Introduction. Many years of experience in design and operation of structures prove that the reliability of structures cannot be ensured by strength calculations alone. In addition to strength and stiffness of structures, their vibrations are often required to be considered. These types of calculations appear highly comprehensive, involving a large number of different factors to be taken into account. At present, as structures are becoming more and more complex, great attention is paid to seismic design, which is especially relevant for buildings subjected to high seismic loads. Engineering structures experience increased loads associated with the above-mentioned and other reasons. Free and forced vibrations of various elastic structures obtain a significant relevance among researchers as manifested by numerous publications on this issue.

Aim. To present a complete mathematical problem for the two most common methods of end restraint, to determine natural frequency spectrum and eigenforms of beam vibrations.

Materials and methods. The present study involves a beam of variable cross-section made of homogeneous material, subjected to transverse distributed load, which makes bending vibrations. Free and forced vibrations are described by differential equations. The homogeneous equation is solved first, then – the nonhomogeneous equation. The study involves application of D’Alembert’s principle, variable separation method, and test checks.

Results. The authors obtained a fourth-order partial differential equation with constant coefficients and determined a natural frequency spectrum and eigenforms of vibrations. A high accuracy of the obtained results enables the characteristics of free and forced vibrations of beams to be determined in a shorter way with fewer calculations. Notably, the amplitude and eigenform of forced vibrations of beams appear dependent on the proximity of the disturbing frequency to the eigenvalues and the phase change of components in vector disturbance process.

Conclusions. The authors advanced hypotheses about a dependence between the damping and linear viscous friction coefficients as well as about the constancy of damping coefficient for all eigenvalues.

Introduction. In addition to the location of cellular communication equipment, dual-purpose poles perform the function of a lighting pole. Since dual-purpose pole are located on the central streets of the city, they have strength margins and minimum dimensions. The growing number of urban dual-purpose poles makes the correct calculation very relevant for ensuring their safe operation.

Aim. Analysis of the change in the wind load on the dual-purpose pole with panel antennas and its effect on the strength of the dual-purpose pole structure. In order to achieve this, the following tasks were formulated: to deter-mine the dependence of the aerodynamic coefficient and the magnitude of the wind load on the dimensions of panel antennas and their location; to formulate recommendations for the installation of panel antennas on the upper dual-purpose pole section with a diameter of 114 mm.

Materials and methods. An analysis of changes in the wind load and aerodynamic coefficient of the dual-purpose pole section, 114 mm in diameter, with panel antennas, installed thereon, depending on the dimensions of antennas and their location.

Results. The aerodynamic coefficient was established to decrease at an increase in the projection of the panel antennas beyond the pipe rack, regardless of their dimensions. The more the panel antennas are pressed against the pipe rack, the closer they are to the neighboring antennas, thereby making it difficult to blow the cross-section in the center. Despite the fact that the aerodynamic coefficient decreases with an increase in the projection beyond the pipe rack, the value of the wind load remains almost constant.

Conclusions. Panel antennas on a pipe rack with a diameter of 114 mm must be designed taking into account the cross-section dimensions of panel antennas. If the panel antenna width and thickness exceed 350 and 150 mm, respectively, the installation of such panel antennas should be as close as possible to the considered pipe rack in order to reduce the wind load on the dual-purpose pole. In other cases, the projection of panel antennas will have no significant effect on the change in the wind load.

Introduction. One of the promising types of joints in wooden structures is the joint using glued steel washers. However, the use of adhesive compounds is, for a number of reasons, characterized by lower manufacturability as compared to a threaded connection. Given the relevance of developing new technological types of joints in structures, it is necessary to study the threaded washer connection of wooden elements without the use of adhesives.

Aim. To study the performance of a threaded washer connection by conducting a full-scale experiment of specimens exhibiting different parameters of threaded washers in order to assess the prospects for further study of the joint in question and its implementation in construction practice.

Materials and methods. The procedure for studying the joint under consideration involves making a series of specimens and conducting an experiment to determine the failure loads and ultimate strains, followed by the visual inspection of these specimens after failure.

Results. The experimental study of twelve specimens (four series of specimens exhibiting different parameters of threaded washers, with three specimens in each) yielded failure loads, and graphs showing their deformation were constructed. The performance of the joint in question was examined; its advantages and disadvantages in terms of bearing capacity, manufacturability, and reliability were identified.

Conclusions. Threaded washer joints in wooden structures are characterized by high bearing capacity and manufacturability. In spite of such a disadvantage as the effect of wood moisture on the strength and reliability of this joint, its advantages make it promising for further study and use in construction practice.

Introduction. The article presents the materials on the activities, carried out in the pipe rolling shops of the Tagmet JSC during the modernization period, starting from 2007. The Research Institute of Building Constructions named after V.A. Koucherenko, conducted prolonged surveys of plant workshop structures in order to issue conclusions on their industrial safety and recommendations for the repair and strengthening of damaged elements in building structures for their further safe operation, including workshops, where the technological process has been changed due to the installation of new equipment.

Aim. To demonstrate one of the ways to reconstruct industrial buildings using the example of workshops, located in the territory of the Tagmet JSC, based on a survey of combined structures, calculations and analyzes of their bearing capacity margins.

Materials. The article provides the drawings of original metal structures and photographs of steel structures, already built to reinforce them and change the existing parameters of the building frame to suitable ones for new operating conditions.

Results. Recommendations for structural strengthening, applicable for similar activities, are given. Due to the scientific and technical support for the design and construction of three modernized Tagmet workshops, the plant continuously increased its productivity in subsequent years.

Conclusions. No defects and damage, which exceed the values, established by the current regulatory documents, and affect the operational suitability of buildings, were revealed during the inspection and operational safety examination of Tagmet plant structures. The results of the calculations, performed to the portal structures at the column demolition sections of the plant workshop building frames, proved the assurance of their strength and stability. The design solutions were successfully implemented during the reconstruction of workshops at the Tagmet JSC.

Introduction. Using loop joints of working reinforcement in flexural reinforced concrete members reduces labor costs when installing reinforcement cages at the construction site. However, the analysis of the available research showed that they were carried out mainly for flexural members. In this regard, additional experimental studies were carried out to assess the effect of various types of design solutions of loop reinforcement joints on the strength of normal sections of eccentrically compressed reinforced concrete elements.

Aim. To obtain the results of experimental studies and assess the effect of design solutions of loop reinforcement joints on the strength of eccentrically compressed reinforced concrete elements.

Materials and methods. The research involved the results of tests of eccentrically compressed reinforced concrete elements with loop joints of working reinforcement. As part of the research, 7 series of samples with different design solutions of loop joints were tested. The total number of samples in the research comprised 22 items.

Results. The research revealed the effect of design solutions of loop reinforcement joints on the strength of eccentrically compressed reinforced concrete elements – on average from 3 to 14 %, depending on the design solution of the loop joint.

Conclusions. It was found that the design of eccentrically compressed elements should be carried out taking into account the design of the loop joint of longitudinal reinforcement.

Introduction. Contemporary methods for the design and calculation of building structures are often limited to the elastic stage of the material work. In order to analyze the stress-strain state of joints, it is necessary to take into account the properties of the material, as well as its operation under the load, including both elastic and non-linear stages. In this case, anisotropic materials, e.g. wood, represent a particular interest. Therefore, the paper presents a theoretical and practical study of the work, performed by wooden samples.

Aim. To perform tests and numerical simulations for analyzing the stress-strain state and improve the calculations of anisotropic structural materials.

Materials and methods. Compression tests of wooden samples, made of second-grade pine, were carried out along the fibers with fixed vertical compression stresses and strains. The tests were performed using a hydraulic press with a maximum load of 50 t. Strain gauge equipment was used to record strains and stresses. Based on the data of compression tests, the numerical simulation of the samples in the LIRA-SAPR and ANSYS software packages was performed.

Results. According to the test results, the elastic stage of the compressed wood ranges up to 90 kN, followed by a transition to the plastic deformation. The performed numerical simulation of the samples in the LIRA-SAPR and ANSYS software packages demonstrated the convergence of the results. However, the ANSYS software package allows for a more detailed simulation and calculation of joints and structures. The comparison of distributions of vertical compression stresses σy, obtained in tests and ANSYS software package numerical simulation, proved the convergence of the results (discrepancy of less than 5 %). This confirms the effectiveness of using this software package for simulating the joints of anisotropic materials.

Conclusions. The results of tests and numerical simulation showed the effectiveness of using the ANSYS software package to calculate complex joints of anisotropic structural materials. The convergence of the results is established for the elastic stage. An additional study is required to simulate the plastic stage.

Introduction. Traditional ways to increase the structural strength and stiffness of beams are now almost exhausted, and optimization of production and operation technologies is mostly based on the use of new materials and increasing their reliability as bearing elements of a complex geometric profile. Bearing elements of building structures operate under high loads and, even despite their predominantly static nature, experience a complex volumetric stress and strain state, which can scarcely ever be confirmed empirically and statistically.

Aim. To propose an approach to assessing the strength and stiffness of beam structures operating under conditions of transverse bending of a complex geometric profile.

Materials and methods. Classical energy methods, including Castigliano, Maxwell–Mohr and Vereshchagin methods (moment area method), have been used to assess the strength and stiffness of non-profile beam structures, initial parameters, differential equations of the deflection curve.

Results. The similarity parameters (fitting criteria) of Mises–Hencky and Zhurkov reflect the behavior of a brittle or plastic beam material reasonably well. These characteristics are proposed to be combined in the Arrhenius–Zhurkov durability functions.

Conclusions. The dependencies given in the calculations can be recommended for improving the flexural static and fatigue strength, as well as the stiffness of the bearing elements of building structures.

Introduction. The present paper provides justification of fire safety measures to protect systems of the main control room of NPP using computational fluid dynamics fire modeling.

Aim. To develop fire protection measures for systems of the NPP control room using computational fluid dynamics model.

Materials and methods. The study involved analysis into purpose and application scope of various methods for modeling dynamics of development and spread of fire hazards. The application of the computational fluid dynamics fire modeling for multifunctional premises was considered.

Results. Following the analysis of different methods for modeling the dynamics of development and spread of fire hazards, the present paper introduces the potential of using various methods of fire modeling in the evaluation of fire hazards for main control room. The obtained computations show that the temperature at the reinforcement site remains below the critical value in the most dangerous fire development scenarios like ventilation controlled fire. Moreover, fire hazards fail to spread through the walls of an uninsulated room within three hours at any value of fire load in main control room.

Conclusions. The study revealed a potential for using computational fluid dynamics fire modeling for evaluating fire hazards in various buildings and premises, as well as for justifying the sufficiency of fire resistance requirements established for building structures. This regularity is obtained under conditions of preventing the spread of fire beyond the fire zone within the estimated burnout time of the entire fire load. The results received for this particular type of premises (cable floor) indicate that the designed fire resistance of the barriers separating safety system premises and normal operation premises guarantees non-proliferation of fire. The obtained regularities can be used in the development/revision of regulatory documents on fire safety at operating NPPs and NPPs under construction.

Introduction. The Russian standards determine the lateral earth pressure at the failure surface stage, which corresponds to the Coulomb’s theory. In this case, the limit values of earth pressure on the flexible wall remain independent from the nature and intensity of deformation of the retaining structure. Therefore, computational methods for retaining walls are to be improved considering the above-mentioned factors.

Aim. To obtain experimental data in order to develop a computational method for determination of the active earth pressure on retaining structures depending on their deformations.

Materials and methods. Experimental tests were carried out by physical simulation for various models of flexible retaining walls using a purpose-designed laboratory test bench. Medium sand was used as a model backfill soil; its physical properties were determined under laboratory conditions in accordance with State Standard 5180-2015.

Results. The tests provided data on the character of backfill soil deformations within the wedge of failure for different kinematic conditions of the retaining wall model and, accordingly, justified the application of inclined block phenomenological model, used to develop a computational method for determining the active earth pressure on retaining walls.

Conclusions. Experimental tests indicate the correlation between deformation nature of the backfill soil and accepted conditions of soil operation during the development of engineering method for determining the lateral earth pressure. The obtained experimental data can be used in adoption and verification of the suggested computational method that enables shoring of excavations to be designed more reasonably in mutual conformity with the actual earth pressure diagrams.

Introduction. High-strength concrete is widely used in contemporary construction. Expanded introduction of high-strength concrete necessitates the need for studying its behavior at high temperatures (in case of fire) in order to ensure the required fire resistance of load-bearing reinforced concrete structures made of high-strength concrete in terms of fire safety of buildings and structures.

Aim. To determine the effect of aggregate types on strength and deformation characteristics of high-strength B100 concrete when heated to temperatures from 100 °C to 800 °C with a step of 100 °C.

Materials and methods. Laboratory tests of prism strength and elastic modulus of basalt and granite high-strength concrete were carried out on prism samples in a heated state according to standard methods using special heating equipment combined with laboratory pressure equipment.

Results. The authors determined structure behavior factors of basalt and granite high-strength concrete during heating, specifying the decrease in compressive strength and elastic modulus. Deformation diagrams during axial compression of high-strength granite and basalt concretes under heating were drawn.

Conclusions. The dynamics of reduction in strength and deformation properties is similar for granite and basalt high-strength concrete under heating and is specific for silicate aggregate concretes. The elastic moduli of basalt high-strength concrete are higher than those of granite high-strength concrete, both at 20 °C and when heated, thereby determining the dependence of high-strength concrete deformation properties on the types of aggregates. Deformation diagrams during the axial compression of high-strength granite and basalt concretes showed specific character: unilinear – when heated to temperatures of about 300–400 °C, bilinear – at higher heating temperatures, therefore differing from traditional ideas and theoretical recommendations.

Introduction. Solving the urgent problem of the production of special concretes using certain varieties of substandard natural raw materials and a number of industrial wastes will support introducing the principles of resource saving and improving the technological features of production.

Aim. To make a comprehensive assessment of the impact of sulfuric acid production wastes and substandard natural clay raw materials on the production of high-quality and durable concretes for special purposes.

Materials and methods. Easily fusible clay rocks serve as a raw material for the production of expanded clay gravel. Organic (solar oil) and ferruginous (pyrite cinders) additives were used. X-ray analysis was carried out to determine the crystalline phases in the clay of the Nikolskoe oil-field, in the resulting expanded clay gravel, as well as to analyze the factory bulk samples of pyrite cinders. A tubular electric furnace was used for firing in a two-stage mode of 700 and 1100 °C to obtain high-strength expanded clay gravel under laboratory conditions. The research involved studying parameters of phosphate binder formation and properties of iron phosphate concrete based on H3PO4 and sulfuric acid industry wastes – pyrite cinders.

Results. It was found that Nikolskoye field clay forms a good raw material for the production of high-strength heavy expanded clay gravel with a strength of up to 550 kg/cm2, water absorption of 1.5 % and resistance to aggressive environments, thereby making it suitable for manufacturing special concretes. The results obtained specify the test methods and technical requirements, control methods and product acceptance rules, thus improving the quality and durability of the concretes considered.

Conclusions. The investigated non-bloating clay can be used with organic and ferruginous additives to obtain high-strength expanded clay gravel for the manufacture of structural concretes. A mixed iron phosphate binder serves for producing heat-resistant concretes for linings of melting and casting units in non-ferrous metallurgy with high resistance and durability.

Introduction. The construction industry in the Russian Federation has good potential for digitalization. In spite of numerous unfavorable factors, a significant number of the most progressive construction companies adopt new technologies in their work, recognizing their high potential and effectiveness. Therefore, the legalization of information modeling technologies, which has been initiated at the governmental level, has a great chance of success. Digital transformation constitutes a necessary step for the sustainable development of the economy and construction industry.

Aim. To identify the advantages of using modern digital technologies in construction in order to further implement them in construction projects for automating routine processes and minimizing errors.

Materials and methods. The study provides a meta-analysis of 18 domestic and foreign studies (VAK or SCOPUS publications) on the application of digital technologies in construction, as well as an effectiveness assessment of the studied technologies.

Results. The advantages of unmanned aerial vehicles and mapping drones are undeniable, as well as the difficulties in using them in urban environments, especially in the centers of million cities. The main advantages of using drone technologies in construction include reception of detailed data from construction sites and their comparison with design documentation; objective monitoring of construction dynamics; a reduction in the number of occupational health and safety violations; improved quality of site monitoring and round-the-clock access to hard-to-reach areas; assessment of the scope of work performed; prompt response to deviations from design documentation and timely corrective actions; work with the BIM (Building Information Model) and digital model of the current object with the possibility of export to convenient CAD programs. The main disadvantages of using drone technology in construction are as follows: the maximum wind resistance of 15 m/s; the data obtained during rain or snowfall may be incorrect; the impossibility of automatic imaging within the project under construction.

Conclusions. The Pix4D Crane Camera is currently the safest solution for capturing aerial images, with subsequent conversion to 2D and 3D.