Structural behavior of lapped cold-formed steel Z sections with generic bolted configurations

Abstract

In order to improve the buildability of cold-formed steel structures, a series of research and development projects have been undertaken by the authors to study the structural behavior of bolted moment connections between cold-formed steel sections. As one of the major applications of cold-formed steel sections in building construction is modern roof structures with multi-span purlin systems, an extensive experimental and theoretical investigation on the structural behavior of lapped moment connections between cold-formed steel Z sections was carried out. Both generic configurations with high structural efficiency were adopted, namely, Config. W4 and W6, in which only the webs of the sections were bolted together for easy installation. Moreover, an analysis and design method was proposed to assess both the moment resistance and the effective flexural rigidity of the generic lapped connections. The research work aims to provide understanding on the structural behavior of cold-formed steel Z sections with lapped connections, and hence, to develop a set of rational design rules for multi-span purlin systems with overlaps. In order to verify the applicability of the proposed analysis and design method for other commonly adopted connection configurations, namely, Config. W2F2 and W4F2 where bolts were installed to both section webs and flanges within the lapped connections, an experimental and theoretical investigation on a total of 12 one point load tests on lapped cold-formed steel Z sections were carried out. Among all tests, section failure under combined bending and shear at the ends of lap was found to be critical while twisting of the lapped Z sections was apparent throughout the entire deformation ranges. In general, the structural behavior of lapped connections with Config. W2F2 and W4F2 was found to be similar to those with Config. W4 and W6. Moreover, the formulation of the proposed analysis and design method was modified to accommodate the presence of the flange bolts, and back analysis of the lapped Z sections against combined bending and shear using the proposed method was performed. After careful calibration against test data, the method was shown to be structurally adequate and efficient for lapped connections with Config. W2F2 and W4F2. Moreover, simple design expressions were also proposed for the evaluation of effective flexural rigidities of the lapped connections. Comparison on the structural behavior between the two sets of connection configurations was also presented.