Thesis (B.S.) -- Cagayan State University, 2025.

The Philippines, located along the Pacific Ring of Fire, is highly susceptible to seismic hazards such as earthquakes and tsunamis due to its numerous active volcanoes both on land and underwater. This geological setting poses significant risks to critical infrastructure, including public bridges, which are among the most vulnerable structures during seismic events. Specifically, the Pinacanauan Josefa Bridge in Peñablanca, Cagayan, has been identified as a key structure requiring seismic vulnerability assessment. This study focuses on evaluating the seismic vulnerability of the Pinacanauan Josefa Bridge by subjecting it to 15 local earthquake records. Using the structural model developed in SAP2000, the study applies both Pushover Analysis and Time History Analysis methods to generate fragility curves that depict the probability of exceeding various damage states under increasing seismic intensity. The yield and maximum displacements obtained from the Pushover Analysis, combined with ductility demands from the Time History Analysis, were instrumental in constructing these fragility curves. Results indicate a high probability that the bridge will experience significant damage at a peak ground acceleration (PGA) of approximately 1.6g in both the X and Y directions. However, when compared to the seismic design base of 0.4g as specified by the National Structural Code of the Philippines (NSCP) 2015, the probability of exceeding damage states is considerably lower. This suggests that while the bridge is relatively safe under the current design base, there remains a notable risk at higher seismic intensities. The findings align with established methodologies in seismic vulnerability assessment, which emphasize the importance of fragility curves derived from nonlinear static and dynamic analyses to predict damage probabilities accurately.

KEYWORDS: yield and maximum displacements, Pushover Analysis, Time History Analysis, peak ground acceleration (PGA), fragility curves