| This thesis presents a research project on the structural behaviour of cold formed steel lapped Z sections.; In order to examine the structural performance of the lapped Z sections, a total of 38 laterally restrained one point load tests were carried out on lapped Z sections with different connection configurations. Both the strength and the deformation characteristics of these connections were examined in detail.; In order to examine the structural behaviour of lapped Z sections over the entire deformation ranges, a numerical investigation using finite element method was also performed. Highly efficient four nodded shell elements were adopted to simulate the cold-formed steel Z sections while spring elements were adopted in modelling the bolted connections. Moreover, material non-linearity was incorporated in order to allow yielding in the sections under combined bending and shear, and the measured stress-strain curves obtained from coupon tests were adopted together with the VonMises yield criteria in the material modelling of the cold-formed steel sections.; Based on the results of various tasks of investigation, a complete analysis and design procedure is formulated for multi-span lapped purlin systems under both gravity loads and wind uplift. The effect of lapped Z sections is fully incorporated in determining the distribution of internal forces of purlin members, and hence the co-existing moment and shear force at the ends of lap in purlin members are readily obtained. Various design coefficients for moments and shear forces in purlin members of practical material and geometrical configurations with different lap lengths are also provided. Moreover, based on the proposed deformation characteristics of lapped Z sections, a non-linear analysis on the multi-span lapped purlin systems are performed to evaluate their ultimate load carrying capacities. Various failure modes are identified in purlin members with different lap lengths, span lengths, and section sizes.; The research work carries a great impact to the conventional design concept on connections between cold formed steel sections that not only the strengths of the connections are important, but also the stiffnesses of the connections are important as well in practical design and construction of indeterminate structures. Moreover, a clear understanding on the structural behaviour of cold-formed steel lapped Z sections with bolted moment connections is presented, and the proposed analysis and design method provides important understandings on the effects of effective flexural rigidities of lapped Z sections in multi-span lapped purlin systems during the entire deformation ranges. (Abstract shortened by UMI.)... |
