SEISMIC PERFORMANCE EVALUATION OF MULTI-STOREY BUILDINGS WITH BASEMENT

Abstract

In metropolitan cities, there is an increasing demand for tall buildings with basements and podiums due to their advantages in space utilization, safety, amenities, and cost-effectiveness, making them an optimal choice for developers and property owners. This dissertation examines the methods and challenges involved in evaluating the seismic performance and behaviour of tall buildings with basement structures under various loading conditions. The main issues involved in such types of structures, are backstay effect, soil-structure interaction and tower-tower interaction are also discussed. The numerical modelling and analysis procedures are conducted using ETABS 20.3.0 software and spectral matching with Seismomatch, and comparisons are made between tower-only models and tower-and-basement models under varying parameters. Backstay sensitivity analysis is also performed by adjusting the stiffness of basement walls and slabs. The dissertation investigates different analysis methods, including equivalent static, response spectrum analysis, linear modal time history, and linear direct time history analysis. Additionally, the study explores modelling and analysis procedures for structures with soil- foundation modelling using the bathtub model, highlighting differences between fixed-base support and soil-influenced behaviour. Detailed calculations of various types of loads on the chosen tall building with a basement are conducted, and manual verification methods are discussed towards the end of the thesis. The thesis also includes comparisons among various methods of analysis to understand their effectiveness and presents the results of all problem statements. The research concludes with key findings that can improve design practices for these complex structures. The thesis concludes that modelling shear walls as wide columns offers advantages over shell elements. Despite the additional computational time required, it is recommended to model the tower and basement together to account for the backstay effect as separate modelling of the substructure results in overly conservative design forces. Additionally, the rigid diaphragm model underestimates forces compared to the semi-rigid diaphragm, which accounts for in-plane stiffness. Finally, the report emphasizes the importance of carrying out time history analysis for complex structures like high-rise buildings with basements, where dynamic behaviour and detailed response are crucial and considering soil interaction during modelling due to its significant influence on seismic response.