The dissertation is devoted to the improvement of the engineering methodology for calculating the masonry strength under the combined action of vertical and horizontal loads based on the variational method of the plasticity theory and experimental research.
Chapter 1 "Review of the literature on the strength of masonry under the combined action of vertical and horizontal forces" states that seismic influences, as the most dangerous of horizontal loads, lead to characteristic damage in buildings with bearing masonry walls, among which it is necessary highlight inclined and cross-shaped cracks in walls and solid walls. It is emphasized that one of the most vulnerable structures of such buildings in terms of seismic resistance is the partitions, which, according to the results of research, are in conditions that are close to those that occur in the frame when it is skewed: the third stage of deformation of the walls is characterized by a significant reduction in the length of the compressed zone due to expansion contour horizontal cracks at the level of the bridge and is accompanied by the formation of diagonal cracks. Experimental studies of the operation of brick blocks under the combined action of vertical and horizontal loads were carried out by testing masonry elements for skew. In most cases, test samples were tested for a concentrated load applied along their diagonals. The nature of the destruction, determining factors affecting the ultimate load were analyzed: masonry material, strength of stone and mortar, internal and external reinforcement of the masonry, reinforcement with mortar and concrete applications, cross and horizontal reinforced concrete strips, carbon fiber, diagonal metal ties, and others.
In Chapter 2 "Calculation of masonry in the presence of a horizontal load component" the standard calculation of masonry for the combined action of vertical and horizontal load is considered, which consists in the application of: eccentricities due to the action of horizontal loads ehi or ehm when determining the reduction factor strength Φ; increased calculated tensile strength of masonry during bending in a plane parallel to the horizontal seam (on an untied cross-section). A parallel analysis of the existing author's methods, which in most cases are empirical in nature, indicates their imperfection and the need to develop a method for calculating masonry for the joint effect of vertical and horizontal load, which would be based on a general theoretical basis.
In Сhapter 3 "Calculation of the strength of masonry with diagonal splitting by the variational method in the theory of plasticity " to determine the bearing capacity of masonry partition, the variational method in the theory of plasticity developed at the National University «Yuri Kondratyuk Poltava Polytechnic» is used to calculate structures, resistance materials whose compression and tension are significantly different. Based on the general provisions of the variation method, the specifics of masonry work are taken into account. Based on the analysis of the nature of the destruction of the test samples, kinematic schemes are proposed, which are the basis of the calculation. The obtained dependences for determining the ultimate load of rectangular masonry elements during diagonal splitting under asymmetric loading as a function of the geometric parameters of the failure surface and the ratio of the speeds of movement of hard disks on the kinematic diagram. The strength problem is solved by searching for the minimum of the ultimate load function, and the "Solver" and the program in VBA workspace can be used as alternative calculation tools. The existing normative method of calculating the bearing capacity of the walls of the building under the combined action of vertical and horizontal load has been clarified, while taking into account both characteristics of masonry strength: in compression and tension; dimensions of the element, load areas and their ratio; number, strength characteristics and location of reinforcement.
Chapter 4 "Methodology and analysis of the results of experimental studies" describes the results of the test of masonry post, which confirmed the effect on the strength of adding 20% Ceresite to the cement-sand solution. The nature of the failure of test samples, which are used to determine the compressive strength of masonry, is analyzed: their failure occurs along an inclined plane or is accompanied by the formation of vertical separation cracks in the middle part of the sample and inclined shear cracks in the supporting areas. The previously obtained solutions of the problems of the strength of the prism when sheared along one plane and along the edges of the sealing wedge by the variational method of the theory of plasticity are in good agreement with the experiments.
