Research On Fatigue Crack Propagation Of Orthotropic Steel Bridge Deck Based On Fracture Mechanics

Orthotropic steel bridge decks are widely used in modern long-span bridge construction projects represented by cable-stayed bridges and suspension bridges due to their own advantages of light weight,good force transmission integrity,short construction period,and high ultimate bearing capacity.At the same time,due to its complex structure and the existence of initial welding defects,the local location of the initial cracks in the welding area will cause serious stress concentration under the load of reciprocating vehicles,which will eventually lead to further expansion of fatigue cracks and reduced service life.Therefore,in the fatigue crack growth study of orthotropic steel bridge decks,the crack growth of fatigue-sensitive and vulnerable details of orthotropic steel decks should be accurately simulated and their fatigue crack growth life should be evaluated.This paper takes the standard girder section of the orthotropic steel bridge deck of the Taizhou Yangtze River Highway Bridge as the engineering background.Based on the fracture mechanics method,combined with the fatigue crack growth test,through the ABAQUS software and FRANC3 D software interactive finite element simulation calculation,the orthotropic steel Three-dimensional fatigue crack growth analysis and fatigue performance evaluation were carried out on the vulnerable welding details of the bridge deck.The specific work content is as follows:(1)Introduce the development status and research results of the fatigue crack growth of orthotropic steel bridge decks,compare the basic principles and scope of application of several more complete fatigue assessment methods,and focus on the steel box girder based on the theory of fracture mechanics.Research results on fatigue crack growth.(2)Multi-scale modeling of the standard section of the steel box girder of the Taizhou Bridge was carried out using ANSYS finite element analysis software.The influence range of transverse and longitudinal bridge stress and the most unfavorable position under typical vehicle load are analyzed.Through the analysis of the local refinement of the orthotropic steel bridge deck,the most unfavorable loading conditions were determined;a fine sub-model of typical welding fatigue details was established,and stress analysis was performed to determine the conditions that need to be met for the boundary selection of the sub-model.(3)The fatigue crack growth test was carried out for the weld between the top plate of the orthotropic steel bridge deck and the U-rib.Three fatigue vulnerable areas are selected for stress measurement and calculation using the hot spot stress method and the nominal stress method,and the measured stress values of the three measurement points are compared with the finite element calculation results.Through the numerical simulation method of interactive design of ABAQUS software and FRANC3 D software based on fracture mechanics theory,the threedimensional fatigue crack growth numerical simulation analysis of the top plate-U-rib weld of the test specimen is carried out,and the stress intensity factor value of the crack tip at each step of crack growth is obtained.Analyze the relationship between the stress intensity factor and the crack growth depth,calculate the fatigue crack growth life of the test specimen under the numerical simulation conditions,and compare it with the fatigue crack growth life measured in the experiment to verify the numerical simulation method based on the theory of fracture mechanics.Effectiveness.(4)Through the numerical simulation method of ABAQUS software and FRANC3 D software interactive design based on the theory of fracture mechanics,the local finite element models of the weld roots and weld toes of the real bridge roof-U-rib connection weld of the Taizhou Bridge were established to carry out three-dimensional cracks.Expansion numerical simulation analysis to obtain the relationship between the stress intensity factor and the crack depth and the number of fatigue crack propagation;combined with the traffic flow statistics of the Taizhou Bridge,the welding of the heavy lane roof-U-rib weld connection of the orthotropic steel bridge deck of the Taizhou Bridge was calculated Fatigue crack propagation life at the root and weld toe details.