Navegando por Assunto "Shear reinforcement"

Agora exibindo 1 - 5 de 5

Acesso aberto (Open Access)
Análise experimental de lajes lisas nervuradas de concreto armado com armadura de cisalhamento
(Universidade Federal do Pará, 2007-11-01) SOUZA, Shirley do Socorro Melo de; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
Two-way waffle flat slabs are structural elements of reinforced concrete supported directly on columns, under bending moments over the two directions, they improve the speed of the execution and save moulds and concrete and, consequently, labor. This work seeks to contribute for the study of the behavior of this kind of slab, as the shear resistance of the ribs and the punching in the solid area, through tests of 8 two-way reinforced concrete waffle flat slabs. Comparative analyses between the experimental results and estimated by national and international design codes had been carried out. The slabs were square, with 1.800 mm of side and total height of 140 mm. The cross section of the slabs was formed by ribs with 50 mm of width for the base and 100 mm for the upper base and the spaces between the ribs had been filled with EPS blocks (expanded polystyrene). The main variables considered were the type of shear reinforcement in the ribs (trusses, closed vertical stirrup and 45 inclined stirrup) and the use of 45 inclined stirrup as shear reinforcement in the solid region. They were presented and analyzed the results observed for the vertical displacements, deformation in the flexural and shear reinforcement, and the propagation of cracks. The values observed for failure loads were compared with the estimated ones. It was observed that the shear reinforcement in the ribs did not increase the failure loads and that the shear reinforcement in the solid region increased significantly the resistance of the slabs.
Acesso aberto (Open Access)
Análise experimental de vigas de concreto armado reforçadas à força cortante com compósitos de fibra de juta, carbono e vidro utilizando a técnica EBR
(Universidade Federal do Pará, 2022-10-18) MACIEL, Luciana Pereira; BANNA, Wassim Raja El; http://lattes.cnpq.br/2005046563115507; https://orcid.org/0000-0001-5085-4352; LIMA NETO, Aarão Ferreira; http://lattes.cnpq.br/0287664572311345; https://orcid.org/0000-0002-5911-1368
The application of FRP (Fiber Reinforced Polymer) with the EBR (Externally Bonded Reinforcement) technique for repairing and reinforcing structures stands out due to the low density of the material and ease of application. In this case, the use of synthetic fibers is common, however, these fibers are considered inaccessible and harmful to the environment. This disadvantages raised studies on the replacement of synthetic fibers by natural fibers. Therefore, this work consists of the experimental analysis of the performance of composites of jute fibers as shear reinforcement. With that aim, seven reinforced concrete beams reinforced with FRP's were molded using the EBR technique, they were dimensioned with greater flexural strength in relation to the shear force and with transverse reinforcement positioned only in a section of the span, to induce shear failure in the region without stirrups. The beams are 2 meters long and have a cross section of (15x20) cm. One beam was not reinforced, to be used as a reference, one beam was reinforced with one layer of FRP with carbon fiber, one beam with two layers of FRP with glass fiber, two with hybrid FRP of layers of glass and jute fiber with three and four layers, and finally two beams with jute fiber FRP with two and three layers. The reinforcements were applied in strips along the length of the shear span of the elements, perpendicular to the axis of the beams, U-shaped. It was observed that the reinforcement with two layers of jute fiber presented a 48% increase in shear force of the beam in relation to the reference beam, this result was similar to that observed in the beam reinforced with one layer of carbon fiber. Other positive behaviors were observed in the other reinforced beams, such as cracking control, increase in maximum shear force and containment of vertical displacement in relation to the reference beam. The experimental results were compared to theoretical results calculated according to ABNT NBR 6118 (2004), ACI 318 (2014), Eurocode 2 (2004), ACI 440.2R (2017) and fib 90 (2019). After analysis, the initial results of this research demonstrate the viability for other in-depth studies on the use of jute fibers in shear reinforcement of reinforced concrete beams.
Acesso aberto (Open Access)
Cisalhamento em elementos de concreto armado com estribos desconectados
(Universidade Federal do Pará, 2017-04-07) TAPAJÓS, Luamim Sales; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485
The use of shear reinforcement can improve shear strength and ductility in reinforced concrete elements. However, depending on the type of reinforcement and the type of construction and solicitation thereof, there may be conflict between the longitudinal and transverse bars. To solve this problem, some researchers have used unconnected shear reinforcements, which are positioned between the longitudinal bars. In addition to avoiding conflict with longitudinal reinforcement, the use of this type of reinforcement can still increase the productivity at the job site, since this type of reinforcement can be prefabricated. However, the use of unconnected shear reinforcement is still limited by the lack of design recommendations supporting their use, as well as there are few experimental studies on the subject. Therefore, this work presents a type of unconnected shear reinforcement, tested in an experimental program and compared with other types of reinforcement. In total, the experimental program involved the testing of 9 reinforced concrete wide beams, where the main variables were the type and rate of reinforcement. In addition to the tests on the beams, tests were carried out on reduced specimens by the push-off test. As results, graphs of displacements, deformations in the flexural and shear reinforcement and in the concrete, cracking maps, surfaces and rupture mode are presented, as well as the last loads observed in the tests with the theoretical loads estimated by different normative recommendations. As the main conclusions, it was observed that the unconnected stirrups can have the same performance in comparison with shear reinforcements with connected anchorage, as well the use of a complementary reinforcement to the W stirrup can improve the shear resistance of a reinforced concrete beam and avoid delamination.
Acesso aberto (Open Access)
Influence of the supplementary reinforcement on the shear strength of beams with prefabricated truss stirrups
(Instituto Brasileiro do Concreto, 2022) PINTO, Rosângela Silva; SOUSA, Vanessa Carolaine de; TAPAJÓS, Luamim Sales; FERREIRA, Maurício de Pina; LIMA NETO, Aarão Ferreira
This paper presents the results of seven experimental tests in reinforced concrete wide beams, aiming to investigate their performance when subjected to shear, using prefabricated truss stirrups as shear reinforcement, as well as a supplementary reinforcement to control cracks by delamination. The main analysed variables were: position of the supplementary reinforcement, inclination of the shear reinforcement, and spacing between stirrups. Results showed that strength increments of up to 142% were obtained using the prefabricated truss stirrups. Furthermore, the experimental results were compared with the theoretical shear strength estimates of the tested beams, following the recommendations of NBR 6118 (2014), Eurocode 2 (2004), and ACI 318 (2014), in order to evaluate the safety level of these codes when designing concrete elements subjected to shear with the reinforcement used in this paper.
Acesso aberto (Open Access)
Influência da substituição de agregados naturais por reciclados de concreto na resistência à punção de lajes lisas de concreto armado com armadura de cisalhamento
(Universidade Federal do Pará, 2023-11-21) PORTILHO, Shara Katharine Melo Silva; LIMA NETO, Aarão Ferreira; http://lattes.cnpq.br/0287664572311345; https://orcid.org/0000-0002-5911-1368
This research experimentally analyzed the mechanical behavior of four reinforced concrete flat slabs with shear reinforcement, when subjected to punching shear forces. Two of these slabs were made using a concrete mixture with a total replacement of natural coarse aggregates (NGA) by recycled concrete coarse aggregates (RCCA), and two slabs served as reference (without replacement). Shear reinforcement had two types: double headed studs and individual stirrups. The specimens were octagonal in shape, with 2,500 mm between opposite faces, thickness of 210 mm, and were supported on square central columns measuring 300 mm on each side. The estimated average concrete strength was 25 MPa, and the flexural and punching shear were 1.4% and 0.34%, respectively. After the laboratory tests, a comparison was made between the experimental behavior and the theoretical predictions from ABNT NBR 6118 (2023), Eurocode 2 (2014), ACI 318 (2019), and the fib Model Code 2010 (2013) models. Regarding the use of shear reinforcement, the results showed that the slabs with double headed studs presented higher punching shear strength when compared to those with individual stirrups. It was also observed that slabs with a total replacement of natural coarse aggregates by recycled concrete aggregates presented lower punching shear strength than slabs with natural aggregates. Regarding the comparison between the estimated punching shear strength of the flat slabs with shear reinforcement using RCCA prescribed by the analyzed codes and the experimental results, it was found that almost all code predictions were very close to the experimental values, except for the Brazilian code, which indicated results against safety.