Characteristics and diagnosing technology of biodegradation in wooden historical buildings A case study on Amida-do in Higashi Hongan-ji Temple in Kyoto

摘要

Most of the historical buildings in Japan involving temples, shrines, castles and houses are made of traditional timber frame constructions and they are often exposed to the risk of biodegradation such as decay and insect attack, mainly by termites and other wood attacking insects. The degradation becomes sometimes serious due to lack of proper maintenance system coupled with periodic and practical diagnose. It was often reported that the biodegradation affects the performance of the buildings to resist a severe earthquake. Amida-do in Higashi-Honganji Temple in Kyoto is one of the largest wooden Buddhist buildings in Japan. Results from the diagnosis of biodegradation in Amida-do were reviewed and the characteristics of biodegradation were summarized. The methods for the diagnosis of biodegradation involving non-destructive techniques were also summarized in this report. The method for diagnose of biodegradation can be classified from three points of view; step, factor and style of operation, respectively. It is classified into three steps according to the precision and object of diagnose, and the apparatus and methods. It is also classified according to three factors to be estimated; direct or indirect detection of agent of the degradation, evaluation of physical and mechanical properties of materials or structures exposed to the degradation, and evaluation of environmental factors to promote degradation. It is again also classified according to operation style; periodic inspection or continuous monitoring, respectively. Principles, advantages and limitation of available diagnose methods were discussed involving non-destructive methods developed by the authors, such as acoustic emission (AE) monitoring and metabolic gas monitoring to detect termites inhabiting wood, detection of biodegradation using micro and millimeter electromagnetic waves, and measurement of mechanical work in screwing, and so on.