Development, testing and performance evaluation of steel beam-through framed connections with curved knee braces for improving seismic performance

Abstract

An innovative beam-through framed connection equipped with curved knee braces is presented in this article. Curved knee braces with pinned connections are employed in semi-rigid beam-to-column joints. The proposed connection is expected to exhibit great deformability and energy dissipating capacity. The working mechanism and the theoretical behavior of the connection are firstly introduced, followed by an experimental study on three full-scale specimens under quasi-static cyclic tests. The test specimens exhibited stable behavior and great ductility. Damages were mainly concentrated on the knee braces within 0.02 rad drift ratio. The failure appeared when loading amplitude was above 0.07 rad drift ratio. The proposed connection is then introduced into beam-through steel frames (BTFs) which use strip braces as lateral force resisting system. To evaluate the contribution from knee braces, nonlinear response history analyses were performed on four demonstration BTFs. Based on the results of analyses, it is found that traditional BTF would exhibit high mode effect due to compressive buckling of strip braces, the inter-story drift is nonuniform along building height. Employing knee braces on traditional BTF stabilizes hysteretic behaviors and improves post-yielding strength for the system, global response of the system is reduced obviously and soft-story mechanism is mitigated. Moreover, results also indicate that satisfying peak transient inter-story drift and deformation uniformity can be achieved when strength demand from knee braces is adopted as 25% of total design inter-story strength demand.