Behaviour of Cold Formed Prestressed Steel Beams

Abstract

Cold Formed Steel (CFS) constructions are gaining more importance in the current era on comparison with the hot rolled sections as they have higher strength to weight ratio, ease in transportation etc. They are easy to construct and wastage of material is minimum as they can be customised on the requirement. Structural shapes which are majorly produced are open sections, closed sections, built up sections such as Cee sections(lipped sections), box sections, U sections etc. Although CFS are highly vulnerable to local instabilities such as local and distortional buckling it is highly recommended for structural applications. The local instabilities limits the member capacity well below the yield capacity of the material. In order to use cold formed steel in structural application these instabilities should be avoided/delayed. The local instability issues can be addressed by stiffening the sections. instabilities prestressing techniques can be used. The delays in formation of instabilities can be achieved by prestressing the cold formed steel sections. A high-strength steel cable that is positioned at the bottom hollow flange eccentric to the major axis is used to apply the prestressing force. Here the beam cable connection is unbounded i.e. beam-cable connection is provided only at the end anchorage where the force transfer mechanism takes place. Two stages of behaviour are considered, stage I is transfer of prestressing force to the cold formed steel beam and stage II is the application of uniformly distributed load to prestressed beam. Finite element model is done to simulate the mechanical behaviour of prestressed cold formed steel beam. This study helps in finding out the visible effect of prestressing and thereby exploiting the structural application of CFS. In the point view of a structural engineer local instabilities where a major drawback/issue of cold formed steel which limited the use of CFS as a structural member. But with the introduction of this new technique and predicting its behaviour and properly addressing the local instabilities using FEM, application of cold formed steel can be increased. In this paper, the state of the art literature review on the prestressed cold formed steel beams are investigated. This paper is much relevant towards the rapid and mass construction without compromising the sustainability and properly addressing the climate resilience.