Evaluation And Comparison Of Fatigue Structure Details Of Welded Joints Of Steel Truss Bridge Based On Hot Spot Stress Method

With the maturity of welding technology,the use of integral welded joints in steel truss bridges will further reduce the amount of on-site work,improve the quality of erection and installation,speed up the construction progress,and meet the current demand for rapid bridge construction.At present,Yangsigang Yangtze River Bridge,Sanguantang Bridge and Pingtan Strait Bridge approach bridges all adopt integral welded joints.All components of the integral welded joint are connected by welding.Large residual stress and stress concentration will be generated at the welded joints,which makes the fatigue problem obvious.Nowadays,the nominal stress method is often used to evaluate the fatigue performance of the structure,which can not reflect the influence of the change of joint geometric parameters on its fatigue performance,and often makes the evaluation result conservative.Therefore,in this paper,the hot spot stress method is used to study the fatigue problem of integral welded joints.The following aspects are mainly carried out in this paper and relevant conclusions are obtained:(1)Summarize and sort out the research results of hot spot stress method in welded steel bridges,give the fatigue calculation flow of welded joints of steel truss bridges,and study the SCF finite element simulation method of linear extrapolation method suggested by IIW.Aiming at the typical structural details in the integral welded joint,the hot spot stress re-analysis of the existing fatigue test data is carried out by numerical simulation,and the S-N curve of hot spot stress fatigue strength corresponding to the structural details is put forward.(2)The parameters of KT-type and K-type integral welded joints commonly used in steel truss bridges are analyzed,and the variation laws of SCF with parameters θ,τ and h/r are obtained.The SCF finite element calculation results under various basic load conditions are regressed,and the SCF parameter calculation formulas for KT-type and K-type integral joints under corresponding basic load conditions are put forward.(3)The whole bridge 3D finite element model is established to evaluate and optimize the fatigue performance of integral welded joints of a 4×50m deck composite truss bridge.The process and difference of joint fatigue calculation between 3D multi-scale finite element model and spatial bar system finite element model are given.Furthermore,the influence of optimization measures,such as filling concrete in chord,setting PBL and increasing arc transition radius,on SCF of various structural details of joints is analyzed.(4)The fatigue performance of welded joints commonly used in steel truss bridges is compared.The results show that the uneven stiffness distribution at the weld joints of intersecting welded pipe joints can be effectively alleviated by filling concrete in chords,and the fatigue resistance of intersecting welded pipe joints can be significantly improved.By analyzing the endurance cycle times of various welded joints under fatigue load model,the order of fatigue performance of welded joints is determined as follows: integral welded joints filled with concrete in chord,integral welded joints,PBL stiffened rectangular concrete-filled steel tubular joints,rectangular concrete-filled steel tubular joints,circular concrete-filled steel tubular joints,circular steel tubular joints,rectangular steel tubular joints,concrete-filled steel tubular joints with principal branches,circular steel tubular joints with principal branches.