Verification of spread footing for punching shear
Verification of spread footing for punching shear
The critical section loaded in shear (Ucr) 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 Vr provided by:
where: | A | - | area of footing |
Q | - | assigned vertical force developed in column | |
At | - | hatched area in fig. |
Dimensioning of shear reinforcement area At
The program computes the maximum shear force V developed in the critical section, the shear force transmitted by concrete with no shear reinforcement Vc, and the maximal allowable force Vu:
where:
The νc values are for fcu below 25 N/mm2 multiplied by (fcu/40)1/3
|
, or νu | - | is ultimate shear stress |
For V < Vc no shear reinforcement is needed.
For V > Vcand Vc < Vu it is necessary to design shear reinforcement. The permissable shear force is given by:
where: | u | - | critical cross-section span |
α | - | angle of crooks | |
Aus | - | overall area of crooks in footing |
For V > Vu the shear reinforcement cannot be designed. It is therefore necessary to increase the cross-section depth.
