Seismic Retrofitting of Non-Compliant RC Structures Using SMA Bracings and Modified DDBD: A Parametric Approach

This paper introduces a novel seismic retrofitting strategy using Shape Memory Alloy (SMA) bracings within a modified Direct Displacement-Based Design (DDBD) framework for non-compliant reinforced concrete (RC) structures. SMA bracings, characterised by superelasticity and energy dissipation, were investigated through parametric analyses considering various configurations, cross-sectional areas, and damping properties. Nonlinear static pushover and nonlinear time history analyses were performed on mid-rise (six-storey) and high-rise (nine-storey) RC buildings. Results indicated that optimal X-bracing designs—1250 mm² cross-sectional area with 0.10 damping for six-storey, and 1600 mm² with 0.15 damping for nine-storey structures—markedly enhanced seismic resilience. Improvements included increased global ductility, reduced inter-storey drifts, and better control of plastic hinge formation. Retrofitted six-storey structures achieved reductions of 94% in peak floor accelerations (PFA) and 95% in residual displacements, while nine-storey structures showed 94% and 63% reductions, respectively. Comparisons with conventional steel bracings confirmed SMA’s superior performance. SMA bracings reduced residual displacements by 70% (six-storey) and 63% (nine-storey), compared to 50% with steel. They also improved global ductility by 35% and 40%, whereas steel achieved only moderate gains. These outcomes highlight SMA bracing’s effectiveness in controlling deformations, enabling recentering, and minimizing permanent damage. Although the study was applied to real Algerian structures, findings can be generalized to RC buildings of varying heights worldwide. SMA bracings emerge as a scalable and cost-efficient solution for seismic-prone regions. Future work should address applications to steel and hybrid structures and assess SMA’s long-term performance under different seismic conditions.