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Investigations on structural interaction of cold-formed steel roof purlin-sheet system

When used as secondary roof purlins, cold-formed steel (CFS) sections are often attached to trapezoidal sheets through self-drilling screws to form a complete roofing system. The load application points are often eccentric to the shear centre, and thus inevitably generate a torsional moment that will induce twisting and/or warping deformations in addition to bending deflection. The connections between purlin and roof sheeting provide a restraining effect on purlin members by preventing such lateral and twisting movements, and hence have a beneficial effect on the load-carrying capacity. 
 
In this thesis the interactional behaviour of CFS purlin-sheeting system have been investigated through the following steps: (1) A F-test is carried out to measure the rotational stiffness at the connections, an engineering-orientated model is developed for quantifying the rotational stiffness regardless to purlin and sheet geometry and loading directions; (2) A set of loading tests on Z- and Σ- roof system are conducted to investigate the impact of rotational stiffness on the overall structural performance, load-carrying capacity and buckling behaviour of the system; (3) Finite element simulations of the existing tests are carried out and successfully validated; (4) Numerical parametric studies are established to study other factors that could affect the rotational stiffness.