SEISMIC LOSS ASSESSMENT CONSIDERING STRUCTURAL DAMAGE AND OVERTURNING OF FREE-STANDING NONSTRUCTURAL COMPONENTS

Abstract eng:
In the last decades, earthquake engineering is dedicating more attention to nonstructural components (elements of a structure with primary function other than sustaining loads). The reason behind their increasing importance is that economic losses associated to damage of nonstructural components (NSCs) may far exceed losses from structural damage [1]. Moreover, damage to NSCs can occur at intensity levels of ground shaking lower than those required to damage the structure and may produce temporary loss of function in the building even if the structural components remain undamaged. Although this issue has been known for a long time, a comprehensive methodology to estimate the expected seismic losses due to damage sustained by both structural and nonstructural components in the life-cycle of a structure has yet to be fully consolidated. This is partly due to the complexity introduced by the variety of existing NSC typologies - see for example the classification proposed by [2]. This paper considers a single type of NSC that can be modelled as an unrestrained symmetric rigid block subjected to rocking, its mass being low enough to avoid any effect on the dynamics of the supporting structure. This type of element can be representative of many NSCs such as: (i) mechanical and electrical systems or furnishings in ordinary buildings; (ii) cabinets, shelves or medical equipment in strategic structures such as hospitals; (iii) sculptures and cultural heritage objects in museums. The proposed procedure is aimed at the life-cycle loss assessment of a building-system consisting of a structure and the described category of NSCs contained in it; the followed approach is in accordance with the performancebased paradigm of [3]. While the dynamic behaviour of rigid blocks directly subjected to ground acceleration has been studied extensively in the past, the present paper presents a study of the dynamic behaviour of the rigid block at a generic floor along a structure’s height, when that structure is experiencing base-acceleration due to an earthquake. Thus, considering the limit state of rigid block overturning, a set of seismic intensity measures (IMs) at the base of the structure and engineering demand parameters (EDPs) at each floor are investigated with regard to fitting fragility curves for the element. Relevant statistical properties for these parameters (e.g., stochastic efficiency, sufficiency and robustness to scaling - [4]) are examined and discussed. Hazard computability of the IMs is always considered. These fragility models are then implemented in a performance-based framework for life-cycle risk assessment of the building, illustrated by means of implementation in a case-study numerical application. The structure considered in the application is a regular code-compliant reinforced-concrete building designed in accordance with Eurocode 8. The building is located in central Italy where the probabilistic seismic hazard assessment is known. Results in terms of rate of expected losses due to structural and nonstructural damage are discussed in order identify limitations and possible generalizations of the simple case considered.

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