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Vilnius, Lithuania

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.

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.

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.

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.

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.

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