></ul></ul><ul><ul><ul><li>Structural Mechanics </li></ul></ul></ul><ul><ul><li>TNO </li></ul></ul><ul><ul><li>RWS </li></ul></ul><ul><li>3715 relevant structures </li></ul><ul><li>2020 built before 1976 </li></ul><ul><li>Study: bridge categories and specific details </li></ul>Highways in the Netherlands
  5. 5. Background Project description (2) <ul><li>Concrete Structures </li></ul><ul><ul><li>Long-term tensile strength </li></ul></ul><ul><ul><li>Beam shear – sustained loads </li></ul></ul><ul><ul><li>Continuous girders – shear </li></ul></ul><ul><ul><li>Prestressed slabs – punching + CMA </li></ul></ul><ul><ul><li>Slab bridges - shear/punching </li></ul></ul>Concrete bridges
  6. 6. Background Project description (3) Shear failure of the de la Concorde bridge, Laval The Netherlands: 60% of bridges built before 1975 Traffic volume and loads have increased
  7. 7. Background Project description (4) <ul><li>Wheel loads: tire contact area + loading </li></ul><ul><li>Tandem loads for local verification </li></ul><ul><li>Eurocode Tire contact area: 400mm x 400mm </li></ul><ul><li>Larger than physical contact area </li></ul>Tandem loads, EC2
  8. 8. Background Project description (5) <ul><li>Wheel loads: tire contact area + loading </li></ul><ul><li>Values for load model 1 </li></ul>Load model 1
  9. 9. Background Project description (6) Shear span to depth ratio Load spreading towards the support Influence of the support
  10. 10. Background Current practice <ul><li>Design: shear capacity of slabs </li></ul><ul><ul><li>Flexural failure before shear failure </li></ul></ul><ul><ul><li>Punching shear formulas </li></ul></ul><ul><ul><li>Beam shear formulas over effective width </li></ul></ul>Beam shear, one-way shear Punching shear, two-way shear
  11. 11. Goals <ul><li>Assess shear capacity of slabs under concentrated loads </li></ul><ul><li>Determine effective width in shear </li></ul>
  12. 12. Experiments Test setup Size: 5m x 2,5m x 0,3m Continuous support, Line supports Load: vary a/d and position along width
  13. 13. Results and discussion Loading history <ul><li>Experiments : </li></ul><ul><ul><li>Lower bound for cracked bridges </li></ul></ul><ul><ul><li>Loading in vicinity of failure </li></ul></ul><ul><ul><li>Influence of local failure </li></ul></ul><ul><ul><li>Connecting existing cracks </li></ul></ul><ul><ul><li>Opening existing cracks </li></ul></ul><ul><ul><li>+/- 84% of peak load undamaged specimen </li></ul></ul>S2T1 cracks Slabs with large cracks: still 84% of uncracked load is carried!
  14. 14. Results and discussion Distance to support (1) beams: influence of arching slabs: decrease due to smaller effective width
  15. 15. Results and discussion Distance to support (1) beams: influence of arching slabs: decrease due to smaller effective width Lower bound: 2 d Influence of the distance to the support on the shear capacity of slabs?
  16. 16. Results and discussion Distance to support (2) Influence of distance to support on measured peak load
  17. 17. <ul><li>Smaller increase than expected from EC2 </li></ul><ul><li>Reasons: </li></ul><ul><ul><li>Cracking behavior </li></ul></ul><ul><ul><li>Possible paths for strut </li></ul></ul><ul><ul><li>Larger effective a/d ratio </li></ul></ul>Results and discussion Distance to support (3) Different behavior for slabs and beams!
  18. 18. Results and discussion Concrete compressive strength (1) <ul><li>f c ’ as parameter in code formulas </li></ul><ul><li>Shear strength related to tensile strength </li></ul><ul><ul><ul><li>Test slabs with normal strength and high strength concrete </li></ul></ul></ul>Eurocode ACI code
  19. 19. Results and discussion Concrete compressive strength (2) Influence of concrete compressive strength on measured ultimate load
  20. 20. Preliminary conclusions <ul><li>Locally failed decks </li></ul><ul><ul><li>84% of peak load </li></ul></ul><ul><ul><li>Redistribution capacity of slabs </li></ul></ul><ul><li>Distance to support </li></ul><ul><ul><li>Smaller influence than for beams </li></ul></ul><ul><ul><li>Suggest different behavior </li></ul></ul><ul><li>Concrete compressive strength </li></ul><ul><ul><li>No measured influence </li></ul></ul>S4T2 Dominant shear crack
  21. 21. Key message Slabs under wheel loads behave differently in shear than beams
  22. 22. Contact: Eva Lantsoght [email_address] +31(0)152787449
  23. 23. Experiments Specimens

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