Navegando por Assunto "Punching shear"

Agora exibindo 1 - 5 de 5

Acesso aberto (Open Access)
Análise da resistência à punção de sapatas de concreto armado
(Universidade Federal do Pará, 2016-06-07) SANTOS, Douglas Freitas Augusto dos; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485
The footings is a kind of superficial foundation rather employed in construction and is used especially for small projects or when the soil is able to withstand the loads without deforming is exaggerated. Footings can present a brittle fracture mode, called puncture. To avoid this kind of disruption that occurs abruptly, it is possible in the design phase to take some measures, such as increasing the shoe height, reinforcement ratio of bending, the strength of concrete or the ratio a/d. In the literature, was carefully collected with a database 216 and tests analyzed by different standards such as the ACI 318 (2011), CSA A23.3 (2004), EUROCODE 2 (2004) and (2010) and NBR 6118 (2014), with the aim of contributing to a better understanding of the punching footings reinforced concrete Then, it was found that the load capacity ranged last much of a provision to another. Besides confirming that the ratio a/d (ratio of shear span the useful height) influence significantly the resistance to puncture. In the case of the standard EUROCODE 2 (2010), was the finding that the locking effect size decreases the resistance to punching footings, increasing the coefficient of variation with the experimental data. The desing recommendations of their countries are used for sizing the punch, but are mainly empirical rules, that is prepared a series of experimental data. Thus, the experimental results must play or come close to reproducing the reality that the component studied issue will be submitted in the case of footings in the soil. The wide range of test systems raises doubts as to need and reliability by verifying discrepancies between the rules and test systems mainly for the ability to last loads, generating uncertainty as to the suitability of these recommendations.
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)
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)
Influência do detalhamento dos estribos na resistência à punção de lajes lisas de concreto armado
(Universidade Federal do Pará, 2021-09-15) COSTA, Mayara Gonçalves; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485; https://orcid.org/0000-0001-8905-9479
Stirrups used as punching shear reinforcement in reinforced concrete flat slabs can provide strength gains to the regions of slab-column connection. To this end, the standards recommend that the details should be made in order to ensure their anchorage in the flexural reinforcement bars, involving them. However, designs that strictly follow the detailing criteria may become difficult to execute, or even unfeasible, due to the concentration of longitudinal bars in these regions. The need for more practicality in the assembly of stirrups has driven the development of reinforcement systems, whose anchorage details are not yet contemplated in the normative prescriptions. Therefore, the scientific validation of such constructive alternatives is necessary. In this context, this work seeks to contribute to the validation process of numerous constructive alternatives for stirrups used as punching shear reinforcement, so that, in this way, they can be properly disseminated in the technical environment. The objective of this work is to evaluate the influence of the variation of the stirrups anchorage on its efficiency, from an extensive review of scientific literature, which enabled the assembly of a database containing 119 punching shear tests in internal slab-column connections, subjected to symmetric loading. The analysis parameters were the increments of strength provided as a function of the increase of force played by the shear reinforcement. At the end, the most efficient anchorage details for different types of stirrups used as punching shear reinforcement were defined and, for such stirrups, assembly instructions were proposed, aiming the optimization of the constructive process.
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.