Building Design and Construction Handbook - Merritt - Ventech!

9.86 SECTION NINE
FIGURE 9.28 Division of flat plate into column and middle strips.
Step 5. Check for shear. Shear strength of slabs in the vicinity of columns or other
concentrated loads has to be checked for two conditions: when the slab acts as a
wide beam and when the load tends to punch through the slab. In the first case, a
diagonal crack might extend in a plane across the entire width of the slab. Design
for this condition is described in Art. 9.47. For the two-way action of the second
condition, diagonal cracking might occur along the surface of a truncated cone or
pyramid in the slab around the column.
The critical section for two-way action, therefore, should be taken perpendicular
to the plane of the slab at a distance d/2 from the periphery of the column, where
d is effective depth of slab. Unless adequate shear reinforcement is provided, the
factored shear force V u for punching action must not exceed �V c; i.e., V u � �V c,