Seismic analysis

Résumé

Seismic analysis is a subset of structural analysis and is the calculation of the response of a building (or nonbuilding) structure to earthquakes. It is part of the process of structural design, earthquake engineering or structural assessment and retrofit (see structural engineering) in regions where earthquakes are prevalent. As seen in the figure, a building has the potential to 'wave' back and forth during an earthquake (or even a severe wind storm). This is called the 'fundamental mode', and is the lowest frequency of building response. Most buildings, however, have higher modes of response, which are uniquely activated during earthquakes. The figure just shows the second mode, but there are higher 'shimmy' (abnormal vibration) modes. Nevertheless, the first and second modes tend to cause the most damage in most cases. The earliest provisions for seismic resistance were the requirement to design for a lateral force equal to a proportion of the building weight (applied at e

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https://en.wikipedia.org/wiki/Seismic_analysis

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Inelastic Analysis of Structures

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Fragility curves for special types of Switzerland buildings

Riccardo Maestrani

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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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

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Fragility curves for special types of Switzerland buildings

Riccardo Maestrani

2021