Method and results of determination of strength and deformation characteristics of heavy concrete at static loading to the specified stress level, followed by high-speed loading with dynamic load, are presented. The process of testing a series of concrete samples of one strength class is described to obtain the performance characteristics of concrete at static, dynamic and static-dynamic loading. Comparative analysis of the obtained experimental data was carried out under different loading modes of prototypes. It was established that during dynamic and static-dynamic loading there is an increase in the level of relative stresses corresponding to the beginning of concrete dilatation by 20-30% relative to the results of static tests. The obtained experimental results are of interest for solving problems related to the problem of survivability of buildings and structures and their protection against progressive collapse, in particular in determining criteria of strength and deformability of concrete at a special limit state.
Аннотация. Приведены аналитические зависимости для определения параметров диаграммы статико-динамического деформирования железобетонных элементов конструктивных систем при гипотетическом удалении из системы одной из несущих конструкций и с учетом трещинообразования в этих элементах. Зависимость "момент-кривизна» для изгибаемых обычных и преднапряженных, а также внецентренно сжатых конструкций приняты билинейными, причем нелинейные участки деформирования для обычных и преднапряженных конструкций приняты параллельными. С использованием полученных зависимостей приведен алгоритм определения динамической кривизны в железобетонных элементах при рассматриваемом режиме нагружения. Даны результаты численного анализа параметров диаграммы статикодинамического деформирования на примере двухпролетной, трехэтажной рамы, ригели которой армированы двойной преднапряженной арматурой.
Statement of the problem. The article presents a computational model, an algorithm for computational analysis and the results of calculating the nonlinear static-dynamic deformation of reinforced concrete frames in out-of-limit states caused by the sudden removal of one of the supporting structures. Results. To design a numerical model of the static-dynamic loading mode of a structural system, the LS-DYNA software package was used that makes use of a detailed 3D model implementing an explicit finite element method. During the computational analysis, the physical and mechanical characteristics of the deformation of materials were taken in three variants: those obtained based on the experimental data by G. A. Geniev, the experimental data by N. V. Fedorova and M. D. Medyankin under the static-dynamic uniaxial testing mode of a limited number of standard samples of prisms and according to the Russian standards SP (СП) 385.1325800.2018. Conclusions. Numerical analysis of the static-dynamic deformation of the reinforced concrete framerod system of a multi-storey building has established that the differentiated accounting of the quantitative value of the concrete viscosity modulus and, accordingly, the time and level of static-dynamic loading of the structure allows one to identify the criteria for the special limit state of the elements of reinforced concrete structural systems of buildings and structures in a more rigid manner.
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