Shear in Reinforced Concrete Slabs under concentrated loads near to supports

Problem description

  • Capacity of slab bridges under increased traffic loads?
  • Under governing design rules: low values for slabs in shear close to support
  • Failure mode: punching shear or wide beam shear?
  • Effective width of support?

Experiments


Test setup for slab experiments

Parameters:

  • Distance to support
  • Simple vs. continuous support
  • Amount of non-principal in-plane reinforcement
  • Deformed bars vs. plain bars
  • Size of load
  • Line support vs. point support
  • Concrete class
  • Position along width
  • Overall width


Cracks on bottom: cracks from load towards support indicate effective width

Results

  • Load plate: 300mm x 300mm gives 40% increase in capacity compared to 200mm x200mm
  • Locally failed slabs with 2cm wide cracks still carry about 75% of peak load of previously undamaged slabs
  • Mode of failure: wide beam shear failure after significant flexural cracking
  • First 4 slabs: mean Pu/Pmethod
    • NEN: 1,72; cov = 23,5%
    • EC : 2,48; cov = 10,3%
    • Regan : 1,22; cov = 10,7%

Preliminary Conclusions

  • Slabs show large redistribution capacity
  • Large observed effective widths
  • Strong influence of size of load/ tire contact area
  • Large residual capacity after local failure
  • Capacity at continuous support is at least equal to capacity at simple support (contradictory to factor kλ from NEN 6720)
  • Design codes give conservative values
  • Best predictor: formula developed by Prof. Regan

Future Work

  • Further testing
  • Comparison to finite element modeling
  • Assessment of effective width


Observed shear failure

Researcher: Eva Lantsoght / E.O.L.Lantsoght@tudelft.nl / 015-2787449
Supervisor: prof. dr. ir. J.C. Walraven, Dr. ir. C. van der Veen
Program/Subprogram: Structural Engineering / Concrete Structures / St-II 2.06
Host University: TU Delft / Civil Engineering & Geosciences

 

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