Seismic resilience assessment of buildings with underground stories considering soil confinement

Many buildings are constructed with multiple underground stories, even if engineers do not commonly incorporate the underground stories in the seismic design. In addition, the common design practice is to neglect the effects of soil confinement on the performance of buildings under seismic loads. However, it is demonstrated that the seismic resilience performance of both low-rise and high-rise buildings, considering the couple effects of underground stories and soil confinement, needs a profound understanding. This paper aims to assess these mechanisms by performing shaking table tests and 3D numerical simulations on seven-story and fifteen-story structures, including several underground story percentages with variable support conditions (fixed, flexible) under different seismic motions. The experimental models were based on a precise geometric scaling factor (lambda = 1:50) to represent the realistic performance of the buildings. Advanced numerical models were developed using PLAXIS 3D software to simulate the complex soil and structure with variable underground story percentages. The experimental and numerical outputs for scaled models were compared with the numerical real models in both support conditions (fixed, flexible), demonstrating that the applied shaking table may represent the complex mechanisms of the soil-structure coupling. The final objective was to compare the two types of buildings in terms of lateral displacement and shear force to demonstrate the impact of the soil-structure couple on the seismic resilience performance of these buildings. It was also shown that underground stories are more affected in cases of low-rise buildings if compared with high-rise buildings, whether fixed or flexible-base cases.