Finite Element Analysis of Shape Memory Alloy Ring Spring System for Steel Frames

Shape Memory alloys (SMAs) are smart materials that are capable of recovering its shape under unloading. This phenomenon is mainly due to its two unique properties such as shape memory effect (SME) and superelasticity (SE). The post-earthquake damages suffered by traditional steel frames can be mitigated by the SMA ring spring system in beam-column junctions. An SMA ring spring system is a combination of an inner ring of high strength alloy enclosing an outer ring, made of shape memory alloy with tapered faces. The force generated due to the wedging action between the HSS inner ring and SMA outer ring is responsible for resisting the external loads. This paper deals with the potentiality of the SMA ring spring system in steel frames for seismic applications. A nonlinear finite element analysis using ABAQUS is carried out to study the response of the SMA ring spring system under cyclic loading. For the SMA outer ring, a user-defined material model based on Auricchio's approach is used for expressing the superelastic behavior of SMA. A kinematic hardening model with von Mises yield criterion was used for evaluating steel material. A global analysis of a 3D multi-story frame is carried out to identify the most critical beam-column in the frame under seismic loading. Subsequently, the critical beam-column junction is modified with the SMA ring spring system. A dynamic implicit acceleration was given to the steel beam. The proposed connection shows a superior hysteresis loop and self-centering ability with a substantial increase in the load carrying capacity of the connection.