Vol 14, No 4 (2018)

A brief characteristic of the process of forming the frameworks of large-span metal domes during the installation process is given. A general description of the structural solutions of the frameworks of ribbed domes with annular rings and lattice large-span metal domes is presented. Alternative ways of modeling structural connections of the elements of the frameworks are discussed for domes with different types of structural systems. The load-bearing structural schemes during the assembly of frameworks differ from those, adopted for their analysis and design. Due to this fact, initial internal forces appear in the structural elements of frameworks that are called assembly forces. For the research purpose, design computer models of ribbed dome with annular rings and of sectorial lattice metal dome were developed with the span of 48 m and the height 12 m. The lattice is made of steel I-bars with rigid connections at the joints. The investigated dome frameworks are supported along the contour by permanent columns through hinge supports. On the basis of de-sign models, additional models were created for incomplete frameworks to study alternative ways of erection, which differed from each other in the number of temporary supports with hinge connection to the framework and hinge connections of the bar elements at the joint above the temporary support. Each of these models interpreted the intermediate state of the erected dome framework with its characteristic structural scheme. Depending on the number of temporary supports, three installation schemes were considered for the ribbed-ring dome, and four schemes - for the sectoral-lattice dome. Assembly computer models included the following types of temporary supports: central support, central and one row of intermediate supports, central and three rows of intermediate supports, support under each joint of a frame-work. For each assembly model of the dome framework, computer analysis was performed for the action of its self-weight in order to determine their stress-strain state. Stresses in the structural members, obtained as a result of the analysis, were compared with the stresses in the corresponding elements of the design model of the framework under the self-weight. Based on the obtained data, graphs and diagrams were constructed reflecting the level of assembly stresses in the structural elements of the frame in comparison with design values taking into account the type of work (compression or tension). Various groups of elements are considered along the entire height of the dome frames. The conclusion is made that the stresses in the elements of frameworks of the large-span metal domes are unavoidable when they are erected, and the level of these stresses for specific erection methods is significant. The methods of erection and the types of structural elements that can affect the reliability of dome frames are indicated. The necessity of compulsory analysis of frame-works for erection conditions in the design of large-span metal domes was noted.

In some cases, architectural, technological or other special requirements dictate the development of buildings and structures with large spans of shells. The choice of the scheme of bearing structures depends on the size of the span, architectural and planning solutions, the shape of the building in plan, the height of the structure, the presence and type of suspended transport, the requirements for the rigidity of the shell, the nature of lighting and aeration, type of roof, size and distribution of loads, the need to accommodate large masses of people and other factors. Differences in the purpose of large-span buildings and structures, features of technological processes, architectural and aesthetic requirements determine the use of a variety of solutions of such coatings. The article presents design measures for the implementation of architectural and artistic solutions of the building of the Dolphinarium in Volgograd. Analytical description of complex architectural and structural forms is performed. The analysis of existing structural forms of large-span structures is given. In the design, the concept of a combined archcable system was implemented, in which the cable system acts as an unloading and supporting system. The study of the work under load of various schemes of the cable system. It was also investigated the influence of pre-tensioning braces on strain supported their designs, and from what was determined optimal value of the efforts of the cables tension.

The effective buckling length of a column in a steel frame depends on the sidesway of the frame. The classification sidesway - no sidesway of a frame depends on all members of the frame and is made on an empirical basis. A change of class leads to large changes in the effective column length, and thus affects the buckling load and the economy of the column design. In order to avoid the uncertainties of the empirical classification, it is proposed to determine the buckling load of the complete frame with a nonlinear analysis. The method is illustrated with an unbraced and a braced frame, which are analyzed for hinged as well as fixed columns at ground floor level. The forces in the columns at buckling of the frames are compared to the buckling loads of the single columns. The design of high-rise steel frames against buckling by sidesway - no sidesway categorization has been compared to the buckling analysis of the frames as a whole with nonlinear models. The results confirm the large differences between the buckling loads of braced and unbraced high-rise frames, which are well known from analytical solutions for simple portal frames.

The technical holes existing in plates create an increased concentration of stress in the plate. In present article, a thin plate with a circular hole from which a rectilinear crack emanates is studied. The plate is reinforced by stringers. The model of crack with interfacial bonds in end zone is used. The plate and reinforcing ribs are made of different elastic and isotropic materials. It is assumed that the stringers are not bending and their thickness does not change during deformation. The plate is assumed to be unbounded and subjected to stretching at infinity. The case of partial crack closure is considered. The action of the stringers is replaced by unknown equivalent concentrated forces applied at the points of connection of the ribs and the plate. To solve the problem under consideration, the method of solution of the elastic problem and the method of construction in explicit form of the Kolosov - Muskhelishvili potentials corresponding to unknown normal displacements along a rectilinear crack are combined. To determine the parameters that characterize the crack closure, a singular integral equation is obtained and converted to a finite nonlinear algebraic system. To determine the unknown equivalent concentrated forces, Hooke's law is used. Solution of the algebraic system was obtained using the method of successive approximations. Directly from the solution of the obtained algebraic systems the cohesive forces in the bonds, contact stresses and size of the crack contact zone were found. Using the obtained relations it is possible to solve the inverse problem, i.e. to determine the characteristics and stress state of the stringer-reinforced thin plate with a circular hole at which the predetermined contact area of the faces of the rectilinear crack emanating from the hole is reached.

Various methods for calculating the shapes and frequencies of natural vibrations of rod structures and blades are described in the literature. At present, there is still no one unified universal technique for ensuring the vibratory strength of blades, based on the exact solution of the problem of calculating the vibrational characteristics of modern impellers of complex design. Thus, the problem of the flexural-torsional flutter of working blades of turbo-machines is extremely relevant, in spite of the insufficient attention given to it in various literary sources. The above drawbacks can be avoided by applying various design analysis methods. Calculation methods for analyzing the strength of structures, as a rule, are divided into analytical and numerical. Analytical methods for studying the stress-strain and vibration state are based in most cases on simplified relations between the theories of rods, shells, and also the theory of oscillations. The advantage of analytical methods is the relative ease of use and convenience in performing valuation calculations at the initial stages of design. The paper reviews and analyzes works on the finding of frequencies and modes of vibrations of rod structures and compressor blades for their subsequent use for multi-layer anisotropic rod structures from composite materials (CM) during the design phase.

In Russia experimental studies of flange joints of beams with columns have not been carried out previously, which led to the absence of normative methods for their calculation and design. The article presents the results of full-scale tests of three models of flange connections. Models vary in bolt strength, flange thickness, and loading pattern. The purpose of the experiments was to study the operation and bearing capacity of flange joints of beams with columns in the elastic and elastoplastic stage under the action of static loads. The experiments were carried out according to a multifactorial plan. The researches were carried out on a test bench developed by the author, representing a closed power circuit receptive the pressure of the jacks without the occurrence of reactions to the laboratory's power floor. The pressure in the loading system was fixed by pressure gauges, the displacement by linear displacement sensors, and deformations by strain gauges. According to the results of the experiments, it has been shown that it is possible to design and operate flange joints without reinforcement elements, such as stiffeners, haunches, back flanges, support tables, etc. Up to loads of 25-35 tf, the connections worked linearly, samples are destroyed at moments of 45-50 tf·m. Efforts perceived by full-scale models proved to be several times higher than those calculated in the “Kometa-2” program and recommended for calculating flange connections.