ECONOMICAL COLD-FORMED THIN-WALL STEEL CROSS-SECTIONS

In Australia, the use of cold-formed thin-wall steel sections as house framing members has gained an increasing acceptance in residential construction market. Cold-formed thin-wall steel members have been widely used in commercial and industrial applications. In this study, currently used cold-formed thin-wall cross-sections are analysed and the results obtained used to develop more economical and stronger sections. In order to achieve a rational analysis model for roof truss system, semi-rigid and full-hinge models of typical residential roof truss are compared. Analysis results have revealed that the bending moment of chord members in the truss system is as important as the axial force. This shows that a semi-rigid model must be used in analysing the roof truss system. Furthermore, the critical load cases for the roof truss of different roof pitches are obtained after a comprehensive analysis. The internal member forces and moments under the critical load cases are then used in later buckling analysis and cross-sectional optimization. Finite strip method software CUFSM is employed to perform the elastic buckling analysis of current chord, web and wall stud sections. Based on the sophisticated Direct Strength Method, the axial capacity and moment capacity of these sections calculated. The results suggest that currently used cross-sections are either not strong enough to resist load actions, or are overdesigned. Using the knowledge obtained from the analyses, two optimized cold-formed thin-wall steel cross-sections, one is symmetric and another is asymmetric that can be doubled, are developed. The buckling capacities of these two cross-sections satisfy the design loads derived from the truss analysis.