Dissertações em Engenharia de Infraestrutura e Desenvolvimento Energético (Mestrado) - PPGINDE/NDAE/Tucuruí

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/9401

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Agora exibindo 1 - 5 de 5

Acesso aberto (Open Access)
Análise experimental da eficiência de bielas de concreto simples e armado em modelos locais e globais
(Universidade Federal do Pará, 2019-03-21) FREIRE, Marília Caires; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485; https://orcid.org/0000-0001-8905-9479
Reinforced concrete beams are usually designed by sectional analysis methods, where Bernoulli hypothesis is taken into account, assuming that strains are linearly distributed along the cross-sectional area of the element. However, many practical situations require distinct calculation alternatives, made by both fundamentally empirical code expressions and numerical or analytical solutions from the Strut-and-Tie Method. This is the case of deep beams, where a bottle-shaped strut is formed and the influence of its reinforcement ratio is generally discounted by the current design codes. Therefore, an experimental study was performed to assess the efficiency of plain and reinforced concrete struts, by local and global models, respectively represented by diamond-shape panels loaded in small bearing areas and deep beams, since in both the resistant mechanism seems to be directly related to the flow of stresses in the concrete strut. The results showed similar behaviors among the models regarding strains in concrete and reinforcement, as well as equivalent failure modes resulting from a splitting crack of the strut. With the increase of transverse reinforcement ratio, gains of ultimate strength, ductility and cracking control were observed, mainly for specimens with mesh reinforcement, as well as higher and safe results for the analysis by the strut efficiency factors. On the other hand, the assessment of shear strength by the design codes showed unconservative predictions with increasing transverse reinforcement. This way, it is confirmed that solutions by strut-and-tie models are more suitable methods for the efficient and safe design of structures with regions of disturbance in the stress-strain distribution.
Acesso aberto (Open Access)
Análise experimental da resistência à punção em lajes lisas com substituição de agregados graúdos naturais por reciclados de concreto
(Universidade Federal do Pará, 2022-05-12) RIBEIRO JUNIOR, Jayron Alves; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485; https://orcid.org/0000-0001-8905-9479
The popularization of the use of recycled concrete aggregates has increased due to socioeconomic aspects, but above all, as sustainability is being pursued and, in this context, some international standards have been published to facilitate and standardize the use of this material. Despite the constant evolution of studies on punching shear, there is a need for national and international regulatory adjustments in relation to the use of recycled concrete aggregates in flat reinforced concrete slabs. Two reasons explain the slight influence of the incorporation of recycled aggregates on the punching shear resistance of concrete slabs: lower mechanical strength and better bond between the cement paste and the recycled concrete aggregate due to the higher cement content, porosity, and roughness, when compared with natural aggregate. Thus, the punching shear strength is influenced by these properties of the aggregates along the shear plane of the cracks, the two effects offset each other, leading to a similar punching shear strength. This research carried out the experimental test of 6 flat slabs of reinforced concrete without shear reinforcement subjected to symmetrical loading, containing variations in the rate of flexural combat reinforcement (0.7% and 1.4%) and replacement rate of natural aggregate by recycled concrete aggregate (0%, 30% and 100%). The study evaluated the influence of these variables on the punching shear resistant capacity and analyzed the upper limits of resistance. The slabs were octagonal with 2500 mm of distance between parallel faces, sides of 1030 mm and thickness of 210 mm, molded with concrete with fck of 25 MPa and supported on columns of 300 mm of side. The standards used as a parameter for estimating resistant capacity were NBR 6118:2014, ACI 318:2019 and Eurocode 2:2004. The experimental results showed that the slabs with ARCO showed a maximum reduction of 6 % in the punching shear resistance when compared to the slabs with conventional coarse aggregates. The reinforcement rate was able to increase the cracking load at the service limit state (ELS) and the recycled concrete aggregate had little influence on the opening of cracks in the slabs with the highest rate of flexural reinforcement.
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)
Efeito da taxa de armadura existente e do sistema de ancoragem na resistência à flexão de consolos curtos de concreto armado reforçados com laminados de PRFC
(Universidade Federal do Pará, 2025-06-13) LIMA, Layse Rafaele Furtado; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485; https://orcid.org/0000-0001-8905-9479
Short corbels are elements used in bridges and buildings to support beams, stringers or concentrated loads of great intensity, and are characterized by having a span-to-height ratio of less than one. Over the course of their useful life, these structures can fail to meet basic safety requirements for reasons such as design error, material degradation, overload or change in use, requiring reinforcement techniques that can be applied quickly and efficiently. With this in mind, this work seeks to experimentally analyze short reinforced concrete beams reinforced externally in bending with Carbon Fiber Reinforced Polymer (CFRP) laminates. To this end, six specimens were analyzed, three with a 0.18% flexural reinforcement rate and three with a 0.47% rate. All the models have the same geometry, with the presence of horizontal and vertical stirrups. The reinforcement was positioned on both sides of the cantilever and anchored at the ends, checking the influence of two systems. The first anchoring system is made up of steel plates and bolts, while the second is made up of overlapping laminates, with transverse bonding in the last layer. As a result, it was possible to analyze that the reinforcement proved to be efficient in terms of increased resistance, which ranged from 14,5% to 50,3%, with the hybrid anchorage standing out as having the highest loading value.
Acesso aberto (Open Access)
Influência do espaçamento das armaduras de cisalhamento na resistência à punção de lajes lisas com estribos treliçados pré-fabricados
(Universidade Federal do Pará, 2022-12-27) COSTA, Denilda Silva; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485; https://orcid.org/0000-0001-8905-9479
The shear check on the slab-column connection of flat slabs in reinforced concrete is the critical point of design in the ultimate limit state. Punching failure is the critical point in the design of flat slabs and is defined as a sudden and fragile failure due to shears in the region of connection between the slab and the column, the best option for the control of failure by flat slabs is to use of shear reinforcement. National and international regulations such as the use of shear reinforcements that involve bending reinforcements in a way that their anchoring is guaranteed. However, this model makes the executive process difficult, requiring configurations between the bending and shear protections at the construction site. This research aims to present a technical and constructive solution to the problem of shear resistance in flat slabs in the slab-column connection through the use of shear reinforcement proposed by Ferreira et al. (2016), prefabricated truss stirrups, varying the values of the shear reinforcement rates and the spacing between the reinforcement layers. Positioned between the upper and lower flexural reinforcements, it has speed in execution and the possibility of manpower, as it is industrially bent and positioned on the job site, the useful height of the slab and the economy eliminates conflicts between the shear and flexural reinforcements. To compare the results and analyze the performance, tests were carried out on 5 flat reinforced concrete slabs, one of the slabs was reinforced with a flexural reinforcement rate ρ 2,0%, and the others with ρ1%, the reinforcement rate of shear (ρw) varies from 0.49% to 0.99%. As the instrumented in a way that could be the non-designed displacement forms, as in the flexural, shear and complementary reinforcements. The slabs were instrumented so that the vertical displacements, the deformations in the concrete and in the flexural, shear and complementary reinforcements could be obtained. The slabs were dimensioned so that the failure occurred by punching within the region of the shear reinforcement following the normative calculation recommendations of NBR 6118 (ABNT, 2014), ACI 318 (2019), Eurocode2 (2014), fib Model Code 2010 (2013) and the EOTA technical report (2017). From the analysis of the results, it was concluded that all slabs failed by punching, the slabs reinforced with prefabricated truss stirrups showed a strength gain of 73% for the SW3 slab when compared to the reference slab (S0) from Freitas (2018) and of 55%, 58%, 45% and 50% for slabs SW4, SW5, SW6 and SW7, respectively, when compared with the predictions of NBR 6118 (ABNT, 2014), slabs with reinforcement positioned up to 1.125d from the column face showed higher strength increase values and ultimate strength values similar to those of slabs with constant spacing, even with reduction of the total amount of steel by up to 95,2% of its weight.

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