Teses em Engenharia Civil (Doutorado) - PPGEC/ITEC
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Navegando Teses em Engenharia Civil (Doutorado) - PPGEC/ITEC por Orientadores "OLIVEIRA, Dênio Ramam Carvalho de"
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Item Acesso aberto (Open Access) Influência do fator de escala, diâmetro máximo e tipo de agregado graúdo na resistência ao cisalhamento de vigas de concreto armado sem armadura de cisalhamento(Universidade Federal do Pará, 2022-08-18) COSTA, Natasha Cristina da Silva; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186The present study evaluated the influence of different types and forms of coarse aggregates on the structural behavior of concrete beams with different useful heights (d) and the same base length (bw), in addition to the same longitudinal reinforcement rates (l) and dosages of concrete. For this test, it is necessary to carry out tests and tests that analyze the performance of some design codes and theoretical models in prescribing the most recent shear strength of reinforced concrete beams, without transversal reinforcement. Regarding the experimental study, 11 experimental tests of the stuttgart type were carried out until the pieces collapsed. The dimensions of the pieces were: (150 x 150 x 1400) mm, (150 x 250 x 1900) mm, (150 x 350 x 2400) mm and (150 x 450 x 2900) mm. The evaluated variables were, in addition to the geometric dimensions, the type, the dimension and the content of coarse aggregates used in the concrete dosages. When using the type of rolled pebble and a crushed stone. As for the dimensions used, pebble with maximum diameter (dmax) equal to 12.5 mm and gravel with two dmax: 9.5 mm and 12.5 mm were used. As for the content, in this work, the amount of engraved aggregate, indicated in the dosage, was reduced by 30%. In this research, transverse arms on all beams were removed, which were placed only on the supports and at the load application points to avoid damage caused by tension. In the analysis of the project codes, the requirements of ACI 318 (2019), EC2 (2004) and NBR 6118 (2014) were evaluated. It does not refer to theoretical models, discussed as proposals by MUTTONI (2019) and HUBER(2019). How to analyze besides evaluating the dispersion and conservatism of the results found, it also ranks the seconds according to COLLINS (2001) records, or the classification of demerit points -DPC. Finally, with a contribution proposal with a proposal for dimensioning reinforced concrete beams subject to shear stress, the present work presents a proposal for a correction factor, which considers the analyzed criteria, to decrease or variation coefficient calculation results based on the formulations analyzed. To suggest the proposed changes to ACI 318 (2019), EC2 (2004) and NBR 6118 (2014), two databases composed of beams tested to failure by shear were used. The first database was used to make interactions between the parameters evaluated, seeking results that would improve the normative predictions, regarding structural safety and data dispersion. And a second database was used to validate these modification proposals. The beams were numerically modeled in a computational software for non-linear finite element analysis. The calibration of the numerical models was made from the experimental results of the reinforced concrete beams tested in the experimental program of this thesis. Analyzing the models, it is observed that the numerical model was able to satisfactorily predict the experimental behavior of the beams.Item Acesso aberto (Open Access) Lajes lisas nervuradas bidirecionais de concreto armado sem armadura de cisalhamento com furos adjacentes ao pilar(Universidade Federal do Pará, 2019-08-23) AGUIAR, Amaury José Oliveira de; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186With the need for a better understanding of the structural behavior of bidirectional ribbed flat slabs of reinforced concrete with opening adjacent to the column, aiming at the passage of installation ducts or ventilation, 15 square slabs measuring 2300 mm sides and 150 mm thickness with different opening configurations. The influence of the rectangularity of the columns was also an important topic analyzed, considering the concentration of tensions in the vertices of the loaded area. In order to do, 5 consecrated standards were used as a calculation parameter to estimate the final loads of the slabs and also to develop a new approach to estimate the loads of ruin. It is worth remembering that the analyzed slabs did not have shear reinforcement, that is, only the concrete contribution was considered to estimate the ultimate strength, although some standards associate this portion of resistance with the flexural reinforcement ratio, assigning an increase on ultimate strength. The results showed that the elongation of the opening and the column affected considerably the behavior of the slabs as well, the distribution of the stresses in the regions of the vertices of the openings. Based on data bases, it was possible to establish new parameters in the normative equations (Hi) which in turn approximated the results and decreased the dispersions of the same ones, besides a non-linear numerical analysis to have provided reliability standards in the models analyzed.Item Acesso aberto (Open Access) Modelo para resistência de cisalhamento em vigas de concreto sem estribos(Universidade Federal do Pará, 2021-11-30) LIMA, João Carlos Lisboa de; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186The analysis of shear strength in concrete beams involves significant complexities and iteration between parameters. The development of models for the design and verification of the ultimate limit state of beams began in the 19th century with empirical, theoretical and numerical models such as the Ritter-Mörsch truss analogy and the modified compression field theory. However, the almost stochastic ratios of compressive strength of concrete, longitudinal reinforcement ratio, loading slenderness, transverse dimensions and coarse aggregate diameter add up to numerous difficulties in creating simple and easily applicable formulas. Thus, the present work aims to develop a model based on proportionality relations and the application of an iterative algorithm to optimize the values of an initial database of 220 beams (62 authors) that failure by shear and define a theoretical model that will be compared with a database of 510 beams (63 authors) and other methods of calculation of relevance. The proposed formula provided a coefficient of variation of 6.23%, being between 34.97% and 59.52% lower than the models analyzed. Thus, the results of the proposed method, when considering the experimental and theoretical relationship of the database, present all values within the appropriate safety range, allowing greater accuracy in defining the ultimate load of concrete beams without stirrups.Item Acesso aberto (Open Access) Proposta analítica para estimar as resistências residuais à tração por flexão em concreto reforçado com fibra de aço(Universidade Federal do Pará, 2022-06-15) CASTRO, Lana Daniele dos Santos Gomes; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186This research presents equations that estimate the residual resistances, fRi (i = 1 to 4), based on the main parameters that influence the performance of steel fiber reinforced concrete (SFRC), such as the geometric properties of steel fibers, the concrete compressive strength (fc) and fiber volume fraction (Vf). For this purpose, the research was divided into three stages, the first one consisted of creating an extensive and diversified database to, from it, develop the residual resistances equations through multiple regression. The next stage was experimental, composed of 15 beams (150x150x550) mm notched and tested to flexural tension, with variable fiber volumes, with contents of 0.0%, 0.5%, 1.0%, 1.5% and 2.0%. Finally, for the analysis of the equations elaborated in the first step, another database is presented, in which experimental results collected from the literature and those obtained in this research were inserted, and, additionally,performance comparisons were performed with four other existing analytical models. It was concluded that the analytical proposal presented by this study to define the residual resistances, in comparison with the other existing empirical models, stood out for its good performance, since it was the most accurate, less penalized and dispersed, demonstrating the reliability of the equations.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%.