Impact of Soil Flexibility on Seismic Behavior of Multi-Story Reinforced Concrete Structures

Abstract

The relationship between the ground and structural system is crucial for the seismic performance of high-rise reinforced concrete edifices. Traditional seismic design approaches typically assume a fixed-base condition, overlooking the flexibility of the underlying soil layers. Soil-structure interaction (SSI) can significantly affect the seismic response by altering natural frequencies, damping ratios, and the overall dynamic behaviour of the structure. This study investigates the influence of soil-structure interaction (SSI) on the seismic performance of high-rise reinforced concrete (RC) edifices, highlighting various soil conditions, structural configurations, and ground motion characteristics. Finite element modelling and time history analyses are employed to simulate real seismic events, highlighting the necessity of including soil flexibility into design approaches to improve structural safety. A thorough parametric analysis is conducted by modelling high-rise reinforced concrete structures of varying heights and stiffness on multiple soil types, including soft clay, medium-dense sand, and hard rock. The results demonstrate that structures on softer soils experience increased lateral displacements, prolonged fundamental periods, and elevated base shear demands relative to those on stronger soils. Moreover, the extent of soil-structure interaction escalates with taller and more flexible structures. The study investigates the critical role of foundation system types—namely shallow vs deep foundations—in mitigating adverse soil-structure interaction impacts. Critical findings indicate that neglecting SSI may lead to an underestimation of seismic demands, hence compromising structural integrity during major earthquakes. Recommendations are provided for incorporating SSI considerations into the seismic design of high-rise reinforced concrete structures based on the findings. The study emphasises the necessity for integrated modelling approaches that account for the interdependent impacts of soil and structure under dynamic loading situations. It advocates for performance-oriented design solutions that incorporate site-specific soil properties to enhance resilience against seismic events. Understanding soil-structure interaction allows engineers to generate more accurate predictions of building performance, leading to safer, more economical, and sustainable designs in seismically active regions.