Seismic fragility of freestanding buildings contents modelled as rigid blocks

The loss of functionality of health care facilities, which should be guaranteed particularly in the aftermath of moderate-to-severe earthquake ground motions, is typically caused by damage to nonstructural elements, such as freestanding cabinets. The assessment of the seismic fragility of such components assumes a key role in the evaluation of the performance of a healthcare facility. The present work is aimed to assess the adequacy of the rigid block modeling approach in predicting the seismic response of freestanding nonstructural components with rocking-dominated response. The outcomes of the numerical analyses show that the considered mod-eling technique can provide a reliable prediction of the occurrence of rocking mechanism and predict the occurrence of the overturning. In particular, the overturning PFA is slightly un-derestimated in case a 1.0 coefficient of restitution is considered. But the question then arises as to which intensity measure (IM) is well correlated to the seismic performance of rigid blocks. A fragility study on a number of rigid blocks is therefore conducted in the present paper. Comprehensive incremental dynamic analyses on different rigid blocks highlight that the dimensionless intensity measure PGA/(g tanα) is an efficient intensity measures to predict rocking occurrence in a generic rigid block. The intensity measure pPGV/ (g tanα) is the most efficient one only for large, say R larger than 2.0 m, rigid blocks. Very small, say R<1.0 m, rigid blocks tend to overturn as soon as they start rocking and are therefore ‘‘PGA-dominated’’. PGA/(g tanα) is therefore more efficient for such blocks. The use of these intensity measures allows assessing a unique fragility curve for rigid blocks characterized by different geometries, which may serve as a simple tool for the estimation of the damage occurred in rigid blocks after earthquakes