The document presents a Modified Bond Model for predicting shear capacity in slabs under concentrated loads. It summarizes that punching shear failure in slabs is a transition between one-way and two-way shear, and that the nature of shear failure is not fully understood. The Modified Bond Model adapts the existing Bond Model to account for loads close to supports by determining a factor to reduce the capacity of radial strips. A comparison shows the Modified Bond Model corresponds well to experimental test results, with an average deviation of only 11%, while code-based methods show more conservatism or variability.

1. Challenge the future
Delft
University of
Technology
Modified Bond Model for shear
in slabs under concentrated loads
Eva Lantsoght, Cor van der Veen, Ane de Boer

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
Unequal loading of strips
• Static equilibrium
• v2,x reaches max before v1,x
'
1, 0.1667x c
a
v f d
L a



11. 11
Loads close to free edge
Edge effect:
when length of strip is too small to develop loaded length lw

12. 12
Comparison to experiments
Comparison between experimental results and (a) Modified Bond Model, (b)
ACI 318-11 code, (c) NEN-EN 1992-1-1:2005.

13. 13
Comparison to experiments
AVG STD COV
Vexp/VACI 2,67 1,00 37%
Vexp,EC/VR,c 1,99 0,27 13%
Pexp/PMBM 1,33 0,14 11%
• Eurocode: increasing conservativism for higher capacities
• MBM: follows 45º line better

14. 14
Summary & Conclusions
• Slabs under concentrated loads
• Transition between one-way and two-
way shear
• Bond Model for concentric punching
shear
• Modified Bond Model corresponds well
to test results

15. 15
Contact:
Eva Lantsoght
E.O.L.Lantsoght@tudelft.nl // elantsoght@usfq.edu.ec
+31(0)152787449