Cyclic Testing and Modeling of Cold-Formed Steel Special Bolted Moment Frame Connections

A cyclic testing of nine full-scale beam-to-column moment connection subassemblies was carried out to support the development of design provisions for a lateral load-resisting system in the AISI S110: Standard for Seismic Design of Cold-Formed Steel Structural Systems-Special Bolted Moment Frames. This type of one-story framing system features C-section beams connected to hollow structural section columns by bearing-type high-strength bolts and is commonly used in industrial platform construction. The test results showed that these specimens had an interstory drift capacity significantly larger than 0.04 rad. The cyclic behavior was characterized by a linear response, a slip range, and a significant hardening response due to bearing at bolt holes. The conventional strong column-weak beam design philosophy is not appropriate for this system. The inelastic action through the bolt slip and bearing in the connection is a ductile yielding mechanism. Beams and columns should be protected to remain elastic by the capacity design principles. Based on the concept of the instantaneous center of rotation of an eccentrically loaded bolt group, a model that can properly simulate the cyclic behavior of the bolted moment connection is presented.