Navegando por Assunto "Cisalhamento"

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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 cisalhamento em vigas de concreto armado reforçado com microfibras
(Universidade Federal do Pará, 2019-01-31) OLIVEIRA, Mateus Gonçalves de; TEIXEIRA, Marcelo Rassy; http://lattes.cnpq.br/8912916360456192
The shear study for small, medium and large works, the latter known as works of art, with the use of reinforced or prestressed concrete presents particularities in the definitions of the traces, since, it has the need to minimize the propagation of fissures, as well as to obtain suitable mixtures considering the high characteristic high diameter of the large aggregates, as well as to avoid deleterious reactions in the concrete. In this sense, the main objective of this research is to analyze the shear behavior of reinforced concrete beams, with reinforcement of glass and polyester microfibers for each type of cited in volumetric fractions (0,024%, 0,032% e 0,048%), comparing them with the behavior of fiber- aiming its application in structural elements. In order to meet the proposal of this research, the methodology was based primarily on the characterization of concrete constituent materials (cement, small and large aggregates and fibers already mentioned), concrete dosage based on the Concrete Dosage method EPUSP -IPT, concrete of the beams, being: one of reference without fiber addition and 6 (six) with additions of microfiber of glass and polyester, being three (three) for each one of them, and later analysis as to shear through the breaking of the experimental beams, and computational analysis between the beam modeled in the Response 200 software considering stirrups throughout its section and the experimental reference without stirrups in 1/3 of its sections. It can be stated that the glass and polyester microfibers have shown that their uses can be used as partial replacement of the transverse reinforcement; contributed to post-peak or post-cracking stability; contributed to the gain in shear strength of 15.1% for VFV01 (beam with addition of glass microfibers with a percentage of 0.024%) and 21.6% of VFP02 (beam with addition of polyester microfiber with a percentage of 0.032%) both in relation to VR (reference beam). Therefore, this study demonstrated that the fibrous reinforcement can be used as control efficiency and as well as shear performance improvement in structural concrete.
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)
Análise experimental do desempenho de conectores de cisalhamento feitos em aço CA-50 para uso em estruturas mistas de perfis em aço e concreto armado
(Universidade Federal do Pará, 2019-10-25) SOUZA, João Pedro Nascimento de; LIMA NETO, Aarão Ferreira; http://lattes.cnpq.br/0287664572311345; https://orcid.org/0000-0002-5911-1368
The steel and concrete composite structures began to increase as a construction system over the years, due to their advantages both in their structural behavior and in their constructive aspects. These structures are those in which both materials (steel and concrete) work together, and for this to be possible, it is necessary to use connectors that combat the shear forces generated between the materials. There are several types of these connectors, but their goal is to make the structure solid and work monolithically. This work aims to experimentally analyze the performance of shear connectors, for use in steel and concrete reinforced composite structures, modifying geometries and arrangement of connectors composed of Ø 12.5 mm diameter CA50 steel bar bent in shape close to a truss, making a comparative to define which model offers the greatest contribution in the connection. Therefore, push-out tests were performed, following the procedure described in the European Standard Norm EN 1994-1-1 (2004), in 7 specimens, consisting of an 800 mm high welded I-metal profile, and two slabs of reinforced concrete, with dimensions of (600x600x150) mm, in contact with the top of flanges of the metallic profile, containing the welded connectors. Among the 7 models, 2 of them, named Isósceles Truss (IT) and Rectangular Truss (RT), were used as reference; in 4 of them were made variations on the arrangement of the connectors used on the reference specimens, which were named Slanted Isosceles Truss. (SIT), Slanted Rectangular Truss (SRT), Piramidal Isosceles Truss Type A (PIT A) and Piramidal Isosceles Truss Type B (PIT B), and in 1 was made a change on the geometry, which was named Straight Truss (ST). Regarding the load capacity, the ST connector presented a load gain of 10.82%, 32.94%, 19.53%, 34.51%, 30.98%, 23.14 % in relation to IT, RT, SIT, SRT, PIT A and PIT B, respectively. Taking into account the design resistance calculation (𝑃𝑅𝑑) of each connector according to EN 1994-11 (2004), the tested connectors had a load capacity 46.54% higher than 𝑃𝑅𝑑. The connectors, in their entirety, presented themselves as they are ductile in their breaking mode. Compared to the others, the RT connector presented a more rigid, and, the SRT, a more flexible behavior. Thus, it is observed that the proposed connectors presented a good performance in relation to the load capacity and rupture mode.
Acesso aberto (Open Access)
Avaliação da resistência ao cisalhamento em vigas de concreto armado reforçadas com macrofibras sintéticas
(Universidade Federal do Pará, 2019-02-01) SOUSA, Diego Lucena de; TEIXEIRA, Marcelo Rassy; http://lattes.cnpq.br/8912916360456192
With the increased use of composite materials, in search of adding to the new technologies, and, through the application in synthetic fiber contents to the concrete, this material can add favorable characteristics in relation to the conventional concrete. From this finding, the present study applied 0.08%, 0.12% and 0.16% for polypropylene fiber and 0.24%, 0.36% and 0.48% for polyethylene fiber in reinforced concrete beams so that the appropriate contributions could be evaluated, when this element was subjected to shear stress. Thus, after the tests, it was possible to observe that the elements with fiber application obtained a resistance above, however, close to the beam produced with the reference concrete. In contrast, as the contents of both fibers were increased, it obtained a ductility increment, a fact proven by the graphics shear x vertical displacement, shear x concrete deformation and shear x bending armor deformation, since, among the fiber contents used, the percentages of 0.36 % and 0.48% of polyethylene and 0.16% of polypropylene were the ones that presented a critical volume corresponding to the fiber content closest to an ideal, thus demonstrating the proximity of the carrying capacity for such produced composite, from the rupture of its matrix. Therefore, according to Figueiredo (2000), the behavior change is a function of the fibers characteristics, the concrete matrix and their interaction. In this way, the material now has specific requirements for its quality control, dosage and even application, different from conventional concrete. In view of this, it can be stated that the application possibilities of the material are amplified, since the reinforced concrete with fibers presented technological advantages in relation to the conventional one, as it showed a more ductile behavior, absorbing na equal load capacity for a longer period of time.
Acesso aberto (Open Access)
Cisalhamento em vigas de concreto armado com armadura transversal interna contínua
(Universidade Federal do Pará, 2019-09-24) SOUZA, Diego Ferreira de; LIMA NETO, Aarão Ferreira; http://lattes.cnpq.br/0287664572311345; https://orcid.org/0000-0002-5911-1368
Reinforced concrete elements can suffer high bending and shear forces, either due to high loads, type of construction or architectural limitation, thus requiring a high longitudinal and transverse reinforcement rate, which can lead to conflicts between the two reinforcements, resulting in reduced productivity during the reinforcement work of the element. As a way to solve this reinforcement conflict, some researchers applied to reinforced concrete elements internal shear reinforcement, in other words, these reinforcements are positioned between the bending reinforcement bars, thus eliminating the conflict between the transverse and longitudinal bars and aiding the productivity of the reinforcement work, as this type of elements could be prefabricated and positioned as designed. However there are no normative standards that indicate the use of internal stirrups. Studies conducted on the subject indicated that the internal stirrups need an auxiliary device, as recommended by NBR 6118 (2014), which would help in the anchorage and allow the transfer of shear forces to the concrete without the delamination effect. Currently, few studies evaluate the performance of the transverse reinforcement with inclinations between 45º and 90º, where inclined stirrups provide better ductility and reduced stresses on compression struts. Therefore, this research presents a type of internal transverse reinforcement, tested in an experimental program and compared with closed-loop stirrups. The experimental program was carried out with a total of 5 beams of reinforced concrete, one as a reference with closed-loop stirrups, and the other 4 with internal stirrups; the main variables were: the inclination of the internal transverse reinforcement at 60º and 90º; and the number of legs of internal transverse reinforcement, keeping the same transverse reinforcement ratio. As results, this paper presents graphs of displacements, bending and shear reinforcement and concrete deformations, cracking maps and failure surfaces, and the last loads observed in the tests were compared with the theoretical loads estimated by different normative recommendations. As conclusions, it was observed that the internal stirrups have great potential in their use, as they present greater ductility and resistance compared to the closed-loop stirrup currently used. The results of inclined internal stirrups showed an increase of up to 14% when compared to the reference beam.
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)
Evolução dos fluidos mineralizantes e modelo genético dos veios de quartzo auríferos em zona de cisalhamento do depósito Ouro Roxo, Província Tapajós, Jacareacanga (PA), Brasil
(2013-12) VELOSO, Ângela Suélem Rocha; SANTOS, Márcio Dias; JAVIER RIOS, Francisco
The Ouro Roxo gold deposit, located near Jacareacanga, Tapajós Gold Province, southwestern Para, Brazil, comprises a hydrothermal system of sulfide quartz veins that was hosted by the calc-alkaline mylonite granitoid Tropas Intrusive Suite of Paleoproterozoic age and controlled by the N-S trending ductile-brittle oblique Ouro Roxo-Canta Galo, crosscutting the granitoid Tropas. Three kinds of fluids were identified as sources of mineralization in the Ouro Roxo deposit: 1) an aqueous fluid within the H2O-NaCl-MgCl2-FeCl2 system, with low-to-middle salinity and homogenization temperature (Th) = 180-280°C; 2) Cu and Bi-bearing H2O-NaCl-CaCl2 brines, with Th = 270-400°C, genetically related to a magmatic event coeval to shearing, which underwent dilution by mixing with meteoric water; 3) gold bearing middle-salinity aquocarbonic fluid, with Th = 230-430°C, which was interpreted as ore fluid related to shearing. The T-P conditions of ore formation, estimated by chlorite geothermometer and fluid inclusion isochors, range from 315 to 388°C and 2,0 to 4,1kb. The two main mechanisms for gold deposition in transtensional sites of the shear zone were: 1) Mixing of aquocarbonic fluid and magmatic brines induced an increasing of fO2 and decrease of pH; 2) interaction between fluids and feldspars and ferromagnesian minerals of the hoster granitoid which reduced fO2 and fS2 during hydrolysis and sulfidation reactions, with precipitation of iron sulfides together with gold. The orogenic environment, the veining style, the structural control by shearing, the hydrothermal alteration (propylitic+philic+carbonatization), the metallic association (Au+Cu+Bi), the association of aquocarbonic ore fluid with magmatic brines in ore deposition, are all consistent with an orogenic model for genesis of the Ouro Roxo deposit with magmatic participation.
Acesso aberto (Open Access)
Geologia e metalogênese do depósito aurífero do Palito, Província Tapajós, Itaituba - Pa
(Universidade Federal do Pará, 2008-07-17) COSTA, Rodrigo de Melo; SANTOS, Márcio Dias; http://lattes.cnpq.br/6977793618030488
The Palito Gold Deposit lies in the Jamanxim river region, easternmost part of the Tapajós Gold Province, sonthern Pará State. The Palito deposit comprises a mineralized quartz vein system hosted by Palito and Rio Novo Paleoproterozoic granites and is controlled by a NW-SE brittleductile stike-slip shear zone which belongs to a regional structure so called Tocantinzinho Lineament. The Palito Granite crosscuts the Rio Novo Granite and is the main host rock for the gold mineralization. The Rio Novo and Palito granites are two oxidized calc-alkaline monzogranitic stocks correlated respectively to Creporizão and Tropas Suites, characterized as magmatic arc granites. The thicker lodes, of metric width, are hosted by the NW-SE main fractures, whereas thinner veins, of centimetric width, associated with the thicker lodes, make both low angle (around E-W direction) and middle to high angle (NE-SW direction) in relation to the main shear direction. Such a structural situation is compatible to the Riedel system, with parallel lodes (D), low-angle veins (R and P), middle-angle veins (gash) and high-angle veins (R’ and X). Stockwork veinlets also occur as a minor ore type. The veins are always involved by a well developed, normally brecciated, hydrothermal alteration halo. Phyllic alteration ( quartz + phengite + pyrite) and chloritization (chamosite) are the two main hydrothermal alteration types which are followed by potassic alteration (K- feldspar + biotite), carbonatization (calcite + siderite + sericite) and subordinated sufidation (pyrite + chalcopyrite + sphalerite). The gold ore, hosted by quartz veins, is always associated to iron and copper sulfides (chiefly pyrite and chalcopyrite), besides sphalerite. Pyrrhotite, bismuthinite, native bismuth and gold are minor metallic phases. Three generations of pyrite, two generation of chalcopyrite and one generation of sphalerite were recognized. Substitution of chalcopirite1 for pyrite1 and pyrite2 for chalcopirite1 are widespread, whereas sphalerite crystallization is controlled by temperature and Cu/Zn ratio of the system, that is, substitution of sphalerite for chalcopirite1 ocurrs when temperature and Cu/Zn ratio are low and, vice versa, substitution of chalcopirite1 for sphalerite occurs in higher temperature and Cu/Zn ratio conditions. The gold is always associated or included in chalcopyrite, bismuthinite and native bismuth. Late sulfide generations are represented by veinlets of pyrite3 and chalcopirite2. The main gangue minerals associated to gold ore are quartz, phengite and chlorite, besides minor carbonate, fluorite, rutile, zircon and ilmenite Three kinds of fluids were recognized in the fluid inclusion study: 1) low salinity H2O-NaCl (up to 2,0 wt.% NaCl equiv.), interpreted as meteoric water; 2) high salinity H2O-NaCl-FeCl2-MgCl2 (45-50 wt.% NaCl equiv.) interpreted as magmatic brines, 3) low salinity H2O-CO2-NaCl (1,0-1,7 wt.% NaCl equiv.), probably of magmatic origin. The temperature and pressure conditions for the Palito gold deposit formation were estimated by combination of hydrothermal chlorite geothermometry and isochores calculated from the fluid inclusion microthermometric data. P-T values for trapping of the brines range from 340 to 405oC and 2 to 4,7 kb. The magmatic brines were interpreted as the main mineralized fluid, that is, sulphur, chlorine and metals (chiefly Au and Cu) were originated and concentrated from the residual phase of the granitic magma which gave rise the Palito Granite. The brines transported the metals as chloride complexes at high temperature (over 400oC). Fluid-rock interaction and mixing between mineralized fluid and low-T and low salinity fluids (probably meteoric water) promote a raising of pH and lowering of fS2 through hydrolysis and sulfidation reactions which have triggered ore deposition at lower temperature conditions (below 400oC) in transtension sites of the shear zone. The geological and hydrothermal alteration features and the mineralizing fluid characteristics are consistent to a structurally controlled intrusion related gold deposit model for the genesis of the Palito deposit. The host granitic rocks of the gold deposit, the vein style, the hydrothermal alteration (seritization and chloritization with minor potassic alteration), the Au-Cu-Zn (Pb-Bi) metallic association and the mineralizing fluid (H2O-NaCl-FaCl2-MgCl2) are consistent to a genetic relationship between the Palito Granite and the gold deposit. The granite supplied fluids, metals and heat to move the hydrothermal system, whereas the shear zone provided the structural traps for the ore deposition.
Acesso aberto (Open Access)
Geologia e metalogênese do depósito aurífero Ouro Roxo, Província Tapajós, Jacareacanga-PA.
(Universidade Federal do Pará, 2011-05-25) VELOSO, Ângela Suélem Rocha; SANTOS, Márcio Dias; http://lattes.cnpq.br/6977793618030488
The OuroRoxo gold deposit is located near São José Village at Pacuriver margin, far around 36 km from Jacareacanga city, western Tapajós Gold Province, SW portion of Para State. The OuroRoxo deposit comprises a hydrothermal system of sulfide quartz veins hosted by mylonitegranitoidTropas Intrusive Suitof Paleoproterozoic age. The ore bodies are controlled by a N-S trending shearing known as OuroRoxo-CantaGalo shear zone. The host granitoids are oxidized calc-alkaline granodiorite and tonalite with magnetite and sphene, characterized as magmatic arc granitoids.The OuroRoxoCantaGalo shear zone is a sinistral oblique ductile-brittle shear of low to middle angle which has turned the granitoids into protomylonites and mylonitesinterlayed with breccias zones. The protomylonites are characterized by predominance of porfiroclasts over the matrix composed by phengite, chlorite and quartz which grade into mylonites and minor ultramylonits with almost 100% of matrix. The mylonitic foliation is defined by chlorite, biotite and phengite along NNE-SSW direction dipping to ESE. Stretched quartz grains define a lineation which indicates the oblique tectonic movement to NNW. Shear features such as mica-fish,shadow pressure, tail recristalization and microboudinage are ubiquitous in theses rocks and indicate a sinistral kinematics for shearing. The ore bodies are quartz veins and pipes hosted by mylonites and breccias, surrounded by prominent alteration halos and concordant to mylonitic foliation. Besides silicification and sulfidation more concentrated in the ore bodies, three types of hydrothermal wall-rock alteration were recognized in alteration halos: 1) propilitic alteration: chlorite+phengite+carbonate. Four chlorite generations were identified, the last one being veinlets; 2) phylic alteration: phengite+quartz+carbonate+pyrite, with three phengite generations; 3) carbonatization with three generations of carbonate, the last one beingveinlets. Besides magmatic quartz and microcrystalline quartz of mylonites, five generations of hydrothermal quartz were recognized in the lodes, the last one beingveinlets.The ore shoots are mainly made up by pyrite and chalcopyrite, with minor bismutinite, native bismuth and gold. Besides the pyrite associated to gold and an earlier pyrite magmatic generation, late pyrite veinlets occur. Two generations of chalcopyrite were identified and the second one substitutes the pyrite 2 associated to ore. The main gange minerals are quartz, chlorite, phengite and carbonate. Azurite, bornite and covellite are copper supergenic minerals derived from alteration of chalcopyrite.Three kinds of fluids were identified in vein quartz of the OuroRoxo deposit: 1) low-to-middle salinity aqueous fluid within the H2O-NaCl-MgCl2-FeCl2systemwhich occurs in quartz 3, with Th=180-280°C; 2) brines within the H2O-NaCl-CaCl2 system which occur in quartz 4 and 6, with Th=270-400°C, and underwent dilution brought about by mixing with meteoric water, lowering its salinity and temperature (Th=120-380); 3) middle-salinity aquocarbonic fluid which occurs in quartz 3 and 4, with Th=230-430°C. The aquocarbonic fluid was interpreted as ore fluid related to shear zone with higher Th in ductile conditions. The brines origin was related to a magmatic event coeval to shearing, with lower Th in the end of the residual magmatic process.The temperature and pressure conditions of OuroRoxo deposit formation were estimated using the hydrothermal chlorite geothermometer and the isochors calculated from the fluid inclusion microthermometric data. Values range from 315 to 390°C and 2,0 to 4,2 k b. Two mechanisms were regarded to be the main cause for gold deposition. 1) Fluid- rock interaction brought about increasing of fO2 and reduction of fS2 during hydrolysis (propylitic and phylic alteration) and sulfidation reactions; 2) Mixing between aquocarbonic fluid and magmatic brines induced an increasing of fO2anddecreasing of pH. These two mechanisms would favor gold deposition in transtension sites of the shear zone.The age of ore formation, obtained by Pb-Pb method in pyrite, was estimated around 1858±130Ma. The large error of that age turn it as reference age only which shows a time relationship between the mineralization, the shearing and the Maloquinha granite event. The orogenic magmatic arc environment, the veining style, the structural control by the shear zone, the hydrothermal alteration (propylitic+philic+carbonatization), the metallic association (Au+Cu+Bi), the middle-salinity aquocarbonic ore fluid and the participation of magmatic brines in ore deposition, are all consistent to a hybrid model (orogenic with magmatic participation) for the genisis of the OuroRoxo gold deposit.
Acesso aberto (Open Access)
Geologia e metalogênese do depósito aurífero São Jorge, Província Aurífera do Tapajós, Novo Progresso-PA
(Universidade Federal do Pará, 2011-01-05) BORGES, Antonio Wanderlei Gomes; SANTOS, Márcio Dias; http://lattes.cnpq.br/6977793618030488
The São Jorge gold deposit lies in the easternmost part of the Tapajós Gold Province, SW portion of the State of Pará, far around 88km from Novo Progresso city. The São Jorge deposit comprises a mineralized quartz vein system hosted by the Young São Jorge Paleoproterozoic granite and it is controlled by a NW-SE trending shear zone. The Young São Jorge granite is an oxidized calc-alkaline monzogranite stock, characterized as magmatic arc type and correlated to the Tropas Intrusive Suite. The São Jorge shear zone is a brittle-ductile sinistral strike-slip shear zone which belongs to a regional structure known as Tocantinzinho Lineament. The thicker lodes, of metric width, are hosted by NW-SE main shear direction, whereas thinner veins in the NE-SW direction make middle to high angle in relation to the chief shear direction. Such a structural situation is compatible to the Riedel system, with parallel lodes hosted by main shear direction (Y/D) and gash veins in extension fractures (T). Minor stockwork veinlets complete the São Jorge vein system. The mineralized veins are always involved by hydrothermal alteration halo. Early alteration is characterized by chloritization of the ferromagnesian minerals (biotite and hornblende) which yielded chlorite+carbonate+magnetite mineral assemblage, followed by sodium metasomatism (albitization) of the K-feldspar and saussuritization of the plagioclase which generated sericite+carbonate+epidote assemblage. Intensification of that process evolved to phallic alteration (phengite+quartz+pyrite assemblage) associated to minor chloritization and sufidation (pyrite+ chalcopyrite+sphalerite assemblage). The gold-bearing ore, hosted in quartz veins, occurs in deep hydrothermal altered rocks, associated to sulfides (chiefly pyrite) and, more rarely, chalcopyrite and sphalerite. Galena, bismuthinite, native bismuth and gold are minor metallic phases. Free gold also occurs in hydrothermal quartz and magnetite. The main gangue minerals associated to ore are quartz, phengite and chlorite. Carbonate, rutile and zircon are minor gangue phases. Three types of fluids were recognized in the São Jorge deposit from fluid inclusion studies: 1) low-middle-salinity aqueous H2O-NaCl-KCl fluid, interpreted as meteoric water; 2) middle-salinity aqueous H2O-NaCl-CaCl2-MgCl2 fluid, with homogenization temperature ranging from 120 to 230°C, interpreted as magmatic brines; and 3) low-middle-salinity aquocarbonic H2O-CO2-NaCl fluid, with homogenization temperature ranging from 260 to 350°C, probably of magmatic or metamorphic origin. The magmatic saline aqueous fluid was interpreted as the ore fluid which transported the metals (mainly gold), the clorine, and the oxidized sulphur (SO2), concentrated in the residual phase of a granitic magma, whereas the aquocarbonic fluid transported the majority of CO2 and the reduced sulphur (H2S). The temperature and pressure conditions for the São Jorge gold deposit were established by combination of hydrothermal chlorite geothermometry and isochore calculated from the fluid inclusion microthermometric data. The temperature values for trapping the ore fluids range from 280°C to 360°C and the pressures vary from 1.35 to 3.6 kb. Such a temperature condition favors the gold transport as tiocomplexes. Early oxidation process brought about an increase of fO2 and magnetite formation which favored first generation of gold deposition. The mixing of ore fluid with aquocarbonic fluid and meteoric water and fluid-rock interaction, with associated phillic and sulfidation alteration reactions, caused increasing of fO2 and reduction of pH, fS2 and temperature which triggered the main gold precipitation in transtension sites of shear zone. The veining style of the São Jorge deposit, the host granitic rocks of the ore, the kinds of hydrothermal alterations, the Au(Cu-Zn-Pb-Bi) metallic association and the ore fluid of magmatic filliation, are consistent to a genetic relationship between the gold deposit and granitic magmatism (intrusion-related gold deposit). On the other hand, the structural control of the ore bodies and the occurrence of aquocarbonic fluid with higher homogenization temperature, deep-collected by the shear zone, hold up the mesozonal orogenic model. Such a characteristics support a hybrid genetic model for the São Jorge gold deposit, in which the granite supplied the ore fluid, the metals and heat to move the hydrothermal system, whereas the shear zone provided the aquocarbonic fluid, the flow paths for the fluids and the structural traps for ore deposition. Since the shear zone had affected the Yong São Jorge granite, the genetic relationship between the gold deposit and that granite, though possible, is little probable. Another more consistent possibility as magmatic source for the São Jorge ore fluid would be a younger granite, as the Maloquinha granite, 14 to 27 Ma younger, which occurs in the whole Tapajós Province and also neighborhood São Jorge area.
Acesso aberto (Open Access)
Geologia, controle estrutural e geocronologia das rochas hospedeiras e do minério: implicações para o modelo genético do depósito aurífero do Palito, Província Tapajós, Itaituba-PA
(Universidade Federal do Pará, 2016-09-24) SERRA, Vitor Felipe Hage; TORO, Marco Antonio Galarza; http://lattes.cnpq.br/8979250766799749
The Palito gold deposit, located at east portion of the Tapajós Gold Province, southwestern Pará State, comprises a nearly vertical mineralized quartz vein system, hosted by the Palito and Rio Novo Paleoprooterozoic granites and controlled by a sinistral strike-slip brittle-ductile shear zone, trending to NW-SE direction, which belongs to the regional Tocantinzinho lineament. The host granites are two oxidized calc-alkaline monzogranite stocks of Orosirian age and magmatic arc affiliation, correlated to the Parauari Intrisive Suite. The thicker lodes of the veining system are hosted by the major shear, along the N40-50W direction, whereas the thinner veins are housed by faults and fractures of second order and oblique to the main shear direction, both at low angle (around 20), moderate angle (nearby 50) and high angle (around 80). Such a structural situation is compatible with the Riedel system, with the major lodes parallel to the main shear direction (D), associated with low-angle veins (in R and P faults), moderate-angle gash veins (in extension T fractures) and high-angle veins (in R’ an X faults). Stockwork veinlets also occur as a minor ore type. The veins are always involved by a well-developed, normally brecciated, hydrothermal alteration halo. Phyllic alteration (quartz + phengite + pyrite) and chloritization are the two main hydrothermal alteration types, associated to minor potassic alteration (K- feldspar), carbonatization (calcite + sericite + quartz) and sufidation (pyrite + chalcopyrite + sphalerite). Three generations of hydrothermal veining quartz are well characterized in the Palito gold deposit. The youngest low-angle veins (R and P) are made up by quartz1, whereas the later thicker lodes (D) are composed by quartz1 and 2. Tension gash quartz veins may occur at any time of the hydrothermal system evolution and are made up by both quartz1 (youngest gash veins) and quartz2 and 3 (later gash veins). Gash veinlets of quartz3 correspond to final stages of the Palito hydrothermal process. The gold ore, hosted chiefly by quartz1 and 2 veins, is always associated to iron and copper sulfides (pyrite and chalcopyrite), besides sphalerite. Pyrrhotite, bismuthinite, galena, native bismuth and gold are minor metallic phases. Three generations of pyrite and chalcopyrite and one generation of sphalerite were recognized. Chalcopyrite1 replaces pyrite1 and it is replaced by sphalerite, which, in turn, is replaced by chalcopyrite2. Pirite2, coeval to sphalerite, occurs in mineralized veins as anhedral masses replacing tiny remnant grains (islands) of chalcopyrite1, showing concave or corroded edges. Gold is always associated or included in chalcopyrite1 and 2 and pyrite2, bismuthinite and native bismuth crystals. Veinlets of pyrite3 and chalcopyrite3, crosscutting sulfide masses in transtension zones of tiny sinistral faults, are the latest sulfide generations. Two generations of phengite and chlorite were identified in the gangue minerals, being veinlets of phengite2, chlorite2 and carbonate the last one. Fluorite, rutile, zircon and ilmenite still occur as minor gangue phases. The Pb-Pb age of 179417 Ma, obtained for the Palito ore, was interpreted as rejuvenation of the Pb-Pb system caused by Sthaterian alkaline granitic magmatism (Porquinho Intrusive Suite) related to the third extensional deformation phase. The geological features of the Palito gold deposit, as structural controlled veining style of ore bodies and hydrothermal alteration halos, predominating sericitization and cloritization and metallic association (Au-Cu-Bi-Zn) of the ore, all favor classification of the Palito deposit as intrusion-related vein gold deposits. It is a non-porphyritic intrusion-related deposit type, possible related to alkaline granites of the Maloquinha Intrusive Suite, which occur around the Palito deposit. The granitic magma should has provided the ore fluids and metals and the shearing should has controlled the fluid circulation and ore deposition of the Palito deposit.
Acesso aberto (Open Access)
Geologia, petrografia e geocronologia das rochas do depósito aurífero Ouro Roxo, Província Tapajós, Jacareacanga (PA), Brasil
(2013-03) VELOSO, Ângela Suélem Rocha; SANTOS, Márcio Dias
The Ouro Roxo gold deposit lies near the city of Jacareacanga, Tapajós Gold Province, southwestern of Pará, Brazil. The Ouro Roxo deposit comprises a hydrothermal system of sulfide quartz veins hosted by mylonite granitoid Tropas Intrusive Suit of Paleoproterozoic age and controlled by the N-S trending Ouro Roxo-Canta Galo shear zone (OCSZ). The host granitoids are oxidized calc-alkaline granodiorite and tonalite of magmatic arc filiation. The OCSZ is a sinistral oblique ductile-brittle shear, which belongs to the third deformation event of the Tapajós Province and has turned the granitoids into protomylonites, mylonites and breccias. The NNE-SSW mylonitic foliation dipping to ESE and stretch lineation in quartz grains indicate the tectonic movement to NW. Mineralized quartz veins and pipes are hosted by mylonites and breccias and surrounded by hydrothermal alteration halos. Besides silicification and sulfidation, concentrated in the ore bodies, three types of wall-rock alteration occur: propilitization (chlorite + phengite + carbonate); phylic alteration (phengite + quartz + carbonate + pyrite); carbonatization. Besides magmatic quartz and microcrystalline quartz of mylonites, five generations of hydrothermal quartz were recognized in the lodes. The isotopic Pb-Pb data do not support a genetic relationship between the gold deposit and the Tropas granitoids, being the deposit coeval to Maloquinha granite. The orogenic environment, the veining style, the structural control, the hydrothermal alteration and the metallic association (Au + Cu + Bi), are all consistent with a mesozona-epizona orogenic model for the genisis of the Ouro Roxo deposit.
Acesso aberto (Open Access)
Influence of the cable´s layout on the shearing resistance of prestressed concrete beams
(Universidade Federal do Pará, 2016-10) SOUZA JUNIOR, Orivaldo de Azevedo; OLIVEIRA, Dênio Ramam Carvalho de
Little information on experimental investigations regarding the influence of the prestressing forces in the shear resistance of prestressed beams is found in the technical literature. Thus, it was experimentally evaluated the shear resistance of six post-tensioned prestressed concrete beams with cross section of (150 x 450) mm2, total length of 2400 mm and concrete’s compressive resistance of 30 MPa, with the variables of this work being the layout of the prestressing cable, straight or parabolic, and the stirrups geometric rate. Verticals displacement, steel and concrete’s strains and a comparison of the experimental loads with the estimates of ACI 318, EUROCODE 2 and NBR 6118: 2014 codes are presented and discussed. The results showed that the cable’s parabolic layout increased the beams’ shear resistance in up to 16% when compared to beams with straight cables.
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)
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.
Acesso aberto (Open Access)
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.
Acesso aberto (Open Access)
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.
Acesso aberto (Open Access)
Influência das armaduras complementares na resistência ao cisalhamento de vigas com estribos treliçados pré-fabricados
(Universidade Federal do Pará, 2019) PINTO, Rosângela Silva; LIMA NETO, Aarão Ferreira; http://lattes.cnpq.br/0287664572311345; https://orcid.org/0000-0002-5911-1368
In the design of structures under great loads, conflicts with the assembly of longitudinal and transverse reinforcement may happen. To avoid this type of occurrence, internal shear reinforcement may be a good option as they are inserted between longitudinal bars. However, if an anchorage failure occurs, a secondary effect caused by the use of these bars may cause a horizontal failure called (delamination). In order to prevent this failure, NBR 6118 (2014) states that stirrups anchorage must be secured by the use of hooks or welded longitudinal bars. Currently, few researches evaluate the influence of complementary reinforcement (hooks), and these are limited to an overall analysis of the specimens. Besides conflict with the assembly of densely reinforced members, another factor that may compromise their mechanical performance is the positioning angle of the transverse reinforcement. According to Eurocode 2 (2004), the use of reinforcement bars at an angle of 90º does not present fully satisfactory behavior, which indicates that different angles would result in more efficient responses. This research experimentally analyzes the influence of the complementary reinforcement anchorage, fixed in the compression and tensile zones of reinforced concrete beams, as a reinforcement for the stirrups. Seven RC beams using pre-fabricated truss internal stirrups were used, assessing the influence of the complementary reinforcement and verifying the behavior of stirrups at an angle of 90º or 60º in relation to the horizontal axis of the specimen. Some variations of the complementary reinforcement (hooks) ratio and the spacing between stirrups were made. As conclusions, it was observed that the use of complementary reinforcement to the pre-fabricated truss stirrup resulted in an increase of nearly twice the shear strength in relation to the reference beam, avoiding delamination until the failure load. The specimens with complementary reinforcement on both faces presented higher strength and ductility when compared to beams with complementary reinforcement only in the lower face. Strains increased from 2.46‰ in beam Wc-0.4-60b1 to 3.20‰ in beam Wc-0.4-60a1, showing that its use results in transferring stresses to shear reinforcement. On the behavior of beams Wc-04-90, by reducing the spacing between stirrups in 40 mm, they presented superior performance in terms of ductility and shear strength compared to beams Wc-04-90 with spacing of 100 mm.