Web crippling behaviour and design of aluminium lipped channel sections under two flange loading conditions

Aluminium alloys have recently drawn significant attention in structural applications due to its outstanding mechanical characteristics. Thin-walled members fabricated by aluminium alloys can be more competitive in construction industries than the conventional cold-formed steel sections, particularly in areas with high humidity and severe environmental conditions. Nevertheless, they are more vulnerable to various types of instability due to their relatively low elastic modulus compared to steel. Applying high concentrated load transversely on thin-walled members can cause critical damage to the web of the cross section called web crippling. Although a large number of studies has been performed to investigate the web crippling mechanisms on different types of sections, the existing studies are primarily of the empirical nature and thus merits further investigations. To fill the research gap, this study was thus performed based on our previously conducted experimental work to further comprehend the web crippling phenomenon of the roll-formed aluminium lipped channel (ALC) sections under the loading conditions of end-two-flange (ETF) and interior-two-flange (ITF). This was done through numerical investigations followed by a parametric study which are reported herein in details. A wide range of roll-formed ALC sections covering web slenderness ratios ranged from 28 to 130, inside bent radii ranging between 2 mm and 8 mm, bearing lengths ranged from 50 mm to 150 mm, and three sheeting aluminium alloy grades (5052-H32, 5052-H36 and 5052-H38) were considered in the parametric study. The acquired web crippling database was then used to assess the consistency and accuracy of the current design rules used in practice. It was found that the web crippling capacity determined by the current international specifications are unsafe and unreliable, whereas the predictions of the recently proposed equations agree very well. Furthermore, a Direct Strength Method (DSM)-based capacity prediction approach was proposed and then validated against the web crippling database acquired here as well as the experimental and numerical data for cold-formed steel lipped channel sections used in the literature.