Navegando por Assunto "Armadura de cisalhamento"

Agora exibindo 1 - 7 de 7

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 dos limites superiores de resistência à punção de lajes lisas de concreto armado com armaduras de cisalhamento
(Universidade Federal do Pará, 2018-10-30) FREITAS, Marcus Vinícius Pereira de; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485; https://orcid.org/0000-0001-8905-9479
In the flat slab system, the slab-column connection is a critical point due to the risk of punching shear failure. Several structural collapses are reported due to this mode of failure and constructive errors are the main causes of such accidents, leading researchers to study new shear reinforcement to minimize them. The use of shear reinforcement is the most efficient way to increase punching shear ductility and strength, but its correct arrangement generates conflict with the flexural reinforcement. Thus, Ferreira et al. (2016) propose a prefabricated truss reinforcement positioned internally to the flexural reinforcement, which generated the patent number BR 10 2015 006518 3 A2. Therefore, the work carried out in this research contributes to the investigation of cases of bidirectional shear for the present reinforcement. In this research, 5 experimental tests of reinforced concrete flat slabs submitted to symmetrical loading, containing both Stud Rails and the pre-fabricated truss reinforcement proposed by Ferreira et al. (2016) as shear reinforcement, were carried out. The study evaluated the performance of the reinforcement in relation to punching shear strength and analyzed the upper limits of strength, since a flexural reinforcement ratio of 2% and shear reinforcement ratios around 1% were used. The slabs were octagonal with a 2500 mm distance between parallel faces, side of 1036 mm and thickness of 210 mm, cast with concrete around 30 MPa and supported on columns with 400-mm-side. The following variables were analyzed: shear reinforcement type, slope and spacing of the shear reinforcement layers, as well as the design parameters of ACI 318 (2014), EC2 (2014), ABNT NBR 6118 (2014) and ETA 12/0454 (2012) codes. The experimental results show that the increase of load, in relation to the slab without shear reinforcement, reached up to 92%, with the use of pre-fabricated truss reinforcement, and 101% with the use of Studs, showing that the upper limit of ultimate load as a function of the concrete strength (Vu/Vc) can be limited to 2 and that the reinforcement studied in this research has a high commercial potential, since its cost per increment of load was lower than the one of the slab reinforced with Studs Rails, except for the design criteria suggested by ETA 12/0454, reducing the total cost by 15.6%.
Acesso aberto (Open Access)
Aplicação de técnicas de identificação de sistemas para previsão de resistência à punção em lajes lisas de concreto armado sem armadura de cisalhamento
(Universidade Federal do Pará, 2019-02-27) AMORIM, Fábio de Oliveira; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485; BAYMA, Rafael Suzuki; http://lattes.cnpq.br/6240525080111166
The structural systems used in reinforced concrete pavements, in which the slabs rest directly on the pillars, without the use of beams, have, among their characteristics, the existence of high concentrated stresses in the slab-pillar connections. These tensions can cause these connections to rupture and cause the structure to collapse progressively. This is called a punching. As the breakage of the punching bonds is fragile, without warning, it is extremely important that the bond strength is checked. For the study in question, information was collected from two databases of several authors who performed experimental tests on plain slabs of reinforced concrete without shear reinforcement, containing several parameters used in the tests, as well as punching resistance values. A lot of studies were developed with the purpose of defining and standardizing procedures and mathematical functions that satisfactorily represented the phenomenon of punching in function of its various parameters of influence. In this way, calculation models and normative instructions have been developed that can be used for the study and development of the subject. Besides, some studies were developed with the rescue of numerical techniques and systems identification, resulting in equations that aim to represent the punching phenomenon satisfactorily. The present work aims to obtain a mathematical function that represents the phenomenon of punching in slabs without shear reinforcement by means of their strain strength, or even group of functions, if this is the case. Therefore, it was possible to propose improvements in the equations present in the norms. The results show that it is possible to predict new mathematical models that describe the phenomenon of punching by means of systems identification techniques. The results also show that it is possible to propose better mathematical models when evaluating better performance metrics than the equations derived from normative data through statistical data. Thus, it is concluded that new mathematical models can serve as reference for engineers of the area of structures and researchers of related areas.
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)
Cisalhamento em vigas de concreto armado com armadura transversal interna contínua
(Universidade Federal do Pará, 2019-09-24) SOUZA, Diego Ferreira de; LIMA NETO, Aarão Ferreira; http://lattes.cnpq.br/0287664572311345; https://orcid.org/0000-0002-5911-1368
Reinforced concrete elements can suffer high bending and shear forces, either due to high loads, type of construction or architectural limitation, thus requiring a high longitudinal and transverse reinforcement rate, which can lead to conflicts between the two reinforcements, resulting in reduced productivity during the reinforcement work of the element. As a way to solve this reinforcement conflict, some researchers applied to reinforced concrete elements internal shear reinforcement, in other words, these reinforcements are positioned between the bending reinforcement bars, thus eliminating the conflict between the transverse and longitudinal bars and aiding the productivity of the reinforcement work, as this type of elements could be prefabricated and positioned as designed. However there are no normative standards that indicate the use of internal stirrups. Studies conducted on the subject indicated that the internal stirrups need an auxiliary device, as recommended by NBR 6118 (2014), which would help in the anchorage and allow the transfer of shear forces to the concrete without the delamination effect. Currently, few studies evaluate the performance of the transverse reinforcement with inclinations between 45º and 90º, where inclined stirrups provide better ductility and reduced stresses on compression struts. Therefore, this research presents a type of internal transverse reinforcement, tested in an experimental program and compared with closed-loop stirrups. The experimental program was carried out with a total of 5 beams of reinforced concrete, one as a reference with closed-loop stirrups, and the other 4 with internal stirrups; the main variables were: the inclination of the internal transverse reinforcement at 60º and 90º; and the number of legs of internal transverse reinforcement, keeping the same transverse reinforcement ratio. As results, this paper presents graphs of displacements, bending and shear reinforcement and concrete deformations, cracking maps and failure surfaces, and the last loads observed in the tests were compared with the theoretical loads estimated by different normative recommendations. As conclusions, it was observed that the internal stirrups have great potential in their use, as they present greater ductility and resistance compared to the closed-loop stirrup currently used. The results of inclined internal stirrups showed an increase of up to 14% when compared to the reference beam.
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.
Acesso aberto (Open Access)
Punching resistance of internal slab-column connections with double-headed shear studs
(Universidade Federal do Pará, 2013-10) OLIVEIRA, Marcos Honorato de; PEREIRA FILHO, Manoel José Mangabeira; OLIVEIRA, Dênio Ramam Carvalho de; FERREIRA, Maurício de Pina; MELO, Guilherme Sales Soares de Azevedo
Punching shear is a brittle failure mode that may occur in slab-column connections, which may be prevented by using shear reinforcement in the slab-column connection. This paper presents comparisons between experimental results of 36 tests in internal slab-column connections with double- headed shear studs, which are largely used in North America, Europe and Asia, with theoretical results using recommendations presented by ACI 318, NBR6118, Eurocode 2 and also the Critical Shear Crack Theory (CSCT).Considering the database used it is possible to observe that ACI 318 presents conservative trends, whereas NBR 6118 showed a low coefficient of variation, but with a large number of unsafe results. Both Eurocode 2 and CSCT showed satisfactory results with Eurocode 2 presenting slightly higher performance.