Finite Element Study of Shape Memory Alloy Butterfly Spring Tie Beam Joints in Double-Column Piers

This paper proposes a repair-oriented steel tie beam joint with shape memory alloy (SMA) butterfly springs for double-column piers. In the proposed detail, the conventional welded connection is replaced by a bolted fuse region to redirect inelastic demand toward replaceable components. Joint component-level finite element simulations under cyclic loading were conducted to evaluate stress redistribution, cumulative plastic strain, hysteretic response, stiffness variation, cumulative energy dissipation, and residual deformation. The results indicate a repairability-oriented response characterized by damage localization and residual deformation control, rather than a strength-dominated enhancement. Compared with the non-SMA bolted reference joint, the SMA joints show a modest reduction in the peak stress of key plates, reduce the relative peak PEEQ indicator by 27.6%. within the adopted no-fracture finite element framework, and lower the residual deformation index by about 21.5%. The dual-row SMA arrangement provides better load sharing and slightly higher energy dissipation than the single-row arrangement. Although the SMA joints dissipate less cumulative energy than the non-SMA reference joint, the results suggest that the proposed detail may provide a repair-oriented connection concept when post-earthquake damage localization, replaceability, and residual deformation control are prioritized.