Evaluation of time-varying dynamic properties of base-isolated high-rise building during lateral extension using monitored data

Understanding how building dynamics evolve during structural modifications is a critical challenge in structural engineering. Among such modifications, horizontal expansions can significantly alter the dynamic characteristics of a building. This paper addresses this challenge by presenting a case study detailing the continuous structural health monitoring of a 20-story base-isolated building during a 16-month lateral extension project. Ambient vibration data were analyzed using the Frequency Domain Decomposition method to track the time-varying changes in the building’s characteristics. The analysis yielded several key findings. A significant shift in the torsional center was observed to be closely associated with construction events, and the real-time dynamic coupling of the two linked structures was captured through a second-mode transition. The study also indicated a correlation between the variations of the dynamic properties, including natural frequency and damping ratio, and the specific construction stages. Finally, distinct evolutionary paths were noted for the translational and torsional damping ratios, suggesting their different sensitivities to physical mechanisms, as reflected by their distinct reaction timings during the construction processes.