Crack Propagation And Residual Life Evaluation Of Steel Deck Of Long-span Cable-stayed Bridge

Orthotropic steel bridge deck(OSD)is widely used,but the fatigue problem is prominent.Many fatigue cracks are found in different structural details of Bridges in practice,among which the cracks initiated at the welded root or welded toe are easy to extend along the thickness of deck until they penetrate the deck and crack the pavement.Taking a cable-stayed bridge of China as the background,different failure criteria are defined in stages according to the influence and damage of penetration cracks on the bridge structure,and the growth characteristics of such cracks and the variation law of fatigue life under each failure criterion are analyzed quantitatively,which can provide a theoretical basis for the crack reinforcement time of bridge deck.The main contents are as follows:(1)The theoretical method of calculating orthotropic steel bridge decks is reviewed,and the causes of fatigue cracking modes are analyzed from the aspects of mechanical factors and structural factors respectively.The research methods for fatigue cracks at home and abroad are summarized,and the appropriate research methods and calculation methods are selected for typical deck penetrating cracks.(2)Based on the statistics of the penetration crack of a cable-stayed bridge deck in China,the position of the deck deck that is most prone to fatigue crack is obtained.According to the actual crack position,a multi-scale finite element model containing multiple typical fatigue cracks is established.To calculate the equivalent stress intensity factor(SIF)amplitude influence and determine the most unfavorable loading position of each crack,model updating methods are adopted to simulate the fatigue crack propagation process,to calculate the stress intensity factor,in view of the influence of bridge system parameters(crack length,thickness of deck,U-rib and diaphragm plate thickness)parameter analysis.The parameters with greater sensitivity were selected,and the response surface mathematical model of the equivalent stress intensity factor(SIF)amplitude was established by using the Regress function optimization and fitting in MATLAB software.(3)The vehicle flow of a cable-stayed bridge in China was statistically analyzed to obtain the total vehicle flow,the proportion of each vehicle type,the total redistribution of vehicles,and the proportion of each axle weight of each vehicle type in the total weight.Combined with Paris formula,all the axle loads were converted into standard axle loads specified in the code,and the times of action of one-way standard axle loads in each year were calculated for the purpose of fatigue life calculation.In view of the influence and harm analysis of deck crack penetration,three kinds of failure principle were defined and analyzed as long crack leads to poor driving comfort,continuous expansion leads to excessive crack growth rate,and further expansion leads to bridge deck pavement cracking.For the first principle,the power spectrum density function of deck roughness was used to simulate and calculate the vehicle’s dynamic amplification factor(DAF)and vertical deflection of bridge under different bridge condition.The crack length corresponding to the local large vertical deflection was taken as the limit of fatigue crack propagation,and the fatigue life was calculated by combining the stress intensity factor(SIF)response surface function equation.For the second principle,the equivalent stress intensity factor(SIF)amplitude curve was fitted to obtain the fastest expansion rate point,and the fatigue life was obtained by integrating the response surface function equation.For the third principle,considering the mechanical property degradation of bridge deck pavement(SMA asphalt mixture)under high temperature and heavy load,the crack length at the moment when the pavement reached the ultimate tensile strain failure was taken as the length limit.The fatigue life of the initial crack was calculated by response surface function equation,and the fatigue life of the initial crack was studied under three principles.Finally,the life of a real bridge with distributed cracks was evaluated under multiple failure principles.The research results could provide some technical support and theoretical basis for the choice of reinforcement time.