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Analiza varijacija građevinskih izolacionih svojstava konstrukcija bazirana na arhivskim merenjima i proračunima
No full textZvučni komfor u zgradama jedan je od elemenata ukupnog komfora koji treba
zadovoljiti. Zbog specifične prirode zvuka i njegove percepcije zvučni komfor je u
subjektivnom smislu kvalitet koji čovek boravkom u zgradi najdirektnije percipira. S druge
strane, povećanje izolacionih svojstava pregradnih konstrukcija uvodi ograničenja u izboru
materijala i vodi ka promenama u ceni koštanja ili tehnologiji gradnje. Pod pritiskom takve
realnosti u projektovanju se, po pravilu, ne uzima nikakva margina sigurnosti za izolacionu
moć pregrada, već se usvajaju minimalne vrednosti da bi se pokazalo da je zvučni komfor
obezbeđen. Posledica toga je da veliki broj zgrada izgrađenih u poslednjoj deceniji ima
nedovoljnu zvučnu zaštitu. Da bi se ovaj problem sagledao sprovedena je analiza bazirana na
poređenju rezultata merenja u realnim zgradama i na njihovim proračunima. Izmerene
vrednosti preuzete su iz arhive Instituta za ispitivanje materijala u Beogradu i Laboratorije za
akustiku Elektrotehničkog fakulteta u Beogradu. Rezultati koji su korišćeni u ovoj analizi
odnose se na tavanice od armiranog betona debljine 14-16 cm u stambenim i poslovnim
zgradama građenim u periodu 1979-1990. godine
Use of iron ore tailings for production of concrete paving blocks
No full textThe possibility of using tailings from the iron mine (IOT) in the production of concrete elements for the pedestrian areas is shown in this paper. To determine the impact of the amount of tailings on the compressive strength of concrete, samples with varying percentage of replacement of aggregate fractions were made. Based on the testing results it was assumed that it is possible to produce the concrete elements with tailings from iron mine as concrete component. The results show that partial replacing natural aggregate with IOT produces concrete elements which meet the requirements of EN 1338
Reparation of damaged sleeves and welded shield sections of guide vanes at hydropower plant Djerdap 1
No full textHybrid Vapor-Solution Sequentially Deposited Mixed-Halide Perovskite Solar Cells
No full textThe recent sky-rocketing performance of perovskite
solar cells has triggered a strong interest in further upgrading the
fabrication techniques to meet the scalability requirements of the
photovoltaic industry. The integration of vapor deposition into the
solution process in a sequential fashion can boost the uniformity
and reproducibility of the perovskite solar cells. In addition, mixedhalide
perovskites have exhibited outstanding crystallinity and
higher stability compared with iodide-only perovskite. An extensive
study was carried out to identify a reproducible process leading to
highly crystalline perovskite films that, when integrated into solar
cells, exhibited a high power conversion efficiency (max. 19.8%).
This was achieved by optimizing the deposition rate of the PbI2
layer and by inserting small amounts of methylammonium (MA) bromide and chloride salts to the primary MAI salt in the solutionbased
conversion step. The optimum MABr/MAI molar ratio leading to the most efficient and stable solar cells was found to be 0.4.
Stabilities were in excess of 90 h for p-i-n type solar cells. This reproducible approach toward the fabrication of triple halide
perovskites using a hybrid vapor-solution method is a promising method toward scalable production techniques
Optimization of adobe clay bricks based on the raw material properties (mathematical analysis)
No full textThis research studies the effects of composition and granulometry analysis of 139 heavy clays on the important characteristics of wet and adobe clay bricks. ANN models were obtained with high prediction accuracy in training cycles (r(2)): 0.580-0.907. Standard score analysis (SS) is performed to evaluate the optimal content of raw materials to gain adobe bricks. Optimal macro-oxides content was 53-66% SiO2, 4.6-7.5% Fe2O3, 12.5-18.2% Al2O3, 0.9-8.8% CaO, 1.2-3.6% MgO. The optimal quantity of alevrolite-sized particles varied between 46 and 65%, and clay-sized particles contents ranged from 20.4 to 40.6%
Bucket wheel excavators_Dynamic response as a criterion for validation of the total number of buckets
Get PDFAn original method for validation of the number of buckets on the working device of a bucket wheel excavator based on the dynamic response of its slewing superstructure (SS) is presented. A set of 16 seemingly acceptable solutions which satisfied the rigid design restrictions, based on the preservation of the existing (a) bucket wheel drivetrain, (b) theoretical capacity, (c) characteristics of the excavated soil and (d) position of the superstructure centre of gravity (CoG), was analysed. Already on the basis of the limiting vertical and lateral accelerations of the bucket wheel centre, which represents a well-grounded indicator of its dynamic behaviour prescribed by the code
DIN 22261-2, 14 out of 16 analysed design variants have been discarded, reducing the set of possible solutions to only two – the originally-designed variant (with 17 buckets), and the variant with 20 buckets. Conclusions on the validity of these two design variants were derived on the basis of the dynamic response analysis of the referent points of the SS. The analysis of the impact of soiling on the dynamic response of the SS has shown that negative dynamic effects, observed in the preceding analysis of the originally-designed solution, increase with the amount
of the adhered material. Although the redesigned variant with 20 buckets has proven as the only suitable solution from the standpoint of dynamic behaviour of the SS, the results have to be assessed carefully due to the fact that the reduction of the mass of the bucket wheel steel structure by more than 14% leads to the appearance of unfavourable dynamic effects, even though the SS CoG position is preserved
Determination of the Pile Stiffness Matrix Based on the Pile Load Test Results and the Effect of Pile Interaction
Get PDFThe paper presents the determination of the elements of the pile stiffness matrix based on pile load test results, made for the needs of modernization of oil refinery for NIS in Pancevo. The tests were carried out on CFA and Franki piles system. However, only the results for CFA piles are shown in this paper. Load tests included axial, tension and horizontal loading. Bearing in mind the geomechanical composition of the terrain and the results of penetration testing (CPT), it has been concluded that the soil resistance can be approximated as a linear function by depth. By approximating the soil by the Winkler model and using the results of the horizontal pile load test, the equivalent gradient of the modulus of soil reaction for the work load level is determined analytically, and then, the pile flexibility coefficients for horizontal load. For vertical load, the coefficient of flexibility is determined directly on the basis of the load-settlement curve. Based on the flexibility coefficient, a matrix of flexibility and a stiffness matrix are determined. The effect of the pile interaction for horizontal and vertical loads was introduced in an approximate way, through the reduction of coefficients of the stiffness matrix. The entire process of determining the stiffness matrix of the pile is illustrated by practical example of a pile group connected by an ideal rigid cap
Has the latest global financial crisis changed the way road public-private partnerships are funded? A comparison of Europe and Latin America
No full textA financial/economic crisis may have an adverse effect on transport public-private partnerships (PPPs) as both traffic demand is negatively influenced, and governments are further under pressure. However, research on awarded road PPP contracts over a 20-year period in the European Union (EU) and Latin America and the Caribbean (LAC) showed that the market slowdown is brief and followed by a re-bounce leading to an overall upward trend. The LAC region has experienced multiple financial setbacks with no significant change in the PPP market structure as opposed to the EU, where significant changes were observed concerning a shift in the remuneration schemes employed
Condition assessment of concrete structures using ground penetrating radar (GPR)
No full textMaintenance costs of concrete structures can be reduced by efficient and extensive condition assessment. Rapid technological development has allowed application of innovative methodologies for the inspection of structures, which has in turn increased precision and efficiency of inspection activities. Potential for using ground-penetrating radar in the assessment of concrete structures has been considered for a long time and, with the improvement of the analysis tools, its application has been constantly increasing. Ground-penetrating radar is a technique based on emission of electromagnetic waves into the material, and on analysis of reflected waves, resulting in information about location and properties of a particular object. GPR is used for assessing condition of concrete structures, i.e. for the localization of reinforcement, determination of concrete cover, and localization of delamination. Recent research has shown that GPR data could be used for assessing corrosion of reinforcement. Following literature results on GPR-based study of concrete condition, main principles of GPR use are outlined in the paper
HSLA Steel - Simulation of Fatigue
No full textIn present paper, based on the results of the experimental study of the behaviour of the samples made of a HSLA steel, in the form of round smooth specimens (RSS) under LCF conditions (with controlled and completely reversible strain Δε/2 = const, Rε = εmin/εmax = −1, according to ISO 12106: 2003 (E)) and square specimens (SqS) under conditions of HCF conditions (with controlled one-way variable load on tension with σmin = const, according to ISO 12110-1:2013), a computational stress analysis was performed using the FE method and the behaviour of this steel in the fatigue behaviour simulation (LCF and HCF) in SolidWorks programme was shown. On the basis of the performed analysis of the results of the stress-strain state and the determination of the life using the life isolines for a particular load cycle involving the entire RSS ligament, i.e. SqS for a particular load in a wide range of LCF and HCF loads and comparison with the results of experimental tests, a figure i.e. graphical presentation was given and conclusions were drawn that justify the efforts for numerical assessment of the life cycle of the loaded machine parts