Numerical investigation and design of cold-formed lean duplex stainless steel Z-sections undergoing web crippling

This paper presents a numerical investigation on web crippling of cold-formed lean duplex stainless steel Z-sections under concentrated bearing loads. The two concentrated loading conditions are End-Two-Flange (ETF) and Interior-Two-Flange (ITF) as specified in North American Specification. The numerical models were firstly validated against the test results obtained from the literature. After successful verification, the models were used to perform a comprehensive parametric study. The critical parameters that affect the web crippling strength were considered and investigated, including web flat height-to-web thickness ratio, bearing length-to-web thickness ratio, inside bent radius-to-web thickness ratio, and bearing length-to-web flat height ratio. The numerical results were used to assess the current codified design rules from American Specification, Eurocode and North American Specification. It was found that these design specifications could not predict well the web crippling strengths of cold-formed lean duplex stainless steel Z-sections under the two loading conditions. Therefore, two design equations were proposed, including the modified unified equation and the Direct Strength Method (DSM). It is shown that the two proposed design equations generally provide more accurate and reliable strength predictions than the current codified design equations. Hence, the two proposed equations are recommended for the web crippling design of cold-formed lean duplex stainless steel Z-sections subjected to ETF and ITF loading conditions.