Longhu pagoda: Advanced numerical investigations for assessing performance at failure under horizontal loads

As an important historical building type for human beings, ancient masonry pagodas have key research significance. They are widely diffused in China, and they are tower-like masonry structures, usually massive and tall. This paper takes the Longhu pagoda as a case-study: it was built in 1342 CE, and it is the only masonry pagoda from the Yuan Dynasty. It is located in the Sichuan Province (China), it has a square plane, and the height is about 33 m. This construction severely suffered the so-called "2008 Sichuan Earthquake". A full 3D model of the Longhu Pagoda has been obtained and subsequently meshed. The FE software Abaqus/CAE has been used for carrying out static analyses, pushover analyses and non-linear dynamic analyses. The material non-linearities have been taken into consideration employing the so-called Concrete Damage Plasticity (CDP) model available in Abaqus. Modal analyses have shown that FEM results and simplified cantilever model results may agree. Pushover analyses (POs) have been performed under different load conditions and along the four principal bending directions to estimate the global capacities and the corresponding collapse mechanisms. Non-linear dynamic analyses (NLDAs) allowed putting in evidence the accuracy of the results provided by the pushover analyses; besides, they gave helpful information about the crack propagation, confirming the damage reported on-site after the 2008 earthquake. The state of damage found and the related failure mechanisms have been deeply commented. Moreover, some sensitivity analyses have been performed to study the influence of some material parameters on the pushover results. Furthermore, two fictitious 3D models of the pagoda have been created by doubling and removing two floors to investigate the influence of the tower slenderness. The before mentioned analyses have also been performed on such models, and the impact of the slenderness on this structural typology has been studied. Finally, the kinematic theorem of limit analysis has been applied, and some values of collapse acceleration have been consequently computed using different a-priori established collapse mechanisms. The results have been compared with FE simulations results, and the ability of limit analysis to quickly predict the seismic vulnerability has been discussed.