A Novel Self‐Centering Mechanical Model for Shape Memory Alloys Incorporating Cyclic Degradation

ABSTRACT Shape memory alloys (SMAs) have gained increased attention in earthquake engineering due to their exceptional self‐centering and energy dissipation capabilities. However, the cyclic degradation behavior of SMA has a significant impact on their mechanical properties, which is often inadequately addressed in existing mechanical models. This paper proposes a phenomenological mechanical model that comprehensively considers the cyclic degradation effects of SMA. The proposed model accounts for key aspects including stiffness degradation, strength degradation, residual strain accumulation, as well as energy dissipation during the hardening stage. The theoretical framework and hysteresis rules governing the mechanical model are first presented, followed by its implementation in OpenSees software as a new material model. Subsequently, experimental data from four different loading protocols are used to validate the feasibility and accuracy of the proposed mechanical model. The comparative analysis demonstrates that the mechanical model proposed and implemented in OpenSees can effectively simulate the hysteretic behavior and various degradation responses of SMA materials under different loading protocols. Furthermore, two different SMA‐braced steel frame structures, one considering cyclic degradation and the other neglecting it, are analyzed and compared to assess the impact of SMA cyclic degradation on the seismic performance of the structures. The results show that SMA cyclic degradation significantly impacts both the maximum transient and residual inter‐story drift ratios (RIDRs) of the structure. Notably, structures that properly account for SMA cyclic degradation exhibit a remarkably higher median RIDR, along with greater variability. This also confirms that the proposed mechanical model can be effectively implemented in OpenSees for practical applications, enabling a more accurate and reasonable assessment of structural responses during seismic events.