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 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 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 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 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 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.

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 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 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 Population growth in urban centers, together with the lack of physical space, has led to the construction of increasingly tall and slender buildings. Multiple-story structures present substantial challenges to civil engineering because they have specific requirements for their design, construction, and use. The increased number of foors leads to more lateral displacements resulting from horizontal actions. Under these conditions, to ensure system stability, structural bracing components are commonly adopted. In addition, along with the use of more resistant materials and new construction techniques, it is necessary to improve the methodologies adopted in the structural analysis to offer professionals in the area the conditions to undertake safer and more economical projects with better speed and efficiency. Thus, in this study, numerical analyses were applied to steel planar reticulated structures to evaluate their stability and strength when inserting bracing systems. The study compared the arrangement of the bars and analyzed the influence of the parameters of the bracing systems, such as the properties of the cross-section and the position of the inverted-V-braced system. The MASTAN2 program was used to perform nonlinear static assessments using reticulated finite elements that considered both geometrical and physical nonlinearities. It was observed that the inverted-V-braced system had a substantial impact on all of the structures that were analyzed, providing increased stiffiness and, as a result, significantly reducing the frame’s lateral displacement.

Abstract Flocculation is a complex process, usually dependant on various conditions to perform adequately. Nevertheless, the relevance and interaction of the process variables are not easily found in literature. In this study, nine variables of ultrafine quartz flocculation systems, defined in Part 1 of this study, were analysed. The effects of each variable and their interactions in the system were investigated based on flocculation and sedimentation tests. The results were statistically evaluated using the supernatant turbidity as experimental response. The evaluations resulting from the statistical approach indicated that suspension pH (5.49%) was the most significant variable, followed by flocculant concentration (4.07%) with the second greatest effect on the turbidity of the supernatant. Solid concentration, agitation intensity, and surfactant conditioning time (4.05%, 3.51% and 3.51%, respectively), also have significant effects on ultrafine quartz flocculation. The flocculant concentration and the surfactant conditioning time were the variables with the most significant interactions with the main variables. The Camp Number values showed a negative exponential relationship with the turbidity results, proving to be an important tool to evaluate flocculation. Backscattered electron scanning microscopy images of flocs formed in the presence of 30 g/t PAM showed compact flocs in the size range between 150 and 365 µm, with noticeable sphericity.

Abstract The objective of this article is to present an optimization problem formulation to reduce the total structural cost of prestressed doubly-symmetric and monosymmetric I-shaped steel simply supported beams with straight tendons. The optimization problem was implemented via MATLAB’s native Genetic Algorithm. The validation and evaluation processes adopted two examples from literature. The design method follows the Brazilian standard NBR 8800:2008 for the Ultimate and Serviceability Limit States. The best result was found for a monosymmetric case by up to 20.00% and 25.70%. Saving in material weight and installation of tendons, without exceeding the security limits, was also effective. Furthermore, the results presented an efficient alternative for structural engineering, providing a significant model for similar analyzes.

Abstract Continuous assessment of slope stability is important to the open pit design and operation. This article aims to present a tool for evaluating the stability conditions of rock slopes in mining, based on a global geotechnical database, using machine learning techniques. Different models are evaluated in this research: the general model, which uses all variables; the mathematical model, which uses only variables selected by the random forest (out-of-bag); and two expert-based models: the Q-Slope model and the Santos model. The validation of the model was done through the test sample, using partition confusion matrices aiming at reproducibility of the results. A study of the types of errors was carried out using Principal Component Analysis (PCA). The study of errors allowed the identification of samples that were inconsistent with the others. Afterwards, the models were redone and compared with the previous ones. The best performers are presented and discussed. The proposed methodology does not replace the classic analysis of slope stability. On the contrary, it contributes to engineers and geologists with a tool for monitoring the stability conditions of slopes in a mining operation. Slope stability analysis must be carried out throughout the mine's lifetime and, therefore, it is believed that the tool proposed here can optimize the selection of slopes most susceptible to instability.

Abstract The family of crystals known as Tutton's salts plays a significant role in physics and chemistry; because they are used in phase transition studies and to define models applied to materials. The importance of salts in material engineering is recent, as in applications in adiabatic degaussing refrigerators and solid-state anodes. Studies of the (NH4)2Ni(SO4)2∙6H2O and (NH4)2Co(SO4)2·6H2O are widely found in literature but do not occur for the mixture of both. In this research, we studied mixed crystals of the general chemical formula (NH4)2NixCo(1-x)(SO4)2·6H2O with x ranging from 0 to 1, utilizing x = 0.7. The objective is to study the modifications caused owing to the ion's weighted composition in the formation of the solid solution and compare it with the pure salts. For this, the growth of these crystals is discussed based on ICP-OES results and optical microscopy concerning the crystal growth theory. The discussion also relates the Raman spectra of the salts with molecular changes according to structured group theory, qualitatively characterizing its crystalline structure. Finally, a Single-crystal X-ray study solves and confirms the structure of pure salts and mixed salt, quantitatively characterizing their crystal structure.

Abstract Mining in Brazil is one of the pillars that support its GDP (gross domestic product). Its execution requires technique and expertise. In a mining venture, the value chain drives the business to achieve its goals. Mine planning has a great influence on its performance, as it is through it that the organization is based to offer its products to the market and, consequently, the low compliance with the established premises will bring undesirable inconveniences. Within the planning, the short term is dedicated to operationalize the plans made possible by the long and medium term teams, in addition to attending to market variations. The indicators that control this process are of great importance, as an incorrect identification inserted in the various criteria that compose it can guide managers towards inefficient decision making. The objective of this study was, through lean methodology, to identify the main performance indicators that impact on the non-exception of the mining plan measured by the adherence and compliance indicators. In this method, the main causes of non-adherence and compliance with the mining plan were identified, enabling short and medium-term actions that leveraged the indicators. This study leveraged the average adherence and compliance by 17% and 54.9%, respectively, exceeding the target set for 6.5% and 49.2% respectively.