Experimental and numerical study on the hysteretic behavior of a hybrid timber buckling-restrained brace with a cross-shaped steel core

Abstract

In this study, a hybrid buckling-restrained brace (BRB) composed of a cross-shaped steel core and a timber casing has been developed for potentially enhancing the seismic performance of heavy-timber frame structures. For such a novel timber buckling-restrained brace (T-BRB), a simplified design procedure has been conducted to preliminarily determine its key design parameters. Then, for investigating the hysteretic behavior of the T-BRB, eight full-scale 3.6-m-length T-BRBs with various design parameters and configurations have been tested. The considered design parameters include the ratio between the Euler buckling load of the casing to the core yield force (i.e., constraint ratio), the fastener type, the fastener spacing, and the welding details of the steel core. Finally, a calibrated numerical model of the T-BRBs has been developed and used to further investigate the specific lower limitation of the constraint ratio, which should be carefully addressed during the engineering design of the T-BRBs. It shows that the T-BRBs can provide stable hysteretic performance with an ideal energy-dissipating capacity. Also, in the T-BRB with un-densified fastener spacing near its casing ends and in the T-BRB adopting an intermittent welding for its steel core, a premature splitting and rupture of the casing ends would occur based on the experimental results. It leads to the ratio between their cumulative inelastic deformation (CID) to their yield deformation to be less than the specified minimum ratio of 200. When using the bolts instead of the self-tapping screws as fasteners, the CID and the energy dissipation of the T-BRB can be enhanced by 43.74% and 39.60%, respectively. For the T-BRB with a cross-shaped steel core, the specific lower limitation of its constraint ratio is recommended to be 1.5.