Punching Shear Perimeter
Punching shear around the columns, piles, etc. It usually checked in footings, raft foundations, pile caps, flat slabs, etc. The definition of the punching shear perimeter is varied slightly with different standards.
Punching shear is the shear force or shear stress considered in distance from the face of the support (example: from the face of the column) to a specified distance in the standards. The perimeter around the given distance is considered to calculate the punching shear and the shear stresses. Once the shear stress is known, it can be checked whether it is required to provide shear reinforcements by considering the Vc value calculated for the particular section. Based on the shear stress and shear capacity values, the requirement of the shear reinforcement is decided.
Variation of the punching shear perimeter with different standards is discussed in the thread.
PUNCHING SHEAR PERIMETER EUROCODE 2
Shear perimeter for solid slabs, waffle slabs with solid areas over the columns and foundations can be calculated as shown in the following figures. Shear perimeter is considered at 2d from the face of the support.
Based on the position of the supports, the perimeter calculation needs to be adjusted. The length and arrangement of the punching shear perimeter are evaluated as shown in the following figure when the column is not at the center.
Further, when the support is close to an edge, the following method shall be followed.
PUNCHING SHEAR PERIMETER BS 5400 PART 4
The method of calculating the punching shear in the solid slab is given in the BS 5400 Part 4 1990 and has a slight difference when compared with Eurocode 2. Distance to punching shear perimeter is 1.5d in BS 5400 whereas it is 2d in Eurocode 2.
PERIMETER IN ACI
Shear perimeter considered as per the ACI code is much less than that of other codes. It recommends considering a distance of (d/2) from the face of the support. However, other codes like Eurocode 2 and BS 5400 consider it as 2d and 1.5d respectively. The following figure extracted from the ACI code indicated the arrangement of the shear perimeter.
Thus, it appears that the ACI code uses a much lesser perimeter for punching shear calculations. When the shear force at the punching shear perimeter is known, shear stress can be calculated.
