Experimental Investigation of Web Crippling in Built-Up Cold-Formed Steel Members

Abstract

Cold-Formed Steel (CFS) built-up sections are widely used in lightweight structural systems because of their high strength-to-weight ratio, ease of fabrication, and construction efficiency. However, their thin-walled webs are vulnerable to web crippling under concentrated loading, especially when openings are introduced for service penetrations. This study experimentally investigates the web crippling behaviour of CFS built-up I-sections subjected to Interior-Two-Flange (ITF) loading. Ten back-to-back built-up specimens were tested to examine the effects of circular web perforations, hole position, C-channel stiffener arrangement, and bolt density on load vs displacement response, the experimental peak load, and failure modes. The test programme considered 50 mm and 70 mm openings, openings located directly beneath the bearing plate and offset from the load application point, unstiffened and stiffened configurations, and four-bolt and eight-bolt connections. The results showed that C-channel stiffeners significantly enhanced web crippling resistance, with centrally placed stiffeners providing the greatest improvement by redistributing concentrated load and restraining local web deformation. Increased bolt density improved load transfer, although the stiffener position had a greater influence. Larger openings reduced capacity, while hole position strongly affected the failure response. The findings emphasize the importance of proper stiffener placement and connection detailing in perforated CFS built-up sections.