This article describes the study of reinforced concrete span bending structures under conditions of highlevel cyclic loading. Previous studies on the development of physical models of bending reinforced concrete element fatigue resistance, cyclic effect of lateral forces, and methods of calculation, are important and appropriate owing to certain features and the essential specificity of the mentioned loading type. These primarily include the nonlinearity of deformation, damage accumulation in the form of fatigue micro-and macro-cracks, and exhausting destruction of construction materials. In this paper, key expressions determining the endurance limits of concrete, longitudinal reinforcement, and anchoring longitudinal reinforcement, which contribute to endurance throughout the entire construction, are considered. Establishing a link between stresses in the elements and deformations in the element under conditions of cyclic loading action is of equal importance because of the presence of cyclic stressinduced creep deformation.
In a few foreign codes (ACI, Eurocode 2, JSCE, CSA, CNR), the principles for calculating flexible concrete elements with (BFRP) are preserved the same as for calculating concrete structures with steel reinforcement. Experimental studies have not confirmed these principles, which indicates the relevance of research. Two calculation models are proposed for determining the strength near the support sections of concrete beams with BFRP. The first model considers the calculation of beams with average (a/d=2) and large (a/d=3) shear spans along the main inclined crack, taking into account the experimentally established length of its projection lcrf1, the coefficients ϕख़2, ϕख़3 and ϕख़4 the magnitude of tensile stresses in the transverse fittings. The second computational model provides for the calculation of these beams with small shear spans (a/d<1) along a compressed inclined strip using the experimentally established coefficient kf,. The use of the presented design models provides good convergence (coefficient of variation ν=8%) of the calculated and experimental values of strength near the support sections of concrete beams with BFRP.
Виконано огляд досліджень по визначенню впливу відхилень поверхні побудованих великопролітних оболонок покриття на їх стійкість. Наведені результати числового експерименту, що показують найбільш небезпечні ділянки оболонки з відхиленнями поверхні та отримані прогини втрати стійкості.
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