Navegando por Assunto "Shear"

Agora exibindo 1 - 11 de 11

Acesso aberto (Open Access)
Análise experimental da eficiência das fibras de aço no reforço ao cisalhamento de vigas em concreto armado
(Universidade Federal do Pará, 2016-08-29) GOMES, Lana Daniele dos Santos; MORAES NETO, Bernardo Nunes de; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
The present study aims to assess the efficiency of steel fibres for shear strength of reinforced concrete beams. For this purpose, some design guidelines were discussed together with an experimental research. For the guidelines analysis, five proposals are presented, RILEM TC 162-TDF (2003), CECS 38 (2004), JSCE (2008), EHE 08 (2010) and MODEL CODE (2010). Within this analysis, the proposals performance were assess from the Vexp/Vteo parameter, which corresponds, respectively, the experimental results, which will be collected from the scientific literature, composing a database (DB), and the theoretical results, which are estimated according to the design guidelines. For the experimental research, four beams are evaluated, where one beam is the reference one (no fibres), and the others are built with steel fibres reinforced concrete (SFRC). It is important to note that all beams are reinforced for shear strength by a minimum amount of web reinforcement (stirrups). For the SFRC beams, two conditions will be discussed. Firstly, the influence of the fiber content (Cf) added to the concrete, which range in 0,5% (≈40 kg/m3), 0,8% (≈60 kg/m3) and 1,0% (≈80 kg/m3) and finally, the possibility to replace conventional web reinforcement (stirrups) by steel fibres reinforcement. The theoretical analysis, it was concluded that the guidelines MODEL CODE (2010), CECS 38 (2004) and JSCE (2008), have provided the best results agreed with Vexp / Vteo≈1,0, however, JSCE (2008) was the most penalized according to the modified version of the DPC (Demerit Points Classification), proposed originally by Collins (2001). RILEM TC 162-TDF (2003) behaved conservatively and EHE 08 (2010) showed more dispersed results. In relation to experimental research, although it was recorded a resistance increases of 20% for concrete with Cf = 1.0%, the axial compression tests, however, the most significant gain was recorded as ductility and toughness the SFRC, to the point of changing the way of breaking the beams, shear (reference beam) for bending (beams with SFRC).
Acesso aberto (Open Access)
Análise experimental de consolos curtos de concreto com armaduras continuas e descontinuas
(Universidade Federal do Pará, 2019-09-30) ABRANTES, Jedson Henryque Corrêa; TEIXEIRA, Marcelo Rassy; http://lattes.cnpq.br/8912916360456192
Short consoles, as well as some reinforced concrete elements, have discontinuity regions (D regions), where Bernoulli's hypotheses should not be taken into account, since stress flows do not distribute linearly along the cross section. In order to correct the disturbances caused by this flow in specific areas, it is necessary to look for alternatives of calculation through equations idealized by empirical perceptions of researchers, or by means of the Strut-and-Tie Method. In this context and after theoretical and experimental observations of consoles, it was concluded that it is formed in this structure a bottle-shaped strut, and although there is a considerable database in this regard, there is no consensus in the literature and among current codes that relate between continuous reinforcement rates, failure mode and strut efficiency factors . Thus, an experimental study was carried out to evaluate the contribution of three types of fibers (discontinuous reinforcement), polypropylene, polyethylene and steel, which were added to the concrete in three different contents for each one. The results showed that in general there were similar behaviors for the concrete readings, and the opposite when analyzing the continuous reinforcement that suffered tensile stresses (Tie). For the elements with metallic fibers the resistance gain in relation to the reference specimens was noticed for the part that received higher fiber content. For synthetic fibers, polypropylene fiber had better gain in the specimen with second best fiber volume, and for polyethylene was registered for the lowest percentage. These consoles also presented better ductile behavior among all the test elements that did not receive horizontal stirrups. Regarding the results compared to the specimen with continuous reinforcement only the one with polyethylene fiber achieved superior result. Regarding the strut efficiency factors, the method presented results against and in favor of safety, while with respect to the shear strength the codes estimates had very favorable results. Therefore, MBT is a very suitable method for design that presents efficiency and safety through structures that present stress and deformation disturbances.
Acesso aberto (Open Access)
Análise experimental do desempenho de conectores de cisalhamento de vergalhões dobrados para estruturas mistas via ensaios push-out
(Universidade Federal do Pará, 2022-11-25) SOUSA, Vanessa Carolaine de; LIMA NETO, Aarão Ferreira; http://lattes.cnpq.br/0287664572311345; https://orcid.org/0000-0002-5911-1368
Advances in civil engineering have led to the development of new techniques and materials that optimize the construction process. In this context, steel-concrete composite structures have emerged, which use steel and concrete efficiently through the collaborative work of the materials, exposing the metal part to tensile stresses and the concrete to compressive stresses. Shear connectors are essential in steel-concrete composite structures. They ensure the interaction between the materials and the transfer of stresses, making the structures lighter, stronger, and more durable. It is important to understand their operation and to seek new materials and technologies to optimize the structures. In this sense, this research continues the work of Souza (2019) and Barbosa (2016), who studied shear connectors made with CA-50 steel bars bent. The experimental program includes 7 models (varying the bar size, reinforcement rate, and the inclination of the connectors relative to the table of the metal profile) that were tested according to the recommendations of Eurocode 4 (2004). Of these 7 models, 2 were made with 12.5 mm rebar (models A1 and A2), 2 with 10.0 mm (models B1 and B2), 2 with 8.0 mm (models C1 and C2), and 1 model made with 6.3 mm diameter assembled in a single module (model D). When analyzing the load-carrying capacity/steel area ratio of the connectors, the results show that connector A1 (12.5 mm) had the best performance among the models in the study and also stands out when compared to other connectors studied such as those of Barbosa (2016), Souza (2019), and Chaves (2009). No significant evidence was observed that the inclination of the connectors positively affects the load-carrying capacity of the models. Analyzing the relative displacement between the profile and the slabs, it was possible to classify the models by ductility, in increasing order: D, A1, C1, C2, A2, B2, and B1. The 10.0 mm models have the highest ductilities, and the influence of the inclination of the connectors on this aspect is not clear. Analyzing the behavior in relation to uplift, it is noted that the best performances are in connectors B and C (10.0 mm and 8.0 mm) and there is a tendency for worse results in inclined connectors.
Acesso aberto (Open Access)
Efeito da adição de agregados reciclados na resistência ao cisalhamento de vigas de concreto armado
(Universidade Federal do Pará, 2018-07-31) CARDOSO, Allan Carvalho; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485
The present work evaluates the influence of the incorporation of recycled concrete aggregate (RCA) on the shear strength of beams in reinforced concrete. An experimental analysis composed of twelve beams will be performed: four executed with conventional concrete (composed of natural aggregates) and eight with RAC. The experiment aims to evaluate the influence of the transverse reinforcement (ρw) and the variation of the longitudinal reinforcement ratio (ρl), on the shear strength of the parts. The concrete beams were divided into two groups, with RCA rates varying from 0 to 100%. In addition, three codes will be discussed: ACI 318 (2014); EUROCODE 2 (2004); NBR 6118 (2014) and MODEL CODE (2010), which will be applied to a concrete beams database (DB) with RCA. The performance of these codes will be evaluated through the parameter λ, by means of the relation between the ultimate experimental load (Vexp) and the theoretical ultimate load (Vteo), λ = Vexp / Vteo. This parameter was analyzed according to the level of conservatism and related to the main variables of this research: ρl, ρw and AGRC. The value of λ is analyzed according to the level of conservatism.
Acesso aberto (Open Access)
Experimental analysis of the efficiency of steel fibers on shear strength of beams
(Associação Brasileira de Ciências Mecânicas, 2016-07) GOMES, Lana Daniele dos Santos; OLIVEIRA, Dênio Ramam Carvalho de; MORAES NETO, Bernardo Nunes de; MEDEIROS, Adelson Bezerra de; MACÊDO, Alcebíades Negrão
The efficiency of steel fibers for shear strength of reinforced concrete beams is assessed. Four beams were evaluated: control consisted of one beam without any steel fibers and three beams with reinforced concrete with steel fibers. All beams were reinforced for shear strength by a minimum reinforcement rate. The influence of fiber content added to concrete, at 0.5%, 0.8% and 1.0%, and the possibility of partial or total replacement of conventional shear reinforcement (stirrups) by steel fibers were evaluated. Results showed a significant increase in ductility and stiffness of the beams with steel fibers and, consequently, changes in the failure mode were observed, of shear (control beam) to flexure behavior (beams with steel fibers).
Desconhecido
Influence of the supplementary reinforcement on the shear strength of beams with prefabricated truss stirrups
(Instituto Brasileiro do Concreto, 2022) PINTO, Rosângela Silva; SOUSA, Vanessa Carolaine de; TAPAJÓS, Luamim Sales; FERREIRA, Maurício de Pina; LIMA NETO, Aarão Ferreira
This paper presents the results of seven experimental tests in reinforced concrete wide beams, aiming to investigate their performance when subjected to shear, using prefabricated truss stirrups as shear reinforcement, as well as a supplementary reinforcement to control cracks by delamination. The main analysed variables were: position of the supplementary reinforcement, inclination of the shear reinforcement, and spacing between stirrups. Results showed that strength increments of up to 142% were obtained using the prefabricated truss stirrups. Furthermore, the experimental results were compared with the theoretical shear strength estimates of the tested beams, following the recommendations of NBR 6118 (2014), Eurocode 2 (2004), and ACI 318 (2014), in order to evaluate the safety level of these codes when designing concrete elements subjected to shear with the reinforcement used in this paper.
Desconhecido
Influência da mesa na resistência ao cisalhamento de lajes nervuradas unidirecionais de concreto armado
(Universidade Federal do Pará, 2013-09-10) SOUZA, Wallace Maia de; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
The shear strength of one-way ribbeds slabs of reinforced concrete without transverse reinforcement in their ribs is evaluated through structural behavior shear. For to quantify the contribution of the height of the table and the flange characteristic resistance shear were fabricated 8 panels one-way ribbeds slabs of concrete with variations of the height of the tables, in order to evaluate the recommendations of NBR 6118 (2007), ACI 318 (2011) and EUROCODE 2 (2002) with consider to the performance of one-way ribbeds slabs of reinforced concrete shear. The slabs, simply supported edges, presented in two groups, seeking cover the limits prescribed by the brazilian standard: the first with 4 slabs (2000 x 1300) mm ² with distance between the axis of the ribs of 610 mm and the second with 4 slabs (2000 x 2000) mm² with distance between the axis of the ribs of 960 mm, and there was a variation of the table height of 30, 50, 80 and 100 mm. The flexural reinforcement was kept constant in all cases and the shear reinforcement has been removed, for that all the slabs had fracture shear. The slabs showed increased resistance with increased height of the table, indicated by considerable increase in the contribution of the concrete shear strength, as well as the large deformation of the longitudinal reinforcement and distribution, and to the high values of the arrows. Therefore, in the calculation of shear strength of one-way ribbeds slabs, could be rethought the lack of use of the height of the table as a variable, since its contribution to the shear strength is real.
Desconhecido
Influência da protensão na resistência ao cisalhamento de vigas de concreto protendido
(Universidade Federal do Pará, 2014-11-21) SOUZA JUNIOR, Orivaldo de Azevedo; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
With the increase of the construction industry, the prestressed concrete has advanced beyond of the stages of evolution, being consolidated as a structural material, evolving and bringing reliable technical and technologies for many different structures, ranging from conventional buildings, with applications in bridges and stadiums, and on to more complex structures such as offshore platforms. The study of shear in reinforced concrete beams and prestressed concrete beams always had many controversies because of the many variables that involve the study of shear. In the case of prestressed beams, which are adopted profiles with different inclinations together with shear reinforcement, there is need for improved theoretical methods and practical, this research may contribute materially to the understanding of these variables. Thus, to determine the influence of the inclination of prestressing strands in the shear strength of prestressed concrete beams, oriented the focus this research to study of six prestressed concrete beams with alternating tracing cable straight and parabolic and transverse reinforcement, in order to observe the structural behavior of these beams, mainly observations about the influence of the stress generated by varying the inclination of the cables and varying the rate of transverse mode rupture, the load capacity, the surfaces of rupture and other factors in order to understand the shear in prestressed concrete beams.
Desconhecido
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/1324105476558186
The 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.
Desconhecido
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/1324105476558186
The 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.
Desconhecido
Resistência ao cisalhamento de vigas “T” de concreto armado: verificação das longarinas da ponte sobre o rio Sororó
(Universidade Federal do Pará, 2011) BRANCO, Vitor Hugo Lopes; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
The structural behavior of a T beam gives assessment of different contributions on shear strength between different parts of the same cross section, allowing to establish guidelines for the provision of shear and flexure reinforcement. To quantify the contribution of the flange and web of such section in the shear strength were experimentally investigated 10 reinforced concrete beams consisting of T section aiming to evaluate the recommendations of NBR, ACI and EC2 standards about T beams subjected to shear. One of the beams was the control beam to be compared with, the others were idealized with a variation on the size of the cross section of the flange, to increase the cross section concrete area. All of the beams had no stirrups and the longitudinal reinforcement was the same in all cases. The concrete compressive strength was 47 MPa. It is clearly observed that the cross section made great influence on the shear ultimate strength of the structural elements tested in the laboratory, despite the sudden collapse, it is understood that the development of critical shear cracks depends on how the longitudinal tension is distributed in accordance with shear. The rise of the ultimate strength in the beams with flanges was observed to a level near the double of the ultimate shear force presented by the beam , and more clearly in beams with hf=80 mm, in which the concrete contributions were able to modify the collapse of those specimens, due to the yield of the tensile reinforcement, and the gain of stiffness that was about 25% higher when compared to the rectangular beam in terms of displacements. Through the acquired results it was possible to estimate the ultimate shear strength gain of the beams of the bridge over the Sororó river of the Carajás railway, giving a gain of a rectangular beam strength multiplied by 1,93 in that case.