The threat posed by strong ground motions acting at the base of unreinforced masonry structures has increased worldwide research on the out-of-plane dynamic capacity of these structures. From an experimental perspective, the shake table is widely regarded as the most appropriate tool to investigate the non-linear dynamic response and the occurrence of collapse. Shake tables operate across a broad range of parameters, such as peak table acceleration, velocity, displacement, and natural frequencies, as well as can accommodate different overloading masses, degrees of freedom, and actuator’s capacities. However, due to the high cost of testing and the complexities of the system, it is crucial to align shake table campaigns with predictive models that ensure targeted behaviours are accurately captured. Out-of-plane responses involve large displacements and rotations, separations of constituents, sudden impacts, and energy dissipation mechanisms. Numerical and analytical models for 2D geometric problems, such as vertically spanning strip walls, are available but require calibration against experimental data. However, no reliable solution currently exists for a 3D geometric problem, such as a U-shape structure, consisting of a main façade and two orthogonal walls. Indeed, the latter is representative of both residential buildings and ancient structures, such as monolithic walls and towers. This contribution presents a discontinuous numerical model adopted to select appropriate ground motion records as input for the extensive shake table campaign conducted at the laboratory of the University of Minho (Portugal). The campaign lies within the scope of the STAND4HERITAGE (New Standards for Seismic Assessment of Built Cultural Heritage) project, which has produced hundreds of tests on dry-stack granite masonry specimens. The results will significantly enhance the understanding of the out-of-plane dynamic capacity of unreinforced masonry structures, which is of utmost importance to ensure the conservation of built heritage, improving public safety, and minimizing economic losses.