Navegando por Assunto "Fiber"

Agora exibindo 1 - 5 de 5

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)
Influência no comportamento mecânico do concreto com a utilização de microfibras de polipropileno para redução do efeito de retração: um estudo realizado em Belém do Pará
(Universidade Federal do Pará, 2022-10-27) CUNHA, Wictor Alencar; SOUZA, Paulo Sérgio Lima; http://lattes.cnpq.br/4933212993218783
Seeking to mitigate the effect of concrete shrinkage, the influence on the mechanical behavior of concrete reinforced with polypropylene microfibers was studied in this study. In the experimental program, 15 (fifteen) study series were produced: one reference without the addition of polypropylene microfiber for each w/c ratio studied, totaling 3 series; and another 12 (twelve) series with the following characteristics: addition of 0.6% and 1.0% of microfiber content varying the length in 12 mm and 25 mm, the w/c ratios being studied with values of 0.45 ; 0.55 and 0.65. Tests were carried out in the fresh state of the concrete to evaluate consistency and workability; and in the hardened state to evaluate compressive strength, flexural traction and modulus of elasticity with age of the specimens at 7 and 28 days; and dimensional variation with age of 48h, 7 and 28 days. The results obtained were studied through analysis of variance (ANOVA) and the Tukey test to determine the statistical significance of the responses found. It was concluded that the optimum content of addition of polypropylene microfiber to concrete was 1.0% with fibers of 12 mm length and w/c ratio=0.55.
Acesso aberto (Open Access)
Nutritional potential of green banana flour obtained by drying in spouted be
(Sociedade Brasileira de Fruticultura, 2013-12) BEZERRA, Carolina Vieira; RODRIGUES, Antonio Manoel da Cruz; AMANTE, Edna Regina; SILVA, Luiza Helena Meller da
This study evaluated the chemical composition of peeled and unpeeled green banana Cavendish (AAA) flour obtained by drying in spouted bed, aiming at adding nutritional value to food products. The bananas were sliced and crushed to obtain a paste and fed to the spouted bed dryer (12 cm height and T = 80 ºC) in order to obtain flour. The flours obtained were subjected to analysis of moisture, protein, ash, carbohydrates, total starch, resistant starch, fiber. The green banana flours, mainly unpeeled, are good sources of fiber and resistant starch with an average of 21.91g/100g and 68.02g/100g respectively. The protein content was found in an average of 4.76g/100g, being classified as a low biological value protein with lysine as the first limiting amino acid. The results showed that unpeeled green banana flour obtained by spouted bed drying can be a valuable tool to add nutritional value to products in order to increase their non-digestible fraction.
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.