Performance evaluation in connection-head-gapped braced frame: Reduced-scale static test and numerical simulation

Abstract

Many existing high-rise buildings in Japan conform to outdated codes and require seismic retrofit to meet current standards. While installing additional seismic devices is a proven solution, these devices usually bring additional stiffness, alter dynamic characteristics of structures and exacerbate uneven stress distribution. This paper proposes a novel connection-head-gapped brace to mitigate such adverse effects and safeguard structures during major earthquake events. The novel device incorporates a gapped connection-head above steel braces. When the earthquake-induced frame displacement is small (gap opens), steel braces remain dormant; when the displacement reaches a predetermined threshold (gap closes), the steel braces engage with frame, enhancing lateral stiffness and limiting further frame displacement. Consequently, the connection-head-gapped brace preserves the dynamic characteristics of structures as much as possible and provides additional stiffness only during major earthquake events. A one-span connection-head-gapped braced frame was designed and subjected to a static cyclic test to validate the performance of the novel brace. This paper details the concept and configuration of the novel brace, along with the reduced-scale static cyclic test and finite element simulation of the connection-head-gapped braced frame. The results demonstrate that only after gap closure the steel braces provide additional stiffness and change stress distribution in frame. The novel connection-head-gapped brace presents a promising retrofit solution for enhancing the seismic resilience of existing buildings.