BEHAVIOR OF FULLY ENCASED COLD FORMED STEEL JOISTS WITH/WITHOUT WEB OPENINGS: EXPERIMENTAL INVESTIGATION

Abstract

This paper presents an experimental investigation on the behavior of encased light cold-formed steel joists with/without web openings. The study is carried on two sets of composite beams constructed of cold-formed steel joists using I-beam built-up sections. The first set has no web openings while the second set has circular web openings. Each set consists of three beams with various steel section-concrete reinforcing ratio. The constant parameters included in this study are the cross sectional area of the specimen, distribution of web openings in the encased steel I-joist, and the compressive strength of concrete. The tests have been conducted by applying two concentrated identical loads. Consequently, a comparative study is carried out to compare between the behavior of specimens within one set, and a comparison between the specimens of the two sets. This comparison is related to strength, stiffness, ductility, energy absorption capacity and failure modes. Based on the testing results, it is concluded that, the load capacity of the composite beams without web openings is greater than that with web openings for the same steel ratio. But the existence of web openings in the encased steel joists enhances the ductility and the energy absorption of the composite beams. Also using cold formed steel I-joists in the composite beams allow the failure mode to be ductile flexural failure.