## 4 Discussion
### Use Case  
The experimental F/T tests performed in the laboratory were basically accelerated ageing tests that simulated the actual state in nature. Because these were simulations or approximations of the actual situation, the expected intervals of extreme temperature change that are predicted by standards were much shorter than intervals that occur in the real environment. The effect of F/T in the presence of water/moisture in the case when materials are saturated with water is much more problematic than the phenomenon of F/T alone. Such a situation can be critical for buildings, causing damage to mortar and bricks, which consequently affects the mechanical properties of the wall as a composite.  
In the use case (Figure 6), we assumed that the life of the building was 100 years and that 150 F/T cycles were expected during that time. In fact, there may be more such cycles. The limitations of the basic study [9] on which the proposed mathematical models in this paper are based were implemented on water-saturated walls. In reality, this would mean that we are dealing with a completely saturated wall (e.g., due to flooding) that is subject to F/T.  
Given the current age of the building (built with lime mortar type M1), which is 70 years, we assumed that it was exposed to at least 105 cycles of F/T in its lifetime. If we are interested in the expected state in 20 years, from the graphs in Figures 2 and 3, for the age of the building of 90 years (or 135 cycles), we can expect a 5.3% and 14.5% reduction in the Young's modulus and ductility (Figure 7).  
For the observed building in the hypothetical scenario, we may also be interested in the probability that the damage will be limited (or acceptable) in the next 20 years (for the expected 135 F/T cycles). Since we are aware that the available data for the observed building are quite unreliable (note again that the demand is taken into account deterministically according to the basic definition of fragility curve), we require that the damage index should not exceed the value of 0.6. With a few iterations (we considered the linear interpolation between the proposed curves; see Figure 8), we arrived at the estimate that the probability for such an event is 0.62, which is a relatively high value (approximately in three cases out of five). If such a risk suits our needs, we can most likely plan appropriate renovation/remediation measures in 20 years. It should be noted, however, that in the  
Figure 6: Existing masonry brick building (mortar type M1) at the age of 70 years and corresponding localized damage after the assumed 105 F/T cycles analyzed for a hypothetical scenario.  
assessment, we assumed that there is a clear relation between the damage index and the actual damage, which ensures the effectiveness of the proposed fragility curves.  
The proposed fragility curves provide different interpretations of the obtained results. In addition, by knowing the theoretical basis of the probabilistic approaches, they also offer us various quantitative answers related to risks connected to the management and maintenance of individual buildings or building stock (optimal planning of renovations and other measures).  
Figure 7: Predicted values for Young’s modulus (**a**) and ductility (**b**) after 20 years for an existing masonry brick building in a hypothetical scenario. The graphs from Figures 2 and 3 were applied.