Punching shear is a phenomenon in flat slabs caused by concentrated support reactions inducing a cone shaped perforation starting from the top surface of the slab. Although generally preceded by flexural failure, punching shear is a brittle failure mode and the risk of progressive collapse requires a higher safety class in structural design.
To prevent punching shear failure, the designs procedure is – check if the concrete is strong enough alone; If not, check if the amount of reinforcement is reasonable; Design reinforcement if reasonable, if not, change form of structure. Changing the form of structure includes deepening the slab, making the column larger, introducing drop panels or flared column heads. There is also the possibility to adapt foreign codes of practice which are more liberal! The reinforcement put in is usually vertical and traverses the potential failure line. Of course, it is not known where the failure plane might be, so it is better to reinforce each possible failure plane.
Punching shear calculations require a demand value and a capacity value. Many hand calculations will consider a punching shear force against a punching shear capacity force. This works if only shear force is present, but is insufficient if a moment is occurring on the column/pedestal. Thus, a stress demand/stress approach is taken. The applied shears and moments, along with the shape of the punching shear failure cone are used to calculate a maximum punching shear stress.
However, carrying out the calculation becomes when you have a solved sample of the calculation. Find hereunder, a sample of punching shear calculation spreadsheet. Once you download, you can understand the overall procedure. You can even use the same spreadsheet to make your calculations with your values.
Download Slab punching Shear Calculation Sheet at: https://shortll.com/slab-punching-shear-calculation