Contribution to the solution of the stability problem of the double layered catenary systems

The paper is theoretical and practical. The double layered catenary systems are elastic suspended structures aimed at bridging great spans. Under the action of external load, these systems are prone to swinging, so the basic problem is making them stable for the potential combinations of real loads. The most efficient and most applied way of stabilization of double layered catenary systems is prestressing. The paper lays out the basic notions, history and the theoretical and practical achievements to the present times in the field of the suspended prestressed systems, and the contribution to the solving the stability problem of double layered and prestressed catenary systems. The conducted research and analysis, unequivocally demonstrate the practical results of the solution of stability problem of cable truss. The contribution to the stability problem is comprised in conclusions, which are derived from the author’s research: - Analytical-numerical model of static design - Criteria of dynamic stability of suspended structures - Analysis of defined models type “D” and “V” by the criteria of dynamic stability and the recommendations for the minimum levels of their prestressing. - Constituting the methodology of the best design of cable truss. - Definition of wind as a harmonic and impact action on the suspended structures. Key words: suspended structures, cable truss, prestressing, stability, dynamic wind actio

Tensile Membrane Structure Forces Dependence on Different Parameters Under Point Load Action

Point load actions may have a significant impact on deflections of tensile membrane structures. Research presented in this paper is aimed at exploring the effects of point load actions on membrane forces of tensile membrane structures. Therefore, three different parameters of the structure were varied, and the membrane forces resulting from point loads were monitored. Variable parameters are the height of the model, the intensity of prestressing forces, and the orientation of the membrane material. The research was done on models in specialized software. In order to evaluate the significance of point load effects, membrane forces were compared to those under snow load. The results of the research show the layout of membrane forces under point load and dependence of maximal membrane forces on the varied parameters. Specific sets of analyzed parameters lead to significant values of maximal membrane forces under point load actionKoncentrisane sile mogu da izazivaju znatne ugibe zategnutih membranskih konstrukcija. Istraživanje predstavljeno u ovom radu bavi se efektima dejstva koncentrisane sile na sile zatezanja membranskih konstrukcija. Kako bi se ovi efekti ispitali, varirana su tri parametra konstrukcije, a praćene su sile zatezanja izazvane dejstvom koncetrisane sile. Varirani parametri jesu visina modela, intenzitet sila prednaprezanja i orijentacija membranskog materijala. Istraživanje je sprovedeno na modelima formiranim u specijalizovanom softveru. Kako bi se ocenio značaj efekata dejstva koncentrisane sile, rezultujuće sile zatezanja upoređene su sa silama zatezanja pod dejstvom opterećenja od snega. Rezultati istraživanja pokazuju raspored intenziteta sila zatezanja u membrani pod dejstvom koncentrisane sile i zavisnost maksimalnih sila zatezanja od ispitivanih parametara. Pri određenim kombinacijama ispitivanih parametara, koncentrisana sila izaziva vrlo značajne sile zatezanja

Symbiosis of intermodal terminals and free zones

Globalism is entering a new phase that creates space for regional investments. The trend of offshoring is beginning to weaken and trend of nearshoring investments are increasing. Jobs and new investments are returning to regions, neighboring countries and parent companies. The new course of development requires the need for spaces where investors will receive customs and tax benefits with a greater need for efficient logistics. Free zones, which offer facilities for investment and business, will have to pay more attention to efficient logistics. The benefits of infrastructure-equipped land, exemptions from paying customs duties and taxes with built-in capacities for intermodal transport, along with other state support measures, will additionally make certain locations attractive for investors. The paper proposed a model of symbiosis of logistics centers and free zones, as well as analyzed instruments that should be used in order to create efficient centers that enable savings in business for future investors

Analysis of Strengthening Variants of Existing Masonry Buildings for Seismic Resistance - Case Studies of Typical Residential Buildings in Niš

The revitalization of existing masonry buildings, built decades ago, is a very topical and complex structural engineering issue, especially when the building was built in the area of significant seismic activity. A large number of masonry buildings in the city of Niš, as well as in other places in Serbia, were built in the period before the adoption of technical regulations on the design and construction of seismically resistant structures and they are at insufficient safety level in the event of an earthquake. Therefore, it is necessary that structural strengthening meets the seismic resistance requirements laid down in Eurocode 8 or other relevant codes. In order to choose the method of structural strengthening, detailed seismic analyses must be carried out in several variants along with the application of relevant technical regulations. The effects of five analyzed structural strengthening methods were checked against the provisions of Eurocode 8, Part 1 and Part 3, which relate to the recommendations for the geometric characteristics of shear walls, and they were applied on two types of existing masonry buildings in Niš. On the basis of the performed analyses, conclusions were drawn regarding the methodological approach of the assessment of the condition of the structure, its seismic resistance and decision-making on remediation and/or strengthening measures

DESIGN OF ATYPICAL FACADE ARCHITECTURAL ELEMENTS AS NOISE REDUCTION BARRIERS - CASE STUDY

The presented work is the result of affirmation of synergistic work of experts dealing with architectural and acoustic design with the aim and purpose of finding an adequate solution for optimal correction of the effect of GHG systems installed on the facade of the subject (case study) office building in Belgrade. Measurements established that the noise of the constructed GHG systems affected the residential building in the immediate vicinity. The effect of the constructed devices (refers to the installed units) of the office building in question in the case when they operate at full capacity was measuring to be about 58 dB (A). The urban zone in which the building is located (Vracar-Belgrade) belongs to the category of "office-residential area" in which the outdoor noise level permitted for the period of day is 60 dB (A), and for the night period is 50 dB (A). Taking into account the stated facts, it has been unequivocally established that GHG systems to a certain extent exceed the permitted noise levels and "endanger" the neighboring observed building. The subject of this professional-scientific research is the design of atypical facade architectural elements as a barrier reducing noise on the example of an office building in Belgrade. The architectural challenge was reflected in the fact that, in addition to designing the facade element which, at the request of the investor must not compromise the architecture of the building, therefore, should be "atypical in architectural design", it must also provide flexibility in applying different variants of acoustic barriers, which in addition to architectonic requirement must provide an adequate response to acoustic requirements. To the satisfaction of the authors, the designed barrier confirmed a successful synergy solution. The adopted architectural-acoustic configuration of the barrier proved to be effective regardless of the type of installed air conditioners, which in some way justifies the initial idea of strong causality of acoustic and architectural design, as a synergistic principle

The Processes of Globalization and Modern Agriculture - Sociological and Economic Aspects

The authors examine current problems of agriculture, the reasons that led to the devastation of the village and the essence of comparative advantage as a prerequisite for the preservation of the monopoly of multinational companies. A particular subject of interest was the hegemony of global corporations and the problem of sustainable development in agriculture. The decline of agriculture and rural areas in developing countries are problems that allow us to draw a certain analogy with Swadeshi, as a philosophy that has preserved Indian village. Developing countries are mostly economically dependent. The land and the villages are devastated. The solution to the problem should be compatibility of the sustainable development and the economic growth, which corresponds to the morals of Swadeshi

ECB monetary policy during Covid-19

This paper aims to point out the monetary policy measures that the European Central Bank has taken since the outbreak of the COVID-19 crisis. In the euro zone, at the start of the COVID-19 crisis, financial conditions deteriorated sharply, potentially threatening to worsen the economic outlook, deepen market fragmentation, jeopardize monetary policy transmission, encourage a downward inflationary trajectory, weaken prices and undermine public and private stability. Aware of the new situation of the ECB, it responded quickly and efficiently with coordinated and ambitious measures to alleviate the perceived financial and economic difficulties. To maintain a flexible monetary policy stance, the ECB adopted an interim non-standard measured COVID-19 Asset Purchase Program (PEPP) to mitigate and improve financial conditions and restart an earlier Asset Purchase Program (APP) aimed at inflation expectations. At the same time, other measures have been strengthened and expanded, such as Targeted Long-Term Refinancing Operations (LTROs, TLTRO III, and PLTRO) aimed at providing liquidity ampleness to the real sector and collateral standards. The implementation of the adopted measures has influenced the stabilization of the economic and financial system of the EU and improved lending to corporate and household banks

THE CHOICE OF SUITABLE FREQUENCIES FOR MEASUREMENTS BASED ON FSM

The measurements which are related to the high-voltage substation grounding system are inevitably affected by electromagnetic interference caused by power frequency and its harmonics. In order to avoid the problem due to interferers, traditional measurements are based on heavy test current injection. In most cases this approach is impractical. In this paper, we evaluate experimentally an effective method for eliminating the effect of interference at power frequency. This approach based on test signal at three frequencies, is slightly different from the power frequency. For that matter, there are two problems: 1. How to choose adequate set of test frequencies, and 2. How to determine optimal intensity of the test current. In this paper, we solve the mentioned problems based on the results of extensive field test measurements at substations 110/X kV, 220/X kV and 400/X kV. We show that the set of suitable test frequencies are: 40 Hz, 60 Hz and 75 Hz. Also shown is a method for finding the optimal intensity of the test current

Improving the Operational Reliability Model of the “Nikola Tesla-Block A” Thermal Power Plant System by Applying an Integrated Maintenance Model

The evaluation of the reliability status of complex technical systems is of great importance for their uninterrupted operation at full capacity and with a preventive maintenance plan in place. Limited research on the subject indicates that there is need to improve models of reliability simulation. The goal of the paper is to outline an improved operational reliability model of a thermal power plant using the power plant block “TENT A” as an example. The model is based on the failure interaction of the system components and is based on probability theory - the Weibull distribution, the Monte Carlo simulation and the established mathematical models of failure interaction of components using new software solutions. The results of the simulations show which direction the development of preventive activities should take in the case of failure interaction, which might lead to minimum downtime in power plant operations in the future

Forest Fire Probability Mapping in Eastern Serbia: Logistic Regression versus Random Forest Method

Forest fire risk has increased globally during the previous decades. The Mediterranean region is traditionally the most at risk in Europe, but continental countries like Serbia have experienced significant economic and ecological losses due to forest fires. To prevent damage to forests and infrastructure, alongside other societal losses, it is necessary to create an effective protection system against fire, which minimizes the harmful effects. Forest fire probability mapping, as one of the basic tools in risk management, allows the allocation of resources for fire suppression, within a fire season, from zones with a lower risk to those under higher threat. Logistic regression (LR) has been used as a standard procedure in forest fire probability mapping, but in the last decade, machine learning methods such as fandom forest (RF) have become more frequent. The main goals in this study were to (i) determine the main explanatory variables for forest fire occurrence for both models, LR and RF, and (ii) map the probability of forest fire occurrence in Eastern Serbia based on LR and RF. The most important variable was drought code, followed by different anthropogenic features depending on the type of the model. The RF models demonstrated better overall predictive ability than LR models. The map produced may increase firefighting efficiency due to the early detection of forest fire and enable resources to be allocated in the eastern part of Serbia, which covers more than one-third of the country's area