The advantages of usingCFS sections are high strength-to-weight ratio. Local buckling and distortionalbuckling are usually the governing failure modes for CFS sections. However,when sections were stiffened by edge and intermediate stiffeners for optimizedsection shapes, the computation of effective width for each plate element couldbe quite tedious that involves iteration processes and the Effective Width Methodbecomes much more complicated compared to the DSM. Hence, the DSM wasrecommended for design of CFS members with complex stiffeners (Schafer et al.,2006).
The use of hot-rolled steel sections become uneconomical for the steelstructures subjected to light and moderate loads,so the study on behaviour ofCFS members is unavoidable to reduce the cost of a building made up of steelstructures. CFS sections such as C-sections with or without lips, I-sections,Z-sections, angles, T-sections, hat sections and tubular are normally used asflexural members. When single sections are not sufficient for design loads,built-up sections made of back-to-back C-sections or nested C-sections arenormally used as flexural members. Schafer B.W. (2007) reviewed on the DSM of CFS member design and concludedthat reliability of the DSM equals or betters the traditional Effective WidthMethod for a large database of tested beams and column.
Wang L et al. (2014)investigated the structural behaviour and evaluate the appropriateness of thecurrent DSM on the design of CFS stiffened cross-sections subjected to bendingand concluded that FE model well predicted the moment capacities and failuremodes of the beams. Wang etal. (2015) found thatthe local and distortional buckling behaviour of the built-up section beamspecimens were found to be different from the single profiles. They consideredYoung et al (2008) recommendation that local buckling stress could be enhancedby employing intermediate stiffeners to the slender plate elements of thesections.
They concluded that design predictions by thecurrent DSM equations are conservative for the built-up open sections butcurrent DSM equations are unconservative for the built-up closed sectionsinvestigated in their study. Previousstudies showed that predicting the Strength of a built-up cold-formed Steelmember as the sum of the strength of the individual profiles is not rational onthe actual structural behaviour of such members. In current scenario, onlylittle work has been carried out on the structural behaviour of built-upsections as flexural members.
So the proposed work aims tosystematically study the structural behaviour and moment capacity of the cold-formedsteel built-up I beam subjected to local buckling and distortional buckling.