轨道交通U型梁的截面优化设计

发布时间：2018-07-25 13:10

【摘要】：U型梁是城市轨道交通中最为新颖的一种高架桥桥型,在国内外都得到了越来越多的应用。U型梁是由底板、腹板及横梁等部分组成的一种新型的预应力混凝土桥梁,属于下承式预应力混凝土桥梁,它具有节省投资、外形美观、轨面标高低、施工周期短等特点。U型梁的横截面比较特殊,腹板和底板比较薄,并且截面整体向上开口,导致抗扭刚度与传统梁截面相比较差,传统的U型梁由于受力比较冗杂,制作步骤较多,并且施工过程繁杂等一系列问题,对U型梁更大范围内的使用造成了一定的限制。而且,现阶段U型梁在我国轨道交通中正处于起步阶段,对于U型梁的研究并不多,国内外对于U型梁的截面优化的研究少之又少。为了使U型梁更加经济适用,使U型梁能够在城市轨道交通中得到更好的应用,就要分析U型梁的受力特性,对于U型梁的截面优化设计就显得尤为重要。设计桥梁的最根本要求就是要保证桥梁安全、适用和经济。优化设计能够使材料的性能得到最合理最充分地利用,使单元内部各个单元最好的协调,使各单元具有规范的安全度。同时,优化设计为结构整体性方案设计进行科学合理的决策,它是实现设计安全和经济的最终目标的有效途径。遗传算法是目前采用最广泛的一种进行截面优化的数学方法,它是建立在优胜劣汰生物进化理论和生物遗传学说基础上的一种并行、高效的整体探求方式,具有适用范围广泛,优化结果准确等很多优点。本文以上海某轨道交通中的U型梁桥作为工程背景,采用有限元分析软件MIDAS CIVIL和数学模型计算软件MATLAB,先使用遗传算法对U型梁截面进行优化计算,再使用梁单元法建立模型对不同截面的U型梁的受力性能进行研究对比,得到符合规范并满足受力条件的最优化的截面。主要内容包括:(1)通过分析U型梁的受力特点,来确定具有主要决定作用的截面参数。对于U型梁来说,决定结构受力特性的变量有梁高、腹板厚度尺寸、底板厚度尺寸和预应力配筋面积等,四种不同的截面参数决定了U型梁的截面形状,也对结构受力有不同的影响。(2)运用遗传算法工具箱,从工程自身的实际问题出发,得到数学模型,确定目标函数、设计变量和约束条件。本文中以预应力U型梁的制造成本为目标函数,以正截面强度要求、规范对结构尺寸的限定以及满足施工和使用阶段的应力等要求作为约束条件,分别以U型梁截面的梁高、腹板厚度、底板厚度和预应力配筋面积为设计变量,应用遗传算法对得到的数学模型进行计算最终得到最佳的截面形式。(3)结合以上数据,利用MIDAS CIVIL软件就优化前后的截面构造形式分别用梁单元法建模,对不同参数下的截面进行受力特性的对比计算,通过对比得出最优截面,分析验算优化后得到的截面形式。
[Abstract]:U beam is the most novel viaduct bridge type in urban rail transit. It has been applied more and more at home and abroad. U beam is a new type of prestressed concrete bridge composed of bottom slab, web plate and crossbeam. It has the characteristics of saving investment, beautiful appearance, high and low rail surface, short construction period and so on. The cross section of U-shaped beam is relatively special, the web plate and bottom plate are thin, and the section is open upward as a whole. As a result, the torsional stiffness is worse than that of the traditional beam section, and the traditional U-shaped beam has a series of problems, such as miscellaneous force, more fabrication steps, and complicated construction process, which has limited the use of the U-shaped beam in a wider range. Moreover, at present, the U-beam is in the initial stage in the rail transit of our country, the research of U-beam is not much, and the research of section optimization of U-beam at home and abroad is very few. In order to make the U-beam more economical and applicable and to make the U-beam be better applied in urban rail transit, it is necessary to analyze the mechanical characteristics of the U-beam, which is particularly important for the cross-section optimization design of U-beam. The most basic requirement of bridge design is to ensure bridge safety, applicability and economy. The optimum design can make the best use of the properties of the material, the best coordination of each unit within the unit, and the standard safety degree of each unit. At the same time, the optimal design is an effective way to realize the ultimate goal of design safety and economy by making scientific and reasonable decision for the structural integrity scheme design. Genetic algorithm (GA) is one of the most widely used mathematical methods for cross-section optimization. It is a parallel and efficient way of searching for the whole, which is based on the theory of evolution of survival of the fittest and the theory of biogenetics, and has a wide range of applications. The optimization results are accurate and so on. In this paper, taking the U-beam bridge in a Shanghai rail transit as the engineering background, the finite element analysis software MIDAS CIVIL and the mathematical model calculation software MATLAB are used to optimize the section of the U-shaped beam by genetic algorithm. Using the beam element method to establish a model to study and compare the behavior of U-shaped beams with different cross-sections, the optimized sections which accord with the specifications and satisfy the stress conditions are obtained. The main contents are as follows: (1) by analyzing the stress characteristics of the U-shaped beam, the parameters of the section are determined. For U-beam, the variables that determine the stress characteristics of the structure are beam height, web thickness, bottom plate thickness and prestressed reinforcement area. Four different cross-section parameters determine the cross-section shape of U-shaped beam. It also has different influence on the structure stress. (2) by using the genetic algorithm toolbox, the mathematical model, the objective function, the design variable and the constraint condition are obtained from the practical problems of the engineering itself. In this paper, the manufacturing cost of prestressed U-beam is taken as the objective function, the strength requirement of normal section is taken as the constraint condition, the restriction of structural size and the stress in construction and use stage are taken as the constraint conditions, and the beam height of the section of U-beam is taken as the constraint condition, respectively. The thickness of web plate, the thickness of bottom slab and the area of prestressed reinforcement are the design variables. The optimum section form is obtained by using genetic algorithm to calculate the mathematical model. (3) combining the above data, By using MIDAS CIVIL software, the cross-section before and after optimization is modeled by the beam element method, and the stress characteristics of the section under different parameters are compared and calculated. The optimum section is obtained by comparison, and the optimized section form is analyzed after checking and calculating.
【学位授予单位】：山东建筑大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U442.5

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