ガンマ線および穿孔抵抗を用いた木製柱の内部劣化の診断

摘要

文化財建造物の多くは，伝統的構法による木造建築であり，その保存修理では，構造補強な どの他に，腐朽や虫害などによって割ヒした部材の交換や補修が行われる。劣化部位の修理方 法は，現場の技術者の視診や打診などによるいわゆる一次診断の結果に基づいて決定されるが， 大断面の柱などの構造部材や大壁内部の劣化の有無，種類，程度や範囲については，外観の一 次診断の結果のみから正確に推定することは困難である。%The feasibility of the combination of two inspection methods, drill resistance method using Resistgraph apparatus and two-dimensional scanning method using gamma-ray transmission, to detect inner cavity of a column generated by insect and fungal attack in historic wooden buildings was investigated. Based on the results of former studies that evaluated the basic performance of the methods, the two methods were applied to octagon columns of zelkova wood about 630mm in diameter in a hall of a temple in Kyoto city. Seventeen columns showing symptoms of bio-degradation were selected out of all the 134 columns by visual inspection. Twelve columns out of the selected 17 were inspected by Resistgraph and 4 of them were inspected also by a gamma-ray scanner. The distribution of inner cavity in the cross section at two heights of the columns estimated by the gamma-ray scanner was confirmed by the change in drill resistance at the corresponding heights. It was clarified that by the combination of two methods a nondestructive evaluation of inner defects of wooden columns can be realized at higher accuracy. Some improvements of the apparatus and procedures are still required for practical application.