【作者】 王雪亮；

【导师】 瞿伟廉；

【作者基本信息】 武汉理工大学 ， 结构工程， 2008， 博士

【摘要】 我国的历史建筑木结构在设计、建造等方面具有明显的独特性,是我国建筑史上珍贵的历史文化遗产,具有极高的历史、文化和艺术价值。但是由于数百年的风化及自然界生物(包括昆虫和微生物)的侵害,存在不同程度的腐朽虫蛀和干裂现象,许多建筑严重破损,甚至消失。因此,研究古木结构的抗力衰减规律,即研究木材腐朽、虫蛀、干缩裂缝和持续荷载效应的时变规律、突发事件对古木结构的抗力的影响程度、古木结构的抗力衰减的数学模型,对历史建筑木结构的寿命延续具有重要指导意义。本文以影响历史建筑木结构剩余寿命的各种因素为出发点,系统研究了各个因素的影响机理、数学模型和木构件多因子抗力随机时变模型,以及历史建筑木结构的剩余寿命预测等问题。本文在已有的木构件持续荷载效应的强度损伤累积模型的基础上,通过考虑年温湿度变化的影响,对木材短期损伤累积模型进行了改进,得到可以进行长期强度预测的损伤累积模型;并对损伤累积模型进行积分修正,得到考虑持续荷载效应的木构件长期强度衰减模型,使其与剩余寿命预测的抗力理论相一致。在总结已有的研究成果的基础上,将澳大利亚Leicester R.H等人提出的虫蛀木构件的四阶段随机模型进行了修正,转换为基于抗力理论的两阶段模型;根据虫蛀特点,提出了以虫蛀面积损伤变量衡量虫蛀的严重程度,并根据试验和调查统计结果给出了虫蛀面积损伤变量的变化规律;推导了虫蛀木构件的抗力衰减模型,为历史建筑木结构的现状评价和剩余寿命预测奠定了基础。针对木构件在结构中的不同部位和受力特点,提出了根据腐朽等级考虑腐朽引起的材料强度衰减和有效截面损失的方法。然后据此推导了各类构件的腐朽抗力衰减模型,采用国内经验公式推导了抗弯腐朽木梁和地面上木柱的随机时变抗力模型;采用澳大利亚的地下木材的腐朽深度—时间模型,推导了初始抗力为正态分布的随机变量的墙内木柱的随机时变抗压承载力模型,并采用该模型对某历史结构的木梁进行了剩余寿命预测。根据木材气干过程中木材含水率变化和裂缝开展的试验数据,建立了裂缝深度与含水率、裂缝深度与时间的拟合曲线,并通过有限元方法模拟分析单双面裂缝对构件抗力的影响程度,裂缝相对深度与构件抗力之间的关系;从而得到干缩裂缝对木构件长期抗力影响的数学模型。综合以上各个单因子抗力衰减模型,并假定虫蛀、腐朽、长期荷载效应和干缩裂缝为相互独立的随机变量,应用随机理论,得到了木构件在这些因素的共同作用下的多因子抗力衰减模型。为了考虑服役历史木结构本身所具有的抗力变化的历史信息对未来抗力发展的影响,本文采用Bayesian方法,用实测数据对已建立的抗力影响因子的随机时变模型进行了修正。编制了历史建筑木结构的剩余寿命预测程序,该程序应用有限元方法计算结构中构件的应力水平,用MATLAB软件计算构件抗力衰减模型,两者结合实现对结构的剩余寿命预测,最后分别对某历史建筑木桁架、某殿堂式木结构进行了剩余寿命预测,验证了该程序的可行性。总之,本课题的研究突破以往对历史建筑木结构维护的经验方法,为历史建筑木结构的长期维护和维修加固提供了一种更为科学的预测手段。应用这种方法,可以更科学地确定历史建筑定期维护的时间,经济合理地延长历史建筑的寿命,具有可持续发展的战略意义。更多还原

【Abstract】 Ancient timber structures in China,unique in design and construction,have great historic,cultural and artistic value.However because of hundreds years of material degradation and natural biological attack,many timber structures have been damaged, some even vanished.Therefore it is very important to prolong the service life of these historic timber structures by studying the rule of resistance degradation,i.e.,the time-dependent models of the timber decay,termite attack,duration of load(DOL) and dry shrinkage crack.Based on the factors which affect the structure’s service-life, the mechanics,quantitative model,time-dependent multi-factor resistance degradation model of the timber and the residual service-life prediction of the structures are studied in this paper.Considering the hygrothermal effects on load-duration behavior,the cumulative damage model for DOL in short time is improved to that for predicting long-time strength.Then the model is integrated and modified to the long-time strength degradation model to be consistent with the resistance theory.The random model for termite attack,composed of four stages,proposed by Leicester R.H etc.in Australia,is modified to two-stage model according to the resistance theory.And the time-dependent function of the damage variable of erosion area,defined to describe the erosion degree,is suggested based on the in-site tests and survey of termite damage.Finally the time-dependent resistance model of the timber member attacked by termite is deducedBecause of different location and different stress state,the strength decrease varies.The method to determine the strength reduction coefficient according to the decay class is proposed and the loss in geometrical property is calculated by the outside decay depth.Then the time-dependent resistance models of the timber beam and timber column are calculated in which the empirical formula in China is used for above- ground,exposed timber beam and column and the decay depth model for under-ground timber in Australia is adepted the timber embedding wall.Based on the test data about the moisture content and dry shrinkage crack development of air-dry timber,the curve between crack depth and moisture content, and that between crack depth and time are fit.Then the relationship between the crack depth and timber member resistance is analyzed by finite element method. Furthermore the different effect on the member between single crack and double cracks is also compared.Consequently the model of crack’s effect on the resistance of timber member is obtained.The multi-factor resistance degradation model is synthesized by assuming the factors,DOL,termite attack,decay and dry-shrinkage crack are mutually independant random variables.In order to consider that the in-site testing data about historic timber structure has the effect on its future resistance,the Bayesian method is employed to improve the multi-factor resistance degradation model by testing sample.The program to predict the residual life of the historic timber structure is developed,in which stress level is calculated by the FEM and resistance degradation model is realized by MATLAB.Finally a historic timber truss and a beam-column frame are analyzed to predict their residual life,and the effectiveness of the proposed model is verified.In word,breaking through the past empirical method,the research provides a more scientific prediction method for historic timber structure’s maintenance and reinforcement,which can prolong the historic structure’s life because the maintenance period can be determined scientifically and economically.更多还原