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Gribniak V.,Vilnius Gediminas Technical University | Kaklauskas G.,VGTU
ACI Structural Journal | Year: 2014

This paper proposes a simple and mechanically sound modification of the deflection prediction model specified by the ACI 318 Building Code. The main idea of the proposal is that shrinkage effect should be taken into account in the assessment of the cracking resistance of bending members. This in turn will have influence on both shortand long-term deflection predictions. The proposed modification has been statistically validated using a database of more than 3500 measurements of short- and long-term deflections of 402 reinforced concrete members collected from 36 test programs. © 2014, American Concrete Institute.

Gribniak V.,Vilnius Gediminas Technical University | Kaklauskas G.,VGTU | Torres L.,University of Girona | Daniunas A.,VGTU | And 2 more authors.
Composites Part B: Engineering | Year: 2013

Present research experimentally and theoretically investigates deformations and tension-stiffening in concrete beams with different types of reinforcement. The paper reports test results of eight beams reinforced with glass fiber reinforced polymer (GFRP) or steel bars, combined with steel fibers. For given uniform reinforcement ratio, different number and distribution of bars was assumed in the section. Experimental curvatures were checked against the predictions by design codes (Eurocode 2, ACI 318 and the new Russian code SP 52-101) and recommendations (Italian CNR-DT 203 and American ACI 440). The study examined capability of different code techniques to predict deformations of beams with varying reinforcement characteristics. It has been shown that distribution of reinforcement had a significant influence on the prediction accuracy. In a more elaborate analysis, the tension-stiffening effect was investigated using an inverse technique earlier developed by the authors. Stress-strain tension-stiffening relationships were obtained for each of the beams using the test moment-curvature diagrams. Unlike the common practice, the analysis took into account the shrinkage effect which was different for steel and GFRP reinforced elements. To verify adequacy of the obtained results of constitutive modeling, the derived tension-stiffening relationships were implemented into finite element simulation as material laws for tensile concrete. It was shown that the above inverse approach offers an alternative and versatile tool for constitutive modeling. © 2013 Elsevier Ltd. All rights reserved.

Gribniak V.,Vilnius Gediminas Technical University | Bacinskas D.,VGTU | Kacianauskas R.,Vilnius Gediminas Technical University | Kaklauskas G.,VGTU | Torres L.,University of Girona
Mechanics of Time-Dependent Materials | Year: 2013

Long-term deflection response of reinforced concrete flexural members is influenced by the interaction of complex physical phenomena, such as concrete creep, shrinkage and cracking, which makes their prediction difficult. A number of approaches are proposed by design codes with different degrees of simplification and accuracy. This paper statistically investigates accuracy of long-term deflection predictions made by some of the most widely used design codes (Eurocode 2, ACI 318, ACI 435, and the new Russian code SP 52-101) and a numerical technique proposed by the authors. The accuracy is analyzed using test data of 322 reinforced concrete members from 27 test programs reported in the literature. The predictions of each technique are discussed, and a comparative analysis is made showing the influence of different parameters, such as sustained loading duration, compressive strength of concrete, loading intensity and reinforcement ratio, on the prediction accuracy. © 2012 Springer Science+Business Media, B. V.

News Article | November 1, 2016

In a new joint pilot project, the open access peer-reviewed journal Business: Theory and Practice (BTP), issued by VGTU Press since 2000, runs on the new journal publishing platform ARPHA, developed by Pensoft. ARPHA provides end-to-end technological solution for all peer-review stages starting from submission to fully functional dedicated new website. Publications are also available in semantically enriched HTML and XML formats, as well as the traditional PDF. The journal's authors and editors enjoy easily manageable peer-review workflow in ARPHA. Business: Theory and Practice publishes original research articles and reviews that integrate economic development and globalization, interpretations and consequences of entrepreneurship, strategic management and organizational behavior, theoretical questions and empirical questions of industrial organizations. It covers a variety of fields, including business environment, economic development and globalization, entrepreneurial finance, interpretations and consequences of entrepreneurship, strategic management, organizational behavior, theoretical questions and empirical questions of industrial organization, and case studies. BTP has opted for the ARPHA-DOC publishing workflow, which provides an individually designed website under the imprint and logo of VGTU Press, a document-based article submission, as well as peer review, publication, hosting and dissemination. The manuscripts submitted to BTP will be subject to double-blind peer review. "It is a great pleasure to work with the Pensoft team on establishing an innovative publishing platform for Business: Theory and Practice. I am sure the new platform will exceed the expectations of all - the authors, the editors and the readers," says VGTU Press Director Eleonora Dagiene. "Academic publishing is in a process of disruptive transition. As a result, small journal publishers and society journals are strongly affected and threatened with decline and even extinction. This is because access to high-level publishing technologies is not easy and, in most cases, not affordable. So, we developed ARPHA specially for them! ARPHA is not only an end-to-end journal publishing platform, covering the whole process from website design, authoring, editorial management and peer-review to publishing and dissemination - it also delivers a wide range of easily customizable end-to-end services, on the choice of the journal. I am glad to see Business: Theory and Practice published by VGTU Press as the first Lithuanian journal coming to the ARPHA platform and becoming a member of ARPHA's growing family of international partners," says Pensoft's founder and CEO Prof. Lyubomir Penev. The articles accepted for the current issue of 2016 in BTP, published via ARPHA, are already available on the journal's new website. ARPHA is open to journals looking for a technologically advanced publishing platform plus all associated services, which can be customized to the journal's preferences. Vilnius Gediminas Technical University (VGTU) is an innovative Lithuanian University, educating highly qualified and creative specialists. The University is the leader among the institutions of technological science education, ensuring modern studies, orientated to the labour market. Scientific research and experimental development is performed by 14 institutes, 2 research centres and 34 research laboratories. VGTU is ranked 43rd in the "QS University Rankings: Emerging Europe and Central Asia 2015-2016" rankings, and is the leader among technical universities of Lithuania. VGTU was awarded top five+ stars for teaching, innovation and facilities in the international "QS Stars" audit that evaluates the quality of higher education institutions against over 50 different indicators. ARPHA is the first end-to-end journal publishing solution that supports the full life cycle of a manuscript, from authoring through submission, peer review, publication and dissemination. With ARPHA, journals and publishers enjoy a complete set of services, which enable tailored, technologically advanced publishing solutions. The platform enables a variety of publishing models through a number of options for branding, production and revenue models to choose from.

Jodko A.,VGTU | Parasonis J.,VGTU
International Journal of Engineering Education | Year: 2012

The purpose of this article is to carry out a comparative analysis of the curricula of 33 Architectural Engineering (AE) undergraduate programs around the world that are labeled in the same way but present different perceptions of the label concept. We applied various types of analysis and evaluated the absolute and relative value of curricula by comparing: study length, number of credits, courses, electives, etc. We discuss our figures, findings, and conclusions in this paper. Not all regions of the world are represented equally, and interpretation of the curricula may be subjective, based on the selected approach. The findings reveal a large spectrum of opinions in academia regarding what constitutes Architectural Engineering, as demonstrated by differing study program contents around the world. Our data and analysis provide valuable insights and a springboard for academia, researchers and curriculum developers in the field of Architectural Engineering to reach consensus. © 2012 TEMPUS Publications.

Baskys A.,VGTU
BEC 2010 - 2010 12th Biennial Baltic Electronics Conference, Proceedings of the 12th Biennial Baltic Electronics Conference | Year: 2010

The input offset voltage of the differential amplifier based on the bipolar junction transistors, which operate at high current density, is analysed in this work. An analytical approach based on the equations in the explicit form is used to determine the input offset voltage reduction means. The obtained results are tested using numerical simulation of the differential amplifier. ©2010 IEEE.

Serackis A.,VGTU | Navakauskas D.,VGTU
Informatica | Year: 2010

The paper addresses the over-saturated protein spot detection and extraction problem in two-dimensional electrophoresis gel images. The effective technique for detection and reconstruction of over-saturated protein spots is proposed. The paper presents: an algorithm of the median filter mask adaptation for initial filtering of gel image; the models of over-saturation used for gel image analysis; several models of protein spots used for reconstruction; technique of the automatic over-saturated protein spot search and reconstruction. Experimental investigation confirms that proposed search technique lets to find up to 96% of over-saturated protein spots. Moreover the proposed flexible protein spot shape models for reconstruction are faster and more accurate in comparison to the flexible diffusion model. © 2010 Institute of Mathematics and Informatics, Vilnius.

Kumslytis V.,AB ORLEN Lietuva | Skindaras R.,AB ORLEN Lietuva | Valiulis A.V.,VGTU
Medziagotyra | Year: 2012

The article deals with the ageing and heat treatment influence on operational reliability of 5% Cr-0.5% Mo steel welded joints and pipeline elements. Separate components of the pipelines in the refineries are manufactured from chrome-molybdenum 5% Cr-0.5% Mo alloy steel. Reduction of internal stresses in chrome-molybdenum steel welded joints can be provided only by thermal treatment. Other methods of stress relieving are not acceptable for these steels. Presented materials analyses the impact of heat treatment on the microstructure and operational reliability of this steel. The objects of research are heat-treated welded joints of piping elements operated at high temperature for an extensive period of time, where degradation of mechanical properties has been observed. When value of the heat treatment temperature or time are exceeded, the structure degradation process is taking place, carbides coagulate within the boundaries of ferrite grains, they form coarse carbide colonies combined into long chains. Mechanical properties - tensile strength and impact strength decrease. Detailed analysis of these objects and the interpretation of the received results allow to select the most appropriate heat treatment parameters for the investigated steel structures.

Kumslytis V.,AB ORLEN Lietuva | Valiulis A.V.,VGTU | Cernasejus O.,VGTU
Solid State Phenomena | Year: 2010

Presented work analyses the impact of heat treatment parameters on the mechanical properties and operational reliability of P5 (5%Cr0.5%Mo) steel welded joints. The key objects of research are heat-treated chrome-molybdenum steel welded joints and piping elements operated at high temperature for an extensive period of time, where degradation of mechanical properties has been observed. The main objective is to investigate the causes of degradation of alloy steel mechanical properties during fabrication and operation of the equipment, and to develop a methodology for identification of optimum heat treatment parameters for chrome-molybdenum steel welded joints. A few key issues are addressed herein: identification of dependence of chrome-molybdenum (5%Cr-0.5%Mo) steel welded joint mechanical properties on heat treatment parameters, identification of the optimum value of temperature/time parameter, and identification of causes of mechanical property changes and degradation of the steel. © (2010) Trans Tech Publications.

Skindaras R.,AB ORLEN Lietuva | Valiulis A.V.,VGTU | Spychalski W.L.,Materials Engineers Group Ltd
Mechanika | Year: 2013

In the petrochemical industries cast steel tube coil sheets with high chromium and nickel content are used. The operation range of these alloys are 533 to 1150°C. A paramount for these alloys are: - corrosion and scaling resistance at high temperatures; - dimensional stability, i.e. resistance to warping, cracking and thermal fatigue; - resistance to plastic flow, i.e. creep strength. Tube coil sheet of furnace resulting in aggregate failures have been considered. Life span of the studied specimens obtained from tube coil sheet was 3 years. After a few years of exploitation several hollow cracks on the heater tubesheet were identified. Preoxidation of the tubes surface are possible and it has not only favourable effects: during cooling cracks may form in the oxide layer. The aim of the performed research was to characterize the microstructure and mechanical properties of the investigated alloy after ageing at the temperature of 900°C. The high temperature determine elements diffusion in the structure, emergence of chromium and niobium carbides and other precipitates and cause the changes in the mechanical properties.

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