Post-fire seismic behaviour of a self-centring connection with buckling-restrained plates and pre-stressed bars

Abstract

Fire hazard is regarded as a significant threat to structural systems, not only the resistance during the fire should be concerned but the post-fire assessment of structural performance is also of great importance. The post-fire seismic behaviour is the key metric for evaluating the residual performance of structures mainly serving seismic demands. However, limited research considers whether the self-centring system, one of the seismic-resilient structures, can still resist seismic loadings after fire exposure. Based on that, this study mainly aims to investigate the post-fire seismic response of a self-centring system with buckling-restrained plates and pre-stressed bars. A sequence of the fire exposure and the post-fire cyclic test was conducted on the cross-shaped specimen, and hysteretic behaviour after air-cooling was analysed and compared with the regular seismic response. Results showed that fire exposure not only significantly influences the geometric conditions of the self-centring system, but also completely transforms the original deformation mechanism. Pre-stressed bars were expanded and stretched during the fire so that could not provide self-centring capacity in post-fire conditions, while the energy dissipation of buckling-restrained plates was postponed and weakened because of the slippage at bolted connections. Compared with the regular seismic behaviour, the post-fire hysteretic response appeared sliding and pinching effect rather than the flag-shaped, with a much lower load-carrying capacity and extremely larger residual deformation. To improve the post-fire seismic resistance, the numerical model was established first to reappear the experimental response by the heat transfer analysis and post-fire static analysis, and then extended to simulate the post-fire repair in proposed strategies. According to the repair effect, it is suggested that the high-strength bolts should be replaced with pre-load, and the bars are required at least to provide additional stiffness and re-tensioned if necessary. The findings reveal the considerable influence of fire exposure on the seismic performance of the self-centring system, and highlight the importance of improving residual resistance of seismic-resilient structural systems in post-fire scenarios.