Stability of Apex Connections in Cold-Formed Steel Portal Frames

Cold-formed steel portal frames are popular structures in industrial and residential sectors, and are commonly used in rural areas for sheds, garages, and shelters. The connections are an integral part of the structure and should have adequate strength to transfer the internal forces between the framing members. The connection stiffness affects the overall frame internal force and moment distributions and deflections. A recent experimental investigation was conducted to determine apex connection strength and stiffness in cold-formed steel portal frames for various rafter channel depths and thicknesses subjected to an opening bending moment. It was found that all specimens failed by apex bracket web buckling. However, the characteristic behavior of the connection was affected by the ratio of the geometric stiffness of the rafter to bracket, and low ratios resulted in an early reduction of connection stiffness compared to connections with higher ratios. Additionally, nominally identical connections showed a variation in strength and connection deflection behavior. An advanced finite element model was created and compared with the experimental results. Modeling details required to accurately capture the instabilities on the connection are discussed, as well as future improvements and parametric studies to further understand the behavior of the apex connection.

View content