Resumo em Inglês:

Abstract The composite structures formed by the association of steel profiles with concrete have shown to be an advantageous alternative, improving the behavior of the steel structures concerning their load capacity, stiffness, and durability, under fire conditions. The concrete-filled tubular columns have become an attractive alternative for the civil construction area, offering constructive and esthetic advantages. The Eurocode 4 (EN 1994-1-2, 2002) and ABNT NBR 14323:2013 show simple methods for the design of the composite columns under fire situations. Nevertheless, these present limitations in their application. In addition, regarding the determination of the temperature field in the cross section, the Eurocode 4 (EN 1994-1-2, 2002) describes a specific procedure for columns with section profile covered with concrete, but it is neglectful about concrete-filled tubular columns. The goal of this paper is to present a simplified procedure to determine the temperature registered in concrete-filled steel columns and apply the procedure to columns with square section tubes. The temperature distribution was determined by simulations using the computer package ABAQUS (Dessault Systemes Simulia Corp. 2013). After the studies, it has been considered that the procedure described in this paper is an effective alternative for the determination of the field's temperature and for the application of the design of the concrete-filled columns under fire conditions.

Resumo em Inglês:

Abstract This article provides an evaluation of the acoustical and thermal performance of some closing systems by referencing materials such as cement plates, plasterboard walls, precast concrete panels and expanded polystyrene. Reverberation time is calculated by applying an empirical formula, which uses temperature and relative air humidity values obtained from simulations that were conducted using the computational simulation program ESP-r (Energy Simulation Program-research). The internal temperature presented by the ESP-r is an indicator of thermal performance. Using a simplified graphic method, the acoustical performance is also evaluated by estimating the loss of sound transmission that occurs through the closing panels. Combinations of these panels, which form multilayer panels mediated by a layer of air and with or without insulating material between them, are applied. The results show that multilayered closing systems, when filled with insulating material, are an efficient solution than can provide adequate acoustical and thermal performance.

Resumo em Inglês:

Abstract Herein is presented a numerical methodology for a static resistance analysis of symmetrically loaded multiplanar KK joints in circular hollow steel sections. This methodology addresses factors related to the simulation of KK joints such as the material properties, the boundary conditions, mesh generation and refinement, incremental load steps and failure criteria. An objective criterion is proposed to identify the two failure modes most often occurring in KK joints. Failure mode 1 is observed when two neighboring diagonal braces loaded in the same sense act as one brace penetrating the chord together. In the failure mode 2, excessive deformation is observed in the chord region between two neighboring braces, folding the chord wall. However, in some cases the failure mode is not easily identified or both failure types are present. The proposed criterion objectively identifies the failure mode. In order to compute the joint resistance, an important failure criterion often adopted in literature for uniplanar K joints is the one known as Lu's deformation. In this paper, a strategy is proposed, which is an extension of Lu's criterion for multiplanar KK joints.

Resumo em Inglês:

Abstract In Brazil, studies to reuse construction and demolition waste are a special issue because a large amount of this material has been delivered to the public landfills and in illegal places. Some researchers have suggested reusing this material in building elements, such as bricks or blocks. It is possible to find a lot of researches in physical/mechanical characterization, while little effort has been made to characterize recycled construction and demolition waste blocks (RCDW) for their thermal properties. The aim of this work was to characterize the RCDW thermal resistance and conductivity in order to provide subsidies for a building's thermal performance analysis. The hot-box method was adapted, together with measuring techniques with a heat-flow meter to determine the RCDW thermal properties. The results indicated that the RCDW block overall thermal resistance and thermal conductivity in the solid region was within the intervals of 0.33≤RT≤0.41m2KW-1 and 0.60≤l≤0.78Wm-1K-1, respectively. The lower resistance and conductivity values are justified by the presence of aggregate with a lower density and lower thermal conductivity than the natural aggregate.

Resumo em Inglês:

Abstract On August 14, 1967, the reporter Saulo Gomes, working at TV Tupi, went to a small city in the State of São Paulo called Buritizal to investigate reports of a meteorite fall and write a newspaper report. He actually recovered three fragments of the meteorite at a small farm. In 2014, he donated one of the fragments to the Museu Nacional of the Universidade Federal do Rio de Janeiro (MN/UFRJ). We named this meteorite Buritizal and studied its petrology, geochemistry, magnetic properties and cathodoluminescence with the intent to determine the petrologic classification of the meteorite. In this manner, the Buritizal meteorite is classified as an ordinary chondrite LL 3.2 breccia (as indicated by lithic fragments). The meteorite consists of ~ 2% of metallic Fe,Ni and many well-defined chondrules with ~ 0.8 mm in average diameter. An ultramafic ferromagnesian mineralogy is predominant in the meteorite, represented by olivine, orthopyroxene, clinopyroxene, Fe-Ni alloy, troilite and glass. The total iron content was calculated as 20.88 wt%. Furthermore, the meteorite was classified as weathering grade W1 and shock stage S3. Buritizal is the 25th observed meteorite fall recovered in Brazil, of 70 meteorites known from Brazil. Thus, the study of the Buritizal meteorite is very important and relevant for the Brazilian scientific community.

Resumo em Inglês:

Abstract The corrosion of C-Mn steels in the presence of hydrogen sulfide (H2S) represents a significant challenge to oil production and natural gas treatment facilities. The failure mechanism induced by hydrogen-induced cracking (HIC) in a Inconel 625 coating / C-Mn steel has not been extensively investigated in the past. In the present work, an API 5CT steel was coated with In625 alloy using laser cladding and the HIC resistance of different regions, such as the coating surface, the substrate and HAZ, were evaluated. SEM observations illustrated that all HIC cracks were formed at the hard HAZ after 96h of exposure. No HIC cracks were observed in the substrate and the In625 coating after the same exposure duration. Pitting was recorded in the substrate caused by non-metallic inclusion dissolving.

Resumo em Inglês:

Abstract The thermal processing of iron ore pellets in pelletizing plants is a decisive stage regarding final product quality and knowledge of its characteristics has a fundamental importance in its process optimization. This study evaluated the variable sensitivity involved in pellet bed formations and their permeability using the artificial neural networks method. The model stated that standard diameter deviation, sphericity and pellet bed height mostly affect bed permeability. The computational model was able to predict pellet bed backpressure by means of pellet geometrical features, thus allowing improving green pellet generation, in order to ensure fuel and energy consumption reduction, final quality improvement and better productivity.

Resumo em Inglês:

Abstract The reuse of rubber waste is very important today, both to reduce the harmful effects on the environment, and to reduce the cost of new material development. Considering that most of the studies reported in literature refer to the reuse of tire waste, this article aims to evaluate the influence of styrene-butadiene-styrene (SBS) and styrene-(ethylene-butylene)-styrene grafted with maleic anhydride (SEBS-MA) compatibilizers on the blend performance of polystyrene (PS)/styrene-butadiene rubber residue (SBRr), which come from the footwear industry. The blends were prepared in a co-rotating twin screw extruder and then were molded by injection. They were analyzed by impact and tensile tests, heat deflection temperature (HDT), ductile-brittle transition temperature, dynamic mechanical thermal analysis (DMTA) and transmission electron microscopy (TEM). The results evidenced that the use of any of the compatibilizers on the PS/SBRr blend significantly increased the impact strength, while the tensile properties and HDT were lower when compared to the polymer matrix. The ductile-brittle transition temperature remains at approximately 25°C range for all the blends. In general, it has been proved that the SBS was the most effective compatibilization process in the PS/SBRr system. The DMTA test shows the presence of two distinct temperature peaks. The morphologies obtained by TEM of binary and ternary blends were quite different and typical of immiscible blend. The results show a good perspective regarding the use of industrial waste (SBRr), since it may enhance a material that would be discarded.

Resumo em Inglês:

Abstract The thermodynamic optimization of Ti-X-Si systems requires that their respective binary systems be constantly updated. The most recent assessments of the Ti-Si phase diagrams used three sublattices to describe the Ti5Si3 phase. The stable version of this phase diagram indicated the presence of Ti(β)+Ti5Si3→Ti3Si and Ti(β)→Ti(α)+Ti3Si reactions in the Ti-rich corner, while the metastable version featured the presence of a Ti(β)→Ti(α)+Ti5Si3 reaction. The present investigation assessed these phase diagrams using two sublattices to describe the Ti5Si3 phase in order to simplify the optimization of Ti-X-Si systems.

Resumo em Inglês:

Abstract Geostatistical simulation comprises a variety of techniques which can help on the decision-making process for uncertainties. They allow the uncertainty assessment of function responses (which depend on the simulated inputs) commonly through a non-linear relationship (net present value, interest tax return, geometallurgical ore recovery...). However, one of their limitations is that running the simulation can take considerable processing time to be executed in large deposits or large grids. Herein is presented an attempt to solve this problem in short-term modeling cases, via the use of Multiple Random Walk Simulation. This algorithm combines kriging with the simulation of independent random walks in order to generate simulated scenarios much faster than via traditional simulation algorithms. A case study is presented to illustrate the application of the method in an iron mine. The Multiple Random Walk Simulation models were properly built, respecting the reproduction of both histogram and variograms. Also, the speed-up was compared with standard methods of geostatistical simulation and there was a considerable speed gain with Multiple Random Walk Simulation (3.39 to 5.65 times faster than the others).

Resumo em Inglês:

Abstract In the early stage of front-end studies of a Mining Project, the global availability (i.e. number of hours a plant is available for production) and production (number of hours a plant is actually operated with material) time of the process plant are normally assumed based on the experience of the study team. Understanding and defining the availability hours at the early stages of the project are important for the future stages of the project, as drastic changes in work hours will impact the economics of the project at that stage. An innovative high-level dynamic modeling approach has been developed to assist in the rapid evaluation of assumptions made by the study team. This model incorporates systems or equipment that are commonly used in mining projects from mine to product stockyard discharge after the processing plant. It includes subsystems that will simulate all the component handling, and major process plant systems required for a mining project. The output data provided by this high-level dynamic simulation approach will enhance the confidence level of engineering carried out during the early stage of the project. This study discusses the capabilities of the approach, and a test case compared with standard techniques used in mining project front-end studies.

Resumo em Inglês:

Abstract Prior to every geostatistical estimation or simulation study there is a need for delimiting the geologic domains of the deposit, which is traditionally done manually by a geomodeler in a laborious, time consuming and subjective process. For this reason, novel techniques referred to as implicit modelling have appeared. These techniques provide algorithms that replace the manual digitization process of the traditional methods by some form of automatic procedure. This paper covers a few well established implicit methods currently available with special attention to the signed distance function methodology. A case study based on a real dataset was performed and its applicability discussed. Although it did not replace an experienced geomodeler, the method proved to be capable in creating semi-automatic geological models from the sampling data, especially in the early stages of exploration.

Resumo em Inglês:

Abstract Starches are widely used as depressant in froth flotation operations in Brazil due to their efficiency, increasing the selectivity in the inverse flotation of quartz, depressing iron ore. The starch market has been growing and improving in recent years, leading to better products attending the requirements of the mineral industry. The major source of starch used for iron ore is the cornstarch, which needs to be gelatinized, by heat or sodium hydroxide (NaOH) addition (also known as caustisized starch), prior its use. This stage has a direct impact on industrials costs, since the lower consumption of NaOH in gelatinization provides better control of the pH in the froth flotation and reduces the amount of electrolytes present in the pulp. In order to evaluate the influence of temperature on the NaOH consumption, gelatinization tests were carried out with temperatures ranging from 25 to 65 ºC, measuring the volume of NaOH. All tests were performed in triplicate. A linear model correlating the temperature and the NaOH need for the cornstarch gelatinization has been stablished. This model can allow mineral industries to optimize the NaOH amount used to prepare the depressant used in froth flotation. For example, the reduction in NaOH could easily reach 480 L per ton of cornstarch when performing gelatinization with the cornstarch solution at 35 ºC instead of 25 ºC (reduction of approximately 34% in the NaOH consumed).

Resumo em Inglês:

Abstract This article aims to review the issues to be considered in choosing primary access and transportation options for underground mines. The main accesses to underground orebodies are declines or vertical shafts. They serve both as a way to transport ore or waste, and move people, equipment or supplies. In underground mines, the ore transport option significantly affects the productivity and profitability of the company. Then, choice of access is a way to reduce costs and improve production. This study is primarily based on some case studies of Brazilian, South African, Australian and Turkish mines, among others. Literature review shows that the depth at which shaft hoisting becomes a more economically attractive alternative to decline truck haulage is changing from being previously 350 m to present 1000 m, depending on the mining country and cultural underground mine development. For some of them the depth of 1000 m would be the threshold for use of the access by decline. The main criteria in determining access are depth, rate of production and mine life. In South Africa, mines reach depths greater than 3000 m and shaft access is more common. In Australia there are mines that use a ramp (decline) to a depth greater than 1000 m. In Brazil, underground mines are still shallow (depth up to 800 m) and feature short mine life and, most of them have chosen access by decline. Results of this study corroborate the statement that decline is ideal for shallow mines and low production rates and that shaft is for deep mines, high production rate and long mine life.