Analysis of the dynamic response and incremental damage of the ancient masonry pagoda under the mainshock-aftershock sequence

Ancient masonry pagodas are susceptible to cracking under seismic excitation, and damage accumulation becomes more complex with subsequent earthquakes. To research the dynamic response and incremental damage mechanism under seismic sequences, the Changle Pagoda in Shaanxi, China, was selected. A more refined numerical model was constructed using the finite element software ABAQUS via a separate modeling. Multiple mainshock-aftershock sequences were constructed, and the dynamic response of the pagoda structure was computed. The tensile damage and equivalent plastic strain distribution were analyzed, and a quantitative assessment of the incremental damage was conducted. Results show that when the mainshock intensity was 0.2 g, damage was concentrated around openings and mortar joints, with a damage volume ratio of 0.1–0.15. As aftershock intensity increased, mortar joints interconnected, raising the damage volume ratio by about 0.03. At a mainshock intensity of 0.4 g, the damage volume ratio in lower-floor masonry exceeded 0.3, with damage propagating upward, causing cracks at the eaves corners and a maximum volume ratio increase of 0.05. The incremental damage index increased with aftershock peak acceleration, mainly influenced by mainshock intensity and post-mainshock damage. Aftershocks aggravated mainshock-induced damage, leading to “secondary damage,” and the cumulative damage effect intensified as the aftershock-to-mainshock peak acceleration ratio increased.