Verification of Spread Footing for Punching Shear
The program allows us to verify spread footing for punching shear or for the design of shear reinforcement. The critical section loaded in shear bo is distant from the column edge by one half of the footing thickness. It is loaded by the prescribed moments Mx, My and by the shear force Vf provided by:
where: | A | - | area of footing |
V | - | assigned vertical force developed in column | |
At | - | hatched area in fig. |
Dimensioning of shear reinforcement area At
The program computes the maximal shear force Vf developed in the critical section, the shear force transmitted by concrete with no shear reinforcement Vc as a minimum value (Art. 13.3.4.1):
where βc is the ratio of a long side to short side od column.
where αs = | 4 | - | inner column |
3 | - | edge column | |
2 | - | corner column |
where
and the maximal allowable force Vmax (Art. 13.3.9.2):
For Vf < Vc no shear reinforcement is needed.
For Vf > Vc and Vf < Vmax the shear reinforcement must be introduced. The ultimate shear force is given by (Art. 13.3.9.4):
where: | bo | - | critical cross-section span |
α | - | is angle of bends | |
Av | - | overall area of bends in footing |
For Vf > Vmax the shear reinforcement cannot be designed. It is therefore necessary to increase the cross-section height.