This study investigates the seismic performance of a theoretical hospital building designed as a Fixed-Base (FB) structure according to TSC-2018 (Turkish Seismic Code) and evaluates its behavior under three scenarios: FixedBase (FB), Soil-Structure Interaction (SSI), and Base-Isolated (SSI+ISO). The study employs Nonlinear Time History Analysis (NLTHA) using scaled acceleration records, including one from the 2023 Maras, earthquake. Structural performance is assessed based on maximum roof displacements, interstory drift ratios (IDR), and isolator displacements. Results show that base isolation systems significantly reduce drift demands and roof displacements, keeping the structure within slight damage limits even under extreme seismic loads. In contrast, SSI effects amplify interstory drift demands, increasing the likelihood of exceeding moderate damage thresholds. The analysis highlights the Maras, Education and Research Hospital, which suffered severe damage and became non-operational during the 2023 Kahramanmaras earthquake. This outcome underscores the limitations of fixedbase designs in regions with soft soil conditions and the necessity of incorporating base isolation systems to improve seismic resilience. The findings emphasize the importance of mandatory adoption of base isolation systems in hospital designs, proper consideration of SSI effects, and the retrofitting of existing hospital buildings to meet modern seismic code requirements (TSC-2018) and prevent similar failures in future seismic events.

In recent years, researchers have taken advantage of the nonlinear characteristics of the underlying soil to mitigate the excessive seismic force demands on the superstructure under earthquake excitation. For this purpose, the conventionally designed foundation can be replaced with rocking foundation. This is achieved by under proportioning the shallow foundation. Although the mechanism of rocking foundations has been well documented, there remains a gap in developing a methodology for reduction of foundation sizes in multi storey Reinforced Concrete (RC) shear wall framed structure. Therefore, this study focuses on the seismic responses of a shallow foundations supporting a multistorey RC shear wall framed structure. The foundation for RC shear wall is proportioned by gradually reducing the earthquake load considered for the foundations to enhance the increased rocking effect and to mitigate seismic force demands. Thereafter, key parameters responsible for seismic behavior of sub-structure are being compared with conventionally designed foundation with increasing foundation rocking, by varying type of underlying soil and with increasing height. Seismic behavior obtained by implementing a series of nonlinear time history analyses indicates that the foundation rocking greatly influences the dynamic properties. With increasing degree of foundation rocking, natural fundamental period of the overall structure gets lengthened, with decreasing peak roof acceleration, thereby mitigating the peak base moment and base shear experienced at the shear wall compared to conventionally designed foundation. On the other hand, it is observed that there is an increase in roof displacement and shear wall settlement at the foundation level. It is found that the foundation of shear wall can be designed by considering 40%, 60% of earthquake loads for zone V and zone II structural designs, respectively without encountering excessive settlements. From the sensitivity analysis it is highlighted that the foundation size and design seismicity impact the base shear contribution ratios between shear wall and column members, fundamental natural period and foundation settlement.

A careful evaluation has been carried out to reveal advantages and disadvantages of linear and nonlinear modelling in dynamic analysis. 4- and 7- story building models representing characteristics of about 500 existing buildings models in Turkey was used in analyses. In the study, displacement demand parameters such as roof drift ratio and interstory drift ratio obtained from linear and nonlinear analyses were compared using a total of 24 ground motion records including forward directivity effects (Set 2) as well as records (Set 1) recorded in type B and C soils. Although the seismic demands for Set 2 are obtained extremely high in the nonlinear models, the demand differences between Set 1 and Set 2 are not excessive for the linear models. In the region where the T/Tp ratio is close to one, the linear analysis predicts unrealistically high demands compared to the nonlinear analysis. Linear analysis results mostly show an increase or decrease depending on dynamic amplification effects. The effects of ground motion intensity and damage mechanism cannot be observed in linear analysis method. For all these reasons, it is recommended not to prefer linear modeling method when using time- history analysis.