## 4 Effect of SSI on the Capacity and Demand Response of Existing Buildings
### Effect of SSI on the Displacement Response of Existing Buildings
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Name of** & **Depth (km)** & **PGA (g)** & **PGV (cm/s)** & **PGD (cm)** & **Vmax/Amax (s)** \\ \hline CAP-RIO270 & 18.50 & 0.39 & 40.58 & 47.44 & 0.11 \\ CHI-TCU74N & 13.67 & 0.35 & 39.54 & 49.12 & 0.12 \\ CHI-TCU95W & 43.44 & 0.38 & 59.39 & 80.09 & 0.16 \\ COA-PLE045 & 8.50 & 0.59 & 59.38 & 14.36 & 0.10 \\ KOC-DZC270 & 12.70 & 0.36 & 61.02 & 252.44 & 0.17 \\ LAN-CLVTR & 21.20 & 0.42 & 41.40 & 22.07 & 0.10 \\ LOM-BRN000 & 10.30 & 0.45 & 50.43 & 16.20 & 0.11 \\ LOM-BRN090 & 10.30 & 0.50 & 43.79 & 13.03 & 0.09 \\ LOM-CYC285 & 21.80 & 0.48 & 43.91 & 81.28 & 0.09 \\ LOM-G03090 & 14.40 & 0.37 & 43.08 & 25.31 & 0.12 \\ LOM-SAR000 & 13.00 & 0.51 & 41.26 & 16.42 & 0.08 \\ NOR-CNP196 & 15.80 & 0.42 & 57.01 & 67.59 & 0.14 \\ NOR-LOS000 & 13.00 & 0.41 & 44.84 & 20.16 & 0.11 \\ NOR-LOS270 & 13.00 & 0.48 & 44.52 & 15.25 & 0.09 \\ NOR-MU2035 & 20.80 & 0.62 & 41.93 & 16.57 & 0.07 \\ NOR-MUL009 & 19.60 & 0.42 & 55.74 & 55.98 & 0.14 \\ NOR-ORR090 & 22.60 & 0.57 & 53.72 & 37.60 & 0.10 \\ NOR-ORR360 & 22.60 & 0.51 & 51.32 & 31.36 & 0.10 \\ NOR-SAT180 & 13.30 & 0.48 & 65.88 & 102.17 & 0.14 \\ NPAL-NPS210 & 8.20 & 0.59 & 72.12 & 13.45 & 0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: General properties of selected real earthquake records. Figure 11: Response spectrum of selected real ground motion records used in this study. Distribution of results also shows that probabilistic roof displacement demands in old buildings (98-) are greater than new ones (98+), as expected. On the other hand, differences among the roof demand curves of especially in five- and six-story buildings are relatively low with respect to other ones. In other words, the effect of SSI is much more pronounced in low-rise buildings having relatively higher stiffness capacities and strength ratios. This situation is much more evident in three- and four-story new buildings (98+). All these investigations have shown that relative effect of SSI especially in soft soil case is much more significant in stiffer and stronger buildings. Numerical evaluations of results have indicated that probabilistic roof drift ratios calculated for soft soil case can be 1.3 to 1.7 times greater than that of fixed-base case in three-story new buildings. However, these ratios decrease to 1.2 to 1.3 in three-story old buildings depending on the probability of exceeding levels (50%, 10% and maximum (0%)). The same ratios in six-story old buildings range from 1.05 to 1.2. These numerical comparisons indicate that the relative effect of SSI is much more effective in stiffer and stronger low-rise buildings. It can be admitted that the obtained results show consistency with the results obtained from similar studies in literature [21]. Figure 14: Cumulative exceedance probability curves of the five-story buildings. Figure 15: Cumulative exceedance probability curves of the six-story buildings. In addition to evaluation of roof drift ratios, effects of SSI on the inter-story drift ratios are also discussed. In Figures 16-23, mean inter-story drift ratios are plotted for different building groups and soil types. While calculating the inter-story drift ratios, the same method was applied. One hundred inter-story drift ratios obtained from five buildings and 20 acceleration records were used and values corresponding to probability of exceeding levels of 50%, 10% and maximum drift ratios were averaged. This method was repeated for each story group. Variation of inter-story drift ratios clearly show that the most significant changes depending on the SSI occur at the bottom stories of the buildings [21] and the most evident increments are again observed in the soft soil case. All of these figures indicate that inter-story drift ratios are increased in the soft soil case in all probability levels. Inter-story drift ratios at 50% probability level are lower than 0.5% and the difference between the soil types in terms of story drift ratios is not obvious.