【作者】 葛金刚；

【导师】 丁阳；

【作者基本信息】 天津大学 ， 结构工程， 2012， 博士

【摘要】 单层网壳是空间结构的主要形式之一,一旦遭遇强震发生破坏甚至倒塌,会造成严重的人员伤亡、财产损失和社会影响。目前关于单层网壳倒塌机理的研究未考虑材料的Bauschinger效应、杆件失效及杆件断裂的影响,将高估网壳结构极限承载力。因此,建立考虑材料Bauschinger效应的材料本构模型以及杆件失效、杆件断裂的模拟方法,对单层球面网壳结构倒塌机理及抗倒塌措施进行深入研究,具有重要的理论意义和工程实用价值。本文对单层网壳结构的材料本构模型、杆件失效及杆件断裂模拟方法、单层网壳结构倒塌机理及抗倒塌措施进行了研究,主要完成了以下四个方面的工作。(1)考虑材料的Bauschinger效应,推导了适用于网壳结构常用杆件圆钢管的考虑损伤累积的混合强化增量本构模型,编写了适用于空间梁单元的材料本构程序,通过理论分析及已有试验测试数据对比,验证了所编写程序的正确性;将国际标准化组织建议的适用于圆钢管的杆件失稳判别条件及Marshall提出的杆件失稳后力学模型引入所编写的材料本构程序中,开发了能够同时考虑材料Bauschinger效应、损伤累积、杆件失稳及失稳后性能的计算程序,对简支梁进行拉压滞回性能分析并与已有试验结果进行对比,验证了所开发的计算程序的正确性;对单层球面网壳进行极限承载力分析,结果表明考虑损伤累积对网壳结构极限承载力影响不大,杆件失稳效应将明显降低网壳结构极限承载力。(2)建立了以损伤累积为杆件失效判别准则,以中心差分法为基础,通过修正杆件特性模拟杆件失效的模拟方法;通过与基于瞬时刚度法、瞬时加载法和初始条件法的双杆模型和悬臂梁模型节点位移进行对比分析验证了所建立模拟方法的正确性;通过对单层柱面网壳结构进行地震响应分析,验证了所建立模拟方法在单层网壳结构连续倒塌分析中的适用性;以杆件失效模拟方法为基础,应用分段纤维梁模型对杆件断裂进行模拟,通过对不同长度杆件断裂过程模拟结果的比较分析,确定了纤维梁模型合理的截面纤维划分数量和沿杆件长度单元划分数量;对单层网壳结构倒塌过程中杆件断裂进行模拟,验证了所建立模拟方法可应用于单层网壳结构倒塌过程中杆件断裂的模拟。(3)推导了地震作用下结构的能量平衡关系,并以能量不平衡为结构倒塌判别准则,考虑材料Bauschinger效应、杆件损伤累积、杆件失稳及失稳后性能、杆件失效及杆件断裂的影响,对强震作用下四类单层网壳结构进行倒塌机理研究,总结了四类单层网壳结构的倒塌机理。(4)采用传统设计方法,将单层网壳局部设计为双层提高网壳结构抗倒塌能力;分析了网壳结构局部采用双层前后结构自振特性及失稳杆件位置的变化,分析了局部双层的位置和厚度对网壳结构极限承载力的影响;结果表明,局部双层对结构竖向振动所对应的频率影响较大,采用局部双层后结构失效时失稳杆件位置分散,结构由整体破坏转变为局部破坏。采用在网壳结构中增设粘滞阻尼器提高网壳结构抗倒塌能力,推导了地震作用下粘滞阻尼器耗能公式,提出了以能量比例系数和位移比例系数为评价指标的阻尼器优化布置准则;以单层球面网壳和单层柱面网壳为例,验证了所提出的阻尼器优化布置准则的正确性;以单层球面网壳为例,分析了增设粘滞阻尼器对结构节点位移和极限承载力的影响;结果表明,采用优化布置准则仅需布置少量的粘滞阻尼器,便可大幅提高网壳结构极限承载力,提高网壳结构抗倒塌能力。更多还原

【Abstract】 Single-layer reticulated shell is one of the main forms of space structures. The collapse of structures will result in serious deaths and economic loss. If some factors, like Bauschinger effect of materials, the member failure and fracture, are ignored in research on collapse mechanism of single-layer reticulated shells, the ultimate bearing capacity will be overestimated. Therefore, it is of significant theorial and practical value to study the collapse mechanism and collapse-resistance measurements of single-layer reticulated shells under strong earthquakes, considering Bauschinger effect of materials, the member failure and the member fracture.In this paper, the material constitutive model, the simulation method of member failure and fracture and the collapse mechanism of single-layer reticulated shell have been analyzed. This study contains the following work:(1) A novel elastic-plastic constitutive of circular steel tube is derived from the combined hardening, the cumulative damage, and Bauschinger effect of materials under cyclic loading. Based on the explicit method, a program is compiled to apply the elastic-plastic constitutive to beam elements. The performance characteristics of the circular steel tube are compared to measured results in the field to certify the correctness of theoretical analysis. The comparison shows that the program is accurate at evaluating mechanical behaviors of structures and members. The discrimination criterion of member buckling and the mechanical model of member post-buckling are all employed in the program. The tension and compression performance characteristics of simply supported beam are compared to measured results in the field to certify the correctness of theoretical analysis. The analysis results about a reticulated shell show that ultimate bearing capacity of structure is little affected by cumulative damage, but significantly affected by member buckling.(2) Based on discrimination criterion for component failure defined by the cumulative damage and the central difference method, the member failure is simulated by modifying member characteristics. Dynamic nonlinearity analysis is applied to the cantilever beam, and the node displacements from different simulation methods are compared to certify the correctness of simulation method for member failure. Considering cumulative damage and member buckling, progressive collapse of the single-layer cylindrical reticulated shell under earthquake is analyzed. The analysis results show that the simulation method for member failure can be used in the analysis of progressive collapse of space grid structures. Based on the simulation method for member failure, fiber beams are adopted to simulate member fracture. Comparing the simulations of different length members in fracture process, the reasonable number of fibers in section and elements along the member length is proposed. The member fracture in collapse process of single-layer reticulated shell is analyzed. The results show that, based on modifying member characteristics, fiber beam could be applied in the analysis of cumulative damage and fracture in member section and the collapse process of space grid structures.(3) The relationship of energy equilibrium is derived from dynamic equilibrium equation of structure under earthquake. Based on discrimination criterion for structure collapse defined by energy equilibrium, collapse mechanism of different types of single-Layer reticulated shells under strong earthquakes are analyzed, considering Bauschinger effect, the cumulative damage, member buckling and post-buckling, member failure and fracture. Collapse mechanisms of different types of single-Layer reticulated shells under strong earthquakes are summarized.(4) Partial double-layer reticulated shell is adopted to improve the collapse-resistance capacity. The natural vibration characteristics, the ultimate bearing capacity and the placement of buckling member in partial double-layer reticulated shell are analyzed. The results show that the ultimate bearing capacity of reticulated shell is increased by adopting partial double-layer, with dispersed position of buckling member and local failure of structures. Formula of energy dissipation of viscous damper under earthquake is derived from the central difference method. Energy proportional coefficient and displacement proportional coefficient are proposed to predict the optimize location of dampers in structures. The displacement reduction factors of single-layer spherical reticulated shell and single-layer reticulated cylindrical shell under earthquake are analyzed to certify the correctness of the optimization criterion.更多还原