Abstract. The joints ensure the joint performance of the load carrying structural systems and they are the most responsible and important elements. Keyed joints are widely used in construction. They are characterized by an increased resistance to shear. On these grounds the structural concepts of keyed joints need further improvement. The article presents the research results of experimental test pieces five series in the form of single keys and one-keyed joints. Those samples have been tested in Poltava National Technical Yuriy Kondratyuk University. Follow strength factors have been varied: geometric parameters of joints (depth, height, width) and their ratio; angle of support surface (rectangular, trapezoidal and triangular key); level of compression; reinforcement (quality of reinforcement and the nature of its location); jointing width. The samples were made of heavy-weight, expanded clay and fibre concrete. The experiments program includes influence study both of one of these factors and their combinations. The deformations, nature of failure, the ultimate load have been studied. Structural parameters of keyed joints which ensure the efficient behaviour have been installed.

The purpose of research resulted in recommendations development for landscapes spatial and territory organization improvement, in particular, on the basis of fields geometric parameters influence analysis. The conducted researches are focused on ordering of arable land territory, having spatial and territory unfavorable conditions for management. Analysis is carried out and estimation of fields geometrical parameters influence on mechanized cultivation is provided. The scale for assessing feasibility of crop rotation separating triangular form fields into trapezoidal form workspaces was formed. Different forms triangular plots (rectangular, equilateral, isosceles, scalene) and areas (from 6 to 72 ha) are considered during the study. For a comprehensive analysis of design decisions, economic indicators were used, namely: capital expenditures, annual expenses, additional products cost. Power polynomials were used to establish trends and describe the functional relationship between the different shapes of land plots area and the annual profit, resulted expenses and payback period. They were described by equations and graphs were constructed. Unprofitable, ineffective, expedient and optimal division of the triangular different types areas into trapezoidal form workspaces are presented in the table. The obtained results can be used in land management projects development for territories spatial development, territory organization, rational use organization and land protection.

The authors analyzed the foreign experience of using keyed joints in reinforced concrete span structures of bridges. Fiber concrete with polypropylene fibers was chosen as the investigated material. Such fibers are chemically neutral, water-resistant, have a high resistance to dynamic loads, reduce the risk of formation and development of cracking, increase abrasion what is important in the manufacture of road construction. Optimization of concrete composition with polypropylene fibers for concreting joints by physical and mechanical parameters was carried out. Parameters of optimization were compressive strength, tensile strength at bending, axial tensile strength, prism strength and abrasion. The authors performed a series of tests to study the behavior of fiber concrete in keyed joints. The analysis of obtained results out depending on the nature of failure, the value of the ultimate load and fiber concrete deformations were carried out. The influence on the joints strength of the cross-section reinforcement percentage and the nature of placement of the reinforcing rods was considered. It was established if to place a cross-reinforcement in two levels it increases the strength of joints in comparison with a single level with the same percentage of reinforcement. It was noted that the fracture of all samples occurred from the sear key. Cracking of fiber concrete experimental samples occurred at later stages of loading compared with samples of ordinary concrete, and the fracture was not brittle, without tearing off parts of concrete. Increase in strength is due to the chaotic placement of polypropylene fibers in concrete, and therefore, to remove fibers from concrete, it is necessary to spend more energy, which ultimately leads to an increase in strength of joint. Experimental data suggest possibility and feasibility of polypropylene fibers in concrete joints in precast concrete structures of bridges

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Based on experiments results brittle duralumin samples, effect on stresses concrete (mortar) strength caused by non-uniform cross-section shrinkage (when dried) or expanding (when moistened) was inevitable. Various authors’ experiments results diversity on concrete (mortar) tensile strength of moistening and drying effect were analyzed. Reasons for increasing air-dry concrete (mortar) strength storage at beginning of humidification were explained. Wetting sample duration (intensity) effect on concrete strength was analyzed in detail and opposite results causes on concrete strength moistening (drying) effects were obtained and justified.