Strength Decrease of Wood Materials in Kintaikyo Bridge used 48 Years

Kintaikyo Bridge has been constructed in 1673, and is an important timber pedestrian bridge with the history in about 334 years in represents Japan. The bridge subjected in this study is the bridge constructed in 1953 and reconstructed in 2001. During 48 years, the static deflection, strain and natural frequency in the field test have been measured to monitor the change of structural performance in every five years by Waseda University. This study was investigated analytically the change of Young’s modulus of the wood materials based on the experimental values of natural frequency over 48 years measured in every five years, and then strength decrease of the wood materials was estimated by the change of Young’s modulus. From the analytical estimation considered the change of unit product weight on wood, it was obtained the result which strength of the main wood materials constituted Kintaikyo Bridge decreased about 64.4 % during 48 years.