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

Abstract

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. The fatigue problems of steel bridges are becoming increasingly prominent owing to influencing factors such as welding defects, stress concentration, and residual stress. Under long-term service conditions, fatigue cracking usually occurs at the diaphragm arc-shape cutouts in the orthotropic steel bridge decks subjected to vehicle-induced vibration and cyclical wheel load. The China-made ferrous-based shape memory alloy (Fe-SMA) is employed to actively repair fatigue cracks in steel bridges through adhesion, which offers the advantage of eliminating the reliance on traditional prestressing techniques that require complex equipment and expensive anchors. When applying Fe-SMA for the proactive repair of fatigue-cracked orthotropic steel deck bridge diaphragms, activating Fe-SMA can introduce precompressive stresses of about 60 MPa at the edge of crack-stop holes, based on the increase of local stiffness at the cracked region. The feasibility and effectiveness of the method of covering crack-stop holes with Fe-SMA plates have been verified through the actual repair applications of cracked diaphragm cutouts in the Sutong Bridge and other kilometer-level steel bridges.