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

In recent years,when orthotropic steel bridge slabs are widely used,the fatigue cracking of the joints between the longitudinal ribs,the slabs and the transverse diaphragms is prominent due to the complex structure and numerous welds.In this paper,stress intensity factor(sif)is used as the analysis index,and the fatigue performance of the joint between the panel and the longitudinal rib and the arc-shaped gap of the diaphragm is studied by combining the theory of fracture mechanics and finite element method.On the basis of the comparison of the arc-shaped notches of diaphragm,the optimized arc-shaped notches are proposed for reference of designers in the future.This paper mainly carries out the following aspects:(1)The crack location and reason of orthotropic steel bridge deck are described,the fatigue crack analysis method based on the theory of linear elastic fracture mechanics is introduced,and the stress intensity factor of crack tip is calculated by finite element method.The accuracy of the finite element method is verified by the plate model with crack,which provides a basis for the subsequent modeling and analysis.(2)A two-dimensional three-rib orthotropic steel bridge panel detail model was established to accurately simulate the fatigue cracks at the connection between roof and longitudinal rib,and the stress intensity factors at the crack tips were calculated.By changing the initial crack length,bridge slab thickness,U rib thickness and other parameters,the change rule of stress intensity factor was analyzed.The analysis shows that reducing the initial crack length and increasing the thickness of the bridge slab can effectively reduce the stress intensity factor at the crack tip,thus improving the fatigue life of the structure.(3)The three-dimensional model of the arc-shaped notch at the connection between the transverse diaphragm and the longitudinal rib is established,and the corresponding most unfavorable load position is determined through calculation.The influence of the thickness and height of diaphragm plate on the stress intensity factor of the arc-shaped notch crack was analyzed.The detailed fatigue life assessment process of orthotropic steel bridge slabs is established and the fatigue life of transverse plate crack propagation is calculated.The results show that the initial crack length has a great influence on the fatigue life,and the fatigue life at the initial stage of crack growth accounts for a large proportion in the whole service process of the structure.(4)Taking the stress intensity factor at the crack tip as the index,four common arc-shaped notched forms of transverse diaphragm were compared,and it was found that the arc-shaped notched forms had the best fatigue performance.On this basis,the influence of arc radius R and gap gap d on the stress intensity factor at the crack tip was analyzed.The arc notch forms were optimized,and the arc notch forms with radius R=45mm and gap d=30mm were proposed.