Web Yielding, Crippling, and Lateral Buckling under Post Loading

Unstiffened, unbraced steel beams used in bridge falsework are subjected to patch loads from timber or steel posts. This paper investigates the critical web limit states in these types of beams experimentally and through finite-element analysis. Existing equations were appropriate for calculating the web yielding and crippling capacity, as observed in experiments, except that a 1:1 stress gradient through the flange and fillet of the web is found to be more appropriate and conservative for web yielding than the 2.5:1 gradient assumed in the current AISC specifications. Lateral deformation of a beam flange, due to buckling of the web, was also observed experimentally. The capacity of the web for resisting lateral buckling can be calculated assuming that the web of the beam acts like a column with an appropriate effective area and length factor. The effect of accidental eccentricity between the flange and post is not significant if limited to three times the web thickness. Blocking is approximately 50% effective in increasing the web yielding and crippling capacity. Bracing or stiffeners should be used to prevent lateral buckling of a web where necessary.