## 5 Results and Discussion
Figure 7: Effect of soil type on the SD response of structures with (10 m \(\times\) 10 m) foundation blocks. Figure 9: Effect of soil type on the SD response of structures with (30 m \(\times\) 30 m) foundation blocks. To examine the impact of foundation block thickness on the SD values, superstructures with a height of \(H\) = 21m and small foundations (10 m \(\times\) 10 m) placed on both hard (ZB and ZC) and soft (ZD and ZE) soils are analyzed. The foundation block thickness values considered are \(h\) = 0.5 m, 1.5 m, and 2.5 m. This analysis investigates how changes in foundation block thickness affect the dynamic SFSI behavior across different soil types. The SD values of the structures do not vary with changes in foundation thickness (\(h\) = 0.5 m, 1.5 m, and 2.5 m) for any soil type (ZB, ZC, ZD, and ZE), as shown in Figures 11-14. However, for soil types ZD and ZE, the SD values of superstructures decrease by more than 15% compared to those on ZB and ZC soils. As expected, dynamic SFSI leads to significant changes in the behavior of superstructures on soft soils. When considering SFSI effects (compared to fixed-base structures), the increased flexibility results in a reduction in the seismic loads experienced by the superstructure. Structures on soft soils experience greater vertical settlements but suffer less structural damage, while higher relative displacement values are observed for structures on hard soils compared to those on soft soil. Figure 11: Effect of varying foundation block thicknesses on the SD response of structures on ZB soil. Figure 10: Effect of soil type on the SA response of structures with (10 m \(\times\) 10 m) foundation blocks. To evaluate the effects of different building heights (\(H\) = 7, 14, and 21 m) on acceleration and displacement response spectra, analyses are conducted on soil-interacting structures with foundations (10 m \(\times\) 10 m \(\times\) 1.5 m) situated on different soil types. As shown in Figures 15-17, SD values significantly decrease as the building height increases for ZB, ZC, and ZD soil classes. When the height of the superstructure increases from 7 to 21 m, the SD values for superstructures with a natural vibration period exceeding 2.4 s decrease by more than 20%. Although the percentage decrease varies for the specified soil types, no consistent pattern is observed for the ZE soil type, particularly in cases where the building heights, with periods longer than 3 s, increase from 14 to 21 m (Figure 18). The decreasing trend in SA values continues as building height increases. Additionally, as the building height on soft soil (ZE) increases from 14 to 21 m, the plateau region expands compared to the response of buildings on hard soil (ZB), as shown in Figure 19. This result indicates that the period value used for design in the hard soil system may fall within the risky plateau region for the soft soil system. Therefore, it is crucial for structural design to account for soil type to ensure safety and optimal performance. Figure 14: Effect of varying foundation block thicknesses on SD response of structures on ZE soil. Figure 15: Effect of changes in building height on the SD response of structures on ZB soil. Figure 6:0 Effect of changes in building height on the SA response of structures on hard (ZB) and soft (ZE) soils. Figure 6:1 Effect of changes in building height on the SD response of structures on ZC soil. Figure 6:2 Effect of changes in building height on the SD response of structures on ZD soil. on ZD soil is approximately four times greater than that on ZC soil, while the displacement on ZC soil is about three times greater than that on ZB soil. This behavior is consistently observed at other time instances as well. In structures on soft soil, a large portion of the earthquake's energy is absorbed at the foundation level, resulting in lower earthquake accelerations being transmitted to the superstructure. This implies that structural damage is generally greater in systems built on hard soils.