Post-fire flexural behaviour and performance of unrestrained cold-formed steel built-up section beams: Experimental and numerical investigation

Abstract

Cold-formed steel (CFS) sections are light gauge materials widely used to construct industrial structures. CFS construction is gaining more interest among researchers, construction industries, and structural engineers due to its lightweight and cost-effective design. Fire safety in the building is a significant factor to be considered in the design and construction practices. However, limited studies are reported on experimental and finite element modelling (FEM) of back-to-back built-up channel sections under flexure with unrestrained conditions. Nine back-to-back built-up CFS sections were considered for the experiment. CFS test specimens were exposed to elevated temperatures following the ISO 834 standard fire curve for durations of 30 min (821 ℃), 60 min (925 ℃), 90 min (986 ℃), and 120 min (1029 ℃). After the temperature exposure, air- and water-cooling methods were adopted to cool the CFS specimens. The influence of temperature exposure and cooling affects CFS sections' residual load-carrying capacity and failure behaviour. A detailed physical observation was made after cooling conditions to observe the failure behaviour of CFS specimens. Experiments were performed to evaluate the influence of elevated temperature exposure on the ultimate flexural capacity, moment-deformation behaviour, load-strain behaviour and stiffness of CFS. The moment of resistance results obtained from FEM and the Direct Strength Method (DSM) were validated with experimental results. The experimental results showed that, while increasing the temperature exposure and heating duration, the CFS's load-carrying capacity decreases drastically. In the case of cooling conditions, air-cooled specimens exhibited a higher residual strength capacity, about 10–15%, compared to the water-cooled specimens. A good correlation was noted between the experiment and FEM results in failure modes.