2 legged vertical stirrups are to be provided when shear stress increases more than 5kg/cm2. The footing undergoes punching shear due to which its stability.One-way shear has to be checked across the full width of the base slab on
a vertical section located from the face of the column, pedestal or wall at a distance equal to
(i) effective depth of the footing slab in case of footing slab on soil.
2) half the effective depth of the footing slab if the footing slab is on
Two-way or punching shear (cls.31.6 and 34.2.4)
Two-way or punching shear shall be checked around the column on a
perimeter half the effective depth of the footing slab away from the face of the column or pedestal
The permissible shear stress, when shear reinforcement is not provided, shall not exceed ks c τ , where ks = (0.5 + β c ), but not greater than one, β c being the ratio of short side to long side of the column, and c τ = 0.25(fck) 1/2 in limit state
method of design, as stipulated in. Normally, the thickness of the base slab is governed by shear. Hence, the necessary thickness of the slab has to be provided to avoid shear reinforcement.