Study on the Definition of Analytical Fragility Functions for Concrete Buildings

Abstract eng:
Development of earthquake risk mitigation strategies is a major concern of the seismology and seismic engineering communities with the main purpose to evaluate the impact of future earthquakes on society and to be able to define appropriate measures to protect citizens and the built heritage. In this way, seismic risk has been defined as the probability of losses, from human, social or economic, due to earthquake scenarios. The assessment of the vulnerability features of the built environment is a key component of a loss model in order to establish the probability of a given level of damage to a given type of structure, and associated with a specific seismic scenario. Within this evaluation, the use of fragility functions is very important since gather the information of the relationships between building performance and ground motions. This study addresses the analysis of different aspects for the definition of the fragility functions, such as: the intensity measure levels, the type of nonlinear analysis to assess the structural performance, the local and global engineer demand parameters (EDP) to characterize the behaviour of the structure and the damage state thresholds. Herein were considered the recommended provisions for seismic risk and safety assessment of structures, included in Hazus [1], FEMA 356 [2] and Eurocode 8 [3] documents and past research works. A comprehensive comparison on the aforementioned parameters and provisions is followed so as to understand how the accuracy of the derivation of the fragility functions relies on such aspects. Therefore, a three-storey gravity designed reinforced concrete building is considered on behalf of its fragility assessment, including a set of 10 real gound motion records homogenized to match the NEHRP design spectrum, defined with a 10% probability of exceedance in 50 years for Los Angeles, scaled by peak (PGA) and spectral (at the fundamental period of the structure, Sa (Te)) accelerations for 36 intensities. Nonlinear incremental dynamic and nonlinear pushover analyses, with the N2 static procedure, are used and the fragility of the building is defined using three global and local quantities: the maximum interstorey drift, the global drift, and the chord rotation of columns and beams.

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