Kuznietsova I. Strength of fiber concrete elements under local compression

The dissertation is devoted to the improvement of the engineering methodology for calculating the strength of fiber concrete (concrete) elements under local compression based on the variational method of the theory of plasticity and experimental research. In chapter 1 “Review of the literature on the perspective of the use of fiber concrete in construction in conditions of local compression” it is stated that in the practice of construction there are quite often cases of transfer of large concentrated loads to concrete wall or foundation elements. As an example, there are options for supporting reinforced concrete columns of multi-story buildings or supports of hanging walls on concrete elements of different heights, thicknesses and dimensions in plan, which are part of the socle, basement or other structural parts of buildings (structures). At the same time, there is a local compression of concrete in the structural elements and the probability of their failure due to punching shear or crushing, depending on the geometric dimensions, which fall under the relevant design schemes accepted in the regulatory documents. Fields of application, types, advantages and disadvantages, features of fiber concrete production technology are presented, and a conclusion is drawn regarding the prospects of using basalt fiber in construction and its optimal dimensions and percentage content in the production of fiber concrete. The factors determining the strength of concrete elements during crushing are highlighted: the shape, dimensions of the sample (stamp), as well as their ratio; scheme and method of load transfer; type of concrete. Most of the existing calculation methods are based on the Bauschinger formula and its variations, operate with a maximum of 2 - 3 significant factors. This leads to significant discrepancies between experimental and theoretical results. Experimental studies of fiber concrete under local compression are not enough (for basalt fiber concrete they are completely absent). In chapter 2 "Methodology and results of experimental studies of the strength of concrete and fiber concrete under local compression" the composition of concrete (fiber concrete) is selected, the method of manufacturing and testing samples is presented. New experimental data obtained are analyzed concerning the character of destruction and ultimate load of concrete (fiber concrete) under local one-sided central compression with square, rectangular and strip stamps. In chapter 3 “Solution of strength problems under one-sided crushing by the variational method in the theory of plasticity of concrete” the variational method in the theory of plasticity developed at the National University “Yury Kondratyuk Poltava Polytechnic” is used to determine the ultimate load. The kinematic failure schemes of a concrete cube in the case of central one-sided crushing under the conditions of volumetric and plane stress states are proposed, which are based on the failure pattern obtained in experimental studies. A formula for determining the cube’s crushing strength for a rectangular loading platform is given. The influence of determining factors on strength under local compression was analyzed. In chapter 4 “Comparison of the results of theoretical and experimental studies” a comparative calculation of the local compression of a concrete basement wall when a column is supporting on it is performed according to regulatory documents, as well as according to some author’s methods. The convergence of the theoretical strength, calculated according to the normative and some author’s methods, with the experimental strength for 78 samples was analyzed. The best statistical indicators among the normative methods has the DSTU method and V.G. Kvasha method – among author’s ones. A comparative analysis of the theoretical strength obtained by the variational method of the theory of plasticity of concrete with experimental data showed their good convergence.