Seismic Assessment of the Carillon Tower in the Philippines Using a Finite Element Model Updated with Operational Modal Analysis

This research is on the seismic assessment of the Carillon Tower in the University of the Philippines in Quezon City, Philippines. Despite being vulnerable and having been exposed to earthquakes in the past, assessment efforts have been limited mainly due to the lack of as-built plans. Consequently, it was aimed to create an FE model updated with Operational Modal Analysis (OMA). First, the Finite Element (FE) model was created using the available limited pre-build plans utilizing ETABS, considering the inclination of practicing engineers and maintenance staff. In-situ measurements revealed that there had been significant modifications, making the available drawings inaccurate. Next, with OMA, stable modes with high modal amplitude coherence values were identified using Natural Excitation Technique and Eigensystem Realization Algorithm (NExT/ERA). Comparison of the OMA results and FE modal analysis revealed a close agreement between the mode shapes but a considerable difference between the modal frequencies. The model was then updated manually to reduce the difference in the natural frequencies. Finally, to obtain the tower’s general dynamic response, Nonlinear Time History analysis was used with a simulated site-calibrated accelerogram of the predicted M7.2 EQ in the Philippine West Valley Fault System.