## 1 Introduction
Examples of OOP failure modes (adapted from [10]): (**d**) mechanism in long walls; (**e**) mechanism in short walls; (**f**) mechanism of the corner; (**g**) mechanism of the tympanum (gable). The comparison between implicit and explicit methods in FEM modelling has been explored in several fields including metal forming, impact, and contact problems. In the case of masonry structures, explicit methods have been applied to study the effects of blast loadings on both unreinforced and reinforced conditions [14]. [PERSON] and [PERSON] [15] used a FEM model with an explicit solver to study explosions in a historical masonry building. A similar approach was carried out by [PERSON] et al. [16] to evaluate the response of a historical structure built with earthen masonry to blast loads. Nevertheless, the studies and applications of explicit methods for the seismic assessment of URM buildings are scarce. [PERSON] et al. [17] created a FEM model using shell elements of a house made of adobe, simulating the results from an experimental campaign conducted on a shake table test. [PERSON] [18] developed a FEM model of a URM building using DIANA FEA 10.3 software to compare the results of implicit and explicit methods. The nonlinear dynamic analyses demonstrated that both approaches yielded similar responses. Finally, [PERSON] [19] studied the OOP behaviour of masonry walls employing shell elements, exploring variations in openings and boundary conditions. The FEM model was then subjected to a lateral incremental load (nonlinear pushover analysis). FEM modelling requires meticulous consideration, including the selection of suitable elements for the specific problem at hand. For example, linear elements that are fully integrated can exhibit shear locking, while linear elements with reduced integration are susceptible to hourglass distortions (Section 6). In the FEM modelling of URM buildings, particularly in explicit solutions, critical aspects such as shear locking, hourglass effects, and hourglass control techniques, among others, have not been addressed in prior works. Therefore, the present study aims to provide some insights into the application of explicit methods in 2D FEM modelling. Its primary objective was to conduct a comparative study between implicit and explicit methods, specifically addressing in-plane behaviour to simulate two frequent failure types observed in masonry walls under seismic loading. This can provide the users with a practical understanding of the effect of each parameter used in an explicit method, specifically in Abaqus/Explicit. Four models were generated to perform a parametric analysis. Two of these models focused on reproducing IP behaviour, targeting shear-diagonal failure and flexural failure, using 2D FEM elements, particularly plane stress elements. This type of element is related to states where the stress component normal to the element plane is negligible. Although masonry can undergo triaxial stress, plane stress elements are frequently used to simulate structural elements with small thickness where the loads act in the plane, such as masonry walls [20; 21; 22]. The other two models represent a section of a URM building (employing 1D and 2D FEM elements). The geometrical characteristics of the models are detailed in Section 4. The concrete damage plasticity model is adopted to account for the nonlinear properties of the masonry (Section 5). A key objective of this work was to compare the simulations conducted for masonry piers using both implicit and explicit methods with the Abaqus/CAE 2019 software [23]. The influence on the results of the element types used for modelling the structural problem, along with other parameters (discussed in Section 6), was considered. Initially, the IP mechanisms allowed the assessment of the performance of each parameter used in the explicit solver.