The shear problem is typically studied by testing small, heavily reinforced, slender beams subjected to concentrated loads, resulting in a beam shear failure, or by testing slab-column connections, resulting in a punching shear failure. Slabs subjected to concentrated loads close to supports, as occurring when truck loads are placed on slab bridges, are much less studied. For this purpose, the Bond Model for concentric punching shear was studied at first. Then, modifications were made, resulting in the Modified Bond Model. The Modified Bond Model takes into account the enhanced capacity resulting from the direct strut that forms between the load and the support. Moreover, the Modified Bond Model is able to deal with moment changes between the support and the span, as occurs near continuous supports, and can take into account the reduction in capacity when the load is placed near to the edge. The resulting Modified Bond Model is compared to the results of experiments that were carried out at the Stevin laboratory. As compared to the Eurocodes (NEN-EN 1992-1-1:2005) and the ACI code (ACI 318-11), the Modified Bond Model leads to a better prediction.

1. Predicting Shear Capacity of RC Slabs
subjected to Concentrated Loads close to
Supports with the Modified Bond Model
Delft
University of
Technology
Eva Lantsoght, Cor van der Veen, Ane de Boer
Challenge the future

2. 2
One-way vs. two-way shear (1)
Beam shear, one-way shear Punching shear, two-way shear
• Punching shear over perimeter
• Beam shear over (effective) width

3. 3
One-way vs. two-way shear (2)
• 3D representation of failure modes

4. 4
Beam Shear Failure
• Since 1899 (Ritter)
• 1955: collapse of warehouse
• Most experiments:
• Beams
• Heavily reinforced
• Small size
• Slender (a/d ≥ 2,5)
• Basis for design codes
amount of shear experiments done

5. 5
Punching Shear Failure
Categories of methods for punching shear
Shear stress Beam analogy
Strut and tie Plate theory / FEM
The nature of shear failure is still not fully understood!

6. 6
Slab bridge under live loads

7. 7
Bond Model (1)
• Alexander and Simmonds,
1990
• For slabs with
concentrated load in
middle

8. 8
Bond Model (2)

9. 9
Modified Bond Model (1)
• Adapted for slabs with concentrated
load close to support
• Geometry is governing as in
experiments
• Determine factor that reduces capacity
of “radial” strip
• Maximum load: based on sum capacity
of 4 strips

10. 10
Modified Bond Model (2)

11. 11
Modified Bond Model: Quadrants

12. 12
Modified Bond Model: Load
redistribution

13. 13
Modified Bond Model: Strips

14. 14
Modified Bond Model: Effect of
continuous support

15. 15
Comparison to experiments
Experiments vs Eurocode shear
2 load spreading methods
Experiments vs Modified Bond Model

16. 16
Summary & Conclusions
• Slabs under concentrated loads
• Transition between one-way and two-way
shear
• Bond Model for concentric punching
shear
• Modified Bond Model improvement as
compared to Eurocode

17. 17
Contact:
Eva Lantsoght
E.O.L.Lantsoght@tudelft.nl // elantsoght@usfq.edu.ec
+31(0)152787449