Navegando por Assunto "Reinforced concrete"

Agora exibindo 1 - 20 de 20

Acesso aberto (Open Access)
Adequação estrutural dos pilares de um edifício residencial em concreto armado na cidade de Rio Branco
(Universidade Federal do Pará, 2013-11-06) SANTOS, Mateus Silva dos; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
The recovery and strengthening of reinforced concrete structures are increasingly common in Brazil, mainly due to the aging of structures built in the 60s and 70s of the twentieth century, which are close to reaching their lifetime. Added to this, factors such as the use of concrete with low strength, execution failures, improper use and lack of maintenance. Due to these factors that society should endeavor to enhance and / or restore these buildings, thus avoiding demolition of the same and even avoid fatal acidentes. This paper presents a case study that aims to recover a building that is abandoned for nearly two decades in the city of Rio Branco, Acre State. Currently, there are various techniques for strengthening reinforced concrete structure. Such as reinforcement through reinforced concrete jacketing, supplemented or enhanced with added armor, enhanced with application of metal sheets and profiles, reinforcing pillars reinforced with carbon fiber (PRCF), among other. In this work, the method adopted for recovery was enhanced by reinforced concrete jacketing. And for a better understanding of the methodology adopted work also presents details of the enhanced configuration adopted, constructive detail and executive procedures of the method adopted. In addition, the wrappers showing the active and resistant efforts before and after the booster.
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 de parâmetros globais de projeto em edifícios com estrutura de concreto armado
(Universidade Federal do Pará, 2015-12-22) VIEIRA, Vitor Vinicius dos Santos; VELOSO, Luís Augusto Conte Mendes; http://lattes.cnpq.br/9476653308517248
The verification of reinforced concrete buildings is carried out by local analysis and by global analysis. In the local analysis are evaluated the effects of deformations in the isolated elements. Already in the overall analysis of the behavior is evaluated considered the structure as a whole. Normally, this overall verification is done through design parameters, which allow to maintain control of problems that can affect the safety or performance of buildings of reinforced concrete. By means of computer systems, it’s possible to obtain, fairly quickly, a series of parameters that offer virtually complete diagnostic of the answers that the structures will present when external actions submitted, like the wind or the vertical loads. Howeverit is not enough process structural models and get results, it is necessary to interpret what these mean and verify its validity. Therefore, this study was done with the intention to contribute with the referring studies the overall analysis of the structures, based on the design parameters to know: 𝛾𝑧 and 𝑅𝑀2𝑀1 coefficients, overall critical load factor of buckling, horizontal displacements, fundamental frequency and acceleration. Are studied several cases of idealized structures, with the objective to evaluate the relation between these parameters and propose simplified equations for calculating the overall critical load factor and the fundamental frequency from the 𝛾𝑧 coefficient. Furthermore, are analyze some real building structures aiming to evaluate the proposed equations and draw comparisons with the limits recommended by Brazilian standards. For the processing of structures were used two analysis programs, the TQS and the SAP2000. Generally speaking, the equations that relate the 𝛾𝑧 coefficient with the critical load factor and with the fundamental frequency showed satisfactory results. For displacement and acceleration, could not establish equations due to inexistence of relation of these as the 𝛾𝑧. As for the normative limits, found to be that even structures that fulfill the safety criteria for the overall instability, nevertheless these may present problems related to excessive horizontal displacements and vibrations perceptible to the human being.
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/1324105476558186
The 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.
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 da influência da adição de fibras e da variação da armadura de costura em consolos curtos de concreto armado
(Universidade Federal do Pará, 2022-06-23) BRANDÃO, Jaciara Santos; LIMA NETO, Aarão Ferreira; http://lattes.cnpq.br/0287664572311345; https://orcid.org/0000-0002-5911-1368
Reinforced concrete corbels are usually characterized by being support elements whose design can be made from the Strut-and-Tie Method (STM) which is based on fundamental assumptions that consider that the tensile stresses are absorbed by the rods (structural steel) and the compressive forces are absorbed by the struts that are formed inside the concrete section, as it is understood that these elements have regions of discontinuity (D) or disturbances in the stress distribution. This method can be applied in the case of short corbels as they also present regions (D), given that their stress flow occurs in a non-linear manner. In this way, this experimental study analyzed the influence of the addition of synthetic fibers (polyethylene and polypropylene) and steel in the composition of the concrete, as well as, to verify the influence of the variation of the seam reinforcement rate in order to validate the MTB as a solution safe and efficient for the design of elements that present discontinuities (D) or disturbances. In the tests, the breaking load, the opening of cracks and the deformations in the tie rods, seam reinforcement and in the concrete, internally and externally, were observed. The results showed that the specimens containing synthetic fibers showed the highest strengths compared to the steel fiber specimen, being on average 10.82% more resistant than the reference specimens, despite not containing the highest fiber contents. In general, the elements showed similar ductile behavior and failure mode, so the cracks occurred in a controlled manner and there was no sudden rupture. As for the deformations in steel and concrete, the results showed a similar behavior among the specimens.
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 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/1324105476558186
Punching 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.
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)
Análise experimental de lajes nervuradas de concreto armado com viga faixa de altura variável
(Universidade Federal do Pará, 2014-11-21) SACRAMENTO, Paulo Victor Prazeres; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
The ribbed slabs have been widely used in the buildings it has several advantages in its execution and performance. In order to get a good design of this type of slab is necessary ensure that the stresses are properly supported, mainly those considered critical, which can lead the structure to the collapse suddenly, as is the case of punching in connection wide beam-column or of the shear in the region of the ribbed. In order to evaluate the punching strength of the slab-column connection and the shear strength of the ribs were manufactured four reinforced concrete ribbed slabs, two slabs one-way and two slabs two-way. The flexural reinforcement rate was constant in all slabs. All slabs were square of side 2200 mm and thickness equal to 150 mm. The main variable in this study was the change in height of the wide beam. This variation has to evaluate the performance of the ribs, even when the limit of spacing between them is ensured. Also, check if the punching is a possibility of rupture in this case. The estimates in this step design were based on three different standards. These were ACI 318 (2008), Eurocode 2 (2004) and NBR 6118 (ABNT, 2014). Studies with ribbed slabs have shown that the estimates of design standards are conservative. In addition, this predictions may lead to inadequate results for resistance slabs. The experimental results of this series of tests were compared to the standard recommendations in order to assess the accuracy of these three standards, which refer to the ribbed slabs. Were also built computational models in order to verify that the behavior of slabs as the stress distribution both in connection wide beam-column range as the beam connection wide beam-ribbed. The results showed that the slabs connection wide beam-ribs must be treated in a careful manner due to the difference in stiffness between the solid area and the ribs.
Acesso aberto (Open Access)
Análise numérica de seções reforçadas de concreto armado considerando o estado inicial de tensões
(Universidade Federal do Pará, 2013-09-30) LAURINDO, Caio Felipe; SOUZA, Remo Magalhães de; http://lattes.cnpq.br/1995895693959225
This work deals with the formulation and computational implementation, in MATLAB, for numerical analysis of reinforced concrete cross-sections, subject to bending, considering the stress state prior to reinforcement. The analysis is made by generating axial load – bending moment interaction diagrams by two methods: a) scan of the ruin domains established by the Brazilian standard NBR6118/2003 b) determination of peaks in Axial Force-Moment-Curvature Relationships. In both methods, the midpoint rule for numerical integration is applied in the resistant stress calculation, and the Newton Raphson root-finding procedure is used to determine the strain in the reference axis of the cross-section, in order to obtain the Axial Force- Moment-Curvature Relationships. Preliminarily, it was concluded that the first of the two methodologies is not feasible. Subsequently, the effectiveness of the second method was confirmed. Finally, it was possible to expand the scope of this work in order to allow the analysis of cross-sections of any shape throughout the course of staged construction, considering the initial stress state of each stage. The computational implementation for this study was based on the program for numerical analysis of sections SECLAB, developed by Professor Remo Magalhães de Souza.
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)
Cisalhamento em elementos de concreto armado com estribos desconectados
(Universidade Federal do Pará, 2017-04-07) TAPAJÓS, Luamim Sales; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485
The use of shear reinforcement can improve shear strength and ductility in reinforced concrete elements. However, depending on the type of reinforcement and the type of construction and solicitation thereof, there may be conflict between the longitudinal and transverse bars. To solve this problem, some researchers have used unconnected shear reinforcements, which are positioned between the longitudinal bars. In addition to avoiding conflict with longitudinal reinforcement, the use of this type of reinforcement can still increase the productivity at the job site, since this type of reinforcement can be prefabricated. However, the use of unconnected shear reinforcement is still limited by the lack of design recommendations supporting their use, as well as there are few experimental studies on the subject. Therefore, this work presents a type of unconnected shear reinforcement, tested in an experimental program and compared with other types of reinforcement. In total, the experimental program involved the testing of 9 reinforced concrete wide beams, where the main variables were the type and rate of reinforcement. In addition to the tests on the beams, tests were carried out on reduced specimens by the push-off test. As results, graphs of displacements, deformations in the flexural and shear reinforcement and in the concrete, cracking maps, surfaces and rupture mode are presented, as well as the last loads observed in the tests with the theoretical loads estimated by different normative recommendations. As the main conclusions, it was observed that the unconnected stirrups can have the same performance in comparison with shear reinforcements with connected anchorage, as well the use of a complementary reinforcement to the W stirrup can improve the shear resistance of a reinforced concrete beam and avoid delamination.
Acesso aberto (Open Access)
Desenvolvimento de um software com interface gráfica para análise e verificação de pontes ferroviárias em concreto armado
(Universidade Federal do Pará, 2010-03-05) QUEIROZ, Rafael Leite de; SOUZA, Remo Magalhães de; http://lattes.cnpq.br/1995895693959225
Development of software with graphical interface for analysis and verification of railway reinforced concrete bridges. The work described here is the development of software capable to do structural analysis with emphasis on bridges. More attention is given to the analysis of railway bridges and the automatic generation of live load in accordance with the vehicles and trains-types user defined by. The software called BridgeLab Laboratory (Bridges) is able to do analysis of extreme importance with respect to the design and verification of civil structures. These analysis are: static analysis, pseudo-dynamic analysis, modal analysis and dynamic analysis. The code at BridgeLab was written in MATLAB® platform, due to some advantages of the language resulting in a shorter time of rogramming. The analyzes performed by the program are based on the direct stiffness method and use finite element of space frame which presents six degrees of freedom per node. In addition to performing the analyzes, BridgeLab performs the structural elements verification from the results of efforts obtained in each analysis according to the Brazilian standards, including verification of fatigue damages that is also verified according to the CEB. The verification is done in an integrated way through the SecLab (Sections Lab). After analysis the visualization results, stress diagrams, deformed configurations and modal shapes are done in the BridgeLab interface itself. The visualization of the deformed configurations of the structure and its modal forms can be done as a bar model or as extruded solids, considering the geometry of the cross section of the elements.
Acesso aberto (Open Access)
Dimensionamento de armaduras longitudinais sujeitas à fadiga em vigas de pontes ferroviárias de concreto armado
(Universidade Federal do Pará, 2014-02-27) LEAL, Anderson Couto; VELOSO, Luís Augusto Conte Mendes; http://lattes.cnpq.br/9476653308517248
Railway bridges reinforced concrete subject to variable dynamic actions due to vehicular traffic. These actions may result in the phenomenon of fatigue of steel and concrete structures such. In the design of reinforced concrete structures subject to cyclic loading, in general, the fatigue is considered simply, by a coefficient kf, called coefficient of fatigue. This coefficient majora area of steel initially calculated to fulfill the Ultimate Limit State (ULS) in order to limit, in operation, the variations in stresses in steel to ensure a shelf life of at least 2 million cycles. This paper presents improvements in the assumptions used by the coefficient kf fatigue, allowing the design of longitudinal reinforcement subject to fatigue, to superior numbers to 2 million cycles, which is proposed by EB-3/67 value, and also in order to meet the service specified in the design fatigue life. In this case, it was necessary to propose a simplified method for estimating the number of operating cycles, starting from a standard cycle obtained by the maximum variation of bending moments caused by train - loaded type. The study was conducted using as a prototype railway viaduct isostatic reinforced the Carajás Railroad ( EFC ) concrete. Trains - type were used which currently operate in the EFC, which correspond to train ore Loaded and Unloaded. To determine the internal forces in the structure of a numerical model was developed in the SAP 2000 program. The fatigue life of longitudinal reinforcement were determined starting from the Miner damage rule and the SN curves of NBR 6118. The methodology proposed in this work allowed the scaling in longitudinal reinforcement fatigue satisfactorily in relation to the specified design life, and the lives that were most useful deviation from the stipulated value were 300 and 400 years.
Acesso aberto (Open Access)
Eficácia da ABNT NBR 6118 (2014) na previsão da carga última de pilares curtos/esbeltos em concreto armado sujeito à flexão composta normal.
(Universidade Federal do Pará, 2019-11-27) LEITE, Jonas dos Santos; MORAES NETO, Bernardo Nunes de; http://lattes.cnpq.br/5790058515094077
Once the short/slender reinforced concrete columns theory has been slightly presented in the national technical/scientific literature, it could be considered as a research goal working up this kind of publication. However, bringing about the accuracy judgment of the ABNT NBR 6118 (2014) design guidelines to predict the load-carrying capacity for short/slender reinforced concrete columns under combined axial load and bending has been the outstanding inquiry target. Wherefore, both the simplest proposals as well as the accurate one have been introduced and taken stock herein. It is worth underscore that two concepts have marked the simplest proposals, namely, standard-column methods with approximate curvature (AC method) and approximate stiffness (AS method). Thus, the interaction diagram concepts together with load-moment curves (P-M), which were addressed in a linear (L) and nonlinear (NL, geometrical issue) way, had accounted for the accurate method. To vouch for the scrutiny undertook before, 17 experimental investigations, which had added up to 320 reinforced concrete columns, composed the database (DB) handled currently. From then on, the performance index ξ has been embraced and assessed by means of descriptive statistic thought, where ξ = Pexp/Ptheo (Pexp = experimental failure load recorded in the DB and Ptheo = theoretical/predicted failure load). Ended up the quest, the effectiveness of whole design guidelines to predict the failure load for short/slender reinforced concrete columns from DB was bearing out by the results had brought forth herein. Notwithstanding the previous positive outcome, it was also pointed out that predicting the failure load of slender columns with slenderness ratio high than 35 the P-M (L) proposal had been in an unsafe condition.
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)
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.
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/1324105476558186
Symmetric 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%.