## 4 Results of Numerical Analysis  
### Parts of Walls  
Results of numerical analysis and experiments were compatible in the range of the load-carrying capacity of models and the failure method. Images of damaged parts of the walls obtained with the non-contact optical system during the laboratory tests and the results of the numerical model at the failure phase are compared in Figure 18.  
The maximum load of 444 kN and the corresponding deflection of 2.89 mm were reached in the first numerical model, NI. Destructive force at the level of 93% and lintel deflection at the level of 129% (2.9 mm) were obtained by comparing values from numerical calculations and mean values for the models of the NI series. First cracks were found at the lintel, above the support edge, under a load of 384 kN and a lintel deflection of 0.6 mm, which was 50% of the deflection and 94% of the load in the NI-1 and NI-2 test models. The lower convergence of results was found when those values were compared with models NI-3 I NI-4, for which the cracks were observed using the optical system. The calculated deflection and loading were respectively 333-375% and 392-469% of the values recorded during the tests.  
For another numerical model, NII, the maximum load was 420 kN, and the deflection at failure was equal to 11.2 mm, which constituted 85% and 220% of mean values obtained from the tests. The first cracks in the numerical model developed at the support edge of the lintel, as in the case of the model with five layers of brickwork. The obtained cracking force was 312 kN and the corresponding deflection was 0.6 mm. When those results were compared with the mean values obtained for the tested models of the NII series subjected to optical analysis, the cracking force and deflection constituted 238% and 167% of the experimental values.  
The smallest numerical model, NIII, was destroyed under a load of 376 kN and a deflection of 5.37, which constituted 85% of the loading force and 70% of the mean values from the tests. Cracking of the model developed simultaneously between the masonry units and at the support edge of the  
Figure 18: Damage recorded by the optical system compared with the damage to the numerical model for the elements of the following series: (**a**) NI, (**b**) NII, (**c**) NIII.  
lintel. The force was 220 kN, which constituted 247% of the cracking force, and deflection was equal to 0.45 mm, which constituted 98% of the deflection determined by the tests. Figure 19 illustrates the relationship between loading and displacement of laboratory and numerical models.  
Figure 19: Compared relationship between the load and deflection of the lintel determined experimentally and from numerical calculations for the models of the following series: (**a**) NI, (**b**) NII, (**c**) NIII.  
By comparing the relationship between force-deflection, illustrated in Figure 19, deflection of the lintel obtained from the numerical model was found to be smaller than in the laboratory models. This was caused by difficulties in proper modelling of cracks. Cracks that appeared in the laboratory models became wider under an increase in loading, and consequently deflection increased. It is difficult to reproduce this effect using the numerical model.