Percorrer por autor "Carneiro, José Ricardo"
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- Determinação de coeficientes de segurança a usar no dimensionamento de geotêxteisPublication . Carneiro, José Ricardo; Rosete, Ana; Paula, António Miguel; Pinho-Lopes, Margarida; Lopes, Maria de LurdesOs geossintéticos podem sofrer alterações de resistência a curto e a longo prazo devido à ação de vários agentes de degradação. Neste trabalho, foram determinados vários coeficientes de segurança a usar no dimensionamento de dois geotêxteis (um tecido e um não-tecido). Para tal, os materiais foram expostos a vários ensaios de degradação: danificação durante a instalação, abrasão, rotura em fluência, imersão em soluções ácidas e alcalinas, hidrólise, termo-oxidação e exposição aos agentes climatéricos. Com base nos resultados obtidos, foram determinados os coeficientes de segurança a usar no dimensionamento dos geotêxteis.
- Determinação de coeficientes de segurança a usar no dimensionamento de geotêxteisPublication . Carneiro, José Ricardo; Rosete, Ana; Paula, António Miguel; Pinho-Lopes, Margarida; Almeida, Paulo Joaquim; Lopes, Maria de LurdesNas suas aplicações, os geossintéticos podem estar expostos a vários agentes de degradação capazes de afetar negativamente o seu desempenho a curto e a longo prazo. Os tipos de degradação mais comuns incluem: a danificação durante a instalação (DDI), a ação de cargas estáticas (fluência), fenómenos de abrasão, ação de espécies químicas existentes nos solos (soluções ácidas e/ou alcalinas, contaminantes químicos), termo-oxidação, ação de agentes atmosféricos (radiação solar e outros agentes climatéricos) e ação de agentes biológicos.
- Resistance of geotextiles against mechanical and chemical degradationPublication . Carneiro, José Ricardo; Carlos, D.M.; Lopes, M.L.; Paula, António Miguel; Pinho-Lopes, Margarida; Almeida, Paulo JoaquimThe geotextiles can suffer short and long-term resistance changes due to the action of many damaging agents. This work studies the resistance of two polypropylene geotextiles with different structures (a woven and a non-woven) against mechanical and chemical degradation. The geotextiles were ex- posed to several degradation tests: installation damage (in laboratory and in field), abrasion, creep rupture, immersion in chemical substances (water and solutions of sulphuric acid and calcium hydroxide), thermo-oxidation and artificial weathering. The damages suffered by the geotextiles (during the degradation tests) were evaluated by tensile tests (except for the creep rupture tests).
- Simple constitutive methods to represent the tensile response of a laboratory-aged nonwoven geotextilePublication . Paula, António Miguel; Carneiro, José Ricardo; Pinho-Lopes, MargaridaSimple constitutive models (polynomial and hyperbolic-based) were used to represent the tensile response of a nonwoven polypropylene geotextile. The model parameters were defined for a virgin sample and for samples submitted to two degradation mechanisms: thermo-oxidation and artificial weathering. Thermo-oxidation tests were carried out by the oven-ageing method (exposure in air, 110 ºC, in the dark during 56 and 112 days). The artificial weathering tests were performed in a laboratory weatherometer with exposure to ultraviolet radiation and water spraying. The virgin and laboratory-aged samples were characterised by tensile tests. The laboratory-aged samples exhibited some changes in their tensile properties. The best constitutive model to approximate the response of the geotextile (virgin and laboratory-aged samples) was the polynomial (order 6). However, the model parameters have no physical meaning. The hyperbolic-based model fitted well the experimental data. Model parameters a and b have physical meaning as they were related to tensile properties. The fit improved by using correction factors. Hyperbolic-based model parameters for the laboratory-aged samples were adequately estimated from tensile properties of the virgin sample and reduction factors for the laboratory ageing induced. This latter approach for estimating model of aged samples is promising and should be explored further.
- Tensile behavior of weathered thermally bonded polypropylene geotextiles: analysis using constitutive modelsPublication . Carneiro, José Ricardo; Paula, António Miguel; Pinho-Lopes, MargaridaWeathering agents can significantly affect the mechanical response of geotextiles, particularly when long exposure periods are involved. Usually, in design, changes in the mechanical behavior of geotextiles are represented by reduction factors for their tensile strength. However, their full tensile force versus elongation response can be affected. The main aim of this work was to contribute to defining simple procedures to estimate tensile force versus elongation curves for weathered samples of geotextiles. The tensile response of two thermally bonded polypropylene geotextiles, before and after natural and artificial weathering, was assessed experimentally and analyzed using different constitutive models: polynomial (Orders 4 and 6) and hyperbolic. The influence of weathering on the mechanical response of the geotextiles was analyzed, polynomial and hyperbolic models for representing the tensile force versus elongation response were adopted and their parameters derived, and simple relations were implemented to estimate model parameters for weathered samples. Results revealed the occurrence of changes in the tensile behavior of the geotextiles, both under natural and artificial weathering conditions. Both groups of models fitted the experimental data properly. The Order 4 and 6 polynomial models are shown to have limited application, as the model parameters had no link to the tensile properties of the geotextiles. By contrast, the parameters of the hyperbolic model were linked to the tensile properties, particularly if affected by correction factors. The hyperbolic model parameters of the weathered samples were estimated using the model parameters of the reference samples and the reduction factors to allow for weathering (initial stiffness and tensile strength). These estimates proved to be adequate for representing the tensile response of weathered samples, particularly for low ranges of elongation. Finally, a simple procedure to represent the tensile response of weathered geotextiles was proposed. This procedure has shown promise in generating realistic tensile versus elongation curves.