## 4 Effect of SSI on the Capacity and Demand Response of Existing Buildings
### Effect of SSI on the Displacement Response of Existing Buildings
Figure 16: Mean of inter-story drift ratios corresponding to different exceedance probability levels for three-story new buildings. Figure 17: Mean of inter-story drift ratios corresponding to different exceedance probability levels for three-story old buildings. Figure 19: Mean of inter-story drift ratios corresponding to different exceedance probability levels for the four-story old buildings. Figure 20: Mean of inter-story drift ratios corresponding to different exceedance probability levels for the five-story new buildings. Figure 18: Mean of inter-story drift ratios corresponding to different exceedance probability levels for the four-story new buildings. Figure 21: Mean of inter-story drift ratios corresponding to different exceedance probability levels for the five-story old buildings. Figure 11:0 Mean of inter-story drift ratios corresponding to different exceedance probability levels for the six-story new buildings. Figure 11:1 Mean of inter-story drift ratios corresponding to different exceedance probability levels for the six-story old buildings. Drift ratios corresponding to probability of exceeding 10% are higher than that of 50% ratios and the effect of SSI becomes more apparent. Inter-story drift ratios at this probability level can be close to 1% in soft soil cases. However, variations of drift demands have indicated that the effect of SSI is not significant in upper stories and the response of upper stories is limited with respect to bottom stories. This situation is similar for all building groups and soil conditions. At this point, it should be stated that drifts caused by the rotations at the base due to SSI were extracted while calculating the inter-story drift ratios of first stories. Distribution of values indicates that the inter-story drift ratios of stiff and moderate soil conditions are closer to the fixed-base case with respect to ratios of soft soil. Story drifts corresponding to the soft soil case are much more remarkable and the level of increment is much more pronounced with respect to other cases. These observations about the effect of soil conditions are compatible with the findings related to the probabilistic roof drift ratios presented in Figures 12-15. Comparisons of probabilistic inter-story drift ratios indicate that there are considerable differences among the maximum and other probabilistic drift ratios. Effect of SSI is much more evident on the maximum drift ratios and results have shown that maximum drifts can approximately be greater than four times from the 50% drifts and two times from the 10% drifts. Graphical distributions show that these trends are almost similar in old (98-) and new (98+) buildings, but differences among the probabilistic drift demands are quite significant. Maximum inter-story drift ratios of buildings resting on soft soils are mostly higher than 1.5% and maximum inter-story drift ratios are generally accumulated at the first stories. This situation is much more apparent in low-rise buildings (three- and four-story) independent from the building group. However, distribution of values has shown that drift demands of especially upper stories are higher in old buildings with respect to new ones (see Figures 21 and 23). Critical stories in five- and six-story old buildings are the second stories and SSI does not change this situation. Decrease in column dimensions in the upper stories and the relatively higher vibration periods caused by upper stories are more critical in old buildings (98-). However, in new buildings the SSI strongly affected the response of first stories and the place of the critical story moved to the first story. The ratio of increment is much more significant in the first stories of new buildings with respect to old ones.