干缩裂缝对历史建筑木构件受力性能影响的试验研究

发布时间：2018-12-27 12:35

【摘要】：木材作为一种建筑材料曾普遍运用于历史传统建筑中,现存的古建聚落绝大部分是木结构建筑。然而,木材因其独特的各向异性特征,使得木结构受温湿度的影响非常明显,主要表现为产生顺纹干缩裂缝,而历史建筑中的木构件历经岁月,干缩开裂现象更是严重。因此,在评定历史建筑聚落残存木结构的安全性时应该考虑干缩裂缝对木构件承载力的影响。为了确定纵向干缩裂缝的存在对木构件受力性能的影响,本文通过设置人工扇形缝模拟自然干缩裂缝的方法,设计了4组共8根带有不同裂缝尺寸的圆形截面杉木长柱的轴心受压试验和4组共8根带有不同裂缝尺寸的方形截面杉木长梁的三分点抗弯试验,研究纵向裂缝对木柱轴压承载力和木梁抗弯承载力的影响。试验结果表明：在构件尺寸、试验条件相同的情况下,设有纵向扇形缝的试验柱轴压极限承载力较未开缝参照柱轴压极限承载力有所降低,且裂缝深度较浅时承载力降低程度可忽略不计,随着裂缝深度的增加木柱轴压极限承载力下降程度会更加明显,当纵向干裂木柱的裂缝深度达到木柱柱径64%左右时构件轴压极限承载力较完整木柱构件下降程度可达20%；设有纵向扇形缝的试验木梁抗弯极限承载力较未开缝参照木梁抗弯极限承载力有所降低,且裂缝深度较浅时承载力降低程度可忽略不计,随着裂缝深度的增加木梁抗弯极限承载力下降程度会更加明显,纵向干缩裂缝对木梁受弯承载力的影响在于改变了承载力验算控制条件。由于裂缝削弱了木梁顺纹抗剪截面面积,随着裂缝深度的增加,木梁受弯承载力验算条件将由抗弯控制转变为抗剪控制,本文通过提出裂缝开展界限指标的计算方法来考虑纵向干缩裂缝对木梁受弯承载力的影响。当裂缝深度等于界限值时,木梁的抗弯强度和抗剪强度同时耗尽；当裂缝深度小于界限值时,木梁受弯控制条件为抗弯承载力,裂缝的影响可忽略不计；当裂缝深度大于界限值时,木梁受弯控制条件为抗剪承载力,应考虑裂缝的影响。借助ABAQUS有限元软件建立木柱、木梁的有限元模型进行数值模拟,将有限元计算结果与试验实测值对比分析,验证了ABAQUS数值模拟木结构构件受力性能的可行性及可靠性。在此基础上,利用有限元软件进行复杂裂缝参数变化分析,根据数值模拟结果对考虑纵向干缩裂缝影响的木构件受力性能进行理论分析,提出考虑纵向干缩裂缝影响的木构件承载力折减系数的计算公式。数值模拟结果表明：构件承载力折减系数与裂缝相对深度、裂缝相对长度均呈二次多项式关系,与裂缝宽度呈线性相关,且裂缝宽度对木柱构件承载力影响程度较小,对于宽度小于3mm的纵向干缩裂缝其影响可忽略不计。将公式计算结果与试验所测值进行对比,验证本文计算方法的正确性。
[Abstract]:Wood, as a kind of building material, was widely used in the historical and traditional buildings, and the majority of the existing ancient buildings and settlements are wooden structures. However, because of its unique anisotropic characteristics, wood structure is obviously affected by temperature and humidity, which is mainly manifested in the formation of dry-shrinkage cracks along grain, while in historical buildings, the phenomenon of dry-shrinkage cracking is even more serious. Therefore, the influence of shrinkage cracks on the bearing capacity of wood members should be considered in evaluating the safety of the remaining wood structures in the settlement of historical buildings. In order to determine the influence of longitudinal dry shrinkage cracks on the mechanical properties of wood members, this paper simulates the natural dry shrinkage cracks by setting artificial fan-shaped joints. The axial compression tests of four groups of round section Chinese fir columns with different crack sizes and four groups of eight square cross-section Chinese fir beams with different crack sizes were designed. The effects of longitudinal cracks on axial compression capacity and bending capacity of wood beams are studied. The test results show that the ultimate bearing capacity of the test column with longitudinal sector joints is lower than that of the unslotted reference column under the same member size and test conditions. When the crack depth is shallow, the reduction of bearing capacity is negligible, and with the increase of crack depth, the decreasing degree of ultimate bearing capacity of wood column under axial compression will be more obvious. When the crack depth of the longitudinal dry split column reaches about 64% of the diameter of the column, the ultimate bearing capacity of the members under axial compression is 20% lower than that of the complete column member. The ultimate flexural capacity of the test beams with longitudinal sector joints is lower than that of the unjointed reference beams, and the reduction of the ultimate flexural capacity of the beams with shallow crack depth is negligible. With the increase of crack depth, the decrease of ultimate bearing capacity of wood beam will be more obvious. The influence of longitudinal shrinkage crack on flexural bearing capacity of wood beam depends on changing the control condition of checking calculation of bearing capacity. With the increase of crack depth, the checking condition of bending capacity of wood beam will be changed from bending control to shearing control. In this paper, the influence of longitudinal dry shrinkage crack on flexural bearing capacity of wood beam is considered by means of calculating the limit index of crack development. When the crack depth is equal to the limit value, the bending strength and shear strength of the wood beam are depleted simultaneously, and when the crack depth is less than the limit value, the bending bearing capacity of the wood beam is controlled, and the influence of the crack can be neglected. When the crack depth is greater than the limit value, the bending control condition of wood beam is shear bearing capacity, and the influence of crack should be considered. The finite element model of wood column and beam is established by ABAQUS software. The feasibility and reliability of ABAQUS numerical simulation of the mechanical behavior of wood structure members are verified by comparing the results of finite element calculation with the experimental results. On this basis, the finite element software is used to analyze the variation of complex fracture parameters. According to the results of numerical simulation, the mechanical behavior of wood members considering the effect of longitudinal dry-shrinkage cracks is theoretically analyzed. A formula for calculating the reduction coefficient of the bearing capacity of wood members considering the effect of longitudinal shrinkage cracks is presented. The results of numerical simulation show that the reduction coefficient of bearing capacity of members is quadratic polynomial relation with the relative depth of crack and the relative length of crack, and it is linearly related to the width of crack, and the influence of crack width on the bearing capacity of timber column member is small. The effect of longitudinal shrinkage crack with width less than 3mm is negligible. The calculation results of the formula are compared with the experimental values to verify the correctness of the calculation method in this paper.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU366.2

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