## 3 Results
### Parameters of Strong Ground Motion
Regarding the seismic code improvement, there are requirements in design codes for complex or high-risk structures. However, this type of analysis not only influences the standards but also actively helps to rewrite them, which is beyond the scope of this study. The bounding effect caused by insufficient separation distances during earthquakes [60] is not discussed in detail in this work. Seismic bounding occurs when adjacent buildings have insufficient separation during earthquakes, resulting in excessive vibration and potential damage. For a 20 m-tall building, the required separation distance is calculated based on the maximum lateral drift. With a drift ratio of 1.5%, the total drift is 29.7 cm. The 22 May 2012 earthquake did not cause non-elastic deformations, highlighting the importance of proper separation and mitigation measures to prevent structural damage. The pulse identification module is used to classify seismic motions as either pulse-like (PL) or non-pulse-like (NPL), following the methodology of [PERSON] et al. [61]. Beyond defining a new pulse indicator (PI) calculated as the cross-correlation factor between the dominant pulse and the original record, the method also identifies the predominant pulse within a seismic record, thereby aiding in the better classification and understanding of ground motion characteristics [62]. The analysis evaluates key parameters to determine whether the 22 May 2012 earthquake near Pernik exhibited a pulse-like or non-pulse-like nature. It also classifies the horizontal (EW, NS) and vertical (UD) components of seismic motion recorded at two instrumented stations: SGL1 (located in the basement) and SGL2 (located on the sixth floor). The processed velocity time histories for the horizontal components at both stations are presented in Figure 5. Seismic motions near fault zones are often characterized by intense velocity and displacement pulses with relatively long periods, distinguishing them from typical far-field ground motions. These high-velocity pulse-like movements can significantly amplify seismic responses in structural systems, potentially leading to adverse effects on physical structures [57]. Looking at the basement NS pulse indicator (Figure 5c), the velocity reaches a prominent peak around 6-8 s, indicating a strong seismic pulse. The oscillations decay gradually, stabilizing around 20-30 s. The oscillations appear relatively smoother, indicating a lower frequency component compared to the response on the sixth floor. The initial peak is sharp and well-defined, suggesting that the basement experiences a direct seismic input. On the sixth floor, the NS pulse indicator (Figure 5d) shows a peak at a similar timeframe (around 6-8 s), but with an overall amplitude higher than that of the basement. The oscillations persist for a longer time with noticeable amplitudes, which is typical for higher structural levels due to dynamic amplification. The sixth-floor response displays more high-frequency oscillations, suggesting greater structural resonance effects on the sixth-floor level. While the initial peak is comparable in timing to the basement, the subsequent oscillations are more pronounced, indicating amplified vibrations. For the SGL2 sixth-floor horizontal component shown in the figure, the computed PI value is 0.50447, which classifies it as non-pulse-like according to established thresholds. Nevertheless, the velocity time history exhibits moderate velocity transients around 7-10 s, which may still influence dynamic amplification at upper floors. Referencing ASCE 7-16 and Eurocode 8, even when motions are classified as non-pulse-like, near-threshold PI values (e.g., \(\sim\)0.5) can still demand increased deformation capacity, underscoring the importance of robust detailing and energy dissipation measures in mid-rise reinforced concrete (RC) frames.