Ljiljana Brajovic

University of Belgrade · Institute of Mathematics, Physics, Descriptive Geometry and Social Sciences

This paper presents research aiming to establish the relationship between track stiffness and the appearance and development of squat defects on running rails. Uneven incidence of squat defects was observed on the rails of the investigated main transit track in arailway station. Inspection of track support conditions was conducted using an electrom...

The interaction between the wheel and the running rails within the railway system introduces intricate stress patterns, resulting in the formation of rolling contact fatigue (RCF) rail defects. The magnitude of this stress is contingent upon factors such as track performance, vehicle characteristics, and service conditions. While advancements in ra...

The commercial multi-mode optical fiber was coated with magnetic composite material prepared using Nd-Fe-B permanent magnet powder dispersed in poly (ethylene-co-vinyl acetate)-EVA. Characterization of microstructure, thermal stability and mechanical properties of the composite coatings with different Nd-Fe-B powder content were performed using Sca...

Abstract— Pearson’s and Spearman’s methods are most often used in popular software packages to calculate the correlation coefficient between two variables in natural sciences. The difference between them is that the Pearson’s method takes actual numerical values into account whereas the Spearman’s operates with their ranks. Ranking is often efficie...

Open pit coal mining affects surrounding populated areas, resulting in terrain surface deformation. Surface deformation should be monitored as often as possible to control deformations and prevent potential incidents. This paper analyzes time series deformation estimated from the Sentinel-1 satellite images using the Persistent Scatterer Interferom...

Višefrekvencijski GNSS satelitski signali i njihova dostupnost omogućavaju istraživanja u nediferenciranom i nekombinovanom modelu u kome je pojedinačni signal na svakoj frekvenciji odgovarajuće nezavisno opažanje. Ovakve mogućnosti izazivaju veliko interesovanje ne samo u geodetskim istraživanjima već i u mnogim oblastima primene GNSS opažanja. Na...

Rail inspection research is a substantive topic for the railway industry. Management of rolling contact fatigue rail defects is crucial for transport safety worldwide because uncontrolled development of these defects could cause railway accidents, including derailments. This paper presents the review of non-destructive inspection methods for surfac...

The paper presents a brief review of the rail defect coding systems, which were recommended by the International Union of Railways during the period from 1959 to today. The recommended classification and numbering of RCF rail defects, defined in the document IRS 70712 from 2018, were critically analysed. In addition, harmonisation of European stand...

In this paper, the possibility of applying Kirchhoff 's scalar approximation model for determining the backscattering coefficient from rough surfaces is investigated. Surfaces of dielectric and metallic materials, which have low roughness are considered. Based on the roughness parameters and electrical properties of these materials, the backscatter...

The main aim of conducted research is determination of temperature stresses due to the uneven temperature distribution in CWR. This paper presents a methodology for determination of temperature stresses in CWR based on (1) measurement system developed by the authors for measurement of rail surface temperatures, and (2) coupled transient thermal-str...

Imperial hegemony established by the Habsburg Monarchy relied upon proper mapping during its conquests. The need for the development of geodesy and establishing reference frames was important. Until the end of the First World War, Vojvodina belonged to the Austrian-Hungarian Empire, so all of its surveys were carried out as part of many organized l...

Rail defects due to the rolling contact fatigue have a significant place in the Handbook of Rail Defects in the framework of UIC Code 712 in 2002. The paper presents the system for coding and classification of rail defects according to UIC recommendation IRS 70712 in 2018. The presented classification does not cover all known defects due to the rol...

The railway track with continuously welded rails is an essential part of the modern railway superstructure around the world. Calculation of the temperature stresses in continuously welded rails has great significance for the planning of maintenance activities in order to maintain traffic safety (risk of derailment due to either rail break, or track...

Continuously welded rails are a part of the track structure since the 1950s. Total stresses in continuously welded rails include residual stresses generated during the manufacturing process as well as the service life of rails. The control of rail stresses is very important for traffic safety. Measurement methods for residual stress in rails are pr...

Based on the railway network performance, Infrastructure Manager is obligated to define the Maintenance plan for railway infrastructure, which contains corresponding values for intervention limits and alert limits. This paper considers vehicle response to track excitation due to the rail defect (code 2202 according to defect classification). It is...

The composite nanofibers were used as reinforcement in acrylic polymer for the overall enhancement of thermo-mechanical properties, adhesion between fibers and matrix, and fracture toughness of the final nanocomposite since acrylic materials lack of this feature. So, a good balance between hardness/toughness and transparency is obtained with the ad...

This paper presents a development of statistical predictive model for relative horizontal displacements of "Vrutci" dam in function of air temperature and reservoir water level, as reversible effects and in function of time passed since the beginning of dam exploitation, which takes irreversible effects into account. Some parts of technical monitor...

This paper proposes a methodology for statistical analysis of data obtained by visual inspection of squat defects on the rail head. Rail inspection by visual observation, including measurement of the squat defect position and depth was performed in Pančevo Varoš railway station in 2017. The obtained data about the squat rail defect (defect type 227...

The residual stresses in rails are generated during the manufacturing process and have uneven distribution in rail cross section. The residual stress is a part of basic tensile stress in rail foot. For used rail, the residual stress value of 80 MPa is commonly used in the engineering calculations. On the other hand, the standard EN 13674 prescribes...

Track stiffness is a parameter which significantly influences to the track geometry deterioration, rail fatigue and deterioration of other superstructure and substructure components during the track service life. Track stiffness measurement has great theoretical and practical importance for the design of new railway lines, as well as for upgrade an...

U radu je opisano ispitivanje sinhronizovanosti podataka koji su uzorkovani putem odvojenih MEMS akcelerometara. Korišceni su bežicni senzorski uredaji razvijeni na Gradevinskom fakultetu u Beogradu, namenjeni merenju vibracija gradevinskih objekata. Poznato je da ovi uredaji mogu da postignu tacnost vremenskog oznacavanja uzoraka reda velicine 10...

Cross-axial or transverse sensitivity of an accelerometer can be compensated by digital processing of the output signal. To perform this, it is necessary to determine coefficients that describe a sensor’s response to excitation experimentally. Many procedures advised by standards and scientific papers use expensive equipment which is not available...

Bismuth germanium oxide Bi12GeO20 (BGO) has very interesting electrical, optical and magnetic properties. In order to make devices based on this material more flexible, its powder was used for preparing polymer composites. This study reports investigation of the effects of using different solvents and polymers in preparation of BGO composite on the...

Historically, both words ”geometry” and “geodesy” refer to the measurement of land. Although geometry became part of mathematics who studies the properties and mutual relations of figures, its principles stayed grate part of geodesy through geometrical methods of measurement and working principle of geodetic instruments. The majority of geodetic in...

In this paper, the use of intrinsic intensity fiber-optic sensors for structural health monitoring was investigated. Polyethylene-based composite samples with glass mat reinforcement and embedded telecommunication fibers were subjected to impact using high-speed puncture impact tester as a calibration device. Transfer function of the sensor was gen...

A lossless compression scheme for the data acquired from three-axial microelectromechanical (MEMS) accelerometer is presented. Time delay estimation (TDE) was applied in conjunction with differential pulse code modulation (DPCM) as the preprocessor to entropy coding, to perform lossless compression on an embedded sensor device with limited memory a...

Control of railway noise is very significant part of the urban traffic policy. An increase of railway noise could significantly reduce the quality of life of citizens. This paper analyzes and suggests necessary measures for managing railway noise and traffic safety by rail inspection and grinding. It considers and suggests inspection methods for ea...

The commercial multi-mode optical fiber was coated with magnetic composite material prepared using Nd-Fe-B permanent magnet powder dispersed in poly (ethylene-co-vinyl acetate)-EVA. Characterization of microstructure, thermal stability and mechanical properties of the composite coatings with different Nd-Fe-B powder content were performed using...

An original wireless sensor network for vibration measurements was designed. Its primary purpose is modal analysis of vibrations of large structures. A number of experiments have been performed to evaluate the system, with special emphasis on the influence of different effects on simultaneity of data acquired from remote nodes, which is essential f...

The measurement of inclination on gravity concrete dams using the instrument tiltmeter is described and discussed with special reference on obtained results on the dam 'Đerdap 2' acquired in the three years period. Tiltmetar way of operation is presented both through physical principle of vibrating wire sensors and through described design of the i...

This paper describes testing of a wireless technique for measuring the actual sleeper vibrations and determination of their dynamic deflection based on the experimentally acquired acceleration data. Practical measurements of sleeper vibrations and calculation of displacements (deflections) along the track provide insight into the actual condition o...

The service life of rails depends especially on the operational loads and speeds on the railway lines, as well as on the rail maintenance policy. There are multiple aspects of rail maintenance optimization. The following article considers optimisation of rail maintenance activities relating to rail head surface condition in order to reduce correcti...

A wireless system for vibration measurements has been developed at the Faculty of Civil engineering, University of Belgrade. It’s comprised of sensor nodes equipped with accelerometers to measure vibrations and radio modems which transfer data to the hub (base station), usually a laptop personal computer. One of the tests of this system was perform...

The rail defects due to rolling contact fatigue represent serious safety hazard for rail traffic all around the world. That hazard is more distinct on railways without adequate maintenance strategy, with the increase of wheel/rail contact stresses and with decreasing wear of rail steel. This paper analyses the example of sporadically conducted main...

Non-destructive structural health monitoring of civil engineering structures is based on vibrations measurements of objects during dynamic tests or during their exploitation. Wireless sensor networks are increasingly being used for this purpose. They make flexible and inexpensive measurement systems because large cables to connect the sensors are a...

Na Građevinskom fakultetu u Beogradu realizovan je originalan bežični senzorski uređaj namenjen prvenstveno za merenje vibracija u građevinarstvu. Jedan od nedostataka bežičnih senzorskih sistema u odnosu na žičane jeste nepostojanje zajedničkog takta (izvora vremena). Zato je značajno postići dobru vremensku sinhronizaciju na druge načine a zatim...

One month results of temperature field and solar irradiance in situ measurements in close vicinity of a window on a building in Belgrade are presented in this paper. Also, physical models for thermal transmittance and solar irradiance calculations for the window are developed. Temperature measurements with data loggers symmetrically placed on the g...

Nedestruktivno praćenje stanja građevinskih objekata se bazira na merenju vibracija objekata pri dinamičkim ispitivanjima ili u toku njihove eksploatacije. U ovu svrhu se sve više koriste mreže bežičnih senzora koje čine fleksibilan i jeftin merni sistem, jer nema razvlačenja kablova velikih dužina za povezivanje senzora. U ovom radu je opisan sist...

Nondestructive structural health monitoring in civil engineering is mostly based on of the structure vibrations measurements during dynamic examinations or in everyday use. Wireless sensor networks (WSN) are used for these purposes lately because they represent flexible and cheap measurement system without long cables connecting sensors with the ma...

Dynamic mechanical analysis (DMA) is one of the most powerful tools to study the behavior of plastic and polymer composite materials and it is a potentially very useful tool to simulate behavior of plastic optic fibers (POF) in real appli¬cations. The possibility of simultaneous measurements of some optical proper¬ties during DMA would significantl...

Razvoj komunikacionih tehnologija poslednje decenije otvorio je mogućnosti primene bežičnih senzorskih mreža u najrazličitijim oblastima. Sve učestalija primena ove tehnologije u građevinarstvu posledica je njihove ekonomičnosti i jednostavnosti instalacije, a osmatranje različitih veličina čini fleksibilnijim i omogućava registrovanje na teško dos...

A group of 72 patients with 111 asymptomatic carotid stenoses (ACS), mean age 65.42 +/- 9.21, and a group of 36 patients with 58 symptomatic carotid stenoses (SCS), mean age 67.63 +/- 8.79, were analyzed prospectively during a 3-year follow-up period. All patients underwent color duplex scan sonography (CDS), carotid arteriography, computed tomogra...

Fiberoptic sensors (FOS), can be either placed on the material surface or can be embedded into the material structure. A network of fiberoptic sensors within composite materials provides real-time information about any deformation in material during manufacturing process or material use. The main advantages of fiberoptic sensors are their shape and...

This article the describes procedure of embedding fiberoptic sensors in laminar thermoplastic composite material, as well as damage investigation after low energy impact, in real time. Experimental testing was carried out in order to observe and analyze the response of material under various load conditions. Different type of Kevlar® reinforced com...

This paper investigates the possibility of applying optical fibers as sensors for investigating low energy impact damage in laminar thermoplastic composite materials, in real time. Impact toughness testing by a Charpy impact pendulum with different loads was conducted in order to determine the method for comparative measurement of the resulting dam...

This paper describes the procedure of embedding fiber optic sensors in laminar thermoplastic composite material, as well as damage investigation after ballistic loading. Thermoplastic-reinforced composite materials were made for increased material damage resistance during ballistic loading. Damage inside the composite material was detected by obser...

The possibility of applying optical fibers as sensors for investigation of real time low energy impact damage in laminar thermoplastic composite materials has been studied. For that purpose intensity based optical fibers were embedded in composite material specimens. Kevlar 129 (DuPont's registered trade-mark for poly (p-phenylene terephthalamide))...

In recent years, optical fibers have received attention as sensors for the purpose of in-service health monitoring in composite materials. Advantages of optical fiber sensors over conventional sensing methods are well-known and include resistance to corrosion and fatigue, similarity of their material properties to the reinforcing fibers, small, fle...

The possibility of applying optical fibers as sensors for investigation of real time low energy impact damage in laminar thermoplastic composite materials has been studied. For that purpose intensity based optical fibers were embedded in composite material specimens. Kevlar 129 (DuPont's registered trade-mark for poly (p-phenylene terephthalamide))...

Multi-mode optical fiber with magnetic composite coating was investigated as an optical fiber sensor element (OFMSE) for magnetic field sensing The composite coating was formed with dispersions of permanent magnet powder of Nd-Fe-B in poly (ethylene-co-vinyl acetate)-EVA solutions in toluene. The influence of the applied external magnetic field on...

In this paper, a characteristic of acoustic response of wood strips subjected to contactless acoustic excitation of 420 Hz has been investigated. The experiments have been performed on an experimental setup specially developed for this purpose. High quality juniper wooden strips of the same dimensions have been made from the same bulk material, che...

An application of the embedded intensity based fiber optic sensors (FOS) for fatigue damage detection in cantilevered composite rods is presented. During the fatigue test with constant amplitude of oscillations, the deflection and the intensity of optical signals were acquired constantly until the optical signal drop has been observed. Characterist...

An application of the embedded intensity based fiber optic sensors (FOS) for fatigue damage detection in cantilevered composite rods is presented. During the fatigue test with constant amplitude of oscillations, the deflection and the intensity of optical signals were acquired constantly until the optical signal drop has been observed. Characterist...

U radu je opisan merni sistem za određivanje inteziteta sila zatezanja u užadima krovne konstrukcije Sportske dvorane u Beogradu. Princip rada sistema se zasniva na merenju osnovne frekvencije oscilovanja užeta pomoću akcelerometra i kompjuterskoj akviziciji podataka. U zavisnosti od pravilnosti harmonijske oscilacije, stepena prigušenja i korisnog...

Prevention of serious damage of composite structures might be achieved by inspecting the structural integrity during exploitation. This paper decribes the design and development of a promising optical fiber sensor system for low velocity impact detection in unidirectional composite that does not have a laminate structure. Obtained results showed th...

The tension intensities in the tendons on the roof structure of the new Sports Hall in Belgrade are measured. The principle of measuring, the developed measurement system, as well as the error analysis are presented.

Optical fiber sensors, due to their small size and weight can be embedded within concrete without affecting its mechanical properties. They can be used for measuring various characteristics of the concrete during its hardening, and later in everyday investigation and exploitation of concrete structures. In this paper we describe some configurations...

For civil engineering, it is of great importance to detect crack onset and propagation in concrete elements. Two type of sensors for crack detection, fiberoptic and graphite are developed in our laboratory. In order to examine their possibilities for crack detection, as well as to experimentally verify the theoretical prediction of concrete fractur...

When designing objects for different civil engineering purposes, as well as thermal and air condition devices, from the aspect of energy saving and comfortable residence, special attention has to be paid to some air parameters among which temperature and humidity are to be pointed out. An arrangement has been developed for measurement of relative a...

Multi-mode optical fiber with magnetic composite coating was investigated as an optical fiber sensor for magnetic field sensing. The optical fiber magnet sensor element presented in this paper was constructed on the base of intensity-based optical fiber vibration sensors. The commercial multi-mode optical fiber was coated with magnetic composite. T...