Uso da perfuração controlada na avaliação de degradação da madeira em edificações antigas : estudo de caso

Este trabalho apresenta uma aplicação da técnica experimental de perfuração controlada como ferramenta auxiliar na estimativa do estado de deterioração de peças antigas de madeira. A inspeção visual é sempre necessária, mas às vezes não conclusiva. Nestes casos, o uso de uma técnica complementar contribui para uma melhor avaliação da seção residual da peça de madeira. Um método que possa ser aplicado de forma rápida, precisa e sem provocar danos na madeira é valioso instrumento no estudo de edifícios que se constituem patrimônio histórico a ser preservado. Entre as técnicas não-destrutivas, que podem ser aplicadas na estimação das características mecânica da madeira e de seu estado de integridade, está o método de perfuração controlada. Este ensaio mede a resistência do material à perfuração por uma broca com velocidade constante ajustada ao estado de conservação da madeira. O equipamento utilizado pelo Grupo de Alvenaria e Construções Históricas do Departamento de Engenharia Civil, Universidade do Minho, Portugal, é o Resistograph® modelo 3450. O principal objetivo deste trabalho é apresentar o potencial de uso do equipamento Resistograph® e a aplicação da técnica a um estudo de avaliação da deterioração da madeira conduzido por pesquisadores da Universidade do Minho em parceria com a Universidade Federal de Santa Catarina, durante um Projeto de Cooperação Internacional. Neste trabalho, a inspeção visual, por percussão e os ensaios de perfuração realizados são descritos, bem como o tratamento dos dados, e são apresentadas conclusões sobre a condição da madeira da estrutura e possível uso das peças avaliadas.This work presents the practical use of applying drilling testing in the estimate of decaying level in ancient timber pieces in service. The visual appraisal is always necessary but sometimes not conclusive. In this situation the aid of another technique allows to reduce the degree of uncertainty in an analysis of decay and residual sound section. A method that can evaluate the quality of the wood rapidly, accurately and without provoking damage is valuable in the case of historical building heritage. The non-destructive techniques that can be applied in the estimation of the mechanical characteristic of wood include the drilling resistance method. This test measures the resistance to the advance of a drill at an adjusted speed rate according the wood state. The equipment that the Masonry and Historical Constructions Group in the Department of Civil Engineering, University of Minho, has used is the Resistograph® Model 3450. The main objective of this work is to present a case study in evaluation of timber decay conducted by University of Minho research group with University of Santa Catarina as a partner during an International Cooperation Project. In this paper the visual, percussion and drilling tests affected are described, the data treatment and the attainment conclusions for the wood condition and possible safe use of timber pieces evaluated

Avaliação das propriedades mecânicas da madeira in situ por ensaios em mesoprovetes

Uma das principais dificuldades da avaliação do estado de segurança de estruturas de madeira existentes é a determinação das propriedades mecânicas a utilizar para efeitos de cálculo. Os procedimentos habituais de estabelecimento das propriedades mecânicas com base no estabelecimento de classes de resistência por avaliação visual validada com ensaios não-destrutivos conduzem a resultados muito conservativos. No presente trabalho será apresentado um método semi-destrutivo que avalia a resistência à tracção da madeira através de amostras recolhidas do elemento estrutural, sendo estabelecidas relações entre resultados análogos de mesoprovetes e provetes normalizados para peças de pinho bravo (Pinus pinaster Ait.) e castanho nacional (Castanea sativa Mill.)

Thermal enhancement of upconversion emission in nanocrystals: a comprehensive summary

Luminescence thermal stability is a major figure of merit of lanthanide-doped nanoparticles playing an essential role in determining their potential applications in advanced optics. Unfortunately, considering the intensification of multiple electron-vibration interactions as temperature increases, luminescence thermal quenching of lanthanide-doped materials is generally considered to be inevitable. Recently, the emergence of thermally enhanced upconversion luminescence in lanthanide-doped nanoparticles seemed to challenge this stereotype, and the research on this topic rapidly aroused wide attention. While considerable efforts have been made to explore the origin of this phenomenon, the key mechanism of luminescence enhancement is still under debate. Here, to sort out the context of this intriguing finding, the reported results on this exciting topic are reviewed, and the corresponding enhancement mechanisms as proposed by different researchers are summarized. Detailed analyses are provided to evaluate the contribution of the most believed ‘‘surface-attached moisture desorption’’ process on the overall luminescence enhancement of lanthanide-doped nanoparticles at elevated temperatures. The impacts of other surface-related processes and shell passivation on the luminescence behaviour of the lanthanide-doped materials are also elaborated. Lack of standardization in the reported data and the absence of important experimental information, which greatly hinders the cross-checking and reanalysis of the results, is emphasized as well. On the foundation of these discussions, it is realized that the thermal-induced luminescence enhancement is a form of recovery process against the strong luminescence quenching in the system, and the enhancement degree is closely associated with the extent of luminescence loss induced by various quenching effects beforehand.publishe

Cobertura da sala do relicário no Mosteiro de Santa Cruz: notas sobre a intervenção

A alvenaria e a madeira são materiais de construção tradicionais, que surgem actualmente com interesse renovado na indústria de construção. No caso da madeira, e de um modo geral, muitos sistemas estruturais continuam a desempenhar as suas funções (embora muitos deles tenham sido substituídos por lajes aligeiradas em betão armado no decurso do século XX), o que requer frequentemente inspecções para averiguar a segurança estrutural, bem como trabalhos de conservação e reabilitação. É apresentado neste artigo um caso de estudo relativo à cobertura da Sala do Relicário no Mosteiro de Santa Cruz, em Coimbra. Trata-se de uma situação onde existiam diversas anomalias, intervenções sucessivas no passado e uma configuração estrutural particularmente complexa. Depois de analisadas as diferentes possibilidades de intervenção, decidiu-se em conjunto com o dono de obra (IPPAR, Direcção Regional de Coimbra), substituir a cobertura existente por uma cobertura nova, recorrendo a madeira maciça. Pela dimensão das peças e pela complexidade da estrutura, entende-se que esta obra é única no contexto nacional, tendo sido possível verificar que a utilização de técnicas e processos construtivos tradicionais constitui uma opção válida no projecto corrente

A semi-destructive tension method for evaluating the strength and stiffness of clear wood zones of structural timber elements in-service

The paper presents a new semi destructive method for obtaining a prediction of the tension parallel to the grain properties of clear wood of structural timber members. This method is less intrusive than other existing methods and consists in extracting four small specimens along the length of the timber members. The tension strength and stiffness obtained is intended to be used as input data for the assessment of timber members in situ. Since the method only provides information regarding clear wood, it will have to be used together with other non or semidestructive methods that could accommodate the effect of defects on the loss of clear wood properties. The validation of the method was carried out by a comparison with results obtained from a standard method used for determination of clear wood properties. The results show a good agreement between stiffness values but a medium agreement in the case of tension strength.The authors acknowledge the support given by the Fundacao para a Ciencia e a Tecnologia (FCT) for the PhD Grant SFRH/BD/27353/2006, as well as for the research Project "Safety evaluation of timber structures by means of non-destructive tests and stochastic analysis" (FCT PTDC/ECM/66527/2006)

Selected research and case studies in ancient portuguese structures

The present paper presents some of the recent activity of University of Minho, regarding case studies for Portuguese timber structures in four ancient buildings, including the Cathedral of Porto, a Church in Coimbra and a Church in Braga. NDT is combined with analysis methods aiming at non-invasive strengthening solutions or replacement of the timber structure (only as a last resort). Research studies carried out in UM and currently running on LNEC and UM are also presented, being showed the relevance of this research studies for the assessment and analysis of historical timber structures

Avaliação da segurança de cobertura tradicional de madeira sujeita a degradação biológica

O presente trabalho propõe-se apresentar a modelação probabilística de uma estrutura-tipo de uma cobertura tradicional de madeira, sendo tomadas como variáveis aleatórias as dimensões geométricas das secções transversais, as propriedades mecânicas da madeira e as acções aplicadas à estrutura, dando especial ênfase ao vento e neve. Depois de estabelecido o índice de fiabilidade β para uma situação de não degradação, será avaliada a sua variação em função da evolução da degradação biológica provocada por fungos, modelada probabilisticamente como uma variação de secção transversal

In situ measured cross section geometry of old timber structures and its influence on structural safety

Old timber structures may show significant variation in the cross section geometry along the same element, as a result of both construction methods and deterioration. As consequence, the definition of the geometric parameters in situ may be both time consuming and costly. This work presents the results of inspections carried out in different timber structures. Based on the obtained results, different simplified geometric models are proposed in order to efficiently model the geometry variations found. Probabilistic modelling techniques are also used to define safety parameters of existing timber structures, when subjected to dead and live loads, namely self-weight and wind actions. The parameters of the models have been defined as probabilistic variables, and safety of a selected case study was assessed using the Monte Carlo simulation technique. Assuming a target reliability index, a model was defined for both the residual cross section and the time dependent deterioration evolution. As a consequence, it was possible to compute probabilities of failure and reliability indices, as well as, time evolution deterioration curves for this structure. The results obtained provide a proposal for definition of the cross section geometric parameters of existing timber structures with different levels of decay, using a simplified probabilistic geometry model and considering a remaining capacity factor for the decayed areas. This model can be used for assessing the safety of the structure at present and for predicting future performance.Fundação para a Ciência e a Tecnologia (FCT

Stochastic differential equations death rates models : the Portuguese case

In recent years, the increasing life expectancy of the world’s population, due to increased availability of prescribed medication, quality of health care services, quantity of health care institutions and quality of life, combined with a sharp decrease in birth rates over time, has proven to be a challenging problem for governments worldwide (particularly in developed countries). Both of these factors put at risk the sustainability of state-funded welfare programs (e.g., social security) and also lead to a decrease in available workforce and tax revenue (including social benefit contributions) in the near future. With the tendency for these problems to worsen in the next decades (severity varies between countries), it is of paramount importance to estimate the extension of human life in order to analyse the severity of this phenomenon. Stochastic differential equations have been used recently to model the evolution of death rates. In fact, such models have some advantages when compared to the deterministic ones since we can input random environmental fluctuations and evaluate the uncertainty in forecasts. The main goal of this paper is to apply and compare stochastic differential equations death rate models separately for each age and sex and forecast Portuguese death rates until the year 2030.info:eu-repo/semantics/publishedVersio