Yearly changes in dynamic characteristics of a three-story mass timber building based on long-term SHM

The Peavy Forestry Science Center (“Peavy Hall”) at Oregon State University is a living laboratory for long-term Structural Health Monitoring (SHM) of a three-story mass timber building. Various structural and environmental data have been measured continuously from construction to the present, and more than five years have already passed since completion. The SHM project of Peavy Hall has multiple purposes including monitoring material behavior, serviceability, environmental conditions and structural vibration. In this study, we focused on the yearly changes in vibration characteristics obtained from accelerometers, to identify long-term variations in natural frequencies and mode shapes and to evaluate the influence of indoor climates and wood moisture changes. Operational modal analysis was performed using a stochastic subspace identification (SSI), and mode-shape consistency was examined using Modal Assurance Criterion (MAC) values between datasets collected at different times. The results indicate seasonal variations in natural frequencies associated with environmental conditions were detected. In addition, specific seismic and wind events that occurred in the surrounding area were identified, and corresponding dynamic responses of the building were clarified for those events. These methods and findings support the use of long-term SHM for evaluating structural characteristics of mass timber structures and for developing future numerical models.