# Seismic Assessment and Strengthening of a Load-Bearing Masonry Structure Considering SSI Effects
## 6 Discussion
Interestingly, the second-floor masonry in Model M1 is reinforced with timber laces at both the floor and roof levels, yet exhibits greater stiffness and strength compared to M2. In contrast, in Model M2 there is a reinforced concrete beam at roof level. Nevertheless, stress exceedances are observed in both models, while the structural system of M2 appears to be more vulnerable under the seismic scenarios examined in this study. Concerning interstorey drift ratios (IDRs), SSI increases the relative floor displacements--typically by nearly double--across most seismic combinations and structural models. The sole exception is case M2 Kah2, in which the maximum IDR value remains unchanged. Regarding in-plane deformation, no IDR value exceeded the 4% threshold, with drift ratios remaining low (around 0.2%). However, out-of-plane deformation exhibited significantly higher values on the second floor, particularly in cases M2 ssiKah1, M2 ssiKoc1, M2 ssiKoc2, M2 fixNor2, and M2 ssiNor1 and Nor2, where the 8% threshold was surpassed. The IDR differences for each seismic scenario are listed below in detail:  
Model 1
* In the Kahramanmaras earthquake, the maximum IDR on the second floor is recorded in case M1 ssiKah1, reaching 6.8%--the highest IDR value among all M1 seismic cases, in agreement with the values reported in Table 11. The increases observed in the SSI models are 117% for the Kah1 event and 78% for Kah2. * In the Northridge earthquake, the maximum IDR on the second floor is recorded in case M1 ssiNor2, reaching 6.5%. The increases observed in the SSI models are 97% for the Nor1 event and 99% for Nor2. * In the Kocaeli earthquake, the maximum IDR on the second floor is recorded in case M1 ssiKoc2, reaching 6.35%. The increases observed in the SSI models are 89% for the Koc1 event and 88% for Koc2. Model 2
* In the Kahramanmaras earthquake, the maximum IDR on the second floor is recorded in case M2 ssiKah1, reaching 9.53%. With regard to the SSI models, the Kah1 event exhibits a 25% increase, while SSI has virtually no effect in the Kah2 event, as the IDR increases by only 1%. * In the Northridge earthquake, the maximum IDR on the second floor is recorded in case M2 ssiNor2, reaching 10.41%--the highest IDR value among all M2 seismic cases, in agreement with the values reported in Table 11. The increases observed in the SSI models are 30% for the Nor1 event and 27% for Nor2. * In the Kocaeli earthquake, the maximum IDR on the second floor is recorded in case M2 ssiKo1, reaching 9.69%. (Koc2 exhibits a nearly identical value of 9.63%). The increases observed in the SSI models are 29% for the Koc1 event and 54% for Koc2. A comparison between models M1 and M2 regarding the effects of SSI on IDRs leads to the same conclusion previously drawn concerning maximum stresses--namely, that SSI has a greater influence in model M1. Overall, the increase in IDRs observed in the SSI models is in line with [16], where the incorporation of soil-structure interaction (SSI) into the analysis of historical load-bearing masonry structures revealed significant increases in drift ratios. Finally, comparing models M1 and M2 in terms of IDR values, it is observed that, for the same seismic combination, maximum relative floor displacements exhibit significant increases on the second floor in M2. It is also observed, that the largest percentage increases are recorded in fix-based models. Specifically, the greatest percentage change is recorded in the M1 fixKah2 and M2 fixKah2 models (217%), with a range of values for all combinations spanning from 85% to 217%. The SSI models show an average percentage change in IDR of approximately 60%, with a range between 40% and 76%. It should be noted that this analysis refers to percentage changes; however, as mentioned above, the highest values are recorded in the Mssi models. The detected concentration of maximum displacements on the second floor in M2 could indicate that the RC interventions have led to an irregular distribution of stiffness, fostering soft-story behavior.