Seismic resistant design of building structures with rigid basement levels

In this study, a representative building with laterally-rigid basement levels is analyzed under design earthquake loads, using the latest approaches recommended in the Turkish Building Seismic Code 2018 (TBSC 2018). The same structure is used to apply the earthquake analysis methods suggested in the previous version of the Turkish Seismic Code (TEC 2007), as well as ASCE 7-10 and Eurocode 8, for comparative assessment of analysis results. In TBSC 2018, two main approaches are proposed for strength-based design of building structures with rigid basement levels. In the first approach, for buildings that satisfy the code definition to be considered as buildings with a rigid basement, it is permitted to consider the upper and the lower portion masses separately in the analysis, yet using the same structural model, since the two portions have modal characteristics that are well-separated from each other. This approach is similar to the methodology in the previous 2007 Turkish Seismic Code, as well as the Two-Stage Analysis method in ASCE 7-10. An interesting point about the TBSC 2018 method is the permission to use Modal Response Spectrum Analysis for the rigid lower system, which is not permitted in both TEC 2007 and ASCE7-10. Results obtained using another analysis method specified in TBSC 2018, which involves considering the total mass of the structure including the basement levels, referred to as the Total Structure Approach are also evaluated, using both the Equivalent Lateral Load and Modal Spectral Analysis procedures. Finally, a nonlinear model of the representative building is generated and Nonlinear Response History Analysis results are compared with the response quantities obtained using the TBSC 2018 methods, in order to assess the level of reliability or overconservatism in the different analysis methods specified in TBSC 2018.