Risque sismique

Résumé

thumb|upright=1.2|Cet immeuble s'est cassé et effondré parce qu'il était construit sur des sédiments insuffisamment compacts susceptibles de subir des phénomènes différenciés de liquéfaction lors de certains séismes, à une certaine fréquence et intensité de tremblement du sol (ici séisme de 2010 au Chili). Dans ce cas, le lieu et le bâtiment étaient vulnérables. Le risque sismique désigne la combinaison entre l'aléa sismique, les biens et les populations qui y sont soumises, et leur vulnérabilité face à cet aléa. En fonction des situations géodynamiques, politiques, sociales et économiques, le risque sismique dans le monde est très variable, selon les régions considérées. Dans les régions les plus exposées à l'aléa sismique, la réduction du risque passe notamment par l'information des populations et la construction de bâtiments aux normes parasismiques. Afin de définir le risque sismique, les sismologues doivent caractériser : l'aléa, par l'étude des paléo-séismes enregistrés dans les

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https://fr.wikipedia.org/wiki/Risque_sismique

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Vulnérabilité sismique à grande échelle. Typologie typique de bâtiments lausannois

Hajand Zainal

Seismic assessment of existing buildings is a very important area of research to predict the impact of an earthquake on an area. Over the years, unreinforced masonry buildings have shown to be highly vulnerable to seismic risk. Although Switzerland is considered a low to moderate seismic zone, studies have shown that seismic risk is the country's most significant natural risk. This is mainly due to the fact that the majority of the Swiss real estate stock was built with little or no seismic consideration. This thesis focuses mainly on a typical typology of Lausanne buildings. First, an inventory was taken of buildings with characteristics common to this typology. Five prototypes of buildings most representative of this type of construction were then created. In a second step, a detailed seismic analysis was carried out, in particular using the Extreme Loading for Structures (ELS) software, which uses the applied element method. Finally, fragility curves for each of the prototypes were derived, linking the structure's capacity according to spectral acceleration.

2020

Chargement

The Basel region is one of the most seismically active regions in Switzerland. Already devastated by Nature in 1356, the city of Basel is now actively involved in assessing the seismic risk on its buildings in order to protect its patrimony and its population as effectively as possible. Through innovative assessment methods, researchers and scientists throughout Switzerland are working to effectively and accurately assess seismic risk through the three components that define it: hazard, exposure and vulnerability. It is this latter element that is addressed in this report. While the assessments carried out so far deal with the buildings one by one, an essential aspect of Basel's built environment is hidden in the row configurations of many buildings. Indeed, due to the desire to optimize space, many buildings are adjacent to each other, modifying thus their seismic behaviour. This document is therefore a first study of the vulnerability of building rows in order to reveal whether the effects of this particular configuration are beneficial or not. Thanks to epoch plans collected from the archives of the Canton of Basel-Stadt and dynamic simulations based on the Applied Element Method, the consequences on the vulnerability of two types of rows of masonry buildings are estimated. As a conclusion, the impact of introducing new fragility curves on the assessment of damage in the Iselin district makes it possible to highlight the effects of taking into account the row configuration of the buildings it contains.

2020

Chargement

Seismic risk analysis, at large scale and local scale, is fundamental support for mitigating the investment costs and recovery works, impacting society's economy. The presented article's main purpose is to present a mechanicalbased model to evaluate the fragility curves through nonlinear static analysis. The results achieved from statistical analysis allows defining a representative building stock for two height classes. Material properties for typical masonry typologies that characterise the unreinforced masonry building heritage for the specific area of investigation are assigned to the prototype buildings. The paper proposes a procedure for fragility function evaluation to reduce computation time and limit the results' loss of reliability. A technique based on macro-element formulation and threedimensional equivalent frame model is proposed to evaluate the assessed buildings' seismic response. The proposed model includes implementing the macro-element formulation in open-source software, Opensees, that allows higher versatility and the possibility to include in the analysis sources for better reliability and representation regarding the real building. Equivalent frame modelling allows an efficient way to represent the seismic response and a compromise between computation costs and high accuracy. Modelling technique validation is proposed by comparing results derived on specified studies concerning, ambient vibration and seismic response. A limited set of capacity curves is generated from the aleatory variation on the material properties. Then, the number of capacity curves is expanded by a correlation between the seismic response parameters. The increase in capacity curves aims to cover the variability on the structural capacity. Fragility curves are then derived from a stochastic selection of response spectra, by using GMPE allowing to estimate the probability distribution of each damage state, as a function of the reached displacement. Reliability of the mechanical fragility curves is proved by comparing recent studies, involving both empirical and mechanical based fragility functions. The assessment's feasibility is demonstrated by applying the procedure over most representative prototype building configurations for the Switzerland city of Basel.

2021

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2021