Navegando por Assunto "Fibra"

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Acesso aberto (Open Access)
Análise experimental do desempenho à flexão de vigas de concreto armado reforçadas com laminado de fibra de carbono com variação da taxa de armadura existente e do mecanismo de ancoragem
(Universidade Federal do Pará, 2025-06-17) LEÃO JÚNIOR, Paulo Sérgio Barreiros de; LIMA NETO, Aarão Ferreira; http://lattes.cnpq.br/0287664572311345; https://orcid.org/0000-0002-5911-1368
The strengthening of existing reinforced concrete structures with Fiber-Reinforced Polymers (FRP), using techniques such as Externally Bonded Reinforcement and Near-Surface Mounted, is common in practical applications, especially when using Carbon FRP (CFRP). However, in strengthening scenarios that require higher load capacities, these methods may be less effective due to premature debonding failure, highlighting the importance of anchorage systems to improve reinforcement efficiency. There is limited information in the literature regarding the influence of steel reinforcement ratio on the behavior of beams strengthened with anchorage systems. Therefore, this study experimentally investigates the flexural performance of reinforced concrete T-beams strengthened with CFRP, considering two steel ratios (0.44% and 1.12%) and two anchorage systems. Flexural tests were conducted on six T-section beams (2200 mm length, 280 mm height, 180 mm web width, and 80 mm thick by 350 mm wide flange). Each beam had 21 stirrups made of 12.5 mm bars spaced at 100 mm. For each steel ratio, one beam was unstrengthened (reference), and two were strengthened using either a friction-based mechanical anchorage (Hybrid Bonded – HB) or an anchorage system using bonded CFRP strips (FT). Strengthening was more effective in beams with the lower steel ratio, with strength increases of 58% for HB and 11% for FT. For the higher steel ratio, gains were limited to 10% for HB and none for FT. The HB system achieved a flexural capacity of 117.72 kN·m and showed better performance in intermediate displacements, with ductility increases up to 57 times at cracking and up to 100% at steel yielding. At maximum load, all strengthened beams showed reduced ductility. In the HB system, ductility loss increased with steel ratio, from 25% in the less reinforced beam to 49% in the more reinforced one. In the FT system, the trend was reversed, with a 66% loss for the lower steel ratio and 24% for the higher. Failure modes were governed by laminate slip in HB and cover delamination in FT.
Acesso aberto (Open Access)
Concreto reforçado com fibras de bambu (Dendrocalamus Giganteus)
(Universidade Federal do Pará, 2019-11-14) FERNANDES, Robson da Silva; PICANÇO, Marcelo de Souza; http://lattes.cnpq.br/4535052395600357; https://orcid.org/0000-0001-7313-1229
Vegetable fibers appear as an alternative to manufacture structural elements in relation to metal and synthetic fibers that have high costs, also causing pollution to the environment due to their manufacturing process. This study analyzes the results of mechanical tests of a fiber reinforced concrete of bamboo bark (Dendrocalamus Giganteus), for use in cementitious plates, obtained experimentally in cylindrical and prismatic specimens according to ABNT standards and international recommendations. Composite traces were determined by means of a pilot study, 1: 2.12: 2.88: 0.58 using the CP-IV pozzolanic cement. The experimental program consisted of a 25 MPa Fck reference concrete and three dosages corresponding to 0.5%, 1.0% and 1.5% by volume of bamboo fiber to the concrete mass, forming four dosages in total. After curing, according to NBR 5738 (2003), prismatic specimens were tested for flexural tensile strength according to NBR 12142 (2010) / JSCE-SF4 (1984) and cylindrical specimens to evaluate the strength. from CRB to axial compression, according to NBR 5739 (2018), to diametric compression tensile, according to NBR 7222 (2011) and static modulus of elasticity, according to NBR 8522 (2008). In the axial compression test the presence of bamboo did not provide an increase of resistance in relation to the reference concrete. However for the tensile and flexural strength, the mixing with the addition of bamboo fiber generated a strength gain of 7% and 9%, respectively, compared to the concrete without addition. It can be concluded that insertion of fiber from bamboo bark increases the tensile strength of the composite.
Acesso aberto (Open Access)
Resíduo de garrafão de agua inserido em pavimento de concreto como agente de reforço da matriz
(Universidade Federal do Pará, 2019-01-25) SILVA, Cristiane Araujo dos Santos; PICANÇO, Marcelo de Souza; http://lattes.cnpq.br/4535052395600357
In the face of the problematic situation witnessed by the world population due to the lack of recycling practices, urban pollution has been growing considerably. Recycling needs to be more present in the daily lives of people and industries so that the environment "breathes" in a healthier way. Intending to assist with the theme, the aim is to evaluate the reuse of the water bottle waste (GA) as fibers with the intention of contributing to concrete reinforcement in pavement. The interest to study the waste in question was through a visit to a recycling plant in the city of Ananindeua/PA, where there was a large amount of bottled mineral water stored and cannot longer return to the food sector, because it’s had an expired period of validity. The work consists of evaluating both the physical, mechanical and chemical characteristics of the waste as well as the mechanical characteristics of the composites (axial compression, diametral compression, flexural tensile strength, tensile analysis and modulus of elasticity), according to current standards described in the methodology item, with ages of 28, 56 and 84 days. According to preliminary characterizations of the materials, concrete with 0%, 0,5%, 1,0% and 2,0% with water bottle residue addition was elaborated and another one for comparative effect with addition of 0,5 % of commercial polypropylene microfibers. A concrete composition (c: a: b: a / c-1: 2,36: 3,33: 0,42) was used as reference for rigid paving for heavy traffic in Belém-PA with fct, k = 4.50MPa. In general, the results presented in this research, shows a performance of the reinforced concrete with compatible GA fiber and / or superior with respect to the concrete with addition of commercial microfiber, but the residue of GA to become a commercial product still needs a beneficiation process.
Acesso aberto (Open Access)
Secagem da fibra do pseudocaule da bananeira: avaliação de modelos cinéticos, difusividade efetiva, propriedades termodinâmicas e caracterização estrutural
(Universidade Federal do Pará, 2021-11-04) OLIVEIRA, Genardo Queiroz de; MAGNO, Rui Nelson Otoni; http://lattes.cnpq.br/9017163598972975
The drying process of banana pseudo-stem fibers was studied, experimentally, in a vertical fixed-bed convective dryer (at 60, 75, and 90 °C). Nine mathematical models (theoretical, semi-theoretical and empirical) were used to analyze the drying behavior and effective diffusivity, activation energy and thermodynamic properties were calculated. Dry fibers were evaluated also by thermogravimetric, spectroscopic, and morphological analyses. Diffusion approximation with adjusted coefficient of determination, r2adj ≥ 0.978, reduced chi-square χ2 ≤ 2.21×10-4 and root mean square error RMSE ≤ 0.0140 was the model that better fitted experimental data. The effective diffusion coefficients (𝐷𝑒) increased with temperature, reaching the order of 10-7 m2 s-1. Its dependence on temperature was described by the Arrhenius Equation and its activation energy was 47.61 kJ mol-1. When temperature increases, enthalpy decreases contrarily to entropy and Gibbs free energy, indicating that drying is an endergonic and non-spontaneous process. Characteristic absorption bands of lignocellulosic components were identified (1423, 1327, 1160 cm-1) and the degradation of this material only occurred at temperatures above 190 °C, as confirmed by thermogravimetric analyses. Morphological changes were observed in dry fibers. These mainly occur at 90 °C and led to an irreversible damage of sample structure. Alterations are caused by the tensile strength generated because of temperature and humidity gradient, produced during the drying process.