Geotechnical impact of outrigger-induced lateral response in tall buildings: a numerical study

Outrigger belt systems are widely adopted in tall buildings to enhance global lateral stiffness and control inter-story drift under wind and seismic loading. While their structural benefits are well documented, the associated geotechnical implications and soil–structure interaction (SSI) effects remain insufficiently explored in current design practice. This study investigates the geotechnical response of tall buildings equipped with outrigger systems using advanced three-dimensional finite element modeling in PLAXIS 3D V20. A representative 20-story reinforced concrete building is analyzed under various outrigger configurations and soil conditions to evaluate changes in load transfer mechanisms, foundation response, settlement distribution, and lateral ground deformation. The numerical framework incorporates realistic soil constitutive models and staged construction to capture coupled structural–geotechnical behavior. Results indicate that incorporating an outrigger system significantly enhances overall structural performance, reducing global building drift by up to 53% for structures founded on stiff clay with an undrained shear strength of Cu = 40 kN/m². However, the increased stiffness of the superstructure modifies load paths and leads to geotechnical consequences, including an approximate 10% increase in total settlement and up to 30% higher lateral displacement at the foundation level. The study demonstrates that although outrigger systems are highly effective in controlling lateral deformation, they may introduce additional demands on the foundation and surrounding soil. These findings emphasize the necessity of integrating SSI considerations into the design and optimization of outrigger systems to achieve a balanced and performance-based approach that accounts for both structural efficiency and geotechnical safety in tall building applications, The findings highlight the importance of considering soil-structure interaction in outrigger design to balance structural stiffness and geotechnical performance.