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 V 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 above 25 N/mm2 multiplied by (fcu / 25)1/3
|
or 5 where: | 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 bends | |
Aus | - | overall area of bends in footing |
For V > Vu the shear reinforcement cannot be designed. It is therefore necessary to increase the cross-section depth.