###### Abstract  
The effect of the vertical component of earthquakes on the structural behaviour of unreinforced masonry (URM) walls is usually not considered by technical codes for ordinary buildings. Recent scientific literature, however, indicates that the earthquake vertical component may play a significant role in the crack pattern of URM walls and their collapse. This paper investigates the effect of the vertical seismic component on the capacity and damage scenario for a two-story regular URM wall, described with a detailed micro-modelling approach. Pushover and nonlinear time history analyses are carried out with and without the vertical component and under different dead loads representative of typical stress states for URM structures. The inter-story drift and roof drift ratios are introduced as Engineering Demand Parameters (EDPs), and their correlation with the Ground Motion Parameters (GMPs) of the horizontal and vertical components is discussed. The results show a very good correlation between the seismic demand and the GMPs of the vertical component, demonstrating the influence of the vertical component on the global seismic response. Moreover, the study shows that the influence of the vertical component increases with the vertical load applied to the structure, which indicates that the vertical ground motion component cannot be a priori neglected for URM walls when moderate to large vertical GMPs are expected. m 2023 13 2459 2023 13 2023 13 2023  
studies that analysed the 2012 Emilia Romagna earthquake [8; 9; 10]. The analysis of the crack pattern of some structures, e.g., the clock tower in Emilia Romagna [11], confirmed that, for low-strength masonry structures, the influence of the vertical component of the earthquake leads to severe damage of the structures or even to their collapse. Recent papers on historic masonry structures studied the effects of the earthquake vertical component considering different conditions: the characteristics of the seismic event affecting the area [12; 13; 14; 15; 16], the distance from the epicentre [16], and the type of structure [17; 18]. In [PERSON] et al. [19], the damage potential of vertical accelerations was investigated through a series of multidirectional shake table tests on full-scale structures under simulated near-source ground motions of increasing intensity. The experiments comprised three nominally identical building specimens subjected to the principal horizontal component alone, the horizontal component combined with the vertical one, and the full three-component ground motion. In [PERSON] et al. [20], a FEM model of the Banloc castle, a historical building in Romania, was investigated in the nonlinear dynamic field to evaluate the influence of the vertical seismic component in terms of displacement stress and crack pattern, accounting for only the horizontal component and the horizontal and vertical components. In [PERSON] et al. [21], to simulate the seismic performance of the \"[PERSON]\" school in Visco, the Marche Region (Italy), under a series of seismic motion events similar to those produced by the 2016-2017 Central Italy earthquake, the sequence of acceleration time histories recorded along both horizontal directions X and Y at the base and the vertical component were applied to nonlinear EF models with both fixed and compliant bases. This paper aims to evaluate the influence of the vertical component of the earthquake on a 2D wall implemented in the OpenSees framework with STKO analysis software [22] using a micro-modelling approach. The choice of this modelling approach is made considering the type of analysis to be carried out and the case study. Following a bibliographic study, it is possible to affirm that the main advantage of this type of modelling is the accuracy in predicting the failure load and the collapse mechanism, as demonstrated in [23; 24]. It has been shown that the micro-model is able to obtain results of very similar collapse mechanisms on unreinforced masonry structures.