Resumo em Inglês:

Abstract The design codes for structural design traditionally establish the adoption of partial safety factors to deal with uncertainties. These standards do not allow one to know the real probabilities of failure of a structure. What is needed, from a practical and scientific point of view, is a more consistent approach, based on reliability theory. This article addresses an initial attempt at determining the safety levels of structures based on advanced analysis and design with structural reliability theory. In this context, the authors consider the effects of the geometric nonlinearity and flexibility of connections in the reliability analysis, which aims at setting a certain displacement as the service limit state. For this purpose, a computer program was written called Structural Reliability Module. This program uses a First Order Reliability Method to analyse reliability. To carry out the structural analysis of steel structures, this study uses the program Computational System for Advanced Structural Analysis. Validating the Structural Reliability Module involved comparing the results from other authors with those generated by the program. Results for the structures under study indicate the efficiency of the implemented measures. Results suggest that, when a certain displacement is set as a service limit state, the reliability of the structures under analysis are only slightly influenced by geometric nonlinearity but considerably so by semi-rigid connections.

Resumo em Inglês:

Abstract Until the beginning of the 21st Century, the characteristics of wind for purposes of structural analysis and design, as reflected in wind codes worldwide, were based on the behavior of wind currents in the vicinity of the ground surface observed in so-called synoptic events. It was only recently recognized that the latter are not the only cause of wind damage to buildings and structures, not even its main cause. In view of the absence of any reference to non-synoptic winds in most South American wind codes, their urgent revision to include the effects on non-synoptic winds is badly needed. The downburst is a relevant meteorological phenomenon that causes extreme winds in the lower atmospheric boundary layer. The present article briefly describes an introduction to an simplified approach recently proposed by the second author to describe the wind velocity field in this type of meteorological phenomenon, that is, downbursts within instability lines. The method is examined by a comparative study of tall building response to synoptic and non-synoptic wind action.

Resumo em Inglês:

Abstract This article reports the results of an investigation on the effects of internal moments on the vibration behavior of thin-walled steel members. The analyses are based on the Generalized Beam Theory (GBT), a thin-walled bar theory accounting for cross-section in-plane deformations - its main distinctive feature is the representation of the member deformed configuration by means of a linear combination of cross-section deformation modes, multiplied by their longitudinal amplitude functions. The study concerns a simply supported T-section (with unequal flanges) members exhibiting a wide range of lengths and subjected to uniform internal moment diagrams - their magnitudes are specified as percentages of the corresponding critical buckling values. After providing a brief overview of the main concepts and procedures involved in performing a GBT-based structural analysis, the vibration behavior of load-free and loaded T-section members is addressed - the influence of the applied loadings is assessed in terms of (i) the fundamental frequency difference and (ii) the change in the corresponding vibration mode shape. For validation purposes, some GBT results are compared with values yielded by shell finite element analysis performed in the code ABAQUS (Simulia, 2008).

Resumo em Inglês:

Abstract Risk management is of paramount importance for the success of tunneling works and it is linked to the main excavation methods used: the Conventional Excavation Method (CEM) and the Tunnel Boring Machine Method (TBM). Considering the importance of the “Safety and Health” criterion for the choice of the excavation method, the fact that this criterion is usually mostly focused on the structural component, and taking in account that there is no research showing the advantages of one of the methods over the other, this research intends to conduct a comparative risk analysis between both methods, taking into consideration the different constraints that might appear. In order for this comparison to hold true, a risk evaluation is presented, analysing 12 risks and 4 risk factors in 3 phases, so that the impact of the different variables can really be appraised. This research is made in a scenario of the construction of a 3.5 km-long tunnel in a non-urban area, with an unproblematic rock mass. The final result will be a detailed analysis of the influence of “Safety and Health” criteria, useful for both the technical and the scientific community, something that has never been done before.

Resumo em Inglês:

Abstract This article shows a study of the level of reliability of welded and bolted connections in cold formed steel members, for some limiting states, adopted by AISI and Brazilian codes. The aim of this study is the assessment of the reliability index β for a variation of the nominal live-to-dead load ratios as well as comparison of the value found considering different load combinations. The first order reliability method is used to calculate the reliability index β. In this study, reliability indices smaller than 3.5 were obtained, especially for bolted connections. Consideration of the model errors and FORM method, lead to significant reductions in reliability indices, which are found to be less than the recommended target reliability levels.

Resumo em Inglês:

Abstract The Piranema Sand Cluster, located between the Seropédica and Itaguaí counties of Rio de Janeiro Metropolitan Region, is responsible for 65% of the sand used in construction works of the region and is the home of approximately 47 small mining companies. The construction works in progress in this area make this mining district a critical success factor for these new or expanding ventures, for prices of construction sand increases tremendously with delivery distance. These undergoing works attract many people to the region, increasing the need for urban infrastructure to house them. This search for land comes from mining sites and causes difficulties in obtaining local permits, which are the first step in environmental compliance of the mining activities. The discussion of this paradox: “cheap aggregates for urban infrastructure and the displacement of mining to make room for the installation of these infrastructures”, must be based on a Future Use Project for this area, seeking consensus among communities, mining, government and other stakeholders. This enables the preparation of a Decommissioning Plan for the mines that reconciles the mineral reserves yet to be exploited to the needs of other land uses that development is promoting. By doing this, a regional planning proposition is established in order to recover the degraded area and ecosystems, ensure the well-being of the population, improve employment generation and income of the affected people, and keep the prices of construction sand at low levels, while showing great respect to the environment.

Resumo em Inglês:

Abstract Roughness is a fundamental feature to define rock deformability and resistance. A detailed characterization of discontinuity surface geometry is essential for understanding some of the rock’s mechanical behaviors. Fractal geometry has been used by several authors to correlate parameters such as the Hurst coefficient for JRC (Joint Roughness coefficient) to better describe a surface geometry. Surface profiles might be characterized by a fractal dimension that represents the small scale of the geometric recurrence. In this paper, we propose to modify the methodology used to identify the Hurst coefficient incorporating the rodogram function in the JRC analysis. The proposed function is less influenced by drifting effects, and seems to be more precise than the commonly used variogram function. Robust mathematical models of spatial continuity can be a better alternative to characterize the roughness of rock discontinuities.

Resumo em Inglês:

Abstract Usually, machining employs cooling methods to avoid high temperatures. In most cases, the cutting fluid is applied with high flow and low pressures. This technique consumes a large amount of cutting fluid that causes serious problems in the environment and in the health of the worker. An alternative to the conventional cooling method is the Minimum Quantity of Lubricant. The MQL attempts to minimize the consumption of cutting fluid, which this study is about, whereby the reduction provided by this MQL was 99.99%. This technique consumes only the necessary quantity of cutting fluid to create a thin film of lubricant on the cutting surface grinding wheel. The MQL aerosol is injected with high pressure in the contact zone, efficiently lubricating the grinding process. However, the cooling effect of MQL is not enough to dissipate all heat produced during the grinding process. This study analyzes the improvement in the cooling effect caused by the addition of water in the MQL. The tests were done using different concentrations of cutting fluid in water, e.g. 1:0, 1:1, 1:3, 1:5 (oil:water). The experiment occurred on the external cylindrical plunge grinding with a vitrified cubic boron nitrite (CBN) grinding wheel, serving as the workpiece, the AISI 4340 quenched and tempered steel. The analyzed outputs were: surface roughness, roundness deviation, acoustic emission and vibration.. The results improved with the addition of water in the cutting fluid used in the MQL technique. The comparison with the MQL conditions showed that the best condition was the fluid with more water concentration.

Resumo em Inglês:

Abstract The grinding process is defined as an abrasive cutting action of a tool known as grinding wheel, which is submitted to high rotations, promoting excellent finishing and accuracy in dimensions, respecting the parameters established in each project. During the machining, the cutting edges of the abrasive grains undergo wearing and this increases the contact surface of the tool with the workpiece, increasing the machining temperature and creating possibilities of damaging it. Therefore, it is necessary to use a cutting fluid, responsible for lubricating and cooling the cutting zone, removing the chips from the cutting region between the workpiece and the wheel, and even having an anticorrosive action. However, its composition causes contamination to the environment and to the operator. In face of the increasingly strict environmental laws, it has become necessary to search for new methods of cooling that are at least as effective as conventional one and economically practicable. Thus, the Minimum Quantity of Lubrication was developed as a mist of air and oil applied at high pressure, reducing drastically the use of contaminants. In this work, two oil flows were used for the MQL technique, 30 ml/h and 120 ml/h. The wheel used was a CBN (Boron Cubic Nitride) one, composed of synthetic grains and the workpiece, in a ring format, were produced in AISI 4340 steel quenched and tempered. It was observed from results that MQL can be applied in the industrial processes without losing piece quality.

Resumo em Inglês:

Abstract Ornamental rock production, such as marble and granite plates, have great importance in the southeastern region of Brazil. Its residues are composed of some compounds used in continuous casting as mould fluxes. Therefore, the aim of this article was to study these residues to formulate mould fluxes. First, the raw materials were chemically characterized by energy dispersive X-ray spectroscopy (EDS) and two new fluxes were developed based on two different commercial fluxes used for peritectic and low carbon steels. All fluxes were analyzed for their ability to form crystalline phases, by performing the modified Stollberg test. The slag formed was analyzed by X-ray diffraction (XRD), thin section microscopy (TSM) technique, and a mathematical model for comparison. Also, sample fluidity was measured using the known “boat test” and viscosities were predicted by FactSage® software. Crystallinity and fluidity of new fluxes were compatible with those observed for the commercial fluxes. The FactSage® simulations identified crystalline phases, such as cuspidine (Ca4Si2O7F2), for all fluxes. In commercial low carbon flux (CLC) and new low carbon flux (NLC), X-ray results have shown that non-crystalline phases are formed. And in commercial peritectic flux (CP) and new peritectic flux (NP), X-ray results have shown crystalline phases. The results showed similar characteristics between the new fluxes and the commercial ones; however, further tests in an industrial setting are required to obtain additional information and confirm equivalent behavior during their industrial use.

Resumo em Inglês:

Abstract Electric Arc Furnace Dust (EAFD) is a solid waste originated from electric steelmaking furnaces. Currently, according to some authors, there is an estimated generation of 15 to 25 kg of dust per ton of steel produced. The formation of the dust is related to the following steps of the process: furnace charge, metal volatilization, iron vaporization under the arc, drag of solid particles and, mainly by the collapse of CO bubbles from metallic bath decarburation. The dust has metals that are harmful to the environment. Otherwise, it is mostly composed of the elements iron, zinc and oxygen. Due to increasing costs for disposal and because it is considered a hazardous waste, industry is looking at the possibility of returning the dust to the steelmaking process. One of the alternatives is by reintroducing the waste in an electric melting shop using self-reducing agglomerates as part of the furnace burden. In this study, self-reducing mixtures are prepared with EAFD and petroleum coke (PET), presenting chemical and physical characterizations. An evaluation about the behavior of the mixtures is carried out in thermobalance, regarding the possibility of use in measuring accurate PET content in self-reducing pellets. As results it could be stated that the elements of economic interest, Zn and Fe, represent, respectively, 34.23 and 22.80%, in weight. These elements are present in chemical species frankilinite, zincite and magnetite and the reducible oxygen was estimated as 17.90%. Also, it was concluded the optimal content of petroleum coke in the mixtures varies from 10 to 15%, in weight. Therefore, the utilization potential of the thermogravimetric technique in the industrial field for adjustment of carbon content in batches of self-reducing pellets is satisfactory.

Resumo em Inglês:

Abstract The induration furnace is one of the most important devices in the pellet production system. It is responsible for ensuring the quality of pellets produced, since a high level of thermal energy is necessary to reach the physical properties needed. Therefore, the refractory lining performance is important to guarantee the quality of pellets and to avoid thermal losses. Minor failures in the refractory lining may result in serious damage, if it not previously identified and repaired. This article was written to explain a preventive technique to identify and repair such minor issues with the refractory lining before escalation. The use of this technique in the proper frequency may result in furnace life cycle extension.

Resumo em Inglês:

Abstract The study aimed to characterize the mineral wools obtained from wastes of the cutting step of marble and granite, in order to evaluate the possibility of their use on an industrial scale. Mixtures of marble and/or granite wastes were prepared in order to reach the chemical composition of rock and glass wools. The batches were melted in an electric arc furnace in laboratory scale at 1450ºC and casted with water, in order to obtain a higher cooling rate. Characterization work was performed in batches that formed vitreous material, and with superior incorporation of the residues: 11.7% and 14.6% of marble waste with glass wool and rock wool, respectively; 78.3% and 91.6% of an association of marble and granite wastes with glass wool and rock wool, respectively. Computational thermodynamics was used in order to obtain the main phases at 800ºC and determine the liquid and solid content at 1400, 1450 and 1500ºC. In addition, the materials obtained were characterized via chemical analysis using X-ray fluorescence, DTA, X-ray diffraction and SEM. The results indicate that the marble and granite waste are composed mainly of CaO (34.7 wt.%) and SiO2 (66.3 wt.%), respectively. An amorphous crystalline structure was obtained in all tests, indicating that this material can be used as an insulation material. The crystallization temperatures were determined around 800ºC.

Resumo em Inglês:

Abstract Interest in recycling for the recovery of valuable substances, such as precious metals from electric and electronic waste has been increasing year after year due to the large amount present in such waste compared to primary sources. There is environmental concern, since the amount of this kind of waste is increasing due to rapid technological advances. This study aimed to test the different operating conditions of an electrostatic separator for the concentration of copper from printer circuit boards (PCB). The PCBs were milled in knife mills and separated according to the difference of granule sizes into two fractions: A (<0.5 mm); B (0.5<B<1 mm), followed by scaling. Then, the samples were subjected to a magnetic separator for removing the magnetic materials to obtain a concentrate with a higher content of copper. After the magnetic separator, an electrostatic separator was used, where different conditions were employed for each sample: roller rotation (100 and 175 rpm) and tension (20 and 35 kV). Iron concentrations were observed after the magnetic separator, between 12 and 14.1% for the A fractions and 10.3-11.4% for the B fractions. After the electrostatic separator, the results for the A samples showed that the concentration of copper varies between 17.5 and 51.1%, with the highest concentration obtained through the use of 100 rpm (roller rotation) and 35 kV (voltage). For the B samples, the variation was between 6.4 and 40.5 %. For both particle sizes, the best applied condition was a voltage of 35 kV and a roller rotation of 100 rpm.

Resumo em Inglês:

Abstract Flotation plays a relevant role in the concentration of iron ores. Conventional flotation technology employing mechanical machines and columns and also circuits combining both types of cells have been utilized in the iron ore industry. The top size of particles in the flotation circuit feed is 150 µm and the slimes below 10 µm are removed as overflow in hydrocyclone classification. The conventional flotation technology faces difficulties in achieving tailings with iron grades lower than 12% and concentrates with SiO2 grades lower than 1%, and requires long residence times, resulting in large volume machines and huge footprints. The pneumatic flotation technology was evaluated in the reverse flotation of quartz from an iron ore sample of the Iron Quadrangle, Brazil. Bench and industrial scale tests were conducted in pneumatic flotation machines at low residence time. Both tests were carried out in open circuit stages with the objective of comparison with mechanical cells. The bench scale tests were carried out in three stages (rougher, cleaner and recleaner) in an 11 L pneumatic cell aiming at final concentrate with maximum 2% SiO2 while the industrial tests were carried out in a 25 m3 pneumatic cell in the rougher stage aiming at comparison with a circuit of five 14 m3 cells in the rougher stage and four 14 m3 cells in the scavenger stage. The collision and particle-bubble adhesion occur in a step before the pulp reaches the pneumatic cell vessel. The results indicate the possibility of achieving concentrates with a SiO2 content of approximately 1% and tailings with iron contents lower than 10% with three stages (rougher, cleaner and recleaner) without the need of scavenger stages. Furthermore, the residence time was three times shorter than that required for conventional mechanical cells. The speed of the pulp at the entrance of the pneumatic cell strongly affects the quality of the concentrate.

Resumo em Inglês:

Abstract This article aims to evaluate the use of a truck factor for off-highway trucks in open pit mine operations, thus reducing error on material movement and mine production data entry. This method is current for a copper mine located in South East Pará, Brazil. With a dispatch system, the truck factor is calculated using three data inputs called measured t, dump t and excavator load time. This dispatch system, designed to upload real time data from each truck, acquires measured load information by a truck weightometer and provides the basis for long-term, medium-term and mainly short-term planning. Due to the significant impacts toward mine planning, through data error, a payload truck factor system provides data assurances in place of potential failure of onboard weighing. However, when using a system that is reliant on actual data, caution must be applied when replacing information with assumed fixed figures, thus forming the discussion on which this article attempts to review by providing overview on both the positive and negative impacts of implementing a truck factor system to an open pit mining using a dispatch system.

Resumo em Inglês:

Abstract The use of dynamic simulation is technically advantageous for the project as shown by various authors. However, is it economically advantageous in the early stages of the project (FEL1 and FEL2)? The methodology to economically evaluate the use of dynamic simulation considers the time and development cost compared with the time and cost spent to change the project in the next phase, considering changes that could be avoided with the use of dynamic simulation. Five process plant projects were evaluated, each one with an estimated CAPEX of US$ 300 million. The saved average is US$ 44,200.00 and US$ 182,400.00 for FEL 1 and FEL 2 respectively. The percentage cost savings for FEL2 (2.0%) and FEL3 (3.1%) are significant. The estimated delay avoided for FEL2 (3 weeks) and FEL3 (8 weeks) is directly related to the implementation delay, whose cost is expressively greater than the savings shown. The study concludes that the use of dynamic simulation is economically advantageous for the project.

Resumo em Inglês:

Abstract Several research works have been done to assess the effect of the cutting depth on the cutting forces when using picks. In this case, the cutting tests need im-portant equipment to cut rocks, to register the cutting force and to determine the cutting force value. The purpose of this research work is to simulate the laboratory rock cutting tests to determine the cutting force, using commercial software; and to compare the cutting force values to those obtained in the la-boratory. In the simulation, we took a gypsum rock sample as the specimen,. We simulated the separation of the rock chips from the specimen and the sub-sequent breakage into multiple fragments. In the simulations, a cutting pick was compared with a stationary rock sample. The simulations were conducted at a same constant velocity for different cutting depths. The simulations showed that the depth of cut has a significant effect on the cutting force, and the values of the cutting force in the simulation are very close to those obtained in the laboratory.

Resumo em Inglês:

Abstract The current developments with unmanned aerial vehicles (‘UAVs’) are revolutionizing many fields in civil applications, such as agriculture, environmental and visual inspections. The mining industry can also benefit from UAVs in many aspects, and the reconciliation through topographic control is an example. In comparison with traditional topography and maybe modern techniques such as laser scanning, aerial photogrammetry is cheaper, provides faster data acquisition and processing, and generates several high-quality products and impressive level of details in the outputs. However, despite the quality of the software currently available, there is an uncertainty intrinsic to the surfaces acquired by photogrammetry and this discrepancy needs to be assessed in order to validate the techniques applied. To understand the uncertainty, different surfaces were generated by UAVs for a small open pit quarry in southern Brazil. Well-established topographic surveying methodologies were used for geolocation support and comparison, namely the RTK (real-time kinetic) global navigation satellite system (GNSS) (here called conventional method) and laser scanning. The results showed consistency between the UAV surfaces with a few outliers in when vegetation, water and mobile objects during the flight missions. In comparison with the laser-scanned surface, the UAV results were less erratic surrounding the RTK points, showing that surfaces generated by photogrammetry can be a simpler and quicker alternative for mining reconciliation, presenting low uncertainty when compared to conventional methods.

Resumo em Inglês:

Abstract Companies producing lead-acid batteries are required by law to recycle their battery scrap. The recycling can be performed by a pyrometallurgical process resulting in slags containing mainly lead and iron. A study was carried out with the aim of recovering the lead contained in this slag. This work has economic and environmental implications. Slag characterization was performed by X-ray diffraction, X-ray fluorescence and scanning electron microscopy (SEM). A laboratory-scale mechanical cell was used for flotation tests. The results showed that Pb-Fe selectivity is possible using ethyl xanthate as collector. The coke floats together decreasing concentrate grade. However, this is no problem because coke participates in the metallurgical process for the production of lead. A concentrate containing 22.9% Pb was obtained from a slag with 2.2% Pb. The process removes more than 99.6% of the iron contained. However, the recovery was only 19.0 %. Analyses from scanning electron microscopy detected the presence of lead inside the iron particles, limiting the possibility of lead recovery.