Study On Selecting Methods About Limited Clearance Railway Bridge Across The Existing Line Construction Program

In recent years, with the expansion of railway construction and road network encryption, the new railway line with the existing railway lines crossing each other are growing, while urban spaces is also getting smaller and smaller. These factors contribute to a class of design headroom limited overpass bridge which have low beam bottom elevation and close to the catenary. Railway bridge across the existing line construction is one of the most difficult projects, especially the limited headroom railway bridge across the existing line. Under the limited headroom, the traditional method of bracket is infeasible because of safety and the impact on the existing line. It is a very important issue that how to choose a scientific and rational beam construction program to ensure optimal engineering solutions. At this stage this issue is lying in front of the engineering staffs.Construction scheme optimization of limited headroom railway bridge across the existing line is a multiple attribute decision making problems. Due to bigger traffic density, more skylight time limitation, and many factors such as time, cost, safety, optimization of construction scheme must be based on the thinking of system, considering project complex contact between external and internal, reflecting a certain practicality. The realization of the optimization needs to be under the guidance of system theory through the analysis, modeling, reasoning and judgment process, etc. This paper makes an in-depth theoretical study on construction scheme optimization method about limited headroom Railway Bridge across the existing line. Firstly, this paper analyses the research status at home and abroad in the field, as well as the achievements and deficiencies and put forward the research ideas and methods. Secondly, this paper analyses the related concept of the railway bridge crossing line and railway boundary, discusses related characteristics about construction of limited headroom railway bridge across the existing line, find out the factors that influence the selection based on the analysis of mechanism influencing plan optimization, and establish the optimization evaluation index according to the construction characteristics and principle of selection evaluation index, calculates the degree of cause and the degree of center of various factors through "Decision Making and Trial Evaluation Laboratory" to find out the key factors and to determine its weight in the system. Optimization model is established to evaluate construction scheme comprehensively applying the matter-element model. Then a practical case, Zhegan railway across existing Jianhang railway line construction project, is evaluated to ensure its optimization level. The last part is the summary and outlook. The research results of construction scheme optimization about limited clearance railway bridge across the existing line were reviewed, and objective evaluation is given.