Influence of cyclic degradation behaviors in shape memory alloy on the seismic performance of structures

Abstract

This study investigates the impact of cyclic degradation in shape memory alloys (SMA) on the seismic performance of SMA-based self-centering steel frames. A novel material model, the Self-centering Model with Cyclic Degradation (SMCD), is proposed to comprehensively capture the cyclic degradation behavior of SMA, including stiffness degradation, strength degradation, and residual strain accumulation. The SMCD model is implemented in OpenSees to enable accurate numerical simulations. To evaluate the influence of these degradation factors on structural seismic performance, sixteen SMA braces steel frames with varying SMCD parameters were designed and modeled. Incremental dynamic analysis (IDA) was conducted using 22 ground motion records recommended by FEMA P695. The IDA results were further analyzed through a comprehensive assessment framework, including collapse margin ratio, fragility analysis, and probabilistic seismic hazard analysis. The results demonstrate that the SMCD model effectively captures the cyclic degradation behavior of SMA braces. All three degradation factors: strength degradation, stiffness degradation, and residual strain accumulation, were found to significantly influence the seismic performance of the structures. Ignoring cyclic degradation effects of SMA-based self-centering brace leads to an overestimation of structural seismic performance. Specifically, higher degradation levels were associated with a reduced collapse margin ratio, increased fragility probability, and higher annual exceedance probability. This study provides valuable insights for the design and assessment of SMA-based self-centering systems, highlighting the need to account for material degradation to ensure accurate performance predictions.