Abstract in English:Abstract Seeking to define more robust and executable structures, this article presents a computational framework for the optimal design of steel truss frames, which integrates two software of great prominence in structural engineering, MATLAB and ANSYS. Computational interfaces were created to enable the automation of the iterative optimization process. The optimization algorithm and computational interfaces were developed on the MATLAB platform, while structural analyses were performed with the ANSYS Mechanical APDL platform. Some details of the computational implementation are presented herein. The objective is to minimize the cost of structures by determining the optimal positioning of nodal coordinates and the optimal choice of commercially available structural profiles - shape and size optimization, respectively. For shape optimization, a computational model was defined to automatically generate the geometry of the structure, maintaining some intrinsic relations of symmetry and collinearity between elements. The design constraints are critical nodal displacements, stresses, and slenderness of elements, following the requirements of ABNT NBR 8800:2008. To exemplify the application of the proposed methodology, this article presents the optimal design of trusses for roofs of industrial sheds, considering its non-linear geometric behavior, typical of this type of structure.
Abstract in English:Abstract In geometrically nonlinear problems solved using the Finite Element Method (FEM), the structure response is directly influenced by the level of discretization and the nonlinear solution algorithm used. To reduce the discretization dependence, exact solutions are developed based on the deformed infinitesimal element equilibrium. To deal with the nonlinear solution problem, the two-cycle method can be used, since it is not dependent on load or displacement steps. The two-cycle method developed by Chen & Lui (1991) uses the classical geometric matrix and is not accurate for high axial loads. This happens because the geometric matrix is obtained using Hermitian polynomials which are approximate solutions. To circumvent this issue, the frame element’s tangent matrix is obtained using interpolation functions that match the homogeneous solution of the differential equation of the beam-column problem. The main objective of this study is to carry out a second order analysis of the frames and obtain equilibrium paths using the two-cycle method and the tangent stiffness matrix based on solutions of the differential equations obtained from the element’s deformed configuration. The results in terms of displacements and rotations for the examples studied are identical to the analytical solutions, showing that the combination of the two-cycle method with the exact element formulation is promising and can diminish the need for discretization.
Abstract in English:Abstract Constant growth in the concrete floor sector claims new techniques to improve concrete performance and avoid undesirable issues. In this way, materials used in concrete floors are essential, and it is critical to investigate them. Therefore, this study evaluated the influence of surface hardeners on the surface hardness determined by the rebound hammer test of concrete floors prepared with distinct water/cement ratios, curing ages, and cement types. The control parameters of the concrete’s production, including the compressive strength, flexural tensile strength, and bleeding tests were analyzed. In addition, data were assessed by multifactorial analysis of variance (ANOVA). Thus, hardeners increased the surface resistance of the composites, therefore reducing the chances of pathological manifestations occurring. Taken together, we demonstrated that hardeners improved the concrete surface prepared with all mixture proportions, but it was more significant when using the cementitious hardener and higher w/c content (0.6).
Abstract in English:Abstract The development of eco-friendly composites as insulating materials in buildings offers practical solutions to reduce energy consumption, which is why scientists have started in recent decades to search for more sustainable and eco-friendly materials. It is well known that building materials are among the most commonly used materials and have an obvious negative impact on the environment. Therefore, this article presents a study on the use of a new bio-composite material, composed of natural fibers of date palm, cement, and sand. The objective of this study is to assess the thermal insulation properties, as well as the water absorption and mechanical performance of this material for the construction of buildings. The percentage by weight of date palm fiber in the test samples varied from 0% to 30% for a mixture of two fiber sizes equal to 3 mm and 7 mm. The characteristics of these samples were determined experimentally in terms of compressive strength, as well as thermal conductivity. The results show that the introduction of date palm fibers in mortars causes a decrease in compressive strength and thermal conductivity. This study affirmed that the use of vegetable fibers in cementitious composites has a positive effect on the properties of insulations and on the costs.
Abstract in English:Abstract A thermosetting epoxy polymer composed of diglycidyl ether of bisphenol A and triethylenetetramine (DGEBA/TETA) was modified by incorporating flexographic photopolymer plate residues (rubber microparticles). The photopolymer plate residues were processed in two ways: (a) by grinding and performing particle size classification (where the resulting samples were denoted PP) and (b) by polyester layer separation and grinding the elastomeric fraction by cryogenic grinding (where the resulting samples were denoted ER). Both residual particles were incorporated into the epoxy at concentrations of 2.5, 5 and 7.5 wt%. The main results indicate that PP was not efficient as a modifier of the epoxy system. A reduction in mechanical properties (maximum tensile strength and deformation) was observed in the samples produced with PP in different concentrations. But, when the ER is incorporated, an increase in tensile property and in the deformation capacity, as well as impact resistance was observed in samples produced with ER. Scanning electron microscopy analysis showed a greater presence of voids in formulations produced with PP, which corroborates the decrease in the tensile strength of these samples.
Abstract in English:Abstract Nanocomposites formed of natural-origin iron oxide nanoparticles (magnetite and maghemite, Fe3O4 and γ-Fe2O3, respectively) were processed using the sol-gel process into core-shell structures containing silica and samarium to investigate their potential for applications in cancer treatments combining hyperthermia and brachytherapy. Mössbauer characterization showed that the iron oxides contained 64% magnetite, 18% hematite, 12% maghemite, and exhibit superparamagnetic behavior at room temperature. Transmission electron microscopy determined that the iron oxide particles were smaller than 15 nm, while magnetization was measured at 5 emu/g. Fourier transform infrared indicated the material was formed of Si-O-Si and Fe-O-Si bonds, while X-ray diffraction showed bands of amorphous silica from 5° to 23° and bands of iron oxide phases. X-ray fluorescence indicated 5.17% of incorporated samarium. The nanocomposite suspensions were subjected to an alternating magnetic field and the resulting heat dissipation was measured, falling within the ideal range for hyperthermia applications. Theoretical dosimetric calculation determined significant radioactive activity of 1.68x10-8 MBq.mg-1.Φ -1 after 24h decay time for 153Sm. The characteristics and behavior of these nanocomposites indicate that they may offer promise in applications involving hyperthermia for cancer treatment and a more accessible source for brachytherapy materials.
Abstract in English:Abstract This study presents a review of the methodology for choosing the type of access and exploitation methodology for underground mines, being the choice of the type of access, one of the initial stages of the conceptual projects. To this end, in addition to literature verification, technical feasibility reports of recent projects were analyzed, made available by mining companies listed on the Toronto Stock Exchange. In this report, data were extracted referring to technical and productive characteristics of the projects, thus allowing comparison with classic methodologies for the choice of types of access and the compilation of a new flowchart, adhered to the current mining industry. The data from the projects were separated considering the mining methods with the largest number of samples, as well as the productive and mineral deposit characteristics. As a result, a chart is presented for the choice of access and mining method as a function of productive characteristics, ore body geometry and rock mass quality. Updating the limits considered for depth and daily production corresponded to a significant improvement in the response of the suggested access type and made it compatible with that presented in the feasibility projects.
Abstract in English:Abstract Bench scale flotations were carried out to investigate an alternative collector reagent with a more sustainable bias, with selective action at the mineral interface to replace the standard hydrocarbon-base collector used for graphite’s flotation, the kerosene. A soy bio oil was produced by a transesterification reaction to perform as a collector. The study used graphite ore with 5.85% carbon content obtained from Salto da Divisa/MG region, in Bahia-Minas Province, Brazil. The design of experiments showed that the bio ester performed 11% higher than kerosene as a graphite’s collector, improving the flotation’s selectivity with 62% ore grade by bio oil and 88% recovery, against 54% ore grade using kerosene and 77% recovery. The chemical composition investigated with XPS analysis for both concentrates with kerosene and bio ester demonstrated the influence of esters and oxigenated-groups on oxidized graphite surfaces.
Abstract in English:Abstract Heterogeneity of volcanic materials that constitute the Canary Islands (Spain) means that mining work in water galleries excavated on these islands, drilling into the terrain for many kilometres, is very challenging. They are composed of materials that vary significantly in terms of cohesion, ranging from very consolidated to loose and highly unstable. Water galleries have been key in the development of the Canary Islands, in order to obtain drinking water from the aquifer. Generally, aquifers are located in mountainous areas with difficult access, which complicates the drilling work. This article analyses the main geotechnical problems encountered in the construction of subterranean water galleries in the Canary Islands, as well as possible solutions to these problems, so that these can be applied to similar territories. As a general conclusion, the instabilities inherent in volcanic materials affect this type of work, and it is necessary to take specific measures for each type of geotechnical risk, as proposed in this article.