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.

The reinforced concrete span beam structures work with small, middle and large shear spans under the action of cyclic loads of high levels is investigated. It is established that researches of physical models development of bending reinforced concrete elements fatigue resistance to the cyclic action of transverse forces and calculation methods on its base are important and advisable due to following features of said load type: the nonlinearity of deformation, damage accumulation in the form of fatigue micro- and macrocracks, fatigue destruction of materials etc. The key expressions of the concrete endurance limits definition (objective strength), longitudinal reinforcement, anchoring of longitudinal reinforcement, which consists the endurance of whole construction are determined. Also the role and the features of influence of vibro-creep deformations on the change mechanics of stress-strain state of concrete and reinforcement of research elements are investigated.

В.М. Карпюк, А.І. Костюк, Ю.А. Сьоміна, Д.С. Даниленко. Застосування деформаційно-силової моделі при визначенні напружено-деформованого стану залізобетонних конструкцій. Робота розглядає можливість та доцільність застосування дефор-маційно-силової моделі при вивченні напружено-деформованого стану залізобетонних конструкцій. Спираючись на основні поло-ження механіки твердого деформівного тіла та реальні стадії роботи залізобетонних елементів, авторами узагальнено та встановле-но, що реальний стан залізобетонної конструкції не може бути відображений тільки епюрою напружень або тільки епюрою дефор-мацій. Метою статті є розгляд роботи бетонних і залізобетонних елементів в ключі як силової, так і деформаційної моделі. Теорія опору залізобетонних конструкцій, як і раніше, залишається направленою на якнайточніше визначення чотирьох найважливіших задач: точний розрахунок навантаження, при якому з'являються перші тріщини; визначення ширини розкриття тріщин в експлуа-таційній стадії, починаючи з моменту їх появи; розрахунок жорсткості та величини прогинів, в тому числі гранично допустимих; визначення максимально можливої несучої здатності (міцності або стійкості). Реальний стан залізобетонної конструкції не може бути відображений тільки епюрою напружень або тільки епюрою деформацій. Це може бути зроблено лише при спільному викори-станні обох епюр. При цьому, узагальнена модель деформування елемента повинна бути здатною в однаковій мірі відображати як характер зростання відносних деформацій матеріалів, так і процес постійного перерозподілу напружень в них, особливо на стадіях, близьких до граничної рівноваги.Ключові слова: залізобетонний елемент, напружено-деформований стан, деформаційно-силова модель, епюра V.M. Karpiuk, A.I. Kostiuk, Ya.A. Somina, D.S. Danilenko. Deformation-strength model application at the determining of stressstrain state of reinforced concrete structures.The work considers the possibility and expediency of deformation-strength model application in the study of stress-strain state of reinforced concrete structures. Relying on the basic provisions of the mechanics of solid deformable body and the real stages of work of reinforced concrete elements, it is generalized and established by the authors that the real state of reinforced concrete structures cannot only be described by stresses diagrams or only by strain diagram. Aim of the paper is consideration of concrete and reinforced concrete elements' work as a force and deformation model. The theory of reinforced concrete structures resistance, as before, is aimed at a precise definition of the four major problems: accurate calculation of the load at which the first cracks appear; determination of the width of the cracks in the operational phase, starting from the moment of their appearance; calculation of rigidity and deflections, including the maximum permissible; definition of maximum possible bearing capacity (strength or stability). The real state of the reinforced concrete structure cannot be displayed only by stress distribution or deformations d...

Analysis of the results of both our own tests and studies of other scientists shows that the destruction of structures under the action of repeated loading occurs at lower stresses than the destruction of structures under the action of short-term static loads. Namely, the bearing capacity of beams under the action of cyclic loads is on average 10% lower compared to the bearing capacity of their "twins" under static forces, that must be taken into account when calculating and designing structures. In this regard, the author's method for calculating inclined sections of reinforced concrete beam structures under low-cycle and multi-cycle loads is presented in the paper. Repeated loads are proposed to be taken into account by calculating the fatigue strengths of the beam’s materials, namely the compressed zone of concrete above the critical inclined crack, the longitudinal reinforcement at the intersection with the inclined crack, as well as the anchoring of the longitudinal reinforcement. In particular, the design lines of endurance of concrete and reinforcement are considered. In practical calculations, the change in stresses that occurs due to the development of vibrocreep deformations of compressed concrete at complex stress state is taken into account by the functions of stress accumulation in concrete, longitudinal and transverse reinforcement. These functions of deformations of concrete vibrocreep are calculated according to the theory of vibrocreep. According to the results of the research, the corresponding author's expressions and dependencies are derived and presented, which allow determining the limit forces of structural element with a given shear span. In addition, it is proposed to introduce the coefficient kcyc into the calculation, which takes into account the more destructive effect of a multi-cycle load compared to a low-cycle repeated one. Thus, kcyc is the ratio of the breaking shear force to the minimum design ultimate endurance force of the near support sections of the specimens-beams, calculated using the characteristic values of the strength of concrete and reinforcement, that is, the prismatic strength of concrete and the yield strength of reinforcement.