Two-level performance-based seismic design approach for steel frames with novel self-centring seismic base isolators

A two-level performance-based seismic design (PBSD) approach for frame structures isolated by self-centring isolators (SCIs) is proposed in this study. Unlike the traditional PBSD process that generally designs a structure for a specific seismic intensity level first and then checks structural performance for other levels, the proposed PBSD approach considers both the design basis earthquakes (DBE) and maximum considered earthquakes (MCE) by analysing two different nonlinear equivalent structural models, thereby enabling the accurate control of structural performance objectives at two different seismic intensity levels during the design process. The design method combines the fundamental displacement-based design process and the widely-accepted nonlinear response spectra. A four-storey frame structure, equipped with novel SCIs consisting of rubber bearing, steel Ushaped dampers, and shape memory alloy U-shaped dampers, is designed as an example. Seismic analysis results demonstrate that the two-level PBSD approach can satisfactorily achieve the predefined performance objectives at both DBE and MCE levels. Although the design process is applied to SCI-isolated structures in this study, the design framework can be easily extended to other types of isolated structures to enable the advanced design that can achieve the target performances at DBE and MCE levels simultaneously.