OALib Journal期刊

ISSN: 2333-9721



匹配条件: “Christoforo” ,找到相关结果约8条。
Investigations on cementitious composites based on rubber particle waste additions
Nacif, Glaucio Laun;Panzera, Túlio Hallak;Strecker, Kurt;Christoforo, André Luis;Paine, Kevin;
Materials Research , 2013, DOI: 10.1590/S1516-14392012005000177
Abstract: the amount of waste rubber has gradually increased over recent years because of over-growing use of rubber products. the disposal of waste rubber has caused serious environmental problems. the incorporation of recycled materials into cementitious composites is a feasible alternative that has gained ground in civil construction. the performance of such materials is much affected not only by the rubber addition, but also the particle size which has been controversially reported in the literature. in order to investigate the single effect of rubber particles into cement based materials, rubber cementitious composites were prepared with no silica particle additions. a full factorial design has been conducted to assess the influence of the rubber particle size (0.84/0.58 mm and 0.28/0.18 mm); mass fraction used (5, 15 and 30%); and water/cement ratio (0.35 and 0.50) on the physic-mechanical properties of the composites. the materials were characterized through apparent density, porosity, compressive strength, flexural strength, modulus of elasticity and microstructural analysis. the interactions of rubber particle size, rubber fraction and water/cement ratio affected significantly the density and compressive strength of the composites. the apparent porosity was influenced mainly by the rubber particle size. the flexural strength was affected by the main factors and the modulus of elasticity was affected by the interaction factors rubber particle size and fraction, and rubber fraction and w/c ratio.
Emprego de ferramentas numéricas na avalia??o do módulo de elasticidade em vigas roli?as de madeira
Christoforo, André L.;Zangiácomo, André L.;Panzera, Túlio H.;Silveira, Márcio E.;Lahr, Francisco A. R.;
Engenharia Agrícola , 2012, DOI: 10.1590/S0100-69162012000500016
Abstract: beams are structural elements used in the most of civil constructions. the wood can be found in several applications of engineering due to the moderate mechanical strength and low density. the use of round timber as a beam is very attractive, since it does not need to be processed, such as lumber. the design of structural timber elements requires the determination of its physical and mechanical properties in which are obtained based on the recommendations of engineering standards. in case of round timber, the national standards dealing with the determination of strength and stiffness properties are in term for more than twenty years with no technical review. overall, both national and international standards consider truncated-cone geometry for cylindrical logs of wood, resulting in simplified equations unable to predict the effect of shape irregularities on the longitudinal modulus of elasticity. this paper aims to evaluate the effect of shape irregularity of round timber of corymbia citriodora and pinus caribaea to determine the longitudinal modulus of elasticity. the three-point bending test is used to determine the modulus, considering a simplified analytical model, with constant circular section for the element. the irregularities of the wood are considered in the numerical models based on a beam and three-dimensional finite elements. the results showed statistical equivalence between the modulus of elasticity for both methods of calculation, indicating that the constant circular section is a reasonable assumption for the wooden here evaluated.
Influence of stiffness in bolted connections in wooden plane structure of truss type
Christoforo, André L.;Romanholo, Giuliano A.;Panzera, Túlio H.;Borges, Paulo H. R.;Lahr, Francisco A. R.;
Engenharia Agrícola , 2011, DOI: 10.1590/S0100-69162011000500017
Abstract: trusses are structural systems commonly used in projects, being employed mainly in roof structures, present in most rural buildings. the design of trusses, as well as other structural systems, requires the determination of displacements, strains and stresses. however, the project is developed from an ideal model of calculation, considering free rotation between the elements of a connection. this paper presents a computer program for the analysis of bidimensional wooden trusses with connections formed with two screws per node. the formulation is based on the flexibility method, taking into account the influence of the effect of semi-rigid connections formed by two screws. an example of a structure is presented and analyzed by the program developed here, highlighting the importance of behavior analysis on semi-rigid connections.
Numerical evaluation of the modulus of longitudinal elasticity in structural round timber elements of the Eucalyptus genus
Christoforo, André L.;Panzera, Túlio H.;Batista, Fabiano B.;Borges, Paulo H. R.;Lahr, Francisco A. R.;
Engenharia Agrícola , 2011, DOI: 10.1590/S0100-69162011000500018
Abstract: currently, the standards that deal with the determination of the properties of rigidity and strength for structural round timber elements do not take in consideration in their calculations and mathematical models the influence of the existing irregularities in the geometry of these elements. this study has as objective to determine the effective value of the modulus of longitudinal elasticity for structural round timber pieces of the eucalyptus citriodora genus by a technique of optimization allied to the inverse analysis method, to the finite element method and the least square method.
Cement - steatite composites reinforced with carbon fibres: an alternative for restoration of brazilian historical buildings
Panzera, Túlio Hallak;Strecker, Kurt;Miranda, Jader dos Santos;Christoforo, André Luis;Borges, Paulo Henrique Ribeiro;
Materials Research , 2011, DOI: 10.1590/S1516-14392011005000007
Abstract: steatite is a mineral which has been employed in the carving of elements in facades of brazilian historical buildings and churches since the 17th century. over the years, many of those historical buildings suffered the consequences of weathering with a current need for restoration. recently a special cement-based mortar containing additions of fine powder waste from mineral extraction of steatite has been developed in brazil, as a composite material for restoration of steatite elements. however, the incorporation of steatite waste reduces the flexural strength of the mortar and compromises the restoration of elements where gravity imposes tensile stresses. the addition of carbon fibres may overcome this issue and increase the flexural strength of the cement-steatite composite mortar. this work investigates the effect of carbon fibre addition on the bulk density and flexural strength of compacted precast cement-steatite composites. the results show that the addition of carbon fibres (i) effectively increases the mechanical strength, allowing for a higher amount of steatite powder waste in the mixes; (ii) reduces the weight of the structural elements. this new composite material would help to develop restoration techniques of historical buildings and serve as a disposal route of steatite powder waste in brazil.
Micromechanical analysis of hybrid composites reinforced with unidirectional natural fibres, silica microparticles and maleic anhydride
Silva, Leandro José da;Panzera, Túlio Hallak;Christoforo, André Luis;Rubio, Juan Carlos Campos;Scarpa, Fabrizio;
Materials Research , 2012, DOI: 10.1590/S1516-14392012005000134
Abstract: the work describes the analytical and experimental characterisation of a class of polymeric composites made from epoxy matrix reinforced with unidirectional natural sisal and banana fibres with silica microparticles and maleic anhydride fabricated by manual moulding. the analytical models, rom rule of mixtures and halpin-tsai approach, have been used in conjunction with a design of experiments (doe) analysis from tensile tests carried out on 24 different composites architectures. the following experimental factors were analyzed in this work: type of fibres (sisal and banana fibres), volume fraction of fibres (30% and 50%) and modified matrix phase by adding silica microparticles (0%wt, 20%wt and 33%wt) and maleic anhydride (0%wt and 2%wt). the rom approach has shown a general good agreement with the experimental data for composites manufactured with 30%vol of natural fibres, which can be attributed to the strong adhesion found between the phases. on the opposite, the semi empirical model proposed by halpin and tsai has shown greater fidelity with composites manufactured from 50%vol of natural fibres, which exhibit a weak interfacial bonding. the addition of microsilica and maleic anhydride in the system did not enhance the adhesion between the phases as expected.
The position effect of structural Eucalyptus round timber on the flexural modulus of elasticity
Christoforo, André L;Panzera, Túlio H;Batista, Fabiano B;Borges, Paulo H. R;Lahr, Francisco A. R;Franco, Claudenir F;
Engenharia Agrícola , 2011, DOI: 10.1590/S0100-69162011000600019
Abstract: round timber has great use in civil construction, performing the function of beams, columns, foundations, poles for power distribution among others, with the advantage of not being processed, such as lumber. the structural design of round timber requires determining the elastic properties, mainly the modulus of elasticity. the brazilian standards responsible for the stiffness and strength determination of round timber are in effect for over twenty years with no technical review. round timber, for generally present an axis with non-zero curvature according to the position of the element in the bending test, may exhibit different values of modulus of elasticity. this study aims to analyze the position effect of eucalyptus grandis round timber on the flexural modulus of elasticity. the three-point bending test was evaluated in two different positions based on the longitudinal rotation of the round timber element. the results revealed that at least two different positions of the round timber element are desired to obtain significant modulus of elasticity.
Full factorial design analysis of carbon nanotube polymer-cement composites
Cota, Fábio de Paiva;Panzera, Túlio Hallak;Schiavon, Marco Ant?nio;Christoforo, André Luís;Borges, Paulo Henrique Ribeiro;Bowen, Chris;Scarpa, Fabrizio;
Materials Research , 2012, DOI: 10.1590/S1516-14392012005000077
Abstract: the work described in this paper is related to the effect of adding carbon nanotubes (cnt) on the mechanical properties of polymer-cement composites. a full factorial design has been performed on 160 samples to identify the contribution provided by the following factors: polymeric phase addition, cnt weight addition and water/cement ratio. the response parameters of the full factorial design were the bulk density, apparent porosity, compressive strength and elastic modulus of the polymer-cement-based nanocomposites. all the factors considered in this analysis affected significantly the bulk density and apparent porosity of the composites. the compressive strength and elastic modulus were affected primarily by the cross-interactions between polymeric phase and cnt additions, and the water/cement ratio with polymeric phase factors.

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