This study deals with the high-fidelity block-based finite element simulation of dynamic out-of-plane (OOP) responses of unreinforced masonry (URM) walls, explicitly focusing on two-way bending behaviors under seismic loads, which is a common critical failure mode in real-world masonry structures. While experimental shake-table tests provide valuable insights into these behaviors, their high costs, complexity, and limited scalability highlight the need for advanced numerical modeling approaches. A state-of-the-art block-based finite element modeling strategy that conceives masonry as an assemblage of 3D damaging blocks interacting via contact-based cohesive-frictional zero-thickness interfaces, previously proposed for simulating cyclic quasi-static and dynamic one-way bending tests, is here extended for the first time to the simulation of incremental dynamic shake-table tests on OOP two-way spanning URM full-scale walls, subjected to a sequence of dynamic loads. The numerical models track the reference experimental behaviors with high accuracy in terms of collapse onset, failure mechanism, experienced acceleration and displacements, and hysteretic response. The effects of variations in mechanical properties, boundary conditions, and damping on the dynamic response are explored in a sensitivity study. The results indicate that slight changes in these parameters can lead to considerable differences in outcomes. This highlights the chaotic nature of the dynamic response of masonry walls, especially in near-collapse conditions, which makes probabilistic approaches more suitable for predicting masonry OOP dynamics. The proposed numerical methodology appears compatible with statistical frameworks, given the limited costs with respect to experimental tests, and it extends knowledge beyond physical experiments.

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This paper presents the results of a series of shake table tests carried out on a half-scale single-story unreinforced masonry building with asymmetric openings. First, the unretrofitted building is subjected to seven increasing steps of bidirectional seismic excitation. The damaged building is then rehabilitated using steel mesh and shotcrete layer with two walls retrofitted from the exterior face and the other two from the interior face. Afterward, the shake table test is again conducted on the retrofitted specimen in nine increasing excitation levels. Three cases of interior-to-interior, interior-to-exterior, and exterior-to-exterior shotcrete connections are considered at the intersection of perpendicular walls, and for each case, the development of cracks is investigated. Moreover, the effects of fixity of the shotcrete vertical rebars in the foundation are investigated through releasing the rebar-foundation connection in the last three steps of the test on the rehabilitated specimen. The results indicate the adequacy of the retrofit method in creating a strong bond that leads to an acceptable composite action between the brick layer and shotcrete; though, concentrated cracks were observed at the connections of the perpendicular walls. Furthermore, the shotcrete layer has proven to be able to prevent further propagation of the previously developed cracks, which can provide a practical solution for rehabilitation of damaged masonry buildings.@en