Behavior of a steel coupled beam moment frame based on nonlinear analyses

A steel coupled beam moment frame (CBMF) is an innovative seismic resisting moment resisting frame that is composed of coupled beams and steel columns. A coupled beam features a pair of steel beams, post-tensioning elements, and energy dissipation devices. Coupled beams can be fabricated in shop and pin-connected to columns on site, facilitating the field construction. Energy dissipation is provided by a special energy dissipation device, not by damage to the main structural members or to the energy dissipation device itself. Rotations at beam-column joints are the result of a relative slide mechanism of the coupled beams, not the result of beam plastic hinges. During unloading, the force in the PT elements eliminates coupled beam relative slide as well as rotations at beam-column joints, offering the potential of minimal residual rotations to coupled beam-column connections. This paper presents conceptual details, conceptual behavior, and design considerations for CBMFs. For behavior study, a prototype building using CBMFs as the lateral resisting frames was designed. A nonlinear analysis model for the prototype building was created. Static pushover and cyclic push analyses were conducted to assess the concepts. Dynamic time history analyses using a 44-ground motion record set were performed to study the post-earthquake residual story drift and residual connection rotation response of the prototype CBMF building. Analysis results showed that the global behavior and connection response of the prototype CBMF supported the conceptual behavior and design considerations, and that post-earthquake story drifts and connection rotations of the prototype CBMF building are ignorably small.