Petrone, Crescenzo (2014) Nonstructrual components: seismic capacity and demand. [Tesi di dottorato]

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Abstract

Some research studies concerning nonstructural components are described in this thesis, based on several motivations: (a) the threat to life-safety that the collapse of nonstructural components can cause; (b) the attitude of these components in exhibiting damage (and the consequent evacuation of buildings) even for low-intensity earthquakes; (c) the huge economic loss connected to their damage. Different experimental activities are carried out aiming at the evaluation of the seismic capacity of some nonstructural components, i.e. innovative plasterboard partitions, hollow brick partitions, standard high plasterboard partitions, hospital building contents and plasterboard continuous ceilings. A test setup is defined for each test campaign in order to subject the specimen to the demand that it would experience in a building. Realistic boundary conditions of the specimen are reproduced. A testing protocol is defined according to AC 156, in case shake table tests are conducted, and FEMA 461 prescriptions, in case quasi-static tests are performed. A slight modification to the testing protocol provided by FEMA 461 is proposed, considering a set of European earthquakes in lieu of American ones, while a seismic input is derived based on AC 156 prescriptions for shake table testing. After each test of each campaign the visual damage is correlated to the occurrence of a given Damage State (DS) through the use of a damage scheme. A relationship between an Engineering Demand Parameter (EDP), e.g. the interstory drift ratio or the peak floor acceleration, and a predefined Damage State (DS), is established for the tested components. In case the number of specimens within a test campaign is adequate, the fragility curve of the tested specimens, that expresses the attitude that the specimens have to exhibit damage at different seismic demand levels, is also evaluated. The damage progression is correlated to different properties of the test setup, such as its natural frequency, damping ratio and the dissipated energy. Macro-models of the tested specimens are also defined based on the experimental results for an easy implementation in a structural model of the tested nonstructural components. The evaluation of the seismic demand on nonstructural components is also a main objective of this research study. Nonstructural components should be subjected to a careful and rational seismic design, in order to reduce the economic loss and to avoid threats to the life safety, as well as what concerns the structural elements. A parametric study on five RC frame structures, designed according to Eurocode 8, is conducted. It is found that the Eurocode formulation for the evaluation of the seismic demand on nonstructural components does not well fit the outcomes of the analyses. Some comments on the target spectrum provided by AC 156 for the seismic qualification of nonstructural components are also included and a modification is proposed. The counterintuitive approach of current building codes to the design of nonstructural components is highlighted. For this reason the seismic demand on acceleration-sensitive nonstructural components caused by frequent earthquakes is also investigated. Finally, a novel formulation for the evaluation of such a demand is proposed for an easy implementation in future building codes based on the actual Eurocode provisions. The proposed formulation gives a good estimation of the floor spectral accelerations that result from the analyzed structures.

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