Today we will talk about Punching Shear in Footing for the combined footing design, spread, and raft foundation.
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Punching Shear in Footing
Punching shear is a type of failure that can occur in reinforced concrete footings. It happens when the applied load is concentrated near the column or pedestal and causes a shear force that exceeds the capacity of the footing to resist it. This results in the punching of the footing, causing a hole to form around the column or pedestal.
How to Prevent punching shear?
To prevent punching shear failure, designers need to ensure that the footing is sufficiently reinforced and has adequate thickness.
There are several methods for analyzing and designing footings for punching shear, including the strut-and-tie method and the critical shear crack theory.
The formula for punching shear in a reinforced concrete footing is:
Vc = (Ac + 2dAs) x √f’c
where:
- Vc is the shear capacity of the footing
- Ac is the area of the column or pedestal that is supported by the footing
- d is the effective depth of the footing
- As is the area of the reinforcing steel in the footing
- f’c is the compressive strength of the concrete
This formula is based on the assumption that the load is uniformly distributed around the column or pedestal, which is a conservative assumption. In reality, the load may be concentrated in certain areas, which can increase the likelihood of punching shear failure. Therefore, it is important to also consider the distribution of loads and the layout of the reinforcement when designing for punching shear.
Excel sheet for punching shear in footing
It’s easy to calculate punching shear and check with this spreadsheet. So, download the free Excel sheet for calculating punching shear.
Punching Shear in Footing