A general evaluation of some points of the South American seismic codes is presented herein, comparing them among themselves and with the American Standard ASCE/SEI 7/10 and with the European Standard Eurocode 8. The study is focused in design criteria for buildings. The Western border of South America is one of the most seismically active regions of the World. It corresponds to the confluence of the South American and Nazca plates. This region corresponds roughly to the vicinity of the Andes Mountains. This seismicity diminishes in the direction of the comparatively seismically quieter Eastern South American areas. The South American countries located in its Western Border possess standards for seismic design since some decades ago, being the Brazilian Standard for seismic design only recently published. This study is focused in some critical topics: definition of the recurrence periods for establishing the seismic input; definition of the seismic zonation and design ground motion values; definition of the shape of the design response spectra; consideration of soil amplification, soil liquefaction and soil-structure interaction; classification of the structures in different importance levels; definition of the seismic force-resisting systems and respective response modification coefficients; consideration of structural irregularities and definition of the allowable procedures for the seismic analyses. A simple building structure is analyzed considering the criteria of the several standards and obtained results are compared.Keywords: seismic analysis, seismic standards, comparative analysis.Uma avaliação geral de alguns pontos das normas sul-americanas de projeto sísmico é aqui apresentada, comparando-as entre si, com a norma americana ASCE/SEI 7/10 e com a norma européia Eurocode 8. O estudo é focado nos critérios de projeto para prédios. A borda ocidental da América do Sul é uma das zonas mais sismicamente ativas do Mundo. Ela corresponde à confluência das Placas Sul-Americana e de Nazca. Esta região corresponde aproximadamente à vizinhança da Cordilheira dos Andes. Esta sismicidade diminui na direção das comparativamente mais quietas regiões orientais da América do Sul. Os países sul-americanos situados na borda ocidental da América do Sul possuem normas sísmicas de projeto já há algumas décadas, sendo no entanto a norma sísmica brasileira somente muito recentemente publicada. Este estudo é focado em alguns pontos críticos: definição dos períodos de recorrência para o estabelecimento da solicitação sísmica; definição da zonificação sísmica e dos movimentos de solo de projeto; definição da forma dos espectros de resposta de projeto; consideração da amplificação no solo, da liquefação e da interação solo-estrutura; classificação das estruturas em diferentes níveis de importância; definição dos sistemas sismo-resistentes e respectivos coeficientes de modificação de resposta; consideração das irregularidades estruturais e definição dos métodos permitidos de análise sísmica. Uma estrutura simples de edifício é anal...
This paper presents a comparative evaluation among some international, European and American, seismic design standards. The study considers the criteria for the analysis of conventional (residential and commercial) buildings. The study is focused on some critical topics: definition of the recurrence periods for establishing the seismic input; definition of the seismic zonation and shape of the design response spectra; consideration of local soil conditions; definition of the seismic force-resisting systems and respective response modification coefficients; definition of the allowable procedures for the seismic analysis. A model for a standard reinforced concrete building ("Model Building") has been developed to permit the comparison among codes. This building has been modelled with two different computer programs, SAP2000 and SOFiSTiK and subjected to seismic input according to the several seismic codes. The obtained results compared are leading to some important conclusions.
ResumoThe structural design under seismic loading has been for many years based on force methods to consider the effects of energy dissipation and elastoplastic behavior. Currently, displacement-based methods are being developed to take into account elastoplastic behavior. These methods use moment-curvature relationships to determine the ductility capacity of a structural element, which is the deformation capacity of the element before its collapse. The greater the plastic displacement or rotation a structural member can achieve before it collapses, the more energy it is capable of dissipating. This plastic displacement or rotation capacity of a member is known as the member ductility, which for reinforced concrete members is directly related to efficient concrete confinement. This study investigates at which extents transverse reinforcement detailing influences reinforced concrete column ductility. For this, a bridge located in Ecuador is modeled and analyzed, and its ductility evaluated considering several cases of axial loading and concrete confinement levels. After the performed displacement-based analyses, it is verified whether the response modification factor defined by AASHTO is adequate in the analyzed case.Keywords: seismic resistant structures, reinforced concrete seismic detailing, ductility capacity, plastic dissipation, seismic design of bridges, ductility, displacement-based design.O projeto estrutural para cargas sísmicas tem sido por muitos anos baseado em métodos de avaliação de forças para considerar os efeitos de dissipação de energia e comportamento elastoplástico. Presentemente métodos baseados em deslocamentos estão em desenvolvimento para a consideração do comportamento elastoplástico. Estes métodos usam relações momento-curvatura para determinar a ductilidade disponível de um elemento estrutural, que é a capacidade de deformação do elemento antes de seu colapso. Neste artigo é apresentada a análise e a avaliação do comportamento de pontes usando métodos baseados em deslocamentos. Para isso, uma ponte localizada no Equador é modelada e analisada e sua ductilidade disponível é verificada considerando-se diversos casos de carga axial e de situações de confinamento do concreto. Uma análise "push-over" é também realizada e os resultados obtidos são comparados.Palavras-chave: análise sísmica, análise dinâmica, análise sísmica de pontes, dutilidade, projeto baseado em deslocamentos.
O território brasileiro apresenta baixa atividade sísmica, característica de região tectônica intra-placas. Entretanto, os efeitos dos sismos não podem ser simplesmente desconsiderados em projetos de engenharia. Assim, é apresentado neste trabalho um estudo da sismicidade da região Nordeste do Brasil, que por estar posicionada próxima à falha do Atlântico Central, a leva a apresentar uma taxa de atividade sísmica com con- tinuidade de ocorrência mais alta do que a de outras regiões brasileiras. Dentro deste contexto, são calculadas as recorrências sísmicas e as distribuições probabilísticas de acelerações espectrais para a região. De posse desses valores, são determinados os espectros de resposta de projeto para a região, fazendo as devidas comparações entre os resultados obtidos para cada período de recorrência com o espectro apresen- tado pela Norma Brasileira de Sismos NBR 15421.
<p>The Brazilian territory presents generally low seismicity. Two regions are exceptions, with non- negligible seismicity: part of the Brazilian Northeast and part of the Brazilian Northwest. Due to this low seismicity, up to 2006 Brazil was practically the only South-American country without a seismic design standard. In this year, the first Brazilian Standard for Seismic Design was issued. The available seismological data and the studies performed for defining the probabilistic distribution functions of seismic magnitudes, in several Brazilian regions, are reviewed herein. The considered probabilistic analyses performed for the definition of the nominal values of horizontal accelerations are also presented. Equal probability design spectra are generated and compared with the ones defined in the standard. Some other aspects of the standard, such as, definition of the seismic design spectra and the allowed methods of analysis are also commented.</p>
This paper presents a comparative study of the influence of shear walls on the behavior of a multi-storey concrete building when subjected to seismic actions. Two structures with different earthquake-resistant systems were evaluated. One is composed of concrete frames with usual detailing in both directions (x and y), and the other one is formed by a dual system, composed of frames and shear walls with usual detailing. The Equivalent Lateral Force procedure and the Modal Response Spectrum analysis presented by the Brazilian Technical Code ABNT NBR 15421:2006 were considered. The dual system building presented a greater stiffness with the shear walls arranged parallel to direction y. In the x direction, the responses are equivalent in both buildings. The horizontal forces obtained by the Equivalent Lateral Force method at the base of the buildings were greater than the Modal Response Spectrum method.
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