SEISMIC FRAGILITY OF FREESTANDING BUILDINGS CONTENTS MODELLED AS RIGID BLOCKS

Abstract eng:
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 rockingdominated response. The outcomes of the numerical analyses show that the considered modeling 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 underestimated 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 ‘‘PGAdominated’’. 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.

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