Limit state design of resilient earthquake-resisting systems

Sustainable seismic design (SSD) is the first step towards next-generation earthquake engineering. SSD of mixed multiple seismic systems (MMSSs), in which more than one earthquake-resisting structure is used, is a challenging structural engineering issue. Seismic sustainability implies survivability during and after an earthquake, preceded by post-earthquake realignment and repairs (PERR). Purpose-specific MMSSs are ideally suited for SSD. However, contemporary codes address neither the sequences nor the failure mechanisms of the earthquake-resisting structures of MMSSs. The difference between conventional design and SSD is their approach to expected behaviour during and after an earthquake. Earthquakes are natural and dynamic occurrences, whereas PERR is a manual and static process. SSD does not favour unreal detailing or oversimplifying assumptions; it is a multi-faceted effort that involves realistic structural analysis and planned manual operations. In this context, design implies operability with a view to PERR and requires a change from damageability assessment and performance-based seismic design to performance control and reparability-based design, including the development of new analytic tools and purpose-specific details. This article presents graphical solutions and theoretical principles to help achieve practical SSD for MMSSs. These new techniques may be used for practical reliability, economy and environmental protection.