Dynamic soil-structure analysis of tower-like structures using spectral elements

In this paper general equation system for linear dynamic soil-structure interaction (SSI) in frequency domain is presented. The main objective of the paper is to provide and investigate a possibility to use spectral elements in SSI domain. Spectral elements reduce considerably number of unknowns and in some cases, e.g. in frame structures coupled with analytically obtained impedance functions of sub-grade, produce no modelling errors. Results for two different shallow-founded beam structures with identical foundations excited by harmonic free-field motions are presented

Influence of soil-structure-interaction on dynamic response of a long bridge

In this paper the parametric dynamic analysis of the Danube river bridge “Beska” is presented. The scope of this investigation is to analyze the effects of soil-structure interaction (SSI) and asynchronous earthquake excitations on dynamic response of a long bridge. Dynamic analysis was carried out using the computer program SAP2000, considering four real earthquake records and four different bridge models. For numerical model the recommendations of the Caltrans Bridge Design Practice were taken. The analysis was performed for fixed-base and flexible-base structure (SSI). The influence of asynchronous support motions was analyzed. The descriptions of the cases studded as well as the results analysis are presented

Improving mechanical properties of flowable dental composite resin by adding silica nanoparticles

Background/Aim. The main drawback of flowable dental composite resin is low strength compared to conventional composite resin, due to a low amount of filler, neccessary for achieving low viscosity and ease of handling. The aim of this study was to improve mechanical properties of flowable dental composite resin by adding small amount of nanoparticles, which would not compromise handling properties. Methods. A commercially available flowable dental composite resin material was mixed with 7 nm aftertreated hydrophobic fumed silica and cured by an UV lamp. Four sets of samples were made: control sample (unmodified), the sample containing 0.05%, 0.2% and 1% nanosilica. Flexural modulus, flexural strength and microhardness were tested. One-way ANOVA followed by Tukey’s test with the significance value of p < 0.05 was performed to statistically analyze the obtained results. Furthermore, differential scanning calorimetry (DSC) and SEM analysis were performed. To asses handling properties, slumping resistance was determined. Results. It was found that 0.05% is the most effective nanosilica content. All the tested mechanical properties were improved by a significant margin. On the other hand, when 0.2% and 1% nanosilica content was tested, different results were obtained, some of the mechanical properties even dropped, while some were insignificantly improved. The difference between slumping resistance of unmodified and modified samples was found to be statistically insignificant. Conclusions. Low nanosilica addition proved more effective in improving mechanical properties compared to higher additions. Furthermore, handling properties are unaffected by nanosilica addition

Ispitivanje biokompatibilnosti nanokompozitnog biomaterijala za kontrolisanu dostavu klindamicina - test citotoksičnosti

Nano sfere kompozitnog biomaterijala poli(d,l-laktid-ko-glikolid)/hidroksiapatit u kojima je imobilisan/inkapsuliran antibiotik mogu imati širok aplikativan značaj kao sistemi sa kontrolisanom i ciljanom dostavom lekova u rekonstrukcijama humanih tvrdih tkiva. Ispitivanje citotoksičnosti je prvi korak u ocenjivanju biokompatibilnosti ovog biomaterijala. Cilj ovog istraživanja bio je da se ispita citotoksičnost nanokompozitnog biomaterijala poli(d,l-laktid-ko-glikolid)/hidroksiapatit sa sadržajem antibiotika klindamicina od 0%, 1%, 5% i 10%. Citotoksičnost ispitvanog materijala je određena testom odbacivanja boje (DET-Dye exclusion test) i kolorimetrijskim testom sa tetrazolijum solima (MTT-test). Ispitivanje je rađeno na fibroblastima kontinuiranih ćelijskih linija L929 i MRC5. Rezultati istraživanja su pokazali visoku biokompatibilnost ispitivanog biomaterijala bez obzira na udeo antibiotika klindamicina i nizak nivo citotoksičnosti kod svih sadržaja antibiotika

Experimental Research and FE Model of a Bolted Steel-CLT Composite Connection

Steel-timber composite structures have numerous advantages compared to steel only and timber only structures. One of the most important parts of a composite structure is the composite connection. Object of this research was a steel-CLT composite connection consisting of a steel profile, a cross-laminated timber (CLT) panel and a bolt with nut and washer. Aim of the research was to develop an efficient finite element (FE) model of a bolted steel-CLT composite connection and to validate it experimentally. The research process consisted of several steps: experimental testing of the considered connection using asymmetrical push-out test, numerical modelling and analysis of the connection using Finite Element Method (FEM), validation of the numerical model using experimental results, and parametric study of the proposed numerical model. For numerical analysis, an innovative method for timber modelling has been proposed. The comparison between the experimental and numerical research results demonstrated that the proposed numerical model was convenient for practical application in structure analyses. The parametric study showed that, in some cases, atypical failure modes of the connection occurred. Based on registered behavior, a recommendation is given to calculate the load capacity of the connection integrally, taking into account both the primary (Johansen’s) and the secondary (rope effect) part of the connection strength, instead partially, as proposed by EN standards

COMPARATIVE ANALYSIS OF DIELECTRIC AND STRUCTURAL CHARACTERISTICS OF THE SAMPLES BASED ON POLYETHYLENETEREPHTALATE

Widespread use of polymeric materials from the items for daily use to electrical engineering, electronics and medical applications causes a need for their detailed examination under various external influences. Dielectric spectroscopy allows monitoring changes in the structure of polymers under various external influences. In this paper we analyzed β relaxation recorded in polymer woven structures and meshes based on polyethyleneterephtalate. Based on the results obtained, a comparative analysis of dielectric parameters and structural characteristics of the samples was done.Widespread use of polymeric materials from the items for daily use to electrical engineering, electronics and medical applications causes a need for their detailed examination under various external influences. Dielectric spectroscopy allows monitoring changes in the structure of polymers under various external influences. In this paper we analyzed β relaxation recorded in polymer woven structures and meshes based on polyethyleneterephtalate. Based on the results obtained, a comparative analysis of dielectric parameters and structural characteristics of the samples was done

Understanding the Effect of Synthesis and Sintering Temperature on the Functional Properties of Barium Titanate/ Cobalt Ferrite Composites

To investigate the effect of synthesis procedure and sintering temperature on the functional properties of perovskite/spinel ceramics, BaTiO3/CoFe2O4 composites were prepared by thermal decomposition, coprecipitation, and microemulsion method, and sintered at 1150°C and 1300°C. The phase composition and morphology of as-prepared powders as well as sintered ceramics were thoroughly examined by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS). The dielectric and ferroelectric measurements were performed in detail. Generally, the samples sintered at 1300°C had better performances than those sintered at 1150°C. The composite synthesized by thermal decomposition and sintered at 1300 °C stands out among other prepared BaTiO3/CoFe2O4 ceramics, owing to high stability in the wide frequency range and low leakage currents. The obtained results indicate that such composite might be successfully applied as a functional multiferroic.У циљу испитивања утицаја методе синтезе као и температуре синтеровања на функционална својства керамике перовскитно/спинелне структуре, синтетисани су BaTiO3/CoFe2O4 композити методама термалне декомпозиције, копреципитације и микроемулзије, а затим синтеровани на 1150 °C и 1300 °C. Фазни састав и морфологија синтетисаних узорака детаљно су испитани пре и после синтеровања помоћу рендгенске дифракције на праху (XRPD) и скенирајуће електронске микроскпије (SEM) спрегнуте са елекрон дисперзивном спектроскопијом (EDS). Изведена су опсежна испитивања како диелектричних, тако и фероелектричних својстава датих композита. У већини случајева узорци синтеровани на 1300 °C показали су боља својства од узорака синтерованих на 1150 °C. Композит синтетисан методом термалне декомпозиције и синтерован на 1300 °C издваја се од осталих синтетисаних BaTiO3/CoFe2O4 узорака захваљујући великој стабилносту у широком фреквентном опсегу и малим струјама цурења. Добијени резултати недвосмислено указују да истакнути композит може бити успешно примењен као функционални мултифероик

Polymer nanocomposites filled with core-shell nanoparticles for nanodielectric application

Polymer nanocomposites are prepared by a simple and environmentally friendly technique. First, sheets of isotactic polypropylene (iPP) and atactic polystyrene (aPS) were prepared by compression molding with Servitec Polystat Press 200 T at 473.15 K and 3.0 MPa pressure followed by quenching in water at room temperature. The polymer sheets thus prepared were then immersed separately in three saturated salt water solutions (MnCl2, FeCl2, and NiCl2), at two temperatures (23ºC and 90ºC), and under influence of two DC electrical potentials (+4 kV, and ground potential). Count profiles and generated images of TOF – SIMS records have shown that higher temperature treatment (90ºC) and positive potential (+4kV) have given the highest count of iron ions and better distribution and dispersion of nanoparticles in polymer matrices. Also, the measured concentration of transition metals by ICP-OES confirmed higher concentrations of metals in nanocomposites obtained by these treatment conditions. It was stated that iron(II)-chloride had the highest concentration in iPP and aPS matrices in comparison to the other two transition salts. TEM micrographs showed spherically-shaped cores in the core-shell system and agglomerated particles of irregular shape. Encapsulation of iron cores prevented nanoparticles from agglomeration. The cores of the investigated particles were probably iron oxides and/or hydroxides that occurred during the hydrolysis of iron salts in deionized water solution. Dielectric properties of obtained nanodielectrics were investigated. Relative dielectric constant and loss tangent has been studied in the frequency range from 20 Hz to 9 MHz. It was shown that adding the small amount of core-shell nanoparticles (from 15 nm to 150 nm in diameter) in a very small amount (1.72E-8 mol/cm3 to 1.17E-5 mol/cm3) are resulted in significant improvement and stabilization of relative dielectric constant value and also lowering loss tangent in compare to starting polymer matrices.These dielectric properties were marked as suitable for nanodielectric application for high speed and high dencity microelectronic packaging

Uticaj faznog sastava i temperature sinterovanja na fizička svojstva BaTiO3/NixZn1-xFe2O4 (x =0, 0.5, 1) kompozita sintetisanih metodom termalne dekompozicije

In order to examine the influence of phase composition and sintering temperature on the functional properties of perovskite/spinel composites, BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1), NiFe2O4, ZnFe2O4, and Ni0.5Zn0.5Fe2O4 were in situ prepared by thermal decomposition onto BaTiO3 surface. Acetylacetonate complexes were used as the precursors. The obtained powders were compressed to pellets and sintered at 1150 °C and 1300 °C. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS) were used for the comprehensive investigation of phase composition and morphology. The magnetic, dielectric, and ferroelectric properties were performed in detail. The optimal phase composition was found in the BaTiO3/NiFe2O4 composite sintered at 1150 °C, which resulted in a wide frequency range stability. Furthermore, particular phase composition led to suitable properties such as low conductivity and ideal-like hysteresis loop behavior [1]. These functional properties of BaTiO3/NiFe2O4 make this composite a “material of choice“ for further studies on applications of multiferroic devices.U cilju ispitivanja uticaja faznog sastava i temperature sinterovanja na funkcionalna svojstva perovskit/spinel kompozita BaTiO3/NixZn1−xFe2O4 (x = 0, 0,5, 1), NiFe2O4, ZnFe2O4, i Ni0,5Zn0,5Fe2O4 pripremljeni su in situ metodom termalne dekompozicije. U sintezi su korišćeni acetilacetonatni kompleksi kao prekursori. Dobijeni prahovi su komprimovani u tablete i sinterovani na 1150 °C i 1300 °C. Za detaljno ispitivanje faznog sastava i morfologije sintetisanih kompozita korišćene su metode rendgenske difrakcije praha (XRPD) i skenirajuće elektronske mikroskopije (SEM) spregnute sa energetsko disperzivnom spektroskopijom (EDS). Ispitivana su i magnetna, dielektrična i feroelektrična svojstva sinterovanih kompozita. Ustanovljeno je da optimalni fazni sastav pronađen kod kompozita BaTiO3/NiFe2O4 sinterovanog na 1150 °C dovodi do stabilnosti u širokom opsegu frekvencija. Optimalni fazni sastav pomenutog kompozita povoljno je uticao na funkcionalna svojstva kao što su niska provodnost i feroelektrično ponašenje koje se ogleda u zadovoljavajućem izgledu histerezisa [1]. Ova svojstva nedvosmisleno ukazuju da je kompozit BaTiO3/NiFe2O4 odgovarajući izbor za dalja istraživanja posvećena primeni multiferoičnih materijala