Research On Fatigue Load Model And Fatigue Performance Evaluation Method Of Steel Bridge Based On WIM Data

The steel bridge is one of important types of long-span bridges because of its excellent features such as light weight and convenient construction.Generally,the orthotropic steel deck is employed as the deck of steel bridges.The orthotropic steel deck suffers from frequent traffic loading.Furthermore,the stiffness of the orthotropic steel deck in the two orthogonal directions has much difference.As a result,its mechanism under traffic loading is very complex;and traffic-induced fatigue cracks may easily occur in weld joints.At present,the fatigue cracks in orthotropic steel decks have been reported all over the world,which draws great attention of researchers.Therefore,it becomes significant to study the damage accumulation properties of orthotropic steel decks and developing effectiveness fatigue reliability assessment methods for orthotropic steel decks.This paper focuses on the assessment of fatigue damages in orthotropic steel decks.By using the field testing data,long-term monitoring data and numerical simulation,characteristics of vehicle loading on roads with different levels in the Zhejiang Province is investigated.Moreover,the numerical approach is proposed for simulating the hot spot stress in orthotropic steel decks.Finally,fatigue reliability assessment methods for orthotropic steel decks are developed based on long-term monitoring stress data and field testing vehicle loading parameters.The main work in this paper is listed as follows.(1)The statistical models of vehicle loading parameters and standard fatigue cars for roads with different levels in the Zhejiang Province are studied.Based on long-term monitoring traffic data recorded by weight-in-motion systems in different roads,including highway,first class highway,second class highway and urban arterial road,the composition of traffic flows on roads with different levels is investigated.And then,the timc-dependence characteristic of traffic flows is discussed.The transversal distribution of vehicles on roads with different levels is discussed.Thirdly,the statistical models for speed on all lanes,speed in different lanes,axis weight,total weight and total weight of vehicles with different axes are established.Fourthly,the standard fatigue cars recommended in different bridge design specification in different countries are compared.Subsequently,the standard fatigue cars for roads with different levels in the Zhejiang Province are proposed.Finally,the influence of vehicle parameters on fatigue damages in orthotropic steel decks is discussed.The results indicate that the proposed statistical models can describe the random features of traffic flow parameters very well.The fatigue damages induced by the standard fatigue cars recommended in different bridge design specification have much difference.It is difficult to describe the traffic flow on roads with different levels by using a uniform standard fatigue car.(2)The features of hot spot stress induced by vehicles on orthotropic steel decks and the numerical method for hot spot stress simulation are studied.The field tests of hot spot stress on orthotropic steel decks induced by static vehicles located on different locations and dynamic vehicles with different speeds and different pavement roughness are performed.The properties of hot spot stress induced by vehicle loading are analyzed.The statistical model of the impact factor and the relationship between the impact factor and the vehicle speed are established.The influence range of stress induced by vehicle loading on orthotropic steel decks and the region of the finite element model are proposed.The influence of physical parameters of pavement layer and the dimension of wheel loading on stress in weld joints are discussed.The model updating method for calculating hot spot stress on orthotropic steel decks is developed and verified.The results indicate that the testing impact factor yields to the normal distribution,the mean and variance of which are 1.32 and 0.10,respectively.The impact factor increases with the increasing of vehicle speed.The proposed finite element model of orthotropic steel decks can accurately simulate the hot spot stress in weld joints induced by vehicle loading.(3)The reliability assessment methods for orthotropic steel decks based on long-term monitoring stress data and statistical models of field testing vehicle loading are studied.By using long-term monitoring stress data obtained from the orthotropic steel decks of the Jinchang Road Canal Bridge in Hangzhou,the fatigue damages in weld joints are calculated.The statistical features of the hot spot stress spectrum in weld joints are discussed.And the statistical models are proposed.The fatigue reliability of orthotropic steel decks on the Jinchang Road Canal Bridge is evaluated.The influence of the increasing of traffic volume on the fatigue reliability of orthotropic steel decks is investigated.The simulation method of random traffic flows with complex statistical properties is developed.The influence surface of hot spot stress on the orthotropic steel decks is established.The reliability assessment method for orthotropic steel decks using statistical models of field testing vehicle loading is proposed.The results indicate that the fatigue reliability indexes of weld joints on orthotropic steel decks of the Jinchang Road Canal Bridge are greater that 2 under the present traffic conditions.The vechicle-parameter-based method can provide reasonable results of fatigue re-liabilities of weld joints on orthotropic steel decks.