Long-span cold-formed steel single C-section portal frames

Abstract

This thesis presents a comprehensive study of long-span cold-formed steel single C-section portal frames. The study includes the formulation of a nonlinear beam finite element for thin-walled sections, a series of full-scale frame tests and component tests, finite element modelling and advanced analysis followed by the formulation of design guidelines. The study was aimed at exploring the structural behaviour through experiment and numerical analysis towards developing provisions for the design of cold-formed steel portal frames using Advanced Analysis. A nonlinear thin-walled beam element for general open cross-sections was formulated, incorporating warping effect and non-coincident location of the shear centre and the centroid. It was successfully implemented in the geometric nonlinear analysis framework of the OpenSees finite element software. Towards investigating the behaviour and determining the ultimate strength, six full-scale tests on cold-formed steel single C-section portal frames were conducted. Separate tests were performed on frame connections, point-fastener connections and coupons to obtain the material parameters required for numerical modelling. Advanced shell finite element models of the full-scale frames and frame connections were created and validated against experimental results. The bolts and screws used for the connections between components were represented by point-based deformable fasteners. The force-deformation characteristics of the deformable fasteners were incorporated and successfully implemented in the Advanced Analysis. The strength of cold-formed steel single C-section portal frames determined by the Direct Strength Method and the Direct Design Method were compared. To account for inherent uncertainties in the strength of CFS portal frames, system resistance factors were derived. It was concluded that the Direct Design Method using Advanced Analysis is the likely future method for the design of cold-formed steel portal frames.