Check for Shear Stress:

The permissible average shear stress is τ_av = 0.4 f _y. In case of rolled steel beams or channels the shear force is taken entirely by the web

τ_av  = F/d × t_ω                                                                                                                              

where d is the depth of the web,

t_ω is the web thickness, and

F is the shear force.

Check for Web Crippling and Local Buckling:

Web crippling is caused through concentrated loads or support reactions (R). In the former case, load disposal length will be B = b + 2 √3 h₂ and in the later case it is B = b + √3 h₂, where b is the bearing length and h2 is the depth of root of the fillet from top of flange.

The permissible bearing pressure in steel, σ_p = 0.75 f_y

Hence, σ p  > P/B . t_ω                                                                                                                           

where P is the concentrated load or reaction.

Local buckling of the web is caused by slenderness of the web. The slenderness ratio for the web.

If σ_ac is the permissible bending compressive stress corresponding to this value of λ_ω, we must have

σ_ac > P/Bt_ω