Navegando por Assunto "Laje lisa"
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Item Acesso aberto (Open Access) Análise do efeito da retangularidade dos pilares nos critérios normativos de dimensionamento à punção em lajes lisas de concreto armado(Universidade Federal do Pará, 2013-10-22) PAIVA, Odilson da Silva de; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186The system with flat slabs that do not depend on framework of beam has limited resistance by the resistance to punching shear, since the region of the slab-column is critical due to concentrated loads around the columns. The geometry of the columns is one of the factors influencing the distribution of stresses in the region of slab-column connection affecting turn in sizing the punching shear in the flat slabs. In this study we performed a thorough data collection that aims to collect into a single job the greatest possible amount of slabs covering the biggest names in the study of national and international punch, featuring a total of 131 slabs. A comparison was made between the main normative codes currently used Eurocode 2 (2004), NBR 6118 (2007), ACI 318 (2008) and CEB-FIP (2010). The experimental results were compared with those obtained theoretically taking into account the effects of retangularidade rate index in flat slabs of reinforced concrete, without punching shear reinforcement checking the adequacy, trustworthiness of each recommendation, analyzing the particularities of the rules and guidelines of each normative criterion.Item 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/1324105476558186Two-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.Item Acesso aberto (Open Access) Análise experimental de lajes lisas unidirecionais de concreto armado ao puncionamento simétrico ou assimétrico(Universidade Federal do Pará, 2006-03-02) FERREIRA, Maurício de Pina; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186Punching is normally a critical case in the design of reinforced concrete flat slabs. According to many design codes, punching develops in a more unfavorable way in cases where the load is asymmetrically applied, due to unbalanced bending moments at slab-column connections. In order to evaluate the normative prescriptions in these cases, 12 reinforced concrete oneway flat slabs ( c f ' between 36 and 58 MPa) were submitted to symmetric or asymmetric punching. The slabs dimensions were (1.800 x 1.800 x 110) mm with the load being applied through a metallic plate simulating a square column with (85 x 85 x 50) mm. This research had as variables, in addiction to the load position, the reinforcement rate in transversal direction, in order to evaluate their influence in the punching ultimate resistance of one-way slabs. Results for vertical deflections, concrete surface and flexural reinforcement strains, cracking pattern, observed ultimate loads and failure modes are presented and analyzed. Also were analyzed the estimates of 6 design codes, with 3 European and 1 North-American, beyond the versions from 1978 and 2003 of the Brazilian structural concrete design code. A numerical analysis using the Finite Elements Method to simulate the slabs behavior is presented and its results are compared to the experimentally observed ones. The results showed that, unlike the normative previsions, punching resistance doesnt reduce linearly with the increments in the loads eccentricities, with the flexural effects significantly influencing the ultimate punching resistance. Even in one-way slabs, the transversal reinforcement rate showed significant influence on the slabs force distribution, interfering in the punching resistance.Item Acesso aberto (Open Access) Contribuição ao estudo de lajes lisas unidirecionais de concreto armado com pilares retangulares ao puncionamento(2007-12) FERREIRA, Maurício de Pina; OLIVEIRA, Dênio Ramam Carvalho deAnalysis of recommendations to predict the ultimate punching resistance of flat slabs according to the actual Brazilian code, NBR 6118:2003, which does not consider the effects of the internal columns' rectangularity, and its previous version, NBR 6118:1980, are presented. In rectangular cross sections, the shear stress polarization rate is crescent. Thus, the slab failure mode changes, since the punching failure takes place at the column's ends, without compromizing the larger sides, as recommended by the new version of the code. This behavior tends to reduce the ultimate punching resistance of flat slabs when the normative estimates are compared. In addition to the results from the two codes, are presented a numerical analysis by the Finite Element Method and a proposal to improve the ductility of flat slabs based on the minimal dimensions for rectangular columns. The results showed that the NBR 6118:2003 estimates can be improved.Item Acesso aberto (Open Access) Lajes lisas nervuradas bidirecionais com furos(Universidade Federal do Pará, 2014-08) MATEUS, Gustavo Menezes; AGUIAR, Amaury José Oliveira de; FERREIRA, Maurício de Pina; OLIVEIRA, Dênio Ramam Carvalho deThe position of pipes and hoses for several installations still deserves special attention from designers mainly when the failure mode can be modified due to changes in behavior. This work compares experimental results of six two-way reinforced concrete ribbed flat slabs with rectangular holes close to the column and without shear reinforcement with the estimates obtained from codes ACI 318 and NBR 6118 equations. All slabs were casted and tested in the Civil Engineering Laboratory of UFPA and had dimensions of 1.800 mm x 1.800 mm x 150 mm and were submitted to central loading applied through 120 mm side square steel plates simulating the columns. EPS was used as inert material and the ribs were spaced 250 mm with 130 mm height and 75 mm average wide. The results showed that the codes’ shear equations estimates agree when the ribs are considered as beam and also for punching shear, but trend to be safer when the slabs present two shafts.Item Acesso aberto (Open Access) Lajes lisas nervuradas de concreto armado ao cisalhamento(Universidade Federal do Pará, 2011-10) SOUZA, Shirley do Socorro Melo de; OLIVEIRA, Dênio Ramam Carvalho deThe structural systems with waffle flat slabs are the most used in Brazil when the main requirement is flexible "layouts" and long spans with reasonable economy. However, few studies have been developed in Brazil regarding the behavior of these slabs when the flexural resistance is satisfactory and the shear in the ribs and punching resistances become competitive. This work shows the experimental analysis of 8 two-way reinforced concrete waffle flat slabs under centered load. The dimensions of the slabs were the same and equal to 1800 mm x 1800 mm x 140 mm. The ribs were 80 mm (height) by 50 mm (width) and the compressive concrete strength was approximately 40 MPa. The experimental results were compared to those estimated by the Brazilian code NBR 6118:2003. It was verified that the resistance of the ribs is not satisfactorily estimated by the code, which excessively underestimates the results for ribs with and without shear reinforcement.Item Acesso aberto (Open Access) Punção em lajes lisas unidirecionais de concreto armado com diferentes taxas de armadura secundária e pilares retangulares.(Universidade Federal do Pará, 2022-09-29) BRANCO, Vitor Hugo Lopes; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186Symmetric punching tests and experimental analyses were conducted to evaluate the behavior of nine one-way reinforced concrete flat slabs. The slabs measured (1800 x 1800 x 120) mm, and loads were applied through three types of columns: A (85 × 85) mm, B (85 × 255) mm and C (85 × 425) mm. All slabs were made with constant longitudinal reinforcement ratio at around 1% (ρx) and different secondary flexural reinforcement ratios (ρy), namely type 1 (0.5%), type 2 (1%) and type 3 (2%), approximately. Concrete compressive strength of 28 MPa and elasticity modulus of 27 GPa. Reinforcement yield stress of 573 MPa and elasticity modulus of 244 GPa. Column rectangularity index (cmax/cmín) and secondary reinforcement ratio were the main research variables, and the present study evaluated their influence on the ultimate punching strength of the sampled one way reinforced concrete flat slabs. The experimental results were compared with four current international standards: ACI 318 (2019), EC2 (2004), MC 2010 (2011) and NBR 6118 (2014). They were also compared with the findings from a nonlinear numerical analysis made with the software ABAQUS CAE 6.14, based on the Finite Element Method (FEM) and on the Concrete Damage Plasticity (CDP) model. The results indicated that the standards need to be updated, and that there is a proportional increase of up to 50% approximately in slab punching strength when the secondary reinforcement ratio is increased by up to 2%.