Web buckling occurs when intensity of compressive stress at center of cross section is greater than critical buckling stress. Web act as a column. Buckling depends upon slenderness ratio of web d/tw.

Due to high stress just below the vertical concentrated load and above the reactions from support, web tends to fold at radius of root. This phenomenon is called web crippling.

Web buckling can be controlled by providing stiffeners. Web crippling can be controlled by providing more bearing area and stiffeners as well.

Buckling and Crippling can be reduced by providing thicker web.

(Note: As per IS Code, if beam is safe in crippling, it will be safe for buckling too.)