SMA-Based Low-Damage Solution for Self-Centering Steel and Composite Beam-to-Column Connections

This paper presents a low-damage solution for self-centering steel and composite beam-to-column connections, with the issue of beam-growth being particularly addressed by permitting the connections to rotate only about the top flange of the beam. Self-centering devices incorporating novel shape memory alloy (SMA) ring springs are the kernel components for the proposed connections. The fundamental working principle of the connections is depicted, followed by an experimental study on four proof-of-concept specimens, including three bare steel and one composite connections. The testing parameters are preload of web bolts, training of the SMA ring springs, and influence of the slab. Among other findings, it is shown that the damage to the concrete slab and the reinforcement are minimal for the composite connection. Stable flag-shaped hysteretic responses are typically exhibited, and good ductility, and energy dissipation performance are confirmed. The specimens can be generally classified as rigid and partial-strength connections. Slip-critical HS web bolts could provide an extra source of energy dissipation through friction. Applying training to the SMA outer rings further stabilizes the hysteretic behavior and mitigates the possible degradation. Based on the experimental observations, preliminary design recommendations are proposed, with the focus on the design of the SMA ring springs, web plate, cover plate, and other components of the device. Empirical design equations are also proposed for predicting the moment resistance of the connections, and the predicted values are shown to agree well with test results.