Three-Dimensional Finite Element Simulation of the Seismic Behavior of Multitier Concentrically Braced Frames

Multitier concentrically braced frames (MTCBFs) are often employed as the lateral force-resisting system in structures where a tall, single story is required. To create an MTCBF, a braced frame is subdivided into a series of tiers with intermediate struts. Out-of-plane bracing is not provided at the tier levels, however. Prior studies on the seismic behavior of MTCBFs demonstrated that frames designed according to contemporary seismic provisions are susceptible to inelastic drift concentration within a single tier. Concentration of inelastic drift may lead to brace fracture and in-plane flexural yielding of the columns. In this study, three-dimensional finite element models of full MTCBFs were used to investigate their seismic behavior. Results from static pushover and nonlinear response history analyses revealed that the gusset plate connections at the tier levels aid MTCBFs in preventing inelastic drift concentrations and flexural yielding in the columns. Nevertheless, refinements to existing seismic design provisions appear necessary since excessive panel drifts were observed.