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Statistical evaluation of the lateral-torsional buckling resistance of steel I-beams, Part 1: variability of the Eurocode 3 resistance model
No full textThe EN version of part 1-1 of EC3 introduces significant changes in the evaluation of the lateral torsional buckling resistance of unrestrained beams, as well as alternative design procedures. Simultaneously, as a part of the preparation of the National Annexes of EC3 part 1-1 and the establishment of the corresponding NDP's (Nationally Determined Parameters) it becomes necessary to define the partial safety coefficients for the bending resistance of beams when lateral-torsional buckling is a potential failure mode. In this paper the methodology for the resistance evaluation of beams subjected to instability is briefly described and the results are compared with FEM numerical results for the same elements. Subsequently, to assess the accuracy of the alternative design formulae, a statistical analysis of the results is performed on the basis of EN 1990-Annex D. A methodology is proposed for the evaluation of the design procedures allowing for the uncertainties in the resistance model. Results are presented for a wide set of beam geometries and loading cases and a proposal for the definition of the partial safety factor is presented for the various methods, in line with the target failure probability of EN 1990
Numerical modelling of steel beam-columns in case of fire - comparisons with Eurocode 3
No full textThis paper presents a numerical study of the behaviour of steel I-beams subjected to fire and
a combination of axial force and bending moments. A geometrical and material non-linear
finite element program, specially established in Liege for the analysis of structures submitted
to fire, has been used to determine the resistance of a beam-column at elevated temperature,
using the material properties of Eurocode 3, part 1–2. The numerical results have been
compared with those obtained with the Eurocode 3, part 1–2 (1995) and the new version of the
same Eurocode (2002).
The results have confirmed that the new proposal for Eurocode 3 (2002) is more
conservative than the ENV-EC3 (1995) approach
Towards a consistent safety format of steel beam-columns: application of the new interaction formulae for ambient temperature to elevated temperatures
No full textTwo new formulae for the design of beam-columns at room temperature have been proposed into Eurocode 3, prEN 1993-1-1 (2002), and are the result of great efforts made by two working groups that followed different approaches, a French-Belgian team and an Austrian-German one. Under fire conditions the prEN 1993-1-2 (structural fire design) presents formulae, for the design of beam-columns based on the prENV 1993-1-1 (1992). In order to study the possibility of having, in part 1-1 and part 1-2 of the Eurocode 3, the same approach, a numerical research was made using the finite element program SAFIR, developed at the University of Liege for the study of structures subjected to fire
Seismic vulnerability and risk assessment: case study of the historic city centre of Coimbra, Portugal
No full textSeismic risk evaluation of built-up areas involves analysis of the level of earthquake hazard of the region, building vulnerability and exposure. Within this approach that defines seismic risk, building vulnerability assessment assumes great importance, not only because of the obvious physical consequences in the eventual occurrence of a seismic event, but also because it is the one of the few potential aspects in which engineering research can intervene. In fact, rigorous vulnerability assessment of existing buildings and the implementation of appropriate retrofitting solutions can help to reduce the levels of physical damage, loss of life and the economic impact of future seismic events. Vulnerability studies of urban centres should be developed with the aim of identifying building fragilities and reducing seismic risk. As part of the rehabilitation of the historic city centre of Coimbra, a complete identification and inspection survey of old masonry buildings has been carried out. The main purpose of this research is to discuss vulnerability assessment methodologies, particularly those of the first level, through the proposal and development of a method previously used to determine the level of vulnerability, in the assessment of physical damage and its relationship with seismic intensity. Also presented and discussed are the strategy and proposed methodology adopted for the vulnerability assessment, damage and loss scenarios for the city centre of Coimbra, Portugal, using a GIS mapping application.FCT - Fundação para a Ciência e Tecnologi
Numerical modelling of the cyclic behaviour of RC elements built with plain reinforcing bars
No full textThe bond-slip mechanism is one of the features that significantly controls the response as well as damage evolution of reinforced concrete structures when subjected to severe cyclic loadings, such as those induced by earthquakes. Its effect is particularly important in structures built with plain reinforcing bars. For a rigorous simulation of the response of existing RC structures, built mainly with plain bars, the bond-slip mechanism should be considered. However, the majority of the available concrete-steel bond numerical models were developed and calibrated for elements with deformed reinforcing bars. Moreover, the available experimental data on the cyclic behaviour of RC elements built with plain bars is still limited. In this framework, the objective of the present paper is to calibrate a numerical model based on results of a cyclic test performed on a two-span RC beam built with plain bars, which was collected from an existing structure. The numerical modelling was carried out with the nonlinear OpenSees software platform. Particular awareness was devoted to the bond-slip mechanism. The numerical results obtained with the calibrated nonlinear model are presented and compared with the experimental results. The consideration of the bond-slip effect in the numerical model was fundamental to achieve a good agreement between the numerical simulation and the test results. (C) 2010 Elsevier Ltd. All rights reserved.FCT - SFRH/BD/62110/2009FCT - SFRH/BD/27406/2006FCT - SFRH/BD/63032/2009FCT - SFRH/BSAB/939/200
An IDE for NETCONF management applications
Get PDFThe development of network and system management software typically requires data models definition, the creation of specific applications respecting the data model, and yet the implementation of communication interfaces. Skilled professionals usually perform such tasks in a predefined sequence and using different development solutions, but any error or lacks in the data model frequently force to repeat several time-consuming tasks. In this paper we present an integrated development framework that simplifies the construction of NETCONF management applications, from data model specification to deployment and evaluation. The framework is available at http://atnog.av.it.pt/∼ptavares/ yangplugin
O efeito vencimento dos futuros no ativo subjacente: evidência nos futuros sobre o PSI-20
No full textO sucesso do mercado de derivados impulsionou a investigação neste domínio, nomeadamente no que diz respeito à análise de possíveis influências entre este mercado e o mercado a contado, relativamente aos respectivos activos subjacentes. De entre os vários tipos de influências, destacamos o facto das rendibilidades dos activos subjacentes se comportarem de forma distinta no vencimento (ou na proximidade deste) dos contratos de derivados respectivos, sendo este efeito denominado por efeito vencimento.
Este estudo pretende analisar o impacte que o vencimento dos futuros possa ter na rendibilidade e no volume de negócios dos respectivos activos subjacentes. Para a evidência empírica foi utilizado o índice bolsista PSI-20, bem como as quatro acções mais transaccionadas durante o período em análise, em termos médios, e que servem de activo subjacente para os futuros sobre acções portuguesas que são transaccionados na Euronext Lisbon. A base de dados é composta pelas rendibilidades diárias destes produtos financeiros para o período compreendido entre o seu lançamento no mercado de derivados e 30 de Outubro de 2002.
A aplicação empírica levada a cabo teve como base modelos de regressão múltipla e testes para a detecção da existência ou não de multicolinearidade, heterocedasticidade e autocorrelação dos dados. Os resultados sugerem que, de um modo geral, não existe presença do efeito vencimento nos activos subjacentes analisados, tanto em termos de rendibilidade como volume de transacção, dado que estes não apresentam rendibilidades e quantidades transaccionadas significativamente distintas nos dias que circundam o vencimento dos contratos de futuros respectivos
Multichannel dispersion compensation using a simplified approach SFBG design
No full textIn this work, we present a simple approach to design a multichannel sampled fiber Bragg grating (SFBG) for dispersion compensation, based on groups of SFBG with phase modulation between groups. We present also an apodization technique that minimizes the high group delay ripple that occurs with this approach. This design can be implemented with a uniform phase mask and a low resolution positioning device.PANORAMAADI/QREN-3144CONTACTPTDC/EEA-TEL/114144/200
Rayleigh Assisted Brillouin Effects In Distributed Raman Amplifiers Under Saturated Conditions At 40 Gb/S
No full textThis article analyzes experimentally the limitations observed in lightwave systems using distributed Raman amplifiers operating under large pump power input conditions. The Brillouin effect is observed as the pump power reaches 1 W. The presence of Brillouin peaks degrades the performance of the system. The Raman amplification occurs in single mode and dispersion compensating fibers, being evaluated in a link at transmission rate of 40 Gb/s. (C) 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1331-1335, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.2516
Optical quantum communications: an experimental approach
No full textQuantum laws can be used to implement secure communication channels; this has been named quantum cryptography. In quantum cryptography the security does not depend of limited computational power, but is inherent to the laws that govern the propagation and detection of single and entangled photons. We show how single and entangled photon-pairs can be efficiently generated using four-wave mixing in optical fibers. We analyze the source statistics, degree of entanglement and impact of spontaneous Raman scattering. By coding information in the photons polarization we are able to transmit quantum information over 20 km of standard single mode fiber