# Uncertainties in the Seismic Assessment of Historical Masonry Buildings
## 5 Discussion
This scatter throughout the floors indicates uncertainty on its own, and since out-of-plane was such a significant mode of failure in both directions, this also highlights the importance of floor stiffness and floor-to-wall connections, in particular. This can be seen in Figure 18, where a correlation with floor stiffness could be observed along with a stronger correlation with floor-to-wall friction. This result was expected, since only when the floor-to-wall connection capacity was not exceeded, the full stiffness of the floor could have been exploited. This correlation was on the same order of importance as damping ratio, flexure drift at collapse and modulus of elasticity--all values that were expected to significantly correlate with the PGA at failure. Lausanne Malley models with and without out-of-plane behaviour and non-linear connections also showed differences in performance in terms of the 84 th percentile IDA curves, as shown in Figure 26. The differences with the PGA increment were the most significant in the roof displacements in y-direction. Comparison of the fragility curves for the Malley Lausanne building showed that the model with out-of-plane behaviour and non-linear connections was significantly more fragile, having higher probability of failure for each PGA level, but especially for the lower PGA as shown in Figure 27. The difference was pronounced for lower PGA levels due to a significant occurrence of early out-of-plane failure, whereas the model with only in-plane behaviour started experiencing collapses only for higher PGA levels, when the in-plane capacity was exceeded. Having out-of-plane behaviour and non-linear connections disabled, the floor-to-wall friction coefficient was no longer used and the floor stiffness did not show a correlation with the PGA at failure. This was different in the case of the model with out-of-plane and non-linear connections, where they were correlated with the PGA at failure, stronger for the case of the floor-to-wall friction. The other parameters that passed the P-test remained the same, but with their correlation coefficients increased as a result of governing failure mechanism becoming predominant. Whereas the model with out-of-plane enabled and non-linear connections failed in flexure in 92% of the cases, the model with out-of-plane disabled and rigid connections failed in flexure in 100% of the cases. However, differences were detected in the failure location. In the model with out-of-plane disabled and rigid connections, failure was less scattered and occurred in the fifth storey in most of the cases. Figure 25: Comparison of Holsteiner Hof fragility curves for models with: (i) out-of-plane enabled and non-linear connections, and (ii) out-of-plane disabled and rigid connections. All analyses were carried out with only one ground motion record (see Section 2.5). Some of the findings presented in this study might be record dependent. However, due to the rather broad-band frequency content of the Montenegro Albatros 1979 record, it is expected that the qualitative conclusions are applicable to a wide range of records. [PERSON] found that both record-to-record variability (aleatory variability) and epistemic uncertainty influence the IDA curves [7]. While the aleatory variability influenced the dispersion in the IDA curves, the epistemic uncertainty affected primarily the collapse capacity [7]. Our work focused on the epistemic uncertainties, but in future work, the aleatory and the epistemic uncertainties could be combined using the same methodology to confirm the validity of using a record with a rather broad-band frequency content. Figure 26: Lausanne Malley comparison of IDA curves models with: (i) out-of-plane enabled and non-linear connections, and (ii) out-of-plane disabled and rigid connections, displaying the maximum values of seismic demand parameters: (**a**) Total base shear in x-direction. (**b**) Total base shear in y-direction. (**c**) Average roof displacement in x-direction. (**d**) Average roof displacement in y-direction.