## 4 Evaluation of Design Response Spectra  
The design response spectra derived in the previous section were evaluated against those from the current seismic design code in Romania P100-1/2013 [29]. This code, as well as its previous versions from 1992 [30] and 2006 [31], defines the design response spectra based on two parameters: the design peak ground acceleration (which has a mean return period of 225 years) and the control period T\({}_{\text{C}}\) (which is a proxy for the site conditions). The difference in soil conditions is accounted for in the seismic design code P100-1/2013 [29] by having three values of the control period T\({}_{\text{C}}\), namely 0.7 s, 1.0 s and 1.6 s. Neither version of the Romanian seismic design codes employed the site classifications approach from the original Eurocode 8 [3]. The zonation map for T\({}_{\text{C}}\) from the most recent version of the Romanian design code P100-1/2013 [29] was based on the ground motions recorded during the Vrancea intermediate-depth earthquakes of March 1977, August 1986 and May 1990. More details about the zonation maps in the previous versions of the code can be found in the papers of [PERSON] et al. [32] and [PERSON] et al. [33]. The control period T\({}_{\text{C}}\) was evaluated numerically using the relations proposed by [PERSON] et al. [34]. The reasons for the approach employed in the P100 series of design codes were mainly related to the significant long-period spectral amplifications that were observed in the ground motion recordings of large magnitude Vrancea intermediate-depth seismic events at sites located in the southern part of Romania and could not be captured using the Eurocode 8 [3] approach. For instance, in the case of Bucharest, the study of [PERSON] et al. [35] revealed that the median site amplifications decrease with the increase in the peak ground acceleration for spectral  
Figure 3: (**a**) A comparison between the spectral accelerations that had a mean return period of 475 years for rock conditions for T = 0.2 s obtained from the seismic hazard model of [PERSON] et al. [27] and from the ESHM 2020 model [26]; (**b**) a comparison between the spectral accelerations for rock conditions for T = 1.0 s obtained from the seismic hazard model of [PERSON] et al. [27] and from the ESHM 2020 model [26]. periods of up to 2.0 s, while for longer periods, an increase in the median site amplifications can be observed. As well as the recorded evidence, the significant damage and collapse of high-rise structures in Bucharest were observed during the last two major Vrancea earthquakes in 1940 and 1977, which shows the long-period content of the ground motions in this area. A comparison between the following parameters (control period T\({}_{\text{C}}\) and maximum spectral acceleration corresponding to the plateau of constant values) of the design acceleration response spectra from the current seismic design code of Romania P100-1/2013 [29] and based on the current Eurocode 8 draft revision [1] is shown in Figure 4 for soil class B sites, in Figure 5 for soil class C sites and in Figure 6 for soil class F sites. It can be observed from the comparisons presented in Figures 4-6 that the largest differences between the metrics computed according to P100-1/2013 [29] and based on the Eurocode 8 draft revision [1] were obtained for the control period T\({}_{\text{C}}\). In most of the cases (with the exception of Banloc), the maximum spectral acceleration was obtained based on the approach from Eurocode 8 draft revision [1].