Investigation on fatigue cracks of diaphragm cutout in bridge orthotropic steel deck

Abstract

Fatigue cracks were found at the diaphragm cutouts in the orthotropic steel deck (OSD) of a self-anchored suspension bridge while the in-service time of the bridge was less than 10 years. The causes of fatigue cracks of the diaphragm cutout are investigated in this study. The fatigue cracks initiated from the intersections of the arc curves and the straight lines, which form the geometrical discontinuity to the cutout edge. The in situ monitoring and finite element analysis under fatigue load model indicate that the cracking region in the cutout is in bidirectional compression. However, the thermal-structural analysis and tests show that the rib-to-diaphragm welding process produces high tension residual stress at the cracking points of the cutouts. The cutouts are under tension-compression cyclic loading because of the coupled stress, which is derived from the vehicle-induced stress and the welding residual stress. The results show that the strain energy method can present a reasonable fatigue life estimation for the diaphragm cutouts with full consideration of the residual stress.

Keywords:

• Diaphragm
• fatigue life
• fatigue load model
• orthotropic steel deck
• strain energy density
• suspension bridge
• thermal-structural analysis
• welding residual stress

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was supported, in part, by Grant from the National Natural Science Foundation of China (Project 51878027 and 52108108), Beijing Municipal Education Commission (Project CIT&TCD201904060) and the Fundamental Research Funds for Beijing University of Civil Engineering and Architecture (Project X20174). These supports are gratefully acknowledged.