Study On The Fatigue Property Of Orthotropic Steel Deck Weld Of Highway And Railway Bridge

Orthotropic steel deck is composed of deck,longitudinal rib,diaphragm and stiffening rib.It has the advantages of light weight,high strength and beautiful appearance,so it is widely used in the bridge deck structure of long-span bridges.Because there are many welds on orthotropic steel bridge deck,under the action of wheel load,fatigue cracks are easy to occur at the weld position,so it is of great theoretical significance and engineering value to study the fatigue life at the weld position for the maintenance and reinforcement of orthotropic steel bridge deck.In this paper,based on the maintenance and reconstruction project of Nanjing Yangtze River Bridge,the orthotropic steel deck local model is established by your ABAQUS finite element software.Firstly,through static analysis,the most unfavorable transverse and longitudinal load position is obtained,and the change of fatigue stress at the position of concern under the action of single wheel load is explored.Secondly,based on the elastic-plastic analysis theory,the thermal mechanical coupling analysis of 1 / 2U rib finite element model is carried out By compiling dflux subroutine,the distribution of temperature field and stress field in the welding process and after cooling are obtained.Then,the coupling analysis of residual stress and vehicle load is carried out according to the simplified model of stress superposition,and the distribution of fatigue stress at the weld considering the residual stress is obtained.Finally,the classification of fatigue grade of welding structure in the codes of various countries is compared,Select the appropriate fatigue S-N curve,establish the fatigue load and load spectrum according to the actual traffic volume,use Miner linear cumulative damage criterion to calculate the daily damage degree to get the fatigue life of the typical weld position,and compare the influence degree of residual stress on the fatigue life of the weld position.The main contents and conclusions are as follows:(1)The most disadvantageous load position in RD area is directly above the U-rib web in the midspan,and the most disadvantageous load position in RDF and RF area is directly above the position of concern 30 cm away from the diaphragm.The fatigue control stress in RD area is the third principal stress.The closer to the weld toe,the faster the growth rate of the third principal stress is,and the third principal stress value outside 0.5t away from the weld toe changes approximately linearly and decreases gradually.The fatigue control stress in RDF and RF area is the first principal stress,and the closer to the weld toe,the faster the growth rate of the stress is,and the stress starts to show linearity at 0.4t away from the weld toe Distribution.(2)Compared with Gaussian distribution heat source model and heat generation rate heat source model,double ellipsoid heat source model is more suitable to simulate the welding process of orthotropic steel bridge deck.In the process of double ellipsoid heat source moving,the weld area is only partially heated,and the temperature in the front hemisphere of the heat source is significantly higher than that in the back.The central temperature of the heat source increases sharply and exceeds the melting point of the welding material.After welding,it is cooled to room temperature to form a quasi steady temperature field.When the cooling time is set to 5000 S,the difference between the weld temperature and the ambient temperature is about 0.01 ?.The weld pool shape obtained by the heat source model is basically consistent with the actual welding shape.(3)The stress in the molten pool area is almost 0.When the U-rib is welded with the bridge deck,the residual stress within 50 mm from the heat source center changes greatly.The maximum residual stress value is 511 MPa.When passing through the RDF area,the residual stress in the RDF area is stable at about 365 MPa after sudden cooling,which is very close to the yield strength of the steel.During the use process,local plasticization is very easy to occur.In the thickness direction of the bridge deck,the transverse residual stress decreases first and then increases,the center of the bridge deck is mainly compressive stress,the upper and lower surfaces are mainly tensile stress,the maximum residual stress at the weld toe is 120 MPa,the maximum residual stress at the weld root is 175Mpa;the residual stress in the thickness direction of the U-rib increases first and then decreases.Under the wheel load,the residual stress in the weld area will be redistributed and local plasticizing area will appear,and the plasticizing range will increase with the increase of wheel load.(4)The residual stress has a great influence on the fatigue life state.The fatigue life of RD weld area is reduced by 62%,that of RDF weld area is reduced by 69%,and that of RF weld area is changed from infinite fatigue life to finite fatigue life.The influence of residual stress on fatigue life can not be ignored.