Comportamento sísmico de edifícios com paredes resistentes

O presente trabalho aborda a questão do comportamento estrutural de edifícios tridimensionais de betão armado, compostos por pórticos reticulados e paredes resistentes de betão armado, sujeitos à acção sísmica regulamentar. Para o efeito, foram considerados os Eurocódigos estruturais, nomeadamente o Eurocódigo 0, Eurocódigo 1 e Eurocódigo 8. As paredes resistentes situam-se nas zonas destinadas às caixas de escadas/elevadores, formando os núcleos resistentes que, perante a ocorrência de um sismo, garantem a estabilidade estrutural e a capacidade de dissipação de energia da estrutura. A consideração destes núcleos teve por base a prática corrente de considerar a zona da caixa de escadas e elevadores em betão armado. A fim de avaliar a importância da localização destes elementos estruturais, elemento fundamental para a caracterização da resposta dinâmica, foi desenvolvido um estudo paramétrico, fazendo-se variar a disposição do núcleo em planta, obtendo-se estruturas com distribuição simétrica e assimétrica da rigidez em planta. Os edifícios considerados neste trabalho foram modelados com base no programa comercial de cálculo automático SAP 2000. A análise sísmica foi realizada de acordo com o preconizado no Eurocódigo 8, e no respectivo Anexo Nacional (em preparação), nomeadamente em termos da definição da acção. Posteriormente, apresentam-se e discutem-se os resultados obtidos, nomeadamente a relação entre a disposição estrutural dos núcleos resistentes, as propriedades dinâmicas e a distribuição das forças sísmicas pelos vários elementos resistentes. Por fim, apresenta-se uma solução estrutural obtida a partir das configurações anteriores e capaz de ultrapassar o comportamento dinâmico/sísmico tido como menos satisfatório

Development of an optimal and fuzzy semi-active control system for vehicle suspension

This paper aims to evaluate the performance of a semi-active controlled suspension system using a magneto-rheological (MR) damper to provide better ride comfort and safety to vehicle passengers than an uncontrolled or passive suspension system. Passive systems represent a conventional solution for vibration control of suspension systems. Although this system is a proven, reliable and economic technology, their parameters cannot be modified according to the road conditions. On the other hand, active systems allow a continuous control of the suspension motion, but require a complex and energy demanding actuator. The proposed suspension system has the adaptability of active systems with lower energy consumption, which constitute an economic and efficient option for vibration control in vehicle suspensions. The analysis was carried out with a set of numerical simulations in Matlab/Simulink using a 1/4 vehicle suspension model with two degrees of freedom for a passive system and two semiactive control modes based on fuzzy and optimal controllers.info:eu-repo/semantics/submittedVersio

Validação numérica da resposta cíclica experimental de pórticos de betão armado

Neste artigo avalia-se numericamente o comportamento experimental de um pórtico de betão armado sujeito a carregamento cíclico, com o recurso a um programa comercial de elementos finitos. Os resultados experimentais foram obtidos no Laboratório Nacional de Engenharia Civil. Na simulação numérica utilizaram-se diversos modelos constitutivos, com diferentes graus de complexidade, baseados no conceito de plastificação localizada em zonas críticas (rótulas plásticas) dos elementos que constituem o pórtico

Cyclic experimental response of reinforced concrete frames: validation methodology

This article validates numerically the experimental behavior of a reinforced concrete frame subject to cyclical loads, resorting to a commercial program using finite element analysis. The experimental results were obtained in the National Laboratory of Civil Engineering (LNEC). In the numerical simulation several constitutive models were used, with different degrees of complexity, based on the concept of local plastification in critical zones (plastic hinges) of the elements that constitute the frame as well as on fiber models.This paper reports research developed on Cyclic Response and is associated with a thematic on Base Isolation under the R&D Eurocores Project COVICOCEPAD within the S3T Program, approved independently by European Science Foundation (ESF, Strasbourg), financially supported by “FCT -Fundação para a Ciência e a Tecnologia” (Lisbon, Portugal) under Programa Operacional Ciência e Inovação 2010 (POCI 2010) of the III Quadro Comunitário de Apoio funded by FEDER

Numerical validation of the experimental cyclic response of RC frames

In this paper is estimated the numerical cyclic response of RC frames with and without masonry infill’s through a simplified nonlinear analysis using a commercial finite element method (FEM) package. The numerical model is based on the experiments carried out in the National Laboratory of Civil Engineering (LNEC) and the numerical and experimental results are compared to assess the accuracy of the simplified analysis for the bare frame and for the infill frame. To take into account the highly nonlinear behaviour of reinforced concrete (RC) frames due to large deformations, a numerical model based on the inelastic hinge method is used with a higher complexity of the hinge constitutive laws, which allows verifying the suitability of every hinge model to the experimental results

Comparison of cyclic response of reinforced concrete infilled frames with experimental results

This paper intends to estimate the numerical cyclic response of RC frames with and without masonry infill through a simplified nonlinear analysis using a commercial FEM package. The numerical model is based on the experiments carried out in the National Laboratory of Civil Engineering (LNEC) and the numerical and experimental results are compared to assess the accuracy of the simplified analysis based on the inelastic hinge method either for the bare frame and the infill frame

RTTOOL : a tool for extracting relative thresholds for source code metrics

Meaningful thresholds are essential for promoting source code metrics as an effective instrument to control the internal quality of software systems. Despite the increasing number of source code measurement tools, no publicly available tools support extraction of metric thresholds. Moreover, earlier studies suggest that in larger systems significant number of classes exceed recommended metric thresholds. Therefore, in our previous study we have introduced the notion of a relative threshold, i.e., a pair including an upper limit and a percentage of classes whose metric values should not exceed this limit. In this paper we propose RTTOOL, an open source tool for extracting relative thresholds from the measurement data of a benchmark of software systems. RTTOOL is publicly available at http://aserg.labsoft.dcc.ufmg.br/rttool. Keywords: Source code metrics; Relative thresholds; Software quality; Software measurement

Fatigue behavior of friction stir spot welding and riveted joints in an Al alloy

AbstractThe main aim of this study was to compare the fatigue resistance of welded joints produced by FSSW process and riveted joints of AA2024 alloy. The specimens welded with the best preliminary parameters determined by previous tensile shear tests were tested in fatigue under load control, R=0.1, at room temperature. Two welding parameter sets were used, and P-N curves (load versus cycles) were plotted, using 2×106 cycles as the fatigue life limit. A similar curve was obtained for riveted specimens. The FSSW welding procedures were carried out in a CNC milling machining and the riveted specimens were produced in accordance with aircraft industry parameters. Although the welded specimens presented almost the same results in the tensile shear tests, the results were fairly lower than those observed for riveted joints in fatigue. The main failure mode observed in the welded joints was shearing, besides some cases of crack propagation in the perpendicular load direction, while for riveted specimens occurred mainly fretting nucleation followed by crack propagation in the perpendicular load direction. The evidences of shearing and lower fatigue lives for welded specimens indicate that the joint geometry highly affects the joint properties, due probably to stress concentrators presented locally

Two-band fast Hartley transform

This article has been made available through the Brunel Open Access Publishing Fund.Efficient algorithms have been developed over the past 30 years for computing the forward and inverse discrete Hartley transforms (DHTs). These are similar to the fast Fourier transform (FFT) algorithms for computing the discrete Fourier transform (DFT). Most of these methods seek to minimise the complexity of computations and or the number of operations. A new approach for the computation of the radix-2 fast Hartley transform (FHT) is presented. The proposed algorithm, based on a two-band decomposition of the input data, possesses a very regular structure, avoids the input or out data shuffling, requires slightly less multiplications than the existing approaches, but increases the number of additions

Multi-sectoral partnerships for low income land development in Brazil

This work looks into the potential use of various instruments which rely on a close interaction between different segments of society (the public, the private and the third sectors) for increasing low income urban land development in Brazil. It is based on the recognition that the Brazilian housing problem is serious, threatening the development and environment of urban centres in the country, being also intimately related to the difficult access to adequate land by a significant portion of the urban population. The central objective of this thesis is to analyse the possibility of using such instruments for increasing land access to low income groups in Brazil. The idea of exploring the theme of partnerships for urban land development as an alternative solution to low income groups has arisen from two main arguments: the recognition that neither sector alone has adequately managed to address the issue of housing for low income groups and, the urge for new roles to be performed by the public, the private and the third sectors. Based on the conclusions of the literature review and on the analysis of 4 Brazilian applications of partnership-based instruments, a framework to guide partnership arrangements is proposed, discussing the relevant elements to be addressed when working through partnerships. Finally, the conclusions point out the degree of viability and generalisation of partnership arrangements in the Brazilian context and the different aspects of the changes required for their success, while some recommendations are given (of both practical and theoretical nature)