Design of roll-formed aluminium lipped channel sections with web opening subjected to web crippling under end-two-flange load case

The use of aluminium alloys has recently gained more attention in the construction industry. Roll formed aluminium lipped channel (ALC) purlins have been utilised in roof systems which make them susceptible to different types of buckling instabilities including web crippling. Holes may be perforated in the web element of these sections, which could significantly reduce their web crippling capacity. Such influence has not been investigated for roll-formed ALC sections yet. Therefore, this study is conducted to investigate the effect of web openings on the web crippling strength of ALC sections under the end-two-flange (ETF) load case. Both unfastened and fastened flange restraint conditions were considered. Fifteen specimens with various opening sizes were experimentally tested in accordance with the American Institute of Steel and Iron (AISI) standards. Numerical analysis was subsequently employed and validated against laboratory tests for ALC sections with or without web openings. Based on the validated models, a parametric analysis was performed to evaluate the effect of all influential parameters on the web crippling capacity. The results showed that the web openings could cause a substantial strength reduction for unfastened (up to 53%) and fastened (up to 47%) conditions. Based on the parametric study results, proposed design equations were developed and incorporated in the available direct strength method (DSM). The findings showed that the proposed reduction factor can predict the reductions in the web crippling capacity for roll-formed ALC sections with high accuracy. Hence, it is recommended to adopt these developed reduction factor equations in relevant aluminium standards.

Automated summary

This study investigates the effect of web openings on the web crippling strength of roll-formed aluminium lipped channel (ALC) sections. It is found that the web openings can significantly reduce the strength of the sections, both in unfastened and fastened conditions. Design equations are proposed and validated, and it is recommended to incorporate them into relevant standards.