RC slab shear tests under concentrated loads
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This document summarizes experiments on the shear capacity of reinforced concrete slabs and strips under concentrated loads. It describes 30 specimens tested under 133 experiments to determine the effective width in shear and compare results to design code models and nonlinear finite element analysis. The experiments varied parameters like slab continuity, reinforcement type and amount, load location, and support conditions. Results showed transverse load redistribution increased capacity and the French effective width method compared best to experiments and finite element analysis. Loads near supports had direct load transfer and a 25% reduction factor is recommended.
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RC slab shear tests under concentrated loads
- 1. Shear tests of RC slabs and slab strips under concentrated loads Eva Lantsoght 23-07-2012 Delft University of Technology Challenge the future
- 2. Overview • Introduction • Project description • Previous research • Experiments • Setup • Specimens • Results • Results • Overall width/Effective width • Comparison to Code methods S9T6 at failure • Comparison to NLFEA • Conclusions Shear tests of reinforced concrete slabs and slab strips under concentrated loads 2
- 3. Background Project description (1) Shear failure of the de la Concorde bridge, Laval The Netherlands: 60% of bridges built before 1975 Traffic volume and loads have increased => Loads? Shear Capacity??? Shear tests of reinforced concrete slabs and slab strips under concentrated loads 3
- 4. Background Project description (2) • Capacity of existing bridges in NL • TU Delft • Concrete Structures • Structural Mechanics • TNO • RWS • 3715 relevant structures • 2020 built before 1976 • Study: bridge categories and specific details Highways in the Netherlands Shear tests of reinforced concrete slabs and slab strips under concentrated loads 4
- 5. Background Project description (3) • Concrete Structures • Long-term tensile strength (C-1.4) • Beam shear – sustained loads (A-1.2) • Continuous girders – shear (A-1.2) • Prestressed slabs – CMA (A-1.5) • Slab bridges - shear/punching Concrete bridges Shear tests of reinforced concrete slabs and slab strips under concentrated loads 5
- 6. Background Shear and punching (1) Beam shear, one-way shear Punching shear, two-way shear • Punching shear over perimeter around load • Beam shear formulas over effective width at support • Effective width? Shear tests of reinforced concrete slabs and slab strips under concentrated loads 6
- 7. Background Shear and punching (2) 45 load spreading 45 load spreading – French practice Shear tests of reinforced concrete slabs and slab strips under concentrated loads 7
- 8. Background Previous research (1) • Database: 207 tests slabs and wide beams in shear • a/d = 0,65 – 9,8 • Different categories • simply supported slab • continuous slab • real bridge • cantilever • Failure mode based on pictures/ crack patterns: WB/P Shear tests of reinforced concrete slabs and slab strips under concentrated loads 8
- 9. Background Previous research (2) • Recent research: slabs under line loads • From database: 22 • Concentrated load • a/d < 2,5 • Small: d < 15cm • Comparison to EC2 • Evidence for additional capacity • Experiments on larger specimens needed Shear tests of reinforced concrete slabs and slab strips under concentrated loads 9
- 10. Goals • Assess shear capacity of slabs under concentrated loads • Determine effective width in shear Shear tests of reinforced concrete slabs and slab strips under concentrated loads 10
- 11. Experiments Experimental setup Size: 5m x 2,5m (variable) x 0,3m Continuous support, Line supports Load: vary a/d and position along width Shear tests of reinforced concrete slabs and slab strips under concentrated loads 11
- 12. Experimental results Experimental setup (2) • Distance between load and support (a/d = 1,51 and a/d = 2,26) • Simple or continuous support • Amount of transverse flexural reinforcement • Reinforcement type: plane or ribbed bars • Size of the loading plate • Type of support: line support or bearing • Concrete compressive strength BS2T1 • Loading in the middle of width or near edge • Total width First series: 30 specimens, 133 experiments Shear tests of reinforced concrete slabs and slab strips under concentrated loads 12
- 13. Results Effective width (1) 0 500 1000 1500 2000 2500 b (mm) Specimens with different widths: threshold value observed Shear tests of reinforced concrete slabs and slab strips under concentrated loads 13
- 14. Results Effective width (2) Shear tests of reinforced concrete slabs and slab strips under concentrated loads 14
- 15. Results Effective width (3) Shear tests of reinforced concrete slabs and slab strips under concentrated loads 15
- 16. Results Effective width (4) Shear tests of reinforced concrete slabs and slab strips under concentrated loads 16
- 17. Results Comparison to design models (1) • EN 1992-1-1:2005 • Shear governing over punching • Two load spreading methods • CRd,c = 0,15 • French NA • Larger vmin for slabs • French load spreading method • Regan’s method • Based on punching perimeter • # sides ~ width • Enhancement close to support • Enhancement for CS Shear tests of reinforced concrete slabs and slab strips under concentrated loads 17
- 18. Results Comparison to design models (2) Best results: beff2 and Regan’s method Shear tests of reinforced concrete slabs and slab strips under concentrated loads 18
- 19. Results Comparison to design models (3) beff2 better results than beff1 => smaller range of AVG => better COV Shear tests of reinforced concrete slabs and slab strips under concentrated loads 19
- 20. Results Comparison to design models (4) Ribbed bars vs. plain bars Plain bars: slightly smaller capacity ≠ literature! Shear tests of reinforced concrete slabs and slab strips under concentrated loads 20
- 21. Results Comparison to NLFEA • Sensitive to input parameters • Compared to effective width • beff2 compares best Shear tests of reinforced concrete slabs and slab strips under concentrated loads 21
- 22. Recommendations • Evaluating existing solid slab bridges: • EN 1992-1-1:2005 • Effective width: French method, min 4d • 25% reduction of contribution concentrated load close to support • β =av/2d • Combined: βnew =av/2,5d Shear tests of reinforced concrete slabs and slab strips under concentrated loads 22
- 23. Conclusions • Transverse load redistribution • Larger shear capacity in slabs • Enhancement factor 1,25 • French load spreading method for beff • Literature • Experiments • NLFEA • Loads close to support • Direct load transfer Shear tests of reinforced concrete slabs and slab strips under concentrated loads 23
- 24. Contact: Eva Lantsoght E.O.L.Lantsoght@tudelft.nl +31(0)152787449 Shear tests of reinforced concrete slabs and slab strips under concentrated loads 24
- 25. Experiments Properties of slabs (1) Shear tests of reinforced concrete slabs and slab strips under concentrated loads 25
- 26. Experiments Properties of slabs (2) Test SS/CS Pu (kN) Failure mode Fpres Vmax Vmax,EC (kN) (kN) (kN) S11T1 SS 1194 WB + P 165 998 848 S11T4 CS 958 WB + P 307 886 766 S12T1 SS 931 WB + B + P 162 780 663 S12T2 SS 1004 P 173 839 712 S12T4 CS 773 WB + P + B 147 705 608 S12T5 CS 806 WB + B 158 735 633 S13T1 SS 1404 WB + P 157 1253 593 S13T4 CS 1501 WB + P 240 1411 706 S14T1 SS 1214 WB + P + B 133 1088 518 S14T2 SS 1093 WB + P + B 162 975 462 S14T4 CS 1282 WB + P + B 187 1207 605 S14T5 CS 1234 WB + P + B 142 1157 578 Shear tests of reinforced concrete slabs and slab strips under concentrated loads 26