Study On Mechanical Analysis In Construction Of Long Span Steel Truss Bridge By Means Of Ultra-high Pier

With the rapid development of railway transportation in China,steel truss bridges are widely used in the construction of high-speed railway bridges.In the process of long-span high-speed railway bridge erection,there is a long-distance cantilever erection stage.In order to reduce the bending moment caused by the construction of large cantilever girder,temporary support measures are usually taken as system transformation in the construction stage.Lattice super high buttress is widely used in temporary structure system because of its strong adaptability,simple construction,engineering economy and other advantages.In the erection stage,the lattice super high buttress bears heavy loads from the wind and bridge.The mechanical analysis of the structure system composed of the lattice super high buttress and the steel truss bridge is generally regarded as the key technology in the cantilever erection process of the high-speed railway bridge.Therefore,it has important theoretical significance and engineering application value for the mechanical analysis and research of high buttresses in the design and construction of long-span steel truss bridge.In this thesis,the research status of mechanical properties of long-span steel truss bridge in the construction process with the help of high buttresses at home and abroad is analyzed and summarized.Based on construction background of Yuanjiang super large bridge in Yunnan Province of China,the mechanical analysis strategies and structural reinforcement of large-span steel truss bridge and lattice high buttresses are studied.The main research work and achievements are as follows:(1)In the process of cantilever erection of long-span steel truss bridge,an effective mechanical model is proposed to simulate the nonlinear contact of the high buttress and cantilever truss bridge.Then it is used to establish the mechanical model of the whole system of high buttress and steel truss beam.After the iterative trial calculation and feedback adjustment of the whole model under various working conditions by the finite element method,the reaction forces and the stress distributions of the lattice super high buttress and the steel truss beam in each construction stage are obtained.Through the finite element analysis of the pier and beam system model,it is concluded that the influence of environment temperature should be fully considered when the lattice super high buttress and steel truss beam work begin to contact.It is concluded that with the increase of cantilever length of steel truss,the influence oftemperature difference on the ratio of reaction force and maximum stress of steel truss is decreasing,while the proportion of weight of steel truss is dominant.(2)The multi-scale mechanical analysis method of information transmission is used to analyze the stress states of the key nodes connecting the steel truss and the high buttress under the most unfavorable construction conditions during the cantilever erection.A reasonable mechanical model for local analysis of key joint structure is established.The stress distribution of the joint is obtained by using shell elements of finite element method(FEM).A feasible reinforcement construction scheme is put forward for the local reinforcement of the joint structure which is easy to produce stress concentration beyond the limit.Using multi-scale mechanical numerical simulation,the key joints in the process of cantilever erection of steel truss under dangerous working conditions are analyzed.The evaluation of the local stress strength and construction safety of joints is given,which provides technical support and theoretical basis for the construction method of cantilever erection of large-span structure.The results show that the multi-scale mechanical analysis strategy of the key joint can obtain the local stress field distribution of the complex structure.Considering the bearing beam on the top of super high buttress as the object,the mechanical model of steel truss beam bridge,bearing beam and high buttress is established firstly with three dimensional beam elements.Then the mechanical model for the bearing beam subjected to the most unfavorable loads is established with the shell and solid composite elements.The mechanical analysis and reinforcement design of the bearing beam structure are carried out by using FEM.Under the reasonable structural design,the arrangement of the three-layer bearing beams and the corresponding reinforcement scheme are proposed,which can significantly reduce the unfavorable effect for the bearing beam during the cantilever erection of the steel truss bridge.In the thesis,the mechanical analysis of the cooperative work process between the cantilever erection of long-span steel truss bridge and the super high pier structure is carried out,which provides a theoretical support for ensuring the construction safety and quality of the bridge.The mechanical analytical strategies and results can also be used as reference for similar large-scale engineering construction.