# Investigating the Reliability of Nonlinear Static Procedures
## 5 Results
### Influence of the Criteria Adopted for the Bilinear Idealization of the Pushover Curve  
This paragraph investigates how the method used to bilinearize the pushover curve affects the calculation of the structure's displacement capacity. Firstly, Figure 17 compares the resulting bilinear curves when varying the three alternatives summarized in Table 2.  
Figure 16: Ductility: in the first column is the X-analysis, and in the second column is the Y-analysis; the figures represent, in order, the three examined case studies, i.e., C, A, and B structural configurations of the Visso School building, with the first 125 values of ductility corresponding to the positive direction and the last 125 values corresponding to the negative direction. Figures 18-20 illustrate, through the solid black line, the fragility curves obtained from the NLDAs and, through the colored lines, the ones derived from the application of a given NSP while varying the method of bilinearizing the pushover curve (in red, according to the Updating EC8-3 rel.2019 document; in blue, according to NTC2018; and in green, according to [PERSON]'s proposal). It can be seen that the choice of bilinear has a non-negligible impact on the results when using the methods based on the use of inelastic spectra to calculate the displacement capacity, whereas the CSM method is not affected at all. Thus, it would be sufficient to vary the bilinearization approach to obtain very different results with the same N2-based NSP. The bilinear curves obtained with [PERSON]'s criterion allow us to obtain more conservative fragility curves than others. As shown in the following figures, the fragility curve obtained with NTC's bilinear is the most optimistic, while the one obtained with EC8's bilinear is slightly less optimistic. Figure 17: Resulting bilinear curves when varying the three alternatives summarized in Table 2 as a function of the examined case studies, i.e., A, B, and C structural configurations of the Visso School building [8; 32; 56]. Figure 18: Configuration of Visso C’s fragility curves: in the first column is the X-analysis, and in the second column is the Y-analysis; the method to calculate the displacement capacity is fixed (in order of rows, [PERSON] [PERSON] [33], [PERSON] [57], [PERSON] [32], [PERSON] [34]). In each figure, the solid black line corresponds to the results from NLDAs, while the colored lines to the NSPs with the three different alternatives for the bilinearization of the pushover curve. Moreover, the trend is the same in the X- and Y-directions, but it is more pronounced in the X- than in the Y-direction. It depends on the behavior of the building, i.e., whether the pushover curve shows the more progressive degradation of the stiffness in the initial phase (as in the case of Visso A and B) or behaves more linearly and then reaches the maximum resistance (as in the case of Visso C). Figure 19: Visso A’s fragility curves: in the first column is the X-analysis, and in the second column is the Y-analysis; the method to calculate the displacement capacity is fixed (in order of rows, N2 [PERSON] [33], N2 [PERSON] [57], N2 [PERSON] [32], [PERSON] [34]). In each figure, the solid black line corresponds to the results from NLDAs, while the colored lines to the NSPs with the three different alternatives for the bilinearization of the pushover curve. in the Y-direction, the bilinear curves are much more similar; this is reasonable because, examining the pushover curves, the Y-direction is almost a bilinear itself (the horizontal section of the pushover is horizontal), while, in the X-direction, there is the progressive degradation of the pushover. For this reason, the application of a criterion that changes the resistance (such as the NTC18 and EC8's bilinear), or another one that keeps the resistance equal to the maximum (as with [PERSON]'s bilinear), has a significant impact.