Regan 24 Punching Shear

Vs/Vc

Figure 6.41. Punching capacities related to resistance of the shear reinforcement (Regan [24])

modified upper limit has been defined according to MC'90, according to VRd,max = 0.5v fcd u0 d where u0 is the length of the column periphery, and v is equal to v = 0.60 (1-fck /250)

The distance from the column to the inner shear reinforcement should not be larger than 0.5d, nor should it be less than 0.3d, since steel closer than this will not be well anchored in the compression zone if intersected by cracks at lower inclinations (Regan [24]). The distance between the layers of shear reinforcement in radial direction should not be larger than 0.75d.

It should be verified that no punching failure occurs outside the outermost layer of shear reinforcement. Therefore an additional perimeter un is defined at a distance of 1,5d from the outermost shear reinforcement. It should be shown that here vEd < 0.12 k (100pl fck)1/3 - 0.08acp (6.42)

where vEd is the design calculated of the ultimate shear stress on the perimeter un, see fig. 6.42

circular 1 arms

Figure 6.42. Control perimeter un at interior column

Practically the design of the shear reinforcement is quite simple. At first at the perimeter with distance 2d from the loaded area the punching capacity is checked and the eventual shear reinforcement is calculated. Then the perimeter is determined for which vEd < vRd,c.

Finally the shear reinforcement (with the same cross section per unit area) is extended to a distance 1,5d from the outer perimeter.

6.4.3. Basic equation for eccentric punching

In the draft of 1988 only a very general approach as in combination with a bending moment. The design punching shear stress vEd was formulated as vEd = (pVEd)/(u.d) (6.43)

where

VEd design value of the punching shear p factor taking account of the expected effect of eccentricity, "in the absence of a more rigorous analysis". No further indication on what this "more rigorous analysis" means was given. In Fig. 6.43 the values for the eccentricity factor p are given.

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