Flange and web limit states in beams subjected to patch loading

摘要

Recent field observations during bridge construction revealed excessive localized deformations in sill and cap beams that support falsework posts. Hence, possible limit states associated with flange and web deformations in W and HP sections subjected to patch loading are investigated in this paper. Critical limit states were found to be related to flange bending, post compression, and the interactions associated with patch loading between a beam flange and timber or steel post. Other limit states are associated with web deformations. Two alternative methods based on yield line analyses that establish upper-bound limiting loads for these limit states are proposed. The first method accounts for an interaction between flange bending and post compression strength, whereas the second method uses an effective bearing area of the post. The former method is most effective in characterizing flange-timber posts interactions, while the effective bearing area method was found to be more accurate for steel posts. For beams with relatively thick webs, such as those typically used in bridge falsework, the web was found to have a greater capacity than the flange and post, with the critical web limit state due to web yielding. It was shown that current recommended equations were appropriate with modifications to account for the patch loading condition.