Vol 16, No 6 (2020)

Wooden-composite plate-ribbed bent panels with structural plywood and oriented strand board sheathing with breaks are considered. An overview of studies researching and improving the effectiveness of different types of panels is presented. On the basis of the theory of calculation of composite rods by A.R. Rzha- nitsyn, a mathematical model has been compiled, which makes it possible to calculate the stress-strain state of these structures, taking into account the pre- sence of breaks in the sheathing and the flexibility of the mechanical fasteners of the sheathing and ribs. An equation for finding the coordinates of the most dangerous section of wooden ribs in the presence of breaks in the sheathing, which may not match with the middle of the span, is obtained. Panels with sheathing in a compressed zone with different locations of joints, symmetrically relative to the middle of the panel span are considered. Panels without joints in the skin are considered to compare the results. The graphs of the dependence of the maximum tensile stresses in the ribs in the most dangerous section and the maximum vertical displacements from the stiffness coefficient of the shear ties and the location of the breaks in the sheathing are presented. The values of the coefficients for the engineering design of panels, taking into account the decrease in the strength and deformation characteristics of the composite section of panels with breaks in the sheathing, as compared to panels with a solid sheathing, are obtained. The conclusions and recommendations, based on the results of the investigations, which can be used in the design of wooden-composite plate-ribbed structures, are formulated.

Relevance. To ensure the safety of hydraulic and hydropower facilities, to organize constant monitoring of their condition, including the installation of additional control and measuring equipment is required. It is also necessary to introduce modern information and diagnostic systems that allow in real time to assess the state of both individual elements of the structure, as well as mutually influencing structures and complexes of structures. At the same time, the results presented in the article are aimed for describing the fundamental structure a new generation of information and diagnostic system building, developed within the framework of a software and hardware complex. The aims of the work. The main purpose of the proposed system is to increase the level of monitoring to ensure the safety of hydraulic structures, which have a possible impact on each other during operation and construction. The tasks of creating a unified platform for assessing the safe state of hydraulic structures during the construction and operation of hydraulic structures (hydroelectric and pumped-storage power plants) are being solved, the foundations of a unified information-diagnostic system on a modular basis are laid, which allows comparing monitoring and measuring equipment readings, statistical samples and calculated values obtained within the mathematical modeling objects. Methods. The paper presents the structure of the interaction of individual blocks included in the information-diagnostic system, the interaction of the information-diagnostic system with the user for decision-making during the operation of the hydraulic structures. Results. A modular shell has been implemented, consisting of a combined information-diagnostic system, expert and calculation modules, which allows a comprehensive approach to the issue of safety of mutually affecting hydraulic structures. Software links have been developed to assess the change in parameters that can lead to deviations/irregularities in the operation of the hydraulic structures.

The complete system of equations of a linear theory of thin shells in curvilinear non-orthogonal coordinates proposed in the paper was taken as the basis of the investigation. Earlier, this system was used for static analysis of a long developable helicoid. In the article, this system is applied for the determination of stress-strain state of annular and circular plates under action of the external axisymmetric uniform load acting both in the plane of the plate and out-of-their plane. Presented results for annular plate given in the non-orthogonal coordinates ex-pand a number of problems that can be solved analytically. They can be used as the first terms of series of expansion of displacements of degrees of the small parameter if a small parameter method is applied for examining a long tangential developable helicoid.

Problems of differential equations construction of equilibrium of a geometrically and physically nonlinear continuous medium under conditions of one-dimensional plane deformation are considered, when the diagrams of volumetric and shear deformation are approximated by quadratic functions. The construction of physical dependencies is based on calculating the secant moduli of volumetric and shear deformation. When approximating the graphs of the volumetric and shear deformation diagrams using two segments of parabolas, the secant shear modulus in the first segment is a linear function of the intensity of shear deformations, the secant modulus of volumetric expansion - contraction is a linear function of the first invariant of the strain tensor. In the second section of the diagrams of both volumetric and shear deformation, the secant shear modulus is a fractional (rational) function of the shear strain intensity, the secant modulus of volumetric expansion - compression is a fractional (rational) function of the first invariant of the strain tensor. Based on the assumption of independence, generally speaking, from each other of the volumetric and shear deformation diagrams, six main cases of physical dependences are considered, depending on the relative position of the break points of the graphs of the diagrams volumetric and shear deformation, each approximated by two parabolas. The differential equations of equilibrium in displacements constructed in the article can be applied in determining the stressed and deformed state of a continuous medium under conditions of one-dimensional plane deformation, the closing equations of physical relations for which, constructed on the basis of experimental data, are approximated by biquadratic functions.

The aim of the work. The effect of the curvature of the rounding of torus surfaces during the formation of a cylindrical product (glass) is investigated, taking into account the plastic thinning of the deformable material at the end edges of the matrix and pressing punch. Methods. The existing scheme for determining the power parameters of sheet drawing is analyzed, based on the assumption of the implementation of some abstract stress state in the material; mainly conditional tensile strength. At the same time, the possibility of forming the product without destruction determines the obvious overestimation of the stress level. A mathematical model of the volumetric stress state of the metal is being developed, which makes it possible to assess the deformation and stress state during the formation of a cold-drawn product, i. e. the folding of the sheet blank along the end radius of the rounding of the pressing punch and the steady-state process of drawing the blank into the deformation zone with successive bending/straightening of the material along the edge of the matrix are considered. The level of radial stresses during folding and stretching of sheet material is estimated, taking into account its strain hardening and thinning, which determine the forming force. The obtained results will make it possible to simulate the stress-strain state of the metal during the development of sheet drawing technology: to establish the amount of thinning, to estimate the level of radial stresses in the formation of rounding of torus surfaces along the end edges of the matrix and the pressing punch, as well as to determine the power parameters of the formation, which will prevent the destruction of the pulled part, guaranteeing obtaining high-quality products and more accurately choosing the deforming equipment.

Relevance. When repairing hydraulic structures, it is often necessary to face the task of strengthening them. Among the methods of strengthening retaining structures, the most interesting are those that allow to immediately include reinforcement elements in joint work with the structure and carry out work without removing the backfill soil from the rear edge. When choosing repair materials, attention should be paid to corrosion-resistant composite materials, the use of which in hydraulic engineering is not yet standardized, but the scope of their application is expanding every year. The main aim of experimental research is to strengthen the reinforced concrete structures of hydraulic structures, including those with interblock construction joints and transverse cracks, using prestressed transverse reinforcement. Methods. The investigations were carried out on a reinforced concrete model of a beam type reinforced with prestressed transverse reinforcement in the zone of inclined cracks formation. The model was made taking into account the typical tasks encountered during the repair of long-term operating retaining hydraulic structures with open seams and cracks, insufficient transverse reinforcement, low reinforcement coefficient, and initial deflection. Results. The task of strengthening a special reinforced concrete model using prestressed transverse reinforcement was realized. Experimental data were obtained on the nature of deformation and destruction, the opening of interblock construction joints and cracks, and the stresses in the reinforcement. Recommendations are given for strengthening the operated low-reinforced concrete structures of hydraulic structures with interblock construction joints with prestressed reinforcement.

Most stone-masonry structures were built at a time when seismic risk was not considered in their design. Recent moderate to strong earthquakes have confirmed the vulnerability of heritage buildings, especially those constructed with unreinforced-masonry materials in various developing countries, worldwide. Proper assessment of the seismic performance and of the potential deficiency of existing heritage structures forms the basis for determining the degree of intervention needed to preserve their heritage values. Analysis of masonry wall confined by wooden band has been carried out using various structural analysis programs. In analysis appropriately considered and introduced link element such as hook, gap and spring at connecting nodes of vertical and horizontal timber elements. The result shows that the traditional floors and spandrels of the existing structure are the vulnerable parts which need strengthening of them to assure the structural members are able to resist seismic vulnerability. The required improvement and strengthening technique in existing building are proposed and better results are marked. The analysis of the modified structure shows considerably improvement in the dynamic characteristics of the buildings and overall structural response of those.