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Shear tests of reinforced concrete slabs and slab strips under concentrated loads

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Presentation from fib PhD symposium in Karslruhe

Presentation from fib PhD symposium in Karslruhe

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  • 1. Shear tests of RC slabs and slab stripsunder 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, LavalThe Netherlands: 60% of bridges built before 1975Traffic volume and loads have increased => Loads? Shear Capacity??? Shear tests of reinforced concrete slabs and slab strips under concentrated loads 3
  • 4. BackgroundProject 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. BackgroundShear 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. BackgroundShear 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. BackgroundPrevious 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. ExperimentsExperimental 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. ResultsEffective 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. ResultsEffective width (2) Shear tests of reinforced concrete slabs and slab strips under concentrated loads 14
  • 15. ResultsEffective width (3) Shear tests of reinforced concrete slabs and slab strips under concentrated loads 15
  • 16. ResultsEffective width (4) Shear tests of reinforced concrete slabs and slab strips under concentrated loads 16
  • 17. ResultsComparison 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 barsPlain bars: slightly smaller capacity≠ literature! Shear tests of reinforced concrete slabs and slab strips under concentrated loads 20
  • 21. ResultsComparison 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 LantsoghtE.O.L.Lantsoght@tudelft.nl+31(0)152787449 Shear tests of reinforced concrete slabs and slab strips under concentrated loads 24
  • 25. ExperimentsProperties 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 848S11T4 CS 958 WB + P 307 886 766S12T1 SS 931 WB + B + P 162 780 663S12T2 SS 1004 P 173 839 712S12T4 CS 773 WB + P + B 147 705 608S12T5 CS 806 WB + B 158 735 633S13T1 SS 1404 WB + P 157 1253 593S13T4 CS 1501 WB + P 240 1411 706S14T1 SS 1214 WB + P + B 133 1088 518S14T2 SS 1093 WB + P + B 162 975 462S14T4 CS 1282 WB + P + B 187 1207 605S14T5 CS 1234 WB + P + B 142 1157 578 Shear tests of reinforced concrete slabs and slab strips under concentrated loads 26