Preliminary Fragility Assessment of a 19th-Century Baroque Church Bell Tower Using Multiple Time History Analyses

Philippine structures frequently experience seismic activity, yet the effects of high-intensity earthquakes are often assessed only after they occur. The inadequacy of extensive research on this area, especially for the investigation of structures that were built before systematic building and structural codes were established, poses a problem, especially in heritage preservation and protection. This study aims to develop fragility curves as a preliminary assessment of the seismic vulnerability of the bell tower of Pulilan, Bulacan’s Diocesan Shrine and Parish of San Isidro Labrador through Linear Time History Analysis (LTHA), considering limited inelastic data for adobe masonry and destructive testing on the structure. The material properties of tested concrete and adobe samples were integrated into a 3D structural model in Midas Gen to assess the tower’s seismic response to scaled 11 ground motion records. The fragility curves from the preliminary assessment show that the bell tower is prone to minor damage to weak PGAs. Considering the required basic design PGA of 0.4g in the Philippines, structural compromise is anticipated, having surpassed the 50% probability threshold at the Life Safety (LS) limit. The findings can serve as a reference for future nonlinear analyses and for the implementation of appropriate retrofitting measures on the tower.