竖向荷载下砖石古塔的损伤性能

Damage performance of ancient masonry pagodas under the vertical load

以玄奘塔首层为原结构,分别采用原砖、1/4和1/8模型砖制作了3个1/8缩尺结构模型,进行受压试验,观测加载过程中结构裂缝发展特征,测试了结构荷载、位移及应变;并通过数值模拟,对比了3个模型受力及破坏形式,分析了古砖塔的受压破坏机理和损伤变化。研究结果表明:砖塔受压破坏过程包含沿灰缝开裂、裂缝扩展和延伸、裂缝贯通破坏3个阶段;塔体破坏始于四角顶部,随荷载增加逐渐向下扩展并贯通,形成小截面砖柱,砖柱失稳导致结构破坏;塔壁沿平面内及平面外产生水平向变形,部分砖块开裂,因砖块尺寸不同导致模型的初始损伤及刚度不同,开裂荷载和极限承载能力随砌块尺寸减小而降低,应变随块体尺寸减小而增大,并根据模型的整体变形和局部块体变形特点,分析古塔的受压破坏机制,计算出古塔受压损伤演化趋势。

The failure mechanism of the ancient pagoda under compression was analyzed,based on the total and partial deformation characteristics of the pagoda model structure,and the evolution of the damage was calculated.Taking the first story of a pagoda as the prototype,three model specimens were generated by the use of old bricks at different scales:the original brick,the 1/4 and 1/8 scaled model brick.Compression tests were then carried out.The characteristics of the structural cracks developed during the loading process were observed.Numerical simulation was carried out.structural load,displacements,and strains were determined,and the stresses and failure modes of the three models were compared.The compression failure mechanisms and characteristics of the damage variation of the models were analyzed.The results indicate that the masonry failure of pagodas under compression occurs in three stages,the initial cracking along the mortar joint,the expansion and extension of the cracks,and the running through of the cracks.The cracking of the pagoda starts at the top four corners,gradually extends downwards,and finally runs through the entire structure with the increase in loading.Small sections of brick columns deformed,leading to structural failure owing to instability.In addition,horizontal deformation occurred along both the inside and the outside of the pagoda wall,and some bricks were cracked.The initial damage and stiffness of the model structure varied due to the different sizes of bricks.The cracking load and ultimate strength decreased as the unit block size decreased,while the strain followed an inverse trend.