Simplified direct loss measure for seismic isolated steel moment-resisting structures

Seismic base isolation provides an effective means for resilient structures, protects structures from the damaging effect of seismic action and reduces structural vibration, casualties and financial losses. The life cycle costs and advantages of using base isolation can be quantitatively supported by using the FEMA P-58 methodology, but damage and loss estimation using such an approach is time consuming and costly. This study presents a new direct loss measure (LM) for seismic isolated steel moment-resisting structures. Three steel moment-resisting frames of 4, 6 and 8 stories were studied with and without isolation system and 3D nonlinear model of the structures was developed in Opensees. Using common incremental dynamic analysis (IDA) under far-field and near-field records, the expected annual loss (EAL) based on FEMA P-58 approach was estimated. In this regard, LM was introduced for rapid modeling of response based on two main sources of structural damage, that is, interstory drift ratio and peak floor acceleration considering structural and non-structural elements. A good correlation was observed between the EAL and proposed LM. The fixed-base structures were subject to extensive damage and complete failure in the maximum considered earthquakes (MCE), while the base-isolated structures were subject to moderate failure rate in the same situation, indicating the resilience of these structures. The proposed LM can be used for prompt and efficient loss estimation of the base-isolated structures and demonstrate the cost-effective seismic risk management of these systems.