Fatigue performance of cracked diaphragm cutouts in steel bridge reinforced employing CFRP/SMA

Under long-term service conditions, fatigue cracking occurs at the diaphragm arc-shape cutouts in the ortho-tropic steel deck (OSD) bridges subjected to vehicle-induced vibration and cyclical wheel load. To repair cracks of the diaphragm cutouts, this study proposes two repair methods of the carbon fiber reinforced polymer (CFRP) sheets and shape memory alloys (SMA)/CFRP composite patches on the basis of crack-stop holes. The crack-stop hole eliminates the obvious source of fatigue propagation at the crack tip, but it weakens the section and harms the entirety of the diaphragm. The edge of the crack-stop hole in the cracked section becomes a new stress concentration site and the potential crack initiation point. The CFRP sheets can effectively improve the stiffness and reduce the stress amplitude of the cracked part. Moreover, the SMA/CFRP composite patches can further introduce precompression by activating SMA to reduce the stress level. Relative to the reinforcement by the crack-stop hole only, the fatigue notch factor is reduced by 12.28% and 30.76% after bonding CFRP sheets and SMA/CFRP composite patches, respectively. The fatigue tests show that the bonding of CFRP sheets and SMA/ CFRP composite patches can effectively postpone the initiation of fatigue cracks and inhibit crack propagation, so they are ideal repair methods for strengthening fatigue cracks of the diaphragm cutouts in the OSD bridges.