Sensitivity of design parameters on the stability of apex connections in cold-formed steel portal frames

Cold-formed steel portal frames have joints that are typically connected by bolting the main frame members and connection brackets together for apex, eaves, and knee connections, if applicable. The strength and stiffness of connections have a significant impact on frame capacity and behavior and affect the internal force and moment distributions and deflections. The apex connection, formed by brackets bolted to lipped-channel rafters, has been shown to fail by buckling of the apex bracket plate at loads lower than the capacity of the main frame members. Previously, an advanced finite element model was created and validated with experimental results from a series of apex connection tests, which showed a change in moment-rotation behavior depending on the size and thickness of the connected parts. Parametric studies were conducted using the validated finite element model to further investigate the effect of the connection input parameters on the strength and stiffness of the overall connection. The effects of combinations of the rafter thickness and apex bracket thickness on the connection moment-rotation behavior, stiffness, and strength were examined for apex connections formed from C150 and C200 lipped channel rafters with corresponding brackets. Recommendations for apex connection design improvement is discussed.