624.012.45

залізобетонні балки
несуча здатність
приопорні ділянки
напружено- деформований стан
reinforced concrete beams
support areas
strain-stress behaviour
strength

Розглянуто результати прогнозу несучої здатності приопорних ділянок звичайних, нерозрізних та позацентрово стиснених непереармованих залізобетонних балок прямокутного перерізу за допомогою нелінійного скінчено-елементного розрахунку з використанням ПК «Ліра 9.6». Також показано методику проведення відповідних серій натурних п’ятифакторних, трихрівневих планованих експериментів із використанням плану типу На5. Виявлено характер деформування, тріщиноутворення та руйнування дослідних зразків. Експериментально обґрунтовано фізично-нелінійну модель деформування залізобетону. Розроблено алгоритми, що реалізують обрану модель залізобетону, і включають її до складу скінчено-елементного програмного комплексу «Ліра 9.6».
The results obtained in the course of an experimental study of the bearing capacity of support areas of common, whole and eccentrically compressed non-overreinforced concrete beams of rectangular cross-section with the aid of a numerical non-linear finite element analysis based on the theoretical mechanics of reinforced concrete with the use of «Lira 9.6» software platform were considered and actualized. Methodology for conducting the corresponding series of full-scale 5-factor and 3-level planned experiments with the use of the Na5 plan type is described; the nature of deformation, cracks formation and destruction of the test specimens are revealed; physical and non-linear deformation model of the reinforced concrete is experimentally substantiated; the algorithms that actualize the chosen model of reinforced concrete are developed so, that the model can be included in the finite element software platform «Lira 9.6». The conducted systemic experimental and theoretical studies made it possible to reveal the relevant dependence of the reinforced element bearing capacity both on each individual analysed factor and on their interaction, which allows a reliable simulation of the physical behaviour of the loaded bar-type reinforced concrete structures. The model was tested with the aid of a software platform by comparing the obtained results with the known experimental data; the results of experimental studies were numerically simulated by using the finite element method and the proposed methodology reliability was substantiated by comparing the computed and studied data; the practical recommendations to determine the bearing capacity of the studied elements were developed. The conducted systemic experimental and theoretical studies enabled to reveal the essential dependence of the reinforced concrete elements bearing capacity both on each of the analysed factors individually and on their interaction, which makes it possible to reconstruct reliably a physical performance of loaded bar-type reinforced concrete structures. It was established, in particular that the use of quite strong transverse reinforcement (μsw=0.002...0.005) in the analysed non-overreinforced elements (μs=0.007...0.034) suppresses the «pegging effect» in the axial working reinforcement (Qs/Qu ≤ 0.06), and it can be neglected when making practical calculations. The tangential stresses in the concrete shear span, also above the inclined crack apex in particular, considerably exceed the commonly adopted value of 2,5Rbtn and equals 0.3...0.5 Rbn , their being distributed not over a parabolic curve but according to a trapezoid or a rectangle, and are oriented from top to bottom in common and eccentrically compressed elements and from bottom to top in the middle support of the whole beams.