Navegando por Assunto "Lajes lisas"

Agora exibindo 1 - 13 de 13

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)
Análise experimental de lajes lisas unidirecionais de concreto armado com pilares retangulares ao puncionamento
(Universidade Federal do Pará, 2007-12-20) DAMASCENO, Lins Sandro Resque; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
They were analyzed 8(eight) experimentally one-way flat slabs of reinforced concrete, without punching shear reinforcement, for that the reinforcement rate in secondary direction and the largest dimension of the pillars (cmax). The flat slab were dimensions of (1.800 x 1.800 x 110) mm, same flexing reinforcement, to smallest dimension of the columns (cmin) constant and equal to 85 mm, resistance to the compression of the concrete around 40 MPa and submitted to the load in the center (symmetrical punching shear), that it simulates an internal column of a pavement. The application of the load was accomplished in passages of columns linked moliticamente to the flat slab with height 150 mm, with retangularidade rate (r = cmax/cmin) varying from 1 to 7. The objective was to evaluate the influence of the retangularidade rate, that contemplated in the increase of the control perimeter in this case, in the behavior of the slabs under flexing, and possibly a more ductile failure. The objective went to also analyze the dear rupture loads starting from the recommendations of six national and international project codes, comparing with the obtained experimental results and evaluating the estimates to the punching shear, once, when the dimensions of the pillars are substantially different can happen the polarization of tensions and the resistance earnings doesn't happen in way directly proportional to the increase of the perimeter of the columns. After analyzing the influences of the retangularidade rate of the columns and the contributions that the reinforcement rate in secondary the last loads of the flats slabs and in the failure modes, it was observed that the experimental results indicated that those varied besides elevating the resistance of the connection can supply certain ductility to the failure of the slabs. It was observed that the rate of growth of the resistances obtained in the rehearsals decreases with increments in the control perimeter. Of the observations regarding the comparison among the values of resistances of the flats slabs, it was verified that the increase of the load of experimental rupture didn't come in a lineal way, indicating that the rate of growth of the load decreases with the increase of the perimeter of the column or of the rate cmax/cmin when stays constant to smallest dimension of the column (cmin).
Acesso aberto (Open Access)
Análise experimental de lajes lisas unidirecionais de concreto armado de alta resistência com metacaulim apoiadas em pilares retangulares e armadas à punção
(Universidade Federal do Pará, 2006-03-02) CARVALHO, Adonay Saráty de; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
Ten reinforced concret slabs were tested, using metakaolin and high strength concrete (cc f nearly 60 MPa), The slabs are submitted to central loading, with objective to analyze the influence of the rectangularity rate of the columms (min C CmÃx) and the stirrups in the increase of resistance. The inclined stirrups have used. The slabâs dimensions were (1.800 x 1.800 x 110) mm and the variables considered were the rectangularity rate of the columms and use the stirrups and distribution around the columm. Ultimate loads, deflections, fissure maps, ductility, concrete, stirrups and reinforcement strains and failure types. The experimental results are comparisons with other results of the codes. The numerical results are compared with experimental results. The experimental results indicate that increase of the rectangularity rate of the columms to make the shear forces concentrat around the colummâs ends, suggesting that the region the shear combat are most solicit. The inclinate stirrups have eficient increase in the resistance of the slab and to change the failure types in some slabs. Observed increases than 32% when the stirrups have to distribuite around the colummâs ends. The low capacity resist to flexion have limited the punching resistance.
Acesso aberto (Open Access)
Avaliação dos métodos normativos para previsão da resistência à punção de lajes sem armadura de cisalhamento e com conectores de aço
(Universidade Federal do Pará, 2016-06-06) PEREIRA FILHO, Manoel José Mangabeira; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485
This work presents an evaluation of the code provisions of various standards for the punching shear failure load on slab-column connections without shear reinforcement and reinforced with steel connectors. The code provisions evaluated are the ACI 3118 (2014), Eurocode 2 (2004), AC Eurocode 2 (2010), UK NA (2004), DIN NA (2011), EHE (2008), NBR 6118 (2014), ETA 12 / 5404 (2012), an adaptation of the ETA proposed by MUTTONI and BUJNAK (2012) and the fib Model Code 2010 (2011). These code recommendations are evaluated for accuracy, safety and economy through 340 test results in flat slabs without shear reinforcement and 140 results flat slabs reinforced with various types of steel connectors arranged in two databases, and all slabs had centered load. In both databases the performance of recommendations was evaluated from a statistical analysis, dispersion analysis of the results and penalized according to the "Demeter Points Classification" (DPC). In addition to the database with slabs without shear reinforcement analysis, in order to assess the reason for the dispersion of code provisions observed the influence of various parameters (fc, ρ, d, u0/d) in code provisions of punching shear resistance load. For the database with results of slabs reinforced with connectors, beyond the initial analysis, the database was divided into groups according to the failure modes of slab. In all groups was carried out the evaluation of equations for each mode of breakage by means of a statistical analysis, dispersion penalty and analysis of results using the "Demeter Points Classification" (DPC). In all groups were assessed the influence of various parameters in the provisions.
Acesso aberto (Open Access)
Influence of the column rectangularity index and of the boundary conditions in the punching resistance of slab-column connections
(Universidade Federal do Pará, 2015-06) PAIVA, Odilson da Silva de; FERREIRA, Maurício de Pina; OLIVEIRA, Dênio Ramam Carvalho de; LIMA NETO, Aarão Ferreira; TEIXEIRA, Marcelo Rassy
Experimental evidence indicates that both the column rectangularity index and the boundary conditions of the connection may affect the ultimate punching resistance. This paper presents general aspects of these topics and, through the analysis of experimental results of tests on 131 slabs, evaluates the accuracy and suitability of recommendations presented by ABNT NBR 6118, Eurocode 2, ACI 318 and fib Model Code 2010. Experimental results showed that the security level of normative estimates trend to reduce as the column rectangularity increases, and in some cases, the punching resistance was overestimated. Finally, adjustments are suggested in equations presented by NBR 6118 and MC2010 in order to eliminate this trend of unsafe results.
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.
Acesso aberto (Open Access)
Punção em lajes lisas bidirecionais de concreto armado com furos e pilares com secção transversal em “L”
(Universidade Federal do Pará, 2015-08-21) PINTO, Valdemir Colares; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
Aiming to improve the knowledge of the influence of hole position in reinforced concrete flat slabs with L-shaped column, this research show three different sets of hole position taking into account the effect of this parameter in the punching shear capacity resistance. For this, it have been analyzed 4 flat slabs with dimensions with (1800x1800x120) mm³, where one is the reference (without hole) and 3 have holes of dimensions of (100x100) mm², positioned adjacent to the column, with center of gravity of hole on the critical perimeter at 0,5⋅d and at 2,0⋅d. The load have been applied uniformly on the base of the column and the slab will be simply supported at four slides, simulating an inner column in a standard floor. The slabs have show flexural reinforcement with geometrical rates between 0.92% and 0.94%. To improve the analyses, computational models in finite elements have been elaborated through ABAQUS software, evaluating the stresses, dispacements, cracing and falure mode of slab. The estimative of design was based in four different standards and one theorical model: ACI 318 (ACI, 2008), Eurocode 2 (CEN, 2004), NBR 6118 (ABNT, 2014), Model Code 2010 (fib, 2011) and Critical Shear Crack Theory (MUTTONI, 2008). The results have showed considerably difference between standards estimates and the experimental results.
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.
Acesso aberto (Open Access)
Punching strength of reinforced concrete flat slabs without shear reinforcement
(Universidade Federal do Pará, 2012-10) SACRAMENTO, Paulo Victor Prazeres; FERREIRA, Maurício de Pina; OLIVEIRA, Dênio Ramam Carvalho de; MELO, Guilherme Sales Soares de Azevedo
Punching strength is a critical point in the design of flat slabs and due to the lack of a theoretical method capable of explaining this phenomenon, empirical formulations presented by codes of practice are still the most used method to check the bearing capacity of slab-column connections. This paper discusses relevant aspects of the development of flat slabs, the factors that influence the punching resistance of slabs without shear reinforcement and makes comparisons between the experimental results organized in a database with 74 slabs carefully selected with theoretical results using the recommendations of ACI 318, EUROCODE 2 and NBR 6118 and also through the Critical Shear Crack Theory, presented by Muttoni (2008) and incorporated the new fib Model Code (2010).
Acesso aberto (Open Access)
Slabs strengthened for punching shear with post-installed steel and CFRP connectors
(Universidade Federal do Pará, 2019-06) PEREIRA FILHO, Manoel José Mangabeira; FREITAS, Marcus Vinícius Pereira de; SANTOS, Douglas Freitas Augusto dos; FERREIRA, Maurício de Pina; NASCIMENTO, Alex J. C.
Structural accidents due to punching shear failures have been reported in flat slab buildings. Design recommendations presented by codes can lead to entirely different punching shear resistance esti-mates for similar situations. Furthermore, design codes do not present guidelines for the design of punching shear strengthening of existing slabs. This paper uses a database with 118 experimental re-sults to discuss the performance of theoretical estimates of punching shear resistance using ACI 318, Eurocode 2 and ABNT NBR 6118 in the case of slabs without shear reinforcement. Another database with results of 62 tests on slabs strengthened with post-installed steel and CFRP dowels is used to evaluate the performance of these strengthening techniques and to propose adaptations in codes to allow their use in punching shear strengthening situations of existing slab-column connections.