Behavior of exterior beam‐column joint reinforced with shape memory alloy

Abstract

Beam‐column joints are critical regions in moment‐resisting frames and are particularly susceptible to severe stress concentrations and reinforcement congestion. Conventional design typically relies on dense transverse reinforcement to improve joint performance, resulting in construction difficulties and reinforcement congestion. This study investigates the monotonic structural performance of exterior reinforced concrete beam‐column joints reinforced with hybrid superelastic shape memory alloy (SE‐SMA) and steel bars using nonlinear finite element analysis. Fourteen numerical models were developed to evaluate different coupling arrangements of NiTi and Fe‐based SMAs under monotonic loading. The numerical framework was validated against experimental data and employed the concrete damaged plasticity model to capture the structural response and failure mechanisms. The results show that hybrid SE‐SMA–steel configurations effectively reduce reinforcement congestion by allowing joint stirrup reductions of 33%, 67%, and 100% while maintaining structural integrity. Among the investigated configurations, the AR4 model exhibited the best performance, achieving a 20.3% increase in peak load capacity compared with the conventional steel‐reinforced control specimen. In addition, the hybrid reinforcement altered the failure mode from brittle joint shear failure to a more desirable beam flexural failure. These findings demonstrate that the proposed hybrid SMA–steel reinforcement system enhances the monotonic load‐carrying capacity and structural performance of reinforced concrete beam‐column joints while facilitating construction through reduced reinforcement congestion.