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

Cyclic tests on nine full-scale beam-column subassemblages were carried out in support of the development of a new lateral load-resisting system recently introduced in AISI-S110: Standard for Seismic Design of Cold-Formed Steel Structural Systems—Special Bolted Moment Frames. With double channel beams and HSS columns interconnected by bearing-type high-strength bolts, all specimens showed an story drift capacity significantly larger than 0.04 radian. Typical response is characterized by a linear response, a slip range, followed by a significant hardening region due to bolt bearing. Three failure modes were identified. Confining in the connection region, inelastic action through bolt slippage and bearing is ductile and desirable. Such inelastic action always occurs first, but either column or beam may also experience buckling. Beam buckling is most undesirable due to significant post-buckling strength degradation. Extending the concept of instantaneous center of rotation of an eccentrically loaded bolt group, a model that can reliably simulate the cyclic behavior of the bolted moment connection is presented.