应用相对刚度相似法优化大型塔内桁架梁结构

发布时间：2018-06-19 22:15

本文选题：桁架梁 + 相对刚度相似法　；参考：《天津大学》2013年硕士论文

【摘要】：桁架梁是桥梁、建筑中广泛应用的一种结构，随着石油化工行业中塔的大型化发展，桁架梁以其优良的抗弯性能和较强的变形协调能力作为大型塔内件支撑结构被引进这一行业。但是桁架梁的基本尺寸都是靠经验给出，有时会出现应力分布不合理的现象。此外，支撑结构的力学特性又直接影响着填料床层和液体分布器中液体的均匀分布性。因此，优化桁架梁的结构，改善其应力分布规律，提高其抗弯刚度，实现其具体力学行为的可描述性已成为亟待研究的课题。本论文利用ANSYS有限元优化模块，从截面组合形式、桁架梁高度以及腹杆对数三方面对跨度为11000mm的桁架梁进行了优化设计及局部补强；而有限元模拟结果不能详细描述桁架梁在塔中的具体力学行为，本文针对桁架梁的结构特点，在刚度相似法的基础上，借鉴桥梁和建筑行业的相似结构设计理念，提出“相对刚度相似”模型试验法，对改进桁架梁进行了缩小模型试验，探索了桁架梁在大型塔中理论分析加异材缩微实验用于确定最优桁架结构的方法，得到了沿跨度方向的应变、应力分布规律，失效力学机制并明确了缺陷对桁架梁力学性能的影响。由于桁架梁是薄壁结构，且焊接点较多。因此，试验模型采用制作方便、价格低廉的有机玻璃作为其材料，能够有效降低由于缩小尺寸焊接对试验结果造成的影响，然后按照“相对刚度”相似原理制作了有机玻璃试验模型。通过对模型施加逐级增加的均布载荷，得出桁架梁在塔内的沿跨度方向应变分布均匀，，但跨中和四分之一段对载荷的变化较敏感，且四分之一段焊接处首先局部断裂破坏。比较各测点的试验应变值与模拟值发现，两者吻合性较好，验证了有限元模型的正确性。同时考虑到桁架梁腹杆与连接板处易产生缝隙、气泡等缺陷，本文还对四种缺陷下的桁架梁进行了研究，得出敏感区域的缺陷对桁架梁的力学性能影响较大，而不敏感区域的缺陷则影响不大，并且强调桁架梁的四分之一段的焊接点需加强检测和提高焊接工艺。为进一步验证“相对刚度相似法”的可行性，本文采用此方法对大型填料塔中由格栅、主桁架梁、辅桁架梁组成的桁架梁体系进行了缩小模型试验研究。试验结果与ANSYS数值模拟结果吻合性较好，得出“相对刚度相似法”在大型薄壁结构缩小模型试验中的可推广性。
[Abstract]:Truss beam is a kind of structure widely used in bridge and building. With the development of tower in petrochemical industry, Truss beam is introduced into this industry because of its excellent flexural performance and strong deformation coordination ability as the support structure of large tower internals. However, the basic dimensions of truss beam are all given by experience, and sometimes the distribution of stress is unreasonable. In addition, the mechanical properties of the supporting structure directly affect the uniform distribution of liquids in the packed bed and liquid distributor. Therefore, optimizing the structure of truss beam, improving its stress distribution, increasing its flexural stiffness and realizing the description of its concrete mechanical behavior has become an urgent task to be studied. In this paper, the optimization design and local reinforcement of truss beam with span of 11000mm are carried out from three aspects: cross section combination form, height of truss beam and logarithm of web bar by using ANSYS finite element optimization module. But the finite element simulation results can not describe the concrete mechanical behavior of truss beam in the tower in detail. According to the structural characteristics of the truss beam, this paper draws lessons from the similar structural design idea of the bridge and the construction industry on the basis of the stiffness similarity method. The "relative stiffness similarity" model test method is put forward, and the reduced model test of the improved truss beam is carried out, and the method of determining the optimal truss structure by the theoretical analysis of truss beam in large tower and the microform experiment of different materials is explored. The strain and stress distribution along the span direction, the failure mechanics mechanism and the influence of defects on the mechanical properties of truss beams are obtained. Because truss beam is thin-walled structure, and welding joint is more. Therefore, the test model can effectively reduce the effect of reducing the size of welding on the test results by using organic glass as its material, which is easy to make and low in price. Then according to the similarity principle of relative stiffness, the test model of plexiglass is made. The strain distribution of the truss beam along the span direction of the tower is uniform by applying a gradual increase of uniform load to the model, but the span and 1/4 section are sensitive to the change of load, and the local fracture at the welding site of section 1/4 is firstly broken. By comparing the experimental strain values with the simulated values, it is found that the two are in good agreement with each other, which verifies the correctness of the finite element model. At the same time, considering the cracks and bubbles in the web of truss beam and the connecting plate, this paper also studies the truss beam under four kinds of defects, and draws the conclusion that the defects in the sensitive region have great influence on the mechanical properties of the truss beam. But the defect of insensitive area has little influence, and it is emphasized that the welding joint of 1/4 section of truss beam should be strengthened and the welding process should be improved. In order to further verify the feasibility of "relative stiffness similarity method", this paper uses this method to study the reduction model of truss beam system in large packed tower consisting of grid, main truss beam and auxiliary truss beam. The experimental results are in good agreement with the results of ANSYS numerical simulation, and the extensibility of the "relative stiffness similarity method" in the large-scale thin-walled structure reduction model test is obtained.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU323.4

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