损伤古建筑木构架抗震性能退化机理的研究

It is well known that the aseismic performances of Chinese traditional timber structures are excellent. However, the degeneration problems on material behaviour, open fractures,decayed by insects and pythium, partial crush, shear cracks, unrecoverable plastic deformation,weak connections between structural members,and other issues of ancient building timber structures have commonly been arisen as they have been experiencing or bearing various impacts accompanying their long-standing history. These problems led to the degradation of aseismic performances of ancient building timber structures. Based on the characteristics of aged timber, damage and deformation of the components in timber structure building, damaged and undamaged test specimens will be developed under the complex alternating simulating climate environment with some key influencing media and various load conditions. The material models of aged timber will be studied on the basis of the mechanic tests on corresponding timber specimens. The static tests and dynamic tests on the damaged and undamaged specimens of columns, beams, mortise-tenon joints made from timber will be conducted. The load-bearing characteristics and transferring mechanism of the joints, the stiffness and bearing capacity of timber members could be refined on the basis of test data. The basic mechanical properties and degradation degree of joints and timber members could be sorted out by the comparison on the data from the tests of damaged and undamaged specimens. The correlation curve of strength, bearing capacity, stiffness related to the damage degree could be extracted. The finite element model of timber frames would be established. The failure mode, deformation and ultimate bearing capacity of damaged timber frames under the action of earthquake combined with certain load conditions would be analyzed by FEM. The correlation curve on displacement / drift to stress / bearing capacity under a given earthquake action could be concluded. The damage evolving model would be fitted by numerical analysis and corresponding validating test on the deformation, damage, time-sequence and their distribution of timber joints and structure system. The goals of this research proposal could be to provide theoretical foundation, analysis framework, technical parameters and support methodologies on improving the aseismic performances of ancient building timber structure and preventing them from earthquake disaster.

现存古建木构普遍存在碳化、裂缝、蛀蚀、压溃、断裂等损伤问题，导致其结构性能下降，是古建木构抗震性能评价与维护研究的难点。本项目基于古木材与构件损伤和变形特征的调研和评估，通过模拟复杂交变环境与负载工况，研制损伤试验模型；以材料试验为基础，研究古木材性特征与受载变化模型；对非受损和不同种类损伤状态下的柱子、梁枋、榫卯节点进行静动载试验，分析节点在地震作用下的承载特性和传载机制、木构件的刚度和承载力指标；对比分析非受损和损伤节点、构件的基本力学性能和退化程度，分别给出强度、承载力、刚度与损伤参数的变化关系；建立木构架有限元模型，研究残损古建木构在地震作用下的极限变形、承载力与破坏模式，给出地震作用下的位移/转角与应力/承载力相关性曲线；分析各类节点与构架的变形、破坏及其分布、时序等，建立古建木构损伤模型。项目预期成果可为保护损伤古建木构文化遗产、改善其抗震性能，提供理论支撑、技术参数与途径。

古建筑木结构由于年代久远，普遍存在材性劣变、结构损伤、抗震性能大幅下降等问题。借助应力波仪、针阻仪等现代设备对古建木构损伤进行检测；人工模拟干湿交替变化、日光曝晒、菌虫腐变等环境影响因子对木材的影响，研制了带有不同类型、不同程度的损伤试件；对试件进行材性、抗震性能试验与理论分析研究，取得了预期研究成果。.（1）分别对带有不同孔洞、裂缝损伤的试件进行微钻试验，得到相应损伤对应的微钻阻力图谱，对杉木清材试件进行试验，拟合出可用于检测古建筑木材密度、弹性模量、强度与微钻阻力的关系式。.（2）对损伤试件进行材性试验，结合超微观察、傅立叶红外光谱分析、XRD衍射分析的试验结果，定义木材损伤度等级，分析不同类型、不同程度损伤对木材力学性能变化，建立了杉木材性退化本构关系模型。.（3）对损伤古木节点进行静载、低周往复加载试验，得到不同程度损伤木节点连接各部位的受力传力特征、M-θ滞回曲线、节点工作机制与耗能机理，拟合出损伤对木节点刚度退化、节点耗能的影响。.（4）对损伤木梁、木柱进行静载、低周往复加载试验，得到不同损伤程度下木构件的F-Δ滞回曲线、以及损伤木构件的破坏形态。进一步分析得到了木构件的骨架曲线、刚度退化曲线、等效黏滞阻尼曲线，拟合出损伤木对构件抗震性能的影响。.（5）对损伤木构架进行动力特性、低周往复加载试验，得到如何利用脉动法确定木构架损伤位置的方法、F-Δ滞回曲线、以及损伤木构架的结构响应、局部构件破坏形态，进一步分析了木构架的骨架曲线、刚度退化曲线、等效黏滞阻尼曲线，拟合出损伤构件对木构架抗震性能的影响。.（6）结合典型古木构建筑，对古木建筑抗震性能提升与修复保护方法进行了拓展研究，对古木建筑的损伤节点、构件、结构的局部更新、加固修复、整体复位纠偏，及其对结构抗震性能的影响，进行了理论研究。.课题研究成果可为保护损伤古建木构文化遗产、改善其抗震防灾性能，提供理论支撑。