Research On Fatigue Performance Degradation Of Orthotropic Steel Deck Based On Crack Propagation Analysis

Fatigue cracks have frequently been observed in many orthotropic steel bridge decks(OSD)due to weld defects,heavy traffic load and stress concentration.However,there is little research on the fatigue performance degradation of the cracked structure.In this study,to clarify the fatigue performance degradation process of cracked OSD,the crack growth driving mechanism,the evolution of fatigue stress and deformation under 3 cracking modes have been investigated by simulating the crack propagation.The main conclusions are as followed:(1)Based on an existing fatigue test of the full-scale OSD specimen,a multi-scale finite element model have been established by using ANSYS submodel technology as well as 3D-crack analysis software FRANC3 D to investigate fatigue cracks propagation analysis on diaphragm cutout detail.The accuracy and applicability of FEM model and the propagation criterion in this paper have been clarified by comparing the FEM calculated stress,crack grow path and fatigue life with fatigue test results.The analysis results also revealed that mode Ⅰ is the governing propagation mode of the crack on diaphragm cutout detail,and the effects of mode Ⅱ and Ⅲ can be ignored.(2)To investigate the driving mechanism of crack growth,crack propagation analysis is performed on three fatigue-prone location including diaphragm cutout,rib-to-diaphragm and rib-to deck.The results revealed that the crack at the diaphragm cutout is mode Ⅰ.The cracks at the rib-to-diaphragm and rib-to deck are Ⅰ-Ⅲ mix-mode dominated by mode Ⅰ.(3)The evolution of fatigue stress at the various details of OSD with crack growth have been analyzed.The results showed that there are differences of stress evaluation among each details under different cracking modes.The influence of crack length on fatigue stress has obvious local effect: the stress near the crack position changed greatly,but the stress far from the crack varied slightly.(4)The evolution of deflection under live-load have been analyzed.The results showed that the deflection increased variously with the crack growth.The increasing of deflection is basically linear with the diaphragm cutout crack length.Rib-to-diaphragm crack has little effect on deformation.The growth rate of deflection increases with the rib-to-deck crack propagation.The research results of this paper would provide a reference for the fatigue performance evaluation of cracked orthotropic steel deck.