Seismic Analysis of Two Adjacent High-Rise Buildings Resting on Soft Soils

This study investigates the behavior of two adjacent high-rise steel frames, one with 15 stories and the other with 30 stories, located on soft clay soil, under the effect of seismic loads. The main objective of the research is to assess the impact of soil-structure interaction (SSI) on the performance of tall steel moment-resisting frames. The analysis is carried out using nonlinear time history analysis in Abaqus finite element program, considering both rigid and flexible foundations. The results indicate that the behavior of the structures located on soft soil was close to the life safety zone, highlighting the importance of considering the effect of SSI in the elastic and inelastic seismic analysis and design of bending frames on soft soils. The study reveals that as the dynamic characteristics of the soil, such as the velocity of shear wave and modulus of rigidity, decrease, the maximum expected lateral force ratio on the base of the structure decreases, and the relative displacement of the floors increases. The regular linear and inelastic design process, which does not take into account the interaction effect, cannot guarantee the safety of structures on soft soils. The research findings indicate that the use of a flexible base significantly increases the deformation of the structures compared to a rigid base, with the maximum floor drift ratio increasing by 45% and 31% for the 15- and 30-story frames, respectively, compared to fixed base cases. The average base shear force for the frames located on soft clay soil is also lower than in fixed states. The conclusions of this study have important implications for the design of high-rise structures on soft soils and highlight the need for careful consideration of SSI effects in design processes.