The Structure Mechanical Analysis And Size Optimization Design Of The Urban Underpass Type Interchange Double Positions Frame Culvert

With the urbanization level continuously improving, the urban traffic congestionphenomenon becomes increasingly evident. In order to relieve the urban traffic congestion,widening the traffic line width and building the rail transport are used as a whole. In addition,building the underpass type interchange on the local to solve the important intersection trafficcongestion, making the straight vehicle go along the underpass type interchange to avoid thetraffic lights, these will keep the urban trunk road smooth. The underpass type interchangesare generally built under the urban trunk road where the traffic flow is intensive. So as torelieving the influence brought from the construction to the urban traffic, the constructionduration should be shortened as far as possible when building the underpass type interchange.On the background of practical engineer in this paper, the technology of underpass typeinterchanges construction is foundation open cutting and major structure prefabricatedassembling. The foundation project and the major project are constructed at the same time toachieving the purpose of shortening the construction duration.In this paper, the finite element analysis method is used to study the embedment depthand cross-section component sizes of the frame culvert structure. Whether the building finiteelement model method is correct or not, the static loading test and modal test of the largeproportion model certificate its correctness. On the base of correct modeling method, theembedment depth and cross-section component sizes of the frame culvert structure are studiedby parameters analysis. And then, the best embedment depth and the most optimalcross-section component sizes under the condition of the best embedment depth are obtained.Finally, the underpass type interchange sizes, which are reasonable force and material saving,appear. The main tasks and conclusions in this paper are following:1）According to looking up lots of literature, understanding the development andachievements on tunnel engineering domestic and foreign, mastering relative constructiontechnologies, the theoretical bases are provided in this paper. Furthermore, this paper alsointroduces the construction technology of the practical engineer, the main research content,the research technique route and the research purpose.2）On the basis of similar principles, the frame culvert structure experimental model,whose ratio is1:4, is made. After completing the model, the static loading test and modal testis done. In the static loading test, the dial indicators and the silicone strain gauges are used tomeasure the displacement and the strain respectively of the control section under the differentconditions. While the acceleration sensors are used to measure the natural vibration frequency of the frame culvert structure. The measured data is analyzed and compared with thetheoretical data of the finite element model.3）The three-dimensional model of frame culvert is built by using finite element analysissoftware, where the solid unit is used to simulate concrete material and steel plate that locatesat the upper and lower connections, while the spring unit is used to simulate contact betweenframe culvert and foundation. The concentrated loads are exerted to the nodes of finiteelement model, which are relative to the measuring points of experimental model. Calculatingand extracting the displacement and stress at the measuring points of the finite element model,these are compared with those relative to the experimental model to certificate the correctionof modeling.4）Under the condition of certificating the correction of modeling, the finite elementmodel is expanded to the practical size of frame culvert in engineer. The longitudinal length isdefined as the unit length. Besides the external loads are exchanged to uniform load, the unitsand boundary conditions of finite element model keep changeless. Keeping the sizes of frameculvert cross-section changeless, the variation law of control section force is studied under thecondition that the earth pressure and vehicle load is exerted to the frame culvert. And then, thebest embedment depth is obtained for some cross-section. Furthermore, keeping the frameculvert embedment depth changeless, each member size of frame culvert is studied to analysisthe influence for the frame culvert to obtain the cross-section after optimization.5）In the parameter analysis, using single parametric variable analyze the bestembedment depth and the most optimal cross-section component sizes under the condition ofstructure safety. In addition, the two types of cross-section that before and after optimizationare compared and the conclusion shows that the material consumption of them is identical,but the mechanical performance of frame culvert after optimization is significantly proved.Therefore, if keeping the mechanical performance changeless between before and afteroptimization, the material consumption after optimization will be more economy.