【作者】 余天和；

【导师】 时旭东；

【作者基本信息】 清华大学 ， 土木工程， 2009， 硕士

【摘要】 我国许多古建城台已有数百年历史,在自然及人为因素等作用下,其结构性能和建筑材料的性质均已发生较大变化。城台砌体上出现裂缝,有些城台甚至发生局部破损或倒塌。为了对城台进行保护,需要通过变形监测判断其安全性。本文以故宫午门城台为例,通过有限元软件MARC建立三维接触模型,并在力学分析中考虑它的徐变效应,对午门城台现有损伤产生的原因进行分析,为变形测量方法判断城台的安全性能提供依据。基于相关资料所提供的数据,偏于安全地确定了城台材料的力学性能和砖砌体厚度;并通过城台表观观测,分析了裂缝分布现状,结合多年变形观测结果判定城台目前仍处于稳定状态。针对当前对城台结构的计算多采用非接触模型的现状,本文讨论了砖土接触关系对砖砌体侧移模式、砖砌体最大侧移位置和内力分布的影响,结果表明对城台结构的力学分析必须考虑接触的影响。本文采用接触模型,首先计算分析城台上新建午门展厅对城台位移和应力的影响,表明新建展厅后城台是安全的;然后对影响城台的重要因素如砖砌体抗拉强度、砖土摩擦系数和内填土含水量等进行了计算分析。结果表明当前裂缝主要是由砖砌体抗拉强度的降低和内填土含水量增大造成的。为确保城台安全,必须防止雨雪水渗入城台内填土中。由于午门城台遭受长期持续荷载的作用,其力学分析需考虑其结构材料徐变的影响。通过稳定徐变阶段的计算确定了位移增量最大的测点位置,并给出了徐变引起的内力重分布和裂缝发展情况,表明对古建城台的安全性能评估应考虑徐变的影响。为了通过城台变形监测来判断城台的稳定性,本文对城台材料处于加速徐变阶段的城台安全性能进行了分析,给出了各测点的相对变形发展情况,同时对影响测量结果的其他长短期因素进行了分析,从而可靠地获得城台徐变值,并据此判断城台是否进入加速徐变阶段。此方法可用于类似城台结构的长期安全性能评估。更多还原

【Abstract】 Most ancient platforms in China have a history for hundreds of years. Influenced by those factors such as natural action, human activity, and so on, all ancient platforms generally experienced great changes in the mechanical properties of their structural members and materials. Some ancient platforms have cracks in the brick masonry and even have been partly damaged or broken down. For protecting these platforms, it is necessary to determine their safety status by means of deformation monitoring method. The Wumen Platform in Forbidden City as an example in this thesis, by setting up its 3D contacting modal using FEA software MARC and taking a consideration for its creep efficiency, a judging basis for the platform safety state by deformation monitoring method is provided through analyzing its existing damage causes.Based on relative statistic data, the material mechanical properties of the platform and its brick masonry thickness are determined. Through the macroscopical and external observation for the platform damage and subsequently analyzing for the present crack distribution status with combination of multi-year deformation measuring results, it is shown that the Wumen Platform is still in a steady state.Against the non-contacting modal usually used in analyzing platform structures, the influences of contacting modes between soil and brick masonry on the deformation mode, the maximal lateral displacement location and the stress distribution of the Wumen Platform are discussed. It is shown that the contacting problem should be taken into account in the mechanical performance analysis of platform structures.Adopting the contacting model, the influences of newly-built exhibition hall on the platform on the deformation and stress of the Wumen Platform are firstly analyzed and the results show the platform is still in safety state after the new exhibition hall is built. Then the important factors such as the tensile strength of brick masonry, the friction coefficient between brick masonry and soil, and moisture content of soil are analyzed. It is shown that reducing of the tensile strength of brick masonry and increasing of the moisture content of soil will result in cracking in brick masonry. To make sure of the platform’s safety, some measures for avoiding inleakage of the rain and snow water into platform soil should be given.Because of long-term load action on the Wumen Platform, the creep effect of the platform materials should be taken into account on the platform mechanical analysis. Through calculating analysis in steady creep stage the measuring locations of maximal deformation increment, stress re-distribution and crack development caused by creep are determined. The results show that the creep factor should be taken into account in evaluating the ancient platform’s safety.In order to judge the platform’s stability by deformation monitoring method, the safety properties of the platform in the accelerated creep stage for its materials are analyzed and the relative deformation development status is given. Meanwhile, those long-term and short-term influencing factors on deformation monitoring results are also analyzed. Sequentially the creep value can be reliably obtained and the judge whether the platform has been in accelerated creep stage can be given. This estimation method can be applied to similar platforms for their long-term safety property estimation.更多还原