Research On Mechanical Properties Of Main Beam Joints With High Strength Bolts Of Double Deck Four Line Railway Steel Truss Girder Cable Stayed Bridge

In recent years,with the rapid increase of railway traffic flow,steel truss girder cable-stayed bridge can meet the needs of railway heavy haul transportation and navigation at the same time,and has been widely used in Long-span Railway Bridges.Due to the complex stress of steel truss girder joints,bolt falling off,joint plate cracks and other local diseases occur frequently.in order to ensure the normal use of the bridge,the research on the mechanical performance of beam joints connected by high-strength bolt group,including Web member,chord and crossbeam under complex external forces is of great significance.Therefore,based on a double-layer four line railway steel truss cable-stayed bridge,this paper studies the mechanical properties of bolt groups and connecting plates in each connection area of main beam node by theoretical analysis and numerical simulation,and discusses the influence of bolt missing and bolt preload on theirs mechanical properties,which provides reference for the design,maintenance and reinforcement of similar bridges.The main research contents and results are as follows:(1)The spatial finite element model of the whole bridge is established by Midas /Civil software,and the mechanical performance of the main girder under dead load,multi line train live load and design load combination is analyzed.The results show that: under the dead load,the main girder is mainly subjected to axial force and in-plane bending moment,and the maximum combined stress of the main truss member is distributed near the pier;the four line live load is the most unfavorable train live load condition;the main force + lateral additional force is the most unfavorable load combination,and the E48z node of the main girder near P3 main tower is further determined as the most unfavorable node.(2)A solid finite element model of E48z joints with vertical bars,chords and crossbeams connected by 996 friction type high-strength bolts is established by using ABAQUS software,and the nonlinear analysis of local joint model is carried out.The results show that: under the combination of main force + lateral additional force,The equivalent stress of local model of E48z joint appears stress concentration in a small range,but it is less than the yield limit;the deformation displacement of each member is small,and the maximum deformation occurs at the truncation of the member;and the bolts in each connection area have the phenomenon of increasing or decreasing the preload,which is similar to "over tightening" and "under tightening",but in the normal range Within the allowable range,that should be paid more attention in the construction and tightened pertinently.(3)Through the ABAQUS modeling analysis of specimen 1 in the reference,and comparing with the experimental and calculated values in the literature,the paper summarizes the bolt force transfer ratio,the stress size and distribution of splicing plates and core plates under the action of axial force;and the paper analyzes the bolt force transfer ratio,the stress size and distribution of connecting plates of E48z joint local model in each bolt connection area under the combined action of various external forces and compares them with the former.The results show that the distributions of bolt force transfer ratio,axial stress,contact surface compressive stress and friction stress in each connection area of E48z joint are not exactly the same as those in specimen 1 under axial force.(4)On the basis of numerical analysis,the influences of bolts missing and bolt over or under tightening on the bolt force transfer ratio and the stress of connecting plates of E48z joint are discussed.The results show that the bolt missing and over or under tightening in each area have little influence on other areas,and have obvious influence on bolt force transmission and plate stress in this connection area,but the influence range of bolt is local.