Fatigue crack repair in steel bridges using SMA: Mechanism, modeling, and implementation

This study begins by investigating the recovery stress mechanism in shape memory alloys (SMAs) through controlled phase transformation via heat treatment and pre-tensioning. Furthermore, fatigue tests on SMA specimens were conducted to develop a modified stress intensity factor (SIF) model. Based on these results, a case study was performed on an in-service steel bridge exhibiting a rare fatigue crack pattern at bolt holes, where an SMA plate strengthening system was designed and implemented. Field measurements revealed that the stress amplitudes at the two crack tips were reduced to 52.3 MPa and 50.1 MPa, representing decreases of 60% and 70%, respectively. As a result, critical stresses that initially exceeded code limits were suppressed to compliant levels, effectively arresting crack propagation. Wireless monitoring over a 270-day period confirmed the cessation of crack growth, maintained integrity of the adhesive interface, and overall stability of the system under significant temperature and humidity variations. This study validates the reliability of the SMA-based repair approach and provides valuable insights for addressing similar engineering challenges. • A recovery stress tuning mechanism via thermomechanical processing. • An SIF model for SMAs incorporating transformation-induced plasticity. • A pioneering implementation of SMA-based active strengthening for cracked bolted connections.