Seismic performance and possible damage scenario of an ancient Thai pagoda in Chiang Saen District, Northern Thailand

Abstract

This research investigates the seismic performance and potential damage scenarios of the ancient Wat Chedi Luang pagoda in Chiang Saen, Thailand. The study integrates 3D laser scanning for high-fidelity finite element model reconstruction with nonlinear time-history analysis. The Concrete Damage Plasticity (CDP) model was employed to simulate masonry nonlinear behavior. The reliability of the finite element model was validated against on-site ambient vibration measurements; the fundamental period derived from the analysis (0.441 s) exhibited excellent agreement with the field-measured period of 0.448 s obtained via the horizontal-to-vertical spectral ratio (HVSR) method. The current geometry of the point cloud reveals a structural tilt of 0.398 degrees to the northwest. Material testing reveals significant compressive strength variations (1.89–12.79 MPa), necessitating a sensitivity analysis across different material models. The probabilistic seismic hazard analysis (PSHA) determined the peak ground accelerations (PGA) to be 0.048 g for frequent earthquakes (50% PE in 30 years), 0.1–0.15 g for occasional earthquakes (10% PE in 50 years), and 0.30–0.35 g for rare earthquakes (2% PE in 50 years). The analysis indicates a progression of damage, consistently initiating at the pinnacle before extending to the bell and upper base. The pagoda is susceptible to partial collapse under rare earthquakes, with a damage volume reaching 6.99% (exceeding the global instability threshold). The results identify the pinnacle as the most vulnerable component. Therefore, targeted reinforcement using an embedded deformed steel core is quantitatively verified to prevent a collapse mechanism at the pinnacle.