Flexural strength of innovative thin-walled composite cold-formed steel/PE-ECC beams

A detailed experimental investigation on the flexural behaviour of an innovative precast composite element combining cold-formed steel (CFS) and engineered cementitious composites (ECC) is presented in this paper. Bonding ECC to the lightweight thin-walled CFS sections enhanced the buckling, bearing, and torsional prop-erties of the composite sections. The proposed composite system will be used as precast flexural members in framed structures with large spans or as a rehabilitation approach for corroded cold-formed and hot-rolled steel flexural members. Simply supported beams with comparatively long spans with span-to-depth ratios of 6.83 and 13.48 were installed back-to-back and tested under a 4-point loading configuration. The behaviour of composite CFS/ECC beams under bending was investigated and compared with the bare CFS sections. Composite CFS/MOR beams incorporating high-strength mortar (MOR) as an ECC replacement were also investigated. The test specimens were divided into three series with sixteen tests in total. Series A (SC300) included six tests utilising 300-mm height SupaCee sections, Series B (C300) included four tests using 300-mm height lipped-Cee sections, and Series C (SC150) included six tests utilising 150-mm height SupaCee sections. The composite CFS/ECC beams exhibited high load-bearing capacities after reaching their plastic section capacities, while the bare CFS beams failed to reach their yield section capacities due to distortional buckling. Composite CFS/MOR beams could not reach their plastic moment capacities due to debonding between MOR and CFS after MOR crushing. The moment capacities of the composite CFS/ECC beams increased up to 140.0% over their duplicate bare CFS sections, while composite CFS/MOR beams showed only a 72.0% increase over CFS sections. Lastly, design equations to predict the moment capacity of composite CFS/ECC beams are presented, based on the experimental results.