The Fatigue Research Of Typical Joint To Long-Span Steel Truss Bridge With Rigid Cable

With rapid development of steel truss bridges of dual-purpose for roadway and rail transit,the fatigue behavior of integral joint for the safety of entire bridge became increasingly important.At the integral joint,large stress is exhibited,many members are connected,welds are dense and structures are complex,and fatigue problem is significant.Based on the engineering background of Chongqing Zengjiayan Bridge over Jialingjiang River,this thesis used theoretical analysis,studied the fatigue behavior of the typical integral joint of the long-span steel truss bridge with rigid cable,and rationally designed the integral joint's scale model and test program according to the existing experimental conditions.At first,this thesis introduced the basic theory of fatigue analysis,and explained the equivalent conversion method between variable amplitude cyclic loading and constant amplitude cyclic loading and the calculation rule of discharge counting method.According to "Specifications for Design of Highway Steel Bridges"(JTG D64-2015),"Code for Design of Urban Road Engineering"(CJJ 37-2012),"Railway Design Specification for Chongqing Zengjiayan Jialing River Bridge" and other relevant specifications,combined with the actual conditions of Zengjiayan Bridge,this thesis developed the fatigue load spectrum of dual-purpose bridge for roadway and rail transit.With field inspection of traffic conditions of Yu-Ao Bridge and Niujiaotuo Light Rail Station,this thesis verified that the daily traffic volume of the upper-level highway and the standard fatigue axle weight of the subway used in the process of developing the load spectrum were reasonable.Secondly,based on engineering background of Zengjiayan Bridge,the finite element software Midas Civil was used to establish the entire bridge 3D finite element model,and moving load analyses under the standard fatigue vehicle loading were conducted.According to the principle of member's maximum stress amplitude,the most unfavorable joint of the entire bridge was determined to be B3.According to the specifications for highway and railway steel bridges and foreign specifications,fatigue-check of high-strength bolts connection between gusset plates and members were performed under fatigue load of highway and subway loading.The check results showed that the high-strength bolts connection between gusset plates and members at B3 joint satisfied the specification requirements.Using discharge counting method,statistical processing was performed on the internal force history of axial force for the main truss members at B3 joint.According to Miner's linear damage accumulation theory,determine the equivalent axial force amplitude for fatigue experiment.Finally,in initial design phase of the experimental model,two plans including single-joint model and double-joint model were selected and compared.The advantages and disadvantages of both plans were listed,the limitation of experimental conditions was considered,and the single-joint plan was selected as experimental model for this fatigue test.According to the similarity principle,the 1:2.5 large-scale joint scale test model was reasonably designed,and the vulnerable positions except the test joint were locally strengthened.Fatigue analysis of the test model was performed using numerical simulation in this study.Midas FEA was used to establish the plate element model of the experimental model,and to simulate the test load of 2 million cycles.Combining the fatigue test results of the high-strength bolts of the main truss member and the gusset plate at the typical nodes of the real bridge,the fatigue resistance of the typical joints was evaluated based on the calculated fatigue life and damage degree of the test joint except for the high-strengh bolted connection parts.The calculation results showed that the fatigue behavior of the Zengjiayan Bridge typical joint met the design requirements.