Dynamic Characteristics and Variations of a Historic Timber Building Based on Long-Term Earthquake Monitoring

This study presents a 15-year earthquake monitoring investigation of the Butsuden Hall of Kencho-ji Temple, focusing on long-term variability, displacement dependence, and seasonal effects on its dynamic characteristics. The results show no secular degradation in natural frequencies or damping ratios, while clear displacement-dependent nonlinearity and seasonal variation were identified. Temperature–humidity measurements indicate that moisture-content changes govern seasonal stiffness variation. Numerical evaluation combining column rocking effect and column–nuki joint stiffness successfully reproduced the lower-bound observed frequencies. These findings demonstrate that vibration-based monitoring has a possibility to detect stiffness changes in historic timber structures.