Browsing by Author "Pinto, Cristiana"
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- Caracterização das propriedades físicas e mecânicas da madeira de pinho bravo e de freixo do nordeste transmontanoPublication . Pinto, Cristiana; Ferreira, Débora; Fonseca, E.M.M.O conhecimento das características, propriedades e os fatores que influenciam o comportamento físico e mecânico da madeira ajudarão a compreender o comportamento da mesma. O principal objetivo desta dissertação é conhecer as propriedades físicas e mecânicas de duas espécies de madeira, uma resinosa que é o Pinho e outra folhosa que é o Freixo. Numa primeira fase pretende-se avaliar a influência do teor de água na estabilidade dimensional da madeira de Pinho e Freixo. Nesta avaliação está integrada a variação da massa e a variação das dimensões no sentido longitudinal e transversal das fibras. A metodologia utilizada é baseada nas normas portuguesas NP 614 – Determinação do teor de água e NP 615 – Determinação da retração. Um segundo objetivo desta dissertação consiste na apresentação dos ensaios experimentais de tração no sentido longitudinal e transversal às fibras realizados em provetes de Pinho e Freixo, obtendo-se parâmetros que tentam descrever o seu comportamento mecânico, nomeadamente o módulo de elasticidade, o coeficiente de Poisson e ainda a resistência à tração paralela ao fio. Estes parâmetros são particularmente relevantes quando se pretende efetuar análises numéricas de estruturas, como é objetivo futuro. Em outra das fases foi feita a análise numérica realizada para determinar a resistência à tração da madeira de Pinho e Freixo, nas direções ortotrópicas. O modelo de elemento finito foi feito em 3D e foi usada para avaliar a as tensões, deformações e forças. Por fim foi comparado os resultados obtidos com os ensaios há tração da análise numérica com os ensaios experimentais.
- Dimensional stability of wood in presence of waterPublication . Ferreira, Débora; Pinto, Cristiana; Borges, Paula; Pinto, Tiago; Fonseca, E.M.M.Wood is our most important raw material. It is important not only because it is used for literally hundreds of products, but also because it is a renewable natural resource. Through a carefully and planned use, forests could provide a perpetual supply of wood. All wood in growing trees contains a considerable amount of water as part of the photosynthesis and the growing processes. This water is commonly called sap. The main goal of this work is to study the water movement in wood: first of all, the drying process, which occurs before the manufacture and use as finished wood products, and secondly the gain and loss of water in response to changes in environmental conditions that surround the wood. The moisture content relationship has an important influence on wood properties and performance. Wood is dimensionally stable when moisture content is greater than the fibre saturation point (MCfs). Below MCfs wood dimensional changes and it gains moisture (swells) or loses moisture in the form of bound water. The level of MCfs depends on the relative humidity and temperature of the surrounding air. Shrinkage and swelling are the cause of many of the problems that occur in wood during drying and in use, therefore, an understanding of them will help minimize such problems. Splitting, warping, and open joints are examples of problems that occur due to uneven shrinkage. An experimental program was defined with the aim to evaluate the dimensional stability of hardwood and softwood species. The Pine softwood and the Ash hardwood of the North-east region of Portugal will be analysed. A group of thirty specimens were made for each specimens of wood. The assumed geometry for the specimens is 40×40×10 mm, based on NP EN 614 recommendations. Before running the tests, one half of the specimens of each species were dried in an oven at 103ºC ± 2ºC, while the other one half was saturated in a water tank until a constant mass is attained. The tests were carried out in a climatic chamber with a constant internal environment of 20ºC and 60% (RH), during a period time equal to 24 hours or more, until stabilization of dried and saturated specimens. Mass is considered constant when the difference between two consecutive weight measurements, delayed 2 hours, is less than 0.5%.
- Dimensional stability of wood in presence of waterPublication . Ferreira, Débora; Pinto, Cristiana; Borges, Paula; Fonseca, E.M.M.Moisture is one of the most important causes for building pathology. The material degradation can be affected by the presence of water, both in vapour and liquid phase. Wood has a strong hygroscopic behaviour, with a strong variation of moisture content and dimension stability caused by modifications of the relative humidity of the surrounding air. The properties that define the behaviour of wood against temperature and moisture actions were studied in this work. Hygroscopicity and shrinkage were given special attention.
- Dimensional stability of wood in presence of waterPublication . Ferreira, Débora; Pinto, Cristiana; Borges, Paula; Fonseca, E.M.M.An experimental program was defined aiming to evaluate the dimensional stability of hardwood and softwood species. The maritime pine softwood (Pinus pinaster) and the ash hardwood of the North-east region of Portugal are analysed. A group of thirty specimens were made for each species of wood. The experimental procedure has been conducted according to NP EN 614 and NP EN 615. For each wood species, one half of the specimens were previously dried while the other one half was prior saturated. Two main variables were studied in normal environmental conditions: mass and dimensional variation. Tests were conducted at 20ºC environment temperature and 60% of relative humidity. Measurements were taken allowing to quantify the dimensional variation suffered during the dry/saturation process for both species. The properties that define the behaviour of wood against temperature and moisture actions are assessed in this work. Hygroscopicity and shrinkage are given special attention.
- Estabilidade dimensional da madeira na presença de águaPublication . Ferreira, Débora; Pinto, Cristiana; Borges, Paula; Pinto, Tiago; Fonseca, E.M.M.A madeira é um material higroscópico, cujas propriedades físicas e mecânicas dependem do teor em água. Sendo um material natural exibe uma heterogeneidade significativa e por ter uma estrutura celular, apresenta uma anisotropia acentuada. Um dos principais problemas da madeira está relacionado com o fenómeno de inchamento e retração devido à presença de humidade relativa do ar. O controlo do teor de humidade da madeira, no momento em que se aplica, contribui para minimizar os problemas da sua variação dimensional. Um dos objetivos deste trabalho foi o de compreender a relação da água com duas espécies diferentes de madeira, o Pinho e o Freixo, através de uma metodologia experimental. Foram conduzidos diversos ensaios para o estudo da estabilidade dimensional, atendendo aos fenómenos de retração e inchamento da madeira. A determinação do teor em água e da massa volúmica foi efetuada em conformidade com as normas NP EN 614:1973 e NP 616:1973 do LNEC [1,2], respetivamente. Os provetes analisados foram obtidos a partir de madeira sã e isenta de nós, fendas ou outros defeitos, com forma cúbica e de dimensão igual a 40×40×10mm.
- Tensile strength of pine and ash woods – experimental and numerical studyPublication . Ferreira, Débora; Fonseca, E.M.M.; Pinto, Cristiana; Borges, PaulaTimber stmctures are a competitive solution when compared to steel and concrete stmctures, showing features and advantages that overcome their competitors: weight/strength ratio, rapid assembly, fire resistance and excellent performance in earthquake scenario, natural aesthetic attractiveness, and ecological rationality which leads to sustainable construction. The main goal of this experimental and numerical shidy was to evaluate, using tensile tests, the mechanical characteristics offrwo different wood species: Pine and Ash. For tensile test a total of twelve samples for each wood species were prepared, six of them were cut in the wood transverse to the grain, with dimensions equal to 190x50x9 mm, and the others six were cut in the wood parallel to the grain with the dimensions equal to 210x40x9 mm. A numerical simulation was also conducted in arder to assess the stress-strain behaviour of Pine and Ash woods.
- Tensile strength of pine and ash woods – experimental and numerical studyPublication . Ferreira, Débora; Fonseca, E.M.M.; Pinto, Cristiana; Borges, PaulaThe mechanical properties define the behaviour of the timber under external loads, resulting directly from the timber anisotropic and heterogeneity characteristics. Depending upon the type of applied load the failure can be tensile, shear or torsion. When load enter the plastic regime, the stress-strain relationship passes through a maximum called the tensile strength. The tensile strength of wood being constant above the fibre saturation point, it increases with decreasing moisture content below the fibre saturation. This can be related to where the water is absorbed in the microstructure. Their study is of great interest allowing the rational use of different wood species for structural and building purposes.
- Tensile strength of pine and ash woods – experimental and numerical studyPublication . Ferreira, Débora; Fonseca, E.M.M.; Pinto, Cristiana; Borges, PaulaTimber structures are a competitive solution when compared to steel and concrete structures, showing features and advantages that overcome their competitors: weight/strength ratio, rapid assembly, fire resistance and excellent performance in earthquake scenario, natural aesthetic attractiveness, and ecological rationality which leads to sustainable construction. The main goal of this experimental and numerical study was to evaluate, using tensile tests, the mechanical characteristics of two different wood species: Pine and Ash. For tensile test a total of twelve samples for each wood species were prepared, six of them were cut in the wood transverse to the grain, with dimensions equal to 190×50×9 mm, and the others six were cut in the wood parallel to the grain with the dimensions equal to 210×40×9 mm. A numerical simulation was also conducted in order to assess the stress-strain behaviour of Pine and Ash woods.