Abstract in English:Abstract A two-dimensional interface finite element capable of associating flat shell elements positioned one above the other was developed. The implemented interface element can physically simulate the contact between the flat shell elements and connect the reference planes of the shell elements above and below it. The formulation presented allows consideration of nonlinear behavior for the deformable connection as well as for the concrete and steel materials that make up the shell structure. One of the practical applications analyzed in this research is the numerical simulation of composite floors formed by a reinforced concrete slab connected to steel beams through a deformable connection. In this case, the concrete slab and the steel beams are discretized by flat shell elements and the deformable connection is discretized by two-dimensional interface elements. Experimental and numerical results from literature were used to validate the implemented elements. In the two examples analyzed, the results obtained for the displacements were close, with the difference, in the first case, being associated with uncertainties during the experimental test and in the second, the difference in theories used in the formulation of the implemented elements.
Abstract in English:Abstract The Expander Body pile (EB) is a combination of a cast-in-situ pile method with an inflated, pump-grouted tip. The EB system's pioneering conjunction with the conventional drilling pile technique has improved work load, foundation security, cost reductions and abrupt displacements in lateritic, porous, unsaturated soils. The aim of this article is to analyze settlement estimates of bored piles equipped with the Expander Body System on tropical lateritic soil, using a deformability modulus obtained from laboratory and field tests. The piles were subjected to compression and uplift load tests. In addition, the estimates of the pile settlement are compared with the measured values, and the findings are discussed. The results strongly support that PMT and SPT tests present the optimal ratios between the measured and estimated settlements for both bored piles and bored piles with the Expander Body System. It can also be observed that CPT tests presented reasonable estimates for tensioned piles. Ultimately, it is verified that straightforward elastic models for the settlement assessment of bored piles can be used reliably in practice for piles equipped with the Expander Body System on tropical unsaturated soils.
Abstract in English:Abstract The present research aims to do a numerical study on the behavior of a test embankment reinforced with stone column spacing of 1.85 m in a square grid with an average diameter of 1.0 m and 11.35 m length. The case study investigated the work in a steel company (ThyssenKrupp), located in Santa Cruz, western region of Rio de Janeiro - Brazil, where a large-sized ore yard was built for loading and unloading activities. It was built on very soft and compressible clay with support of several equipment installed to monitor the area. These data were compared with plane strain analysis results of vertical displacement, horizontal displacement and excess pore pressure obtained by two finite element programs: PLAXIS and RS² (Rocsience). Results showed that Mohr Coulomb model predicted well vertical displacement comparing with a Cam-Clay model and the instrumentation data. Simulated curves of excess pore pressure and horizontal displacement presented expected peculiarities that are interpreted throughout the article. Numerical analysis of yielding columns demonstrate compatibility between both models.
Abstract in English:Abstract The installation of solar parks requires extensive areas and results in soil erosion in many cases. One suitable solution is applying lime to improve soil characteristics, such as mechanical strength, stability, workability, durability, and internal and surface erosion resistance. This soil treatment is of particular importance when dealing with hydraulic structures conceived in the solar park drainage systems. The erodibility tests were performed in a solar complex soil in an EFA apparatus constructed to measure the erosion rate of cohesive and non-cohesive soils in different flow rates. The tests were performed with or without 3% lime addition and two compaction conditions. The experiments indicated that the erodibility of lime-treated soils represents between 26% and 12% of the values obtained from untreated soils and under reduced compaction. The values ranged from 16% to 7% for controlled compaction. The results represent a significant reduction in the soil erodibility treated with lime even with reduced compaction, performing an efficient, economical, and sustainable solution for erosion control.
Abstract in English:Abstract The Direct Strength Method (DSM) is a well-known formulation presented in the Brazilian standard ABNT NBR 14762:2010, that estimates the strength capacity of cold-formed steel (CFS) members. However, this formulation requires the elastic critical buckling loads as point of departure, regarding local (L), distortional (D) and global (G) modes, which can be obtained by (i) elastic buckling analysis or (ii) available direct equations. The present study is dedicated to the development of a computer program, FStr Computer Application, with graphical user interface (GUI), in order to make the buckling analysis easier and approachable for both research activities and engineering design of thin-walled structures with arbitrary cross-sections (sections combining closed cells with open branches). The proposed application uses the Finite Strip Method (FSM), mainly focused on a simple and accessible GUI, which was implemented in the MATLAB App Designer. Validation of the FStr was performed with the help of examples of open and closed cross-sections and comparison with the results of acknowledged computer programs, such as CUFSM and GBTul, based respectively on FSM and GBT (Generalized Beam Theory), as well as analytical procedures for the case of the global buckling modes. Both, the critical buckling loads expressed by the computed signature curve and the correspondent critical buckling modes are compared, confirming the adequate performance of the proposed computational tool. As future research, the authors plan updates for the FStr Computer Application, including the computation of the buckling modal participation and the automatic strength predictions, based on the DSM-based design prescriptions.
Abstract in English:Abstract Contemporary organizations are showing a growing interest in the reuse of solid waste from industrial processes with the intention of reducing environmental impacts and reducing costs. The mining activity is one of the main waste generators in Brazil. In parallel, geopolymeric materials have been gaining prominence in studies that make it a possible substitute for ordinary Portland cement, due to its environmental advantages. Therefore, the present research proposes to study the feasibility of using K-feldspar mining waste as a possible raw material for the manufacture of geopolymer cements. In addition, in line with the latest technological trends, the addition of multi-layered graphene was evaluated as a structural reinforcement for geopolymeric mortar. Graphene was added in three percentages: 0.1 wt.%, 0.3 wt.% and 0.5 wt.%. Specimens were produced in order to evaluate the compressive strength of these materials. As a complementary characterization, the analysis of EDX, laser diffraction particle size and XRD of the waste were performed, as well as SEM and TEM analysis of the graphene used. The results showed that the geopolimerization was effective and that the 0.5% graphene content promoted a significant increase of 65% in the compressive strength. It is concluded, therefore, that with the achieved mechanical strength values, the studied waste can be applied as mortar in auxiliary structures using the geopolymerization technique and that graphene can be used to promote increases in the mechanical strength of the material produced.
Abstract in English:Abstract The aim of this study is to assess the floatability of hematite using a crude biosurfactant (BS) extracted from Rhodococcus opacus. Throughout high-pressure ethanol extraction, unrefined surfactant was extracted from the bacteria with a yield of 0.3 g/L. An FTIR analysis on this extract, shows the presence of alcohol (–OH) and ketone (C=O) groups, as well as saturated and unsaturated carbon chains, which might originate from mycolates and trehalolipids moieties reported in literature. In addition, FTIR analysis on the modified mineral surface with the unrefined surfactant, confirms a strong interaction between hematite and the crude biosurfactant, showing similar vibrational peaks regarding the hydroxyl and carboxylate groups at 1631 and 3436 cm-1, respectively. Biosurfactant interaction with the mineral particles shifted the isoelectric point from 7.5 to 3.2, turning the hematite more hydrophobic in acidic environments. Surface tension measurements indicate that the unrefined surfactant is slightly more effective, decreasing the surface tension of water compared to the bacteria itself, with a variation of 4 mM/m. Finally, throughout microflotation tests in a Hallimond tube, it is shown that the surfactant doubles bacteria recovery efficiency, reaching a maximum recovery of around 95 % in acidic conditions, which is consistent with electrophoretic studies. The statistical models adjust well the experimental data, achieving R2 values of 93.6 and 91.1% for the hematite flotation using the biomass and the biosurfactant, respectively.
Abstract in English:Abstract In the present study, microflotation experiments were performed on pure minerals systems involving hematite and quartz in the presence of etherdiamine as collector. The influence of polyacrylamides as co-depressant was investigated in a blend with starch depressant. The results obtained demonstrated that all the polyacrylamides used were efficient in hematite depression, at different levels and following the order of effectiveness: cationic > non-ionic > anionic. The depressant power was proportional to the degree of ionicity and the molecular weight. It is proposed that the enhanced performance is due to the presence of two functional groups, the cationic group adsorbing by electrostatic interaction and the amide group –C(=O)NH2 adsorbing by hydrogen bonding. Non-ionic polyacrylamides indicated similar performances for different molecular weights and the proposed adsorption mechanism is hydrogen bonding associated with the amide group. Electrostatic repulsion did not have deleterious action on the adsorption of anionic polymers on hematite, nevertheless the adsorption on quartz was impaired. Polyacrylamides adsorb on quartz, although at a weaker intensity than on hematite.
Abstract in English:Abstract Adsorption of microorganisms and/or their different components onto a mineral surface would modify the surface characteristics of the mineral. Thus, this investigation evaluated the adsorption capacity of the Rhodococcus opacus strain onto an apatite surface. Zeta potential and contact angle measurements of the mineral showed dislocations of the values after interaction with the microorganism. The maximum adsorption density reached was 24.10 mg of bacterial cells per gram of mineral using a biomass concentration of 400 mg/L. The experimental data were linearly fitted by the Freundlich model and the adsorption density as a function of time was linearly fitted by the pseudo-second order kinetic equation. The results showed that the bacterial strain has affinity for the apatite surface and ability to make it hydrophobic.
Abstract in English:Abstract Checking and treating extreme values is commonplace in modelling workflows. The main methods to manage outliers may be categorized into graphical, Kriging- and simulation-based approaches. While graphical methods usually classify outliers from a global perspective, geostatistical methods evaluate outliers in a local context. Ordinary-Kriging based approaches are affected by conditional bias associated with the distribution tail(s), impacting on the correct classification of extreme values; the simulation method is based on the fact that geostatistical simulation is robust for outlier values. However, this approach ignores the interaction among outliers in the same neighborhood. The proposed approach considers that there are two values available at every sampled position, the sampled value and the conditional probability estimated from nearby data through cross-validation; the sampled value. Each value outside the user-defined threshold is classified as an outlier and is edited by merging the sampled and kriged value through Bayesian Updating. The proposed method is performed in normal-score units using Simple Kriging to (i) correctly estimate conditional distributions in the cross-validation step; (ii) avoid conditional bias; and (iii) minimize the outlier influence on experimental-variogram modelling. The proposed method is compared to three other widely used methods in a case study of a gold deposit. The proposed method substantially improved the local accuracy and reduced the number of misclassified blocks of a reference model.
Abstract in English:Abstract A bench scale study was carried out to investigate the influence of polyacrylamides as co-depressant in a blend with starch depressant on the reverse cationic iron ore flotation. The results indicated that the use of polyacrylamides as dual function polymer should be an alternative to improve the flotation process. These polymers act as a depressant and flocculant reagent, decreasing the mechanical entrainment of hydrophilic iron minerals, forming hydrophobic aggregates. Also, the use of polymers as a co-depressant could prevent the possibility of clathrate formation caused by starch and amine overdose. The results obtained showed that cationic and non-ionic polyacrylamides improve the selectivity when applied at low dosages. Only the slightly charged anionic polyacrylamide yielded good results in flotation tests. The design of experiments carried out with non-ionic polyacrylamides showed that flotation results was were affected by the physico-chemical conditions of the system, such as pH, flocculant molecular weight and amine type.