古建筑七架梁缺陷安全性影响数值模拟研究

Numerical simulation of the safety influence of defects on Qijia-beams of ancient timber building

【目的】七架梁作为大型木结构古建筑的主要承重构件,其承载力安全性直接影响古建筑木结构整体的安全性。由于周围环境和使用长久等原因造成木梁出现不同程度的缺陷,会影响木梁弯曲拉应力和剪切应力的分布,进而影响其承载力安全性。因此,研究不同缺陷类型、尺寸、位置对古建筑七架梁承载力安全性的影响很有必要。【方法】采用Abaqus有限元软件模拟计算梁上存在的裂纹、腐朽和空洞等不同缺陷时的应力分布状态,通过量化缺陷大小和缺陷位置,对不同残损因素进行单参量数值模拟分析,确定带有缺陷木梁的最大工作应力位置,分析木梁破坏的敏感位置,探究木梁承载力安全性的变化规律。【结果】不同缺陷类型对七架梁安全性的影响不同,外部腐朽对七架梁承载力的影响最大,空洞缺陷次之,裂纹缺陷的影响相对最小;对于弹性阶段的受弯木梁而言,缺陷位于两下金瓜柱之间的受拉区域时,对七架梁承载力安全性的影响程度最大;不同缺陷大小对七架梁承载力的影响不同,随着木梁开裂深度、腐朽区域深度、空洞缺陷大小的增加,木梁安全性逐步降低。【结论】局部缺陷的存在会降低七架梁安全性。数值模拟结果可以精确算出木梁最大拉应力值,是定量研究缺陷对七架梁安全性影响和确定七架梁安全性监测位置点的良好方法。

[Objective]The Qijia-beams are used as the main load-bearing members for Chinese ancient timber building.The safety performance of whole wood structure is directly affected by the bearing capacity safety of Qijia-beam.Factors,such as surrounding environment and load for a long period,lead to different degrees of the defects in the wooden beam.These defects will affect the tensile stress and shear stress distribution,as well as the bearing capacity safety of the wooden beam.Therefore,it is necessary to study the influence of different defect types,sizes and locations on the safety of bearing capacity of the Qijiabeam.[Method]Abaqus finite element software was used to simulate the stress state of the beam with different defects such as crack,decay and hole.By quantifying the size and location of the defects,the single parameter numerical simulation analysis of different damage factors was carried out to determine the maximum working stress location of the wood beam with defects,analyze the sensitive location of the damage of the wood beam,and investigate the variation patterns of the bearing capacity of wood beams.[Result]The results showed that the types of different defects had different influence on the safety of the Qijia-beam.External decay had the greatest influence on the bearing capacity of the Qijia-beam,followed by hole defect,and the impact of crack defect was relatively minimal.For the bending beams in the elastic stage,the defects had the greatest influence on the bearing capacity safety of the Qijia-beam when it was located in the tension zone between two under Jiagua-columns.The influence of different defect sizes on the bearing capacity of the Qijia-beam was different.With the increase of the crack depth,the decay depth,and the hole size,the safety of the wooden beam was gradually reduced.[Conclusion]Due to the existence of local defects,the bearing capacity of the Qijia-beams would be decreased.The research of this paper provides numerical simulation,which could accurately determine the maximum tensile stress of the wooden beam.It is a good method to quantitatively study the influence of defect on the safety of Qijia-beam and to determine the location of Qijia-beam safety monitoring.