应县木塔普拍枋用材方法与残损状况分析

Material Application Method and Component Damage Analysis of the Pu-Pai Fang in Yingxian Wooden Pagoda

普拍枋的横纹受压变形积累等残损现象是应县木塔结构发生竖向沉降和损坏的重要原因,严重影响木塔的安全性能。为研究应县木塔普拍枋的取材用材信息与残损现状,通过现场勘察记录各层普拍枋用材的年轮数、髓心位置与受压处的压缩情况,并采用无损检测技术获得木材年轮宽窄面与木材大小头摆放方式,同时对端面图像进行处理以计算端面裂隙率与缺损率。研究结果表明,应县木塔普拍枋用材为树龄大于100年的华北落叶松(Larix principis-rupprechtii Mayr.),且尽可能保证了木材两端髓心处于中心位置,同时木材的年轮宽窄面与大小头摆放存在一定规律;木材横纹受压残损是普拍枋的主要残损形式,其中压缩程度大于20%的木构件在各明层内槽普拍枋中占50%,同时随着木塔的使用普拍枋压缩程度仍在增加;木材局部受压是木构件端面开裂残损的重要原因,其中木构件局部受压压缩程度与端头开裂裂隙率呈高度线性相关。

The accumulation of compression and deformation on the transverse grain in Pu-pai Fang is a primary cause of the vertical settlement and damage to the Yingxian Wooden Pagoda structure.It significantly affects the safety performance of the wooden pagoda.In order to study the structure and damage conditions in the wooden pagodas,the number of annual rings,the location of the pith center,and the compression at the pressure of the wood used in each layer were recorded through on-site investigation.The non-destructive testing technology was used to obtain the annual rings of both wide and narrow surfaces and the placement of the wood ends.At the same time,the images of end faces were analyzed to calculate the missing rate and crack rate.The results of the study show that the timber used in Yingxian Pu-pai Fang is Larix principis-rupprechtii Mayr.which is more than 100 years old.The pith of the wood is in the central position.A certain pattern between the width and narrowness of the timber’s annual rings and the size of the head arrangement of the timber was observed.Wood transverse grain compression damage is the main form of damages in Pu-pai Fang,of which the degree of compression greater than 20%of the components in each bright layer of the inner groove Pu-pai Fang accounted for 50%.The degree of compression in wooden tower Pu-pai Fang continues to increase as it ages.The local compression of the wood is an important reason for the cracking damage on the end faces.The degree of localized compression in the components strongly correlates with the end-cracking fracture rate.