Beam tests of cold-formed steel built-up sections with web perforations

• Cold-formed steel beam tests on 43 built-up sections with web perforations were conducted.
• Web perforations would reduce the moment capacities and cause localized failure of beams.
• Current DSM was extended for the design of cold-formed steel built-up sections with holes.
• Suitable approaches for considering the holes on the beams are recommended.

The aim of this study is to investigate the flexural behavior, including the ultimate moment capacities and failure modes, of built-up cold-formed steel members with circular web holes. A total of 43 beams having ten cross-section sizes with different hole diameters were tested under four-point bending. The built-up sections were assembled by self-tapping screws from either two plain channels or lipped channels. Reduction of moment capacities and localized failure due to the presence of holes in the web plates of beams was observed in the tests. It is shown from the test results that when the hole diameter-to-web depth ratio (dh/hw) is 0.5, the influence of the holes on the moment capacities of beams is very small, however this is not the case when dh/hw further increases up to 0.7. Different approaches of determining the critical elastic local and distortional buckling moments including the influence of holes for the built-up open and closed sections were compared and discussed, and appropriate approach for built-up sections was recommended. The current direct strength method (DSM) was extended for the design of cold-formed steel built-up sections with holes in this study. The design strengths predicted by the DSM were compared with the test results. It is shown that the DSM formulae in the North American Specification are capable for predicting the design strengths of the built-up open and closed section beams with holes, using the critical elastic local and distortional buckling moments including the influence of holes determined by the recommended approaches in this study.