The objective of this study is to analyze the effect of variability of concrete stress-strain characteristics on the bearing capacity of eccentrically compressed reinforced concrete elements. Relevance of this issue is caused by wide application of the nonlinear stress-strain model for calculations of reinforced concrete structures. A distinctive feature of calculations with the use of the nonlinear stress-strain model is the need of joint use of concrete strength and stress-strain characteristics. In addition to that, valid regulations of Russian Federation deal with the average values of stress-strain characteristics, and there are no information on their variability.
In developed countries only loss of property because of fire makes annually up to 2% of their national income [9, 15]. The bearing capacity of reinforced concrete structures at high temperature impact is lost within several dozens of minutes [1, 3, 5, 10, 12, 18, 25]. Disappointing statistics of increase of both the number of fires and the scope of damage due to them aggravates the actual problem of determination of reinforced concrete structures fire-endurance. The main problems and methods of evaluation of reinforced concrete structure fire resistance are stated. Within the framework of block approach to evaluation of strain of flexural reinforced concrete elements with cracks, design model of reinforced concrete thermo-force resistance is made. Extended nomenclature of influences of high temperature at fire on decrease of performance of bearing reinforced concrete structures is considered. Empirical dependencies of strength and strain characteristics of concrete and reinforcement on high temperatures are used. Proposals on specification of evaluation of fire resistance of statically indeterminate reinforced concrete structures are formulated.
On the basis of experimental data, calculating diagrams of non-linear straining of fiber concrete under compression and tension were developed, which take into consideration the qualitative change in strength and stress-strain properties of the concrete matrix at its fiber reinforcement. The obtained diagrams are realized upon the bearing capacity calculation of fiber-reinforced concrete flexural elements. Calculation of fiber-reinforced beam was fulfilled according to the proposed approach and current regulatory documents. Comparison of calculation results was carried out, according to which the regulatory procedure gives an overstated result for its bearing capacity.
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