No abstract

Formulation of the problem. Reliability of buildings and structures from reinforced concrete largely depends on efficiency of construction solutions of supporting areas and joins of elements of bearing systems. At the same time, an important place is given to the issues of ensuring their bearing capacity. One of the ways to solve this problem is to increase the strength characteristics of concrete, in particular by using basalt fiber. The purpose of the article is to improve the method of calculating the strength of concrete elements under the local compression on a general theoretical basis and to clarify the impact on the strength of determining factors. Conclusion. To calculate the strength of concrete elements under the local compression, the theory of concrete plasticity is promising. The application of the variational method and the principle of virtual velocities is proposed. According to research, the strength of concrete, in addition to the ratio of the area of application of the load and the cross-sectional area, is affected by the ratio of the height of the element to the width of the stamp and both characteristics of concrete strength. The proposed kinematic failure schemes have found experimental confirmation. Analysis of test results of concrete elements and assessment of their strength on the basis of the theory of plasticity allowed making the program of experimental research of fibroconcrete on basalt fibers under local compression.

The central one-sided concrete element crushing is considered when the loading platform width is less than the element width (in three-dimensional stress state conditions). A variational method in the concrete plasticity theory, which is developed in the Poltava National Technical Yuri Kondratyuk University, is proposed to calculate the strength. The formula for determining the ultimate load is based on the destruction kinematics, which is observed in the experiments, and takes into account the loading platform size ratio and the element, both concrete strength characteristics, the frictional forces between the support surface and the element. The calculation dependence is rather precise during the cubes central crushing when the element height ratio and the loading platform greater than 4. With other geometric parameters the kinematic scheme changes, which must be taken into account when deriving the formulas for calculating the strength by the variational method. The proposed method allows considering all possible calculation schemes and determining its application limits.