Influence of mortar strength on the compression–shear behaviour of an ancient pagoda

Mortar strength is a key factor influencing the seismic failure mode of brick-and-stone ancient pagodas. To investigate its effect on the seismic performance of ancient pagodas, two 1:8 scaled substructure models of the Xuanzang Pagoda at Xingjiao Temple were designed and fabricated. Cyclic loading tests were conducted to observe the failure process and characteristic data of the specimen. A numerical model was established using a discrete modelling approach for simulation, and the variation range of mortar strength was determined based on the results of an investigation into the masonry materials used in ancient pagodas. Parametric expansion analyses were then carried out on the numerical model. The results show three distinct failure modes: shear–sliding failure, compression–shear failure and compression–bending failure, with corresponding mortar strength thresholds of 1.0 MPa, 3.0 MPa and 4.0 MPa. Increasing mortar strength within a certain range can improve the shear capacity and ductility of the ancient pagoda structure; however, excessively high mortar strength will instead lead to a reduction in both capacity and ductility. The findings of this study can provide a reference for the seismic capacity assessment of ancient pagodas and the selection of repair materials.