Proactive Enhancement on Fatigue Performance of Cracked Diaphragm in Steel Bridge Employing Fe-SMA

Fatigue cracks are prone to occur at the arc-shaped cutouts of the diaphragms in orthotropic steel deck bridges. Based on the crack-stop holes, the China-made ferrous-based shape memory alloy (Fe-SMA) plates are employed for repairing the cracked diaphragm cutouts, utilizing their inherent stiffness and shape memory effect. In this experimental study, a total of eight diaphragm specimens were designed for fatigue tests. Among these, three specimens were repaired solely by the crack-stop holes, while five specimens were repaired by the Fe-SMA plates covering crack-stop holes. By reinforcing the diaphragm cutouts with Fe-SMA plates, significant local stiffness and compressive stresses can be introduced at the cracked regions, which can effectively reduce the stress concentration, delay the initiation of fatigue cracks, and suppress crack propagation after secondary cracking. Via comparison, it has been noted that the fatigue life of specimens repaired by Fe-SMA plates is 3.73–12.68 times that of specimens repaired solely by crack-stop holes, and the enhancing effect of bonding Fe-SMA plates is better than that of bonding carbon fiber–reinforced polymer (CFRP) sheets and SMA/CFRP composite patches. The fatigue strength of the reinforced diaphragms significantly exceeds the fatigue grade of current design standards, indicating that the proposed novel method of bonding Fe-SMA based on crack-stop holes is effective and practical for actively repairing fatigue cracks of diaphragms in steel bridges.