Incremental stiffening approach for CFS built-up-beams with large imperfections: Tests and flexural-behaviour

Abstract

Cold-formed steel (CFS) members generally have slender cross-sections making them more prone to geometric imperfections. The presence of different geometric imperfections with varying magnitudes can significantly influence the structural behaviour of CFS members, which is well-reported in the literature. However, limited data is available on the strengthening of CFS beams with large imperfections. This paper reports the findings of the first experimental investigation that focuses on adopting incremental stiffening approach to strengthen CFS built-up beams with large geometric imperfections induced due to poor fabrication and subsequent testing. CFS channel sections were used to construct both open and closed built-up beams, which were evaluated under four-point loading with simply supported boundary conditions. The incremental adoption of simple, yet effective stiffening approaches helped in attaining considerable improvement in both capacity and stiffness characteristics. The peak load, flexural stiffness, and failure mode exhibited by each tested specimen were used as key performance indicators. The results, in general, confirmed the feasibility of adopting incremental stiffening for improving both the capacity and the stiffness in distressed CFS built-up beams by up to 145% and 125%, respectively. Also, it is shown that a yield capacity of up to 100% and a plastic capacity of up to 80% can be achieved through the proposed stiffening approach. The presented test results will supplement the current inadequate database on distressed CFS beams, and should prove useful for more efficient design of such systems.