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 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 Fl 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 maximal shear force Fl developed in the critical section (the influence of unbalanced bending moment is added according to Appendix F of standard GB50010-2010), the shear force transmitted by concrete with no shear reinforcement Fc (Art. 6.5.1), and the maximal allowable force Fmax (Art. 6.5.3). The shear forces are related to the unit length of the critical section.
βh = 0.9 for h ≥ 2000mm
βh = 1 for h ≤ 800mm, intermediate values are obtained using linear interpolation method.
where βs is the size ratio of the long side and short side of the action area.
where αs: | 40 | - | for interior column |
30 | - | for edge column | |
20 | - | for corner column |
For Fl < Fc no shear reinforcement is needed.
For Fl > Fc and Fl < Fmax the shear reinforcement must be introduced. The ultimate shear force is given by:
where: | um | - | critical cross-section span |
α | - | is angle of bends | |
Asbu | - | area of bends in unit length of critical section |
For Fl > Fmax the shear reinforcement cannot be designed. It is therefore necessary to increase the cross-section height.
Additional check according to article 8.2.9 of standard GB50007-2011 is done for narrow footing or strip footing.
where:
b0 is an average width of the footing.