The fact that the polymorphic outcome of crystallization is the result of the interplay between the relative thermodynamic stability and nucleation kinetics is well known. This paper presents the synthesis...

This paper covers features of rolled steel beams used in composite structures. Composite structures consist of reinforced concrete slabs and rolled steel beams. To calculate its fire resistance it is necessary to know their complete “stress-strain” diagrams. Steel girders, which work together with reinforced concrete slabs, are widely used in bridge building. The tests on samples cut from web and a rack of an I-beam were conducted. The results of experimental studies of the “stress-strain” diagrams of rolled beams indicate the difference in the physicalmechanical characteristics of steel in the web and flanges of the beams. The experimental studies of diagrams were carried out at temperatures of 20, 400, 500, 600, 700 and 800 °C. The properties of the steel were significantly affected by the temperature. The “stress-strain” diagrams of rolled beams and table of results of experimental studies were obtained. The complete “stress-strain” diagrams of the rolled beams were studied. Experimental studies have been conducted using a newly developed patented installation. The differences of diagrams in the web and flanges of the steel I-beams were found.

Abstract. The mathematical model of the stress-strain ratio of compressed concrete at elevated temperatures for composite structures described in Eurocode EN 1994-1-2:2005 Eurocode 4 divided in two stages: Stage 1 -represents the ascending branch and is defined by two parameters: compressive strength fc,θ and corresponding deformations εcu,θ, stage II -the descending branch which is accepted for numerical methods. The design practice showed deficiencies in the provisions on models of deformation diagrams given in Eurocode 2. Part 1-2 General provisions. Structural Fire Design. (EN 1992(EN -1-2:2004, (ENV 1992(ENV -1-2:1995, which were reflected in the national standards in the process of harmonization. A technique for determining the refined diagrams "σc,θ -εc,θ" was developed for the design of composite reinforced concrete structures in case of fire. Diagram parameter values were adjusted for concretes based on silicate filler at high temperatures, the mathematical stress-strain model of the concrete under compression and high temperatures was specified.

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Current codes and regulations are applied to the design of concrete and reinforced concrete structures intended to operate under conditions of systematic exposure to elevated and high technological temperatures. It is proposed to develop a statutory instrument to replace the SNiP 2.03.04-84 changing its status for the DBN one. The purpose of the project is to create a new national regulatory instrument, which is based on the modern achievements of science, machinery and technology, advanced domestic and foreign experience of design and construction and at the same time uses theoretical and experimental studies of the updated version of SNIP 2.03.04-84. This regulatory instrument is extremely necessary for the development of national production of Ukraine. The calculation of “Concrete and Reinforced Concrete Structures for High and High Temperature Exposure” begins with the definition using Eurocode 2 EN 1992-1-1:2005 at normal temperature of 20°C, then is followed by improvements using a mathematical model of the ratio “stress-strain” of concrete at elevated temperatures, refinement of the load-bearing criteria of concrete structures in EN 1994-1-2:2004. The determination of the maximum strain on the basis of the energy approach allowed us to formulate its adjusted dependence on temperature, the values of the parameters of the stress-strain diagram. According to these data, the stress-strain diagrams of concrete during compression and heating according to Eurocode EN 1992-1-2:2004 are calculated using the formulae of the first stage.