Innovative self-centering systems using shape memory alloy bolts and energy dissipating devices

In conventional eccentrically braced frames (EBFs), earthquake input energy is mainly dissipated by plastic deformation of link beams. However, the plastic deformation of link beams can cause extensive structural damage during severe seismic events. The self-centering eccentrically braced frames (SEBFs) are one of the strategies that have been proposed to address this problem. This paper presents two new SEBF systems incorporating shape memory alloy (SMA) bolts and energy dissipation devices, consisting of shear tabs and web hourglass pins (WHPs). SMA bolts are employed in collector beams-to-link beam connections to dissipate energy and recenter the frame with negligible residual drift after an earthquake, while shear tabs and WHPs are utilized in both ends of the link beam web to enhance the seismic performance of the frame. Detailed finite element simulations are performed to assess the cyclic performance of the proposed self-centering systems using experimentally validated models. The results indicate the excellent efficiency of the proposed systems in terms of recentering and energy dissipation capacity. It is shown that the application of shear tabs and WHPs can improve the ultimate strength, equivalent damping and energy dissipation capacity of the system by up to 20%, 35% and 60%, respectively. The experimentally validated models are then used to investigate the effects of key design parameters such as initial prestress of SMA and shear tab bolts, friction coefficient, and the diameter and clear length of the hourglass pins. The results of this study should prove useful in the practical design of the SMA-based self-centering systems.