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Publication# Seismic vulnerability assessment at large scale city of Basel

Résumé

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.

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Bâle

Bâle (prononcé : ; Basel ; en italien et en romanche : Basilea ) est la troisième ville la plus peuplée de Suisse après Zurich et Genève, et le chef-lieu du canton de Bâle-Ville. La commune de Bâle c

Configuration électronique

redresse=1.6|vignette|Planche synthétisant la règle de Klechkowski (en haut à gauche) de remplissage des sous-couches électroniques ; en haut la géométrie des quatre types d'orbitales atomiques ; au c

Risque sismique

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 c

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.

2020Existing unreinforced masonry (URM) buildings, many of which have historical and cultural importance, constitute a significant portion of existing buildings around the world. Recent earthquakes have shown the vulnerability of such URM buildings. This thesis investigates the in-plane seismic behavior of URM walls retrofitted using composites. The thesis includes an extensive dynamic and static cyclic tests followed with development of an analytical model. For the dynamic tests, five half-scale single wythe URM walls were built using either strong or weak mortar and half-scale hollow clay brick units. These five walls were dynamically tested as reference specimens. Then, these reference specimens were retrofitted on single side only using composites and retested. As consequence a total of eleven specimens were tested on the earthquake simulator at ETHZ. For the static cyclic tests, five half-scale single wythe URM walls were built using weak mortar and half-scale hollow clay brick units. Of them, three specimens were tested as reference specimens. Then, two specimens of these three reference specimens were retrofitted using composites and tested again. The third reference specimen was retrofitted using post-tensioning and tested; then, the post-tension forces were released and the specimen was retrofitted using composites and retested. Finally, two virgin specimens were retrofitted directly after construction and tested. As consequence a total of nine specimens were tested in the Structural Laboratory at EPFL. For analytical models, an innovative shear model is developed. In addition, a simple flexural model is developed. For shear analysis, masonry, epoxy, and composites in a URM wall retrofitted using composites (URM-FRP) were idealized as different layers with isotropic homogenous elastic materials. Then, using principles of theory of elasticity the governing differential equation of the system is formulated. A double Fourier sine series was used as the solution for the differential equations. The solution can be used to model the linear shear behavior of URM-FRP. To take into consideration material nonlinearity, step-by-step stiffness degradation has been implemented in a computer program. For flexural analysis, a simple model using linear elastic approach with the well-known assumptions of Navier-Bernoulli and Whitney's equivalent stress block is developed. The experimental work shows that the retrofitting technique improved the lateral resistance of the URM walls by a factor ranged from 1.3 to 5.9 depending on the applied normal force, the reinforcement ratio, and mode of failure. However, improvement in lateral drift was less significant. Moreover, no uneven response was observed during tests due to single sided retrofitting. Several phenomena and relationships have been correctly determined by the model. These phenomena and relationships are originally observed in the literature during tests on reinforced concrete beams that were retrofitted using composites. This includes the relationship between strains in FRP and reinforcement ratio as well as the interaction between masonry lateral resistance and FRP contribution to the lateral resistance of URM-FRP. In addition, effects of epoxy ductility and allowable shear stresses as well as masonry ductility and allowable shear stresses have been studied. Such development is of interest to the structural engineering community and material producers. Regarding flexural analysis, the simple model leads to unconservative designs. Correlation analysis of the test data show that the ratio between the experimental lateral resistance to the estimated flexural lateral resistance is proportional to reinforcement mechanical ratio times the square of the effective moment/shear ratio up to a certain limit. Within the limits of experimental testing, a correlation factor is proposed.