Experimental investigation on cold-formed steel lipped channel beams affected by local-distortional interaction under non-uniform bending

This paper reports an experimental investigation, carried out at The University of Hong Kong, on the behaviour of cold-formed steel lipped channel beams affected by local-distortional (L-D) interaction under non-uniform bending – to the authors’ best knowledge, these are the first tests specifically devoted to this topic. This investigation consists of 16 non-conventional four-point simply supported bending tests involving twin lipped channel beams arranged in a “back-to-back” configuration and laterally restrained at the loading points. The 32 lipped channel specimens were brake-pressed from high-strength zinc-coated G450 grade structural steel sheets. Tensile coupon tests were performed to obtain the specimen material properties and initial geometrical imperfections were measured prior to testing. The beam geometries were carefully selected to enable testing beams that are prone to “true L-D interaction” (close critical distortional-to-local buckling moments) when acted by trapezoidal bending moment diagrams with four distinct gradients – all the tested specimens exhibited the sought L-D interactive nature. The output of the experimental investigation consists of (i) applied moment vs. displacement equilibrium paths, (ii) photos showing beam deformed configurations along those paths (including the failure modes) and (iii) the failure moment data. Lastly, the experimental failure moments obtained are compared with their predictions provided by the (i) current local and distortional Direct Strength Method (DSM) strength curves and (ii) available DSM-based approaches against L-D interactive failures, which were developed and calibrated exclusively in the context of beams subjected to uniform bending.