75504 2712-8172 5 97 2020 1-123

RAR RUS 9701-9701 0000-0002-0252-2115 Kazakhstan Multidisciplinary Institute of Reconstruction and Development Republican State Enterprise on the Right of Economic Use Nuguzhinov Zhmagul kazmirr@mail.ru

Karaganda, Republic of Kazakhstan

M-6585-2013 6508103761 0000-0002-1196-8004 Peter the Great Saint Petersburg Polytechnic University Vatin Nikolai vatin@mail.ru

Polytechnicheskay, 29

0000-0002-4176-4547 Karaganda State Technical University Bakirov Zhetpisbai bakirov_50@mail.ru

Karaganda, Republic of Kazakhstan

57214108408 0000-0001-7909-7201 al-Farabi Kazakh National University Khabidolda Omirkhan oka-kargtu@mail.ru

Almaty, Republic of Kazakhstan

0000-0002-9282-3498 Karaganda State Technical University Zholmagambetov Syrlybek syrlybekzh@mail.ru

Karaganda, Republic of Kazakhstan

0000-0002-8367-7636 Karaganda State Technical University Kurokhtina Irina kurohtina.ira@mail.ru

Karaganda, Republic of Kazakhstan

Stress-strain state of bending reinforced beams with cracks The work is dealing with studying the stress-strain state of bending pre-stressed concrete beams with cracks. The problems of determining preliminary stresses in a reinforced concrete element, determining the moment of crack formation, and determining the stress in a section with a crack are successively solved. The problems were solved for a general section with the vertical axis of symmetry, taking into account the non-linear relationship between strain and stress in concrete. The resolving system of two transcendental algebraic equations is obtained from the equilibrium conditions of a part of the beam on one side of the section with a crack. Analytical expressions have been obtained for determining preliminary stresses, the external bending moment at which a crack normal to the axis appears, as well as the stress state parameters in the section with a crack, including the crack height. The results obtained make it possible to predict the bearing capacity of reinforced concrete structures at the design stage by two groups of limiting states, and to evaluate the real technical condition of the structures in operation. These results can be used to determine the parameters of fracture mechanics and evaluate crack resistance of a reinforced concrete beam. 10.18720/MCE.97.1 reinforced concrete beam bending stress state crack pre-stressing physical nonlinearity reinforcement bearing capacity ultimate state https://engstroy.spbstu.ru/article/2020.97.1/

RAR RUS 9702-9702 Peter the Great Saint Petersburg Polytechnic University Yasmin Begich yasmin1010@yandex.ru

Polytechnicheskay, 29

Belgorod State Technological University named after V.G. Shukhov Klyuev Sergey Klyuyev@yandex.ru 0000-0003-2067-5585 Peter the Great St. Petersburg Polytechnic University Jos Vladislav jos_vlad@mail.ru

St. Petersburg, Russia

Peter the Great Saint Petersburg Polytechnic University Cherkashin Artemiy jizm@mail.ru

Polytechnicheskay, 29

Fine-grained concrete with various types of fibers This paper investigates the strength properties of the fine-grained concrete reinforced with the amorphous fiber based on the Fe-B-C system and obtained by the "spinning" method, and concretes reinforced with commercially available types of fibers: fiber based on mineral wool, basalt fiber, fiberglass, steel and polypropylene fibers. The flexural and compressive strength tests with the fiber-reinforced concrete specimens were carried out in accordance with the standard method corresponding to the Russian State Standard. The analysis of results was made by comparison with the characteristics of the control specimens without reinforcement. The best flexural strength characteristics were shown by specimens with the amorphous fiber, while the highest compressive strength was demonstrated with the steel fiber. The addition of the amorphous fibers leads to an increase of 56 % in the flexural strength, but decreases the compressive strength by 30 % compared to the control specimens, which proves the efficiency of this fiber working in bending. The addition of the steel fiber shows an increase of 20 % in flexural strength and an increase of 14 % in compressive strength, which confirms the positive effect of adding a commercially available fiber to the fine-grained concrete. The compounds of the fiber concrete with the compression strength limit up to 38 MPa and tensile strength in bending up to 12 MPa were developed, which allows to use amorphous fiber as a compound of fine-grained concrete in the construction industry. 10.18720/MCE.97.2 fiber fine-grained concrete amorphous fiber strength properties fiber reinforced materials fiber-reinforced concrete cements binders concretes cementitious concrete mechanical activation https://engstroy.spbstu.ru/article/2020.97.2/

RAR RUS 9703-9703 57194618453 0000-0003-4384-9330 South Ural State University Molodtsov Maxim molodtcovmv@susu.ru

Chelyabinsk, Russia

South Ural State University Vshivkov Evgeniy laito174@gmail.com

Chelyabinsk, Russia

57194618342 South Ural State University Molodtsova Valeriya molodtcovave@susu.ru

Chelyabinsk, Russia

Behavior of concrete beams reinforced with fiberglass composite rebar under load Fiberglass composite reinforcement has been used in Russia for a long time, but there is still not enough research and necessary related data. Therefore this paper focuses on how exposure to loads affects concrete beams with fiberglass composite and metal reinforcement. The concrete beams samples (80×160×1400) were tested for bending as single-span hinged-supported elements. The load was applied within 20 seconds intervals in order to prevent relaxation of the concrete. All samples collapsed along the cross-section having maximum crack opening in the area of pure bending. The experiments show that the nature of beam collapsing and cracking does not depend on the type of reinforcement. However, the maximum crack opening width for beams with fiberglass composite reinforcement is 28.8 % greater than for beams with metal reinforcement. The value of the maximum deflection for fiberglass is 43.3 % greater. In addition, despite the initial experimental condition of equal loading onset time, the value of the crack formation for beams with fiberglass composite reinforcement is 15.5 % less. The average value of the breaking moment for beams with fiberglass composite reinforcement is 18.06 % less. Taken together, the data obtained in the course of the experiments suggest that the bearing capacity of the elements with fiberglass composite reinforcement, bent along the cross-section, decreases due to the low stiffness of the element itself. Therefore, this type of reinforcement is likely to be applicable for concrete structures on the elastic foundation. 10.18720/MCE.97.3 concrete beam fiberglass composite reinforcement deflection crack cracking formation onset bearing capacity https://engstroy.spbstu.ru/article/2020.97.3/

RAR RUS 9704-9704 0000-0002-7556-6573 Perm National Research Polytechnic University Sychkina Evgeniya aspirant123@mail.ru

Perm, Russia

0000-0002-3703-5878 Perm National Research Polytechnic University Ofrikhter Ian ian.ofrikhter@gmail.com

Perm, Russia

6603146403 0000-0001-6521-9423 Saint-Petersburg Mining University Ponomaryov Andrey andreypab@mail.ru

St. Petersburg, Russia

Bearing capacity equations of piles in weathered claystone and sandstone The article proposes models of nonlinear estimation of the bearing capacity of piles on weathered claystone and sandstone. These soils are often used as the foundation for deep foundations for critical structures such as bridges, transport structures, dams. Often, laboratory tests of such soils give underestimated values of the characteristics. As a result, the bearing capacity of the designed pile foundations is much more than necessary. The main goal of this study is to develop equations that allow us to evaluate the bearing capacity of the pile foundation in these soils by a non-destructive method. The authors propose semi-empirical equations based on analytical solutions and empirical data, obtained from plate-bearing tests. These equations can be used for an estimation of the bearing capacity of piles of various diameters without conducting expensive field tests. Assessment of the obtained equations reliability showed that the determination coefficient is 0.90 for claystone, and 0.96 for sandstone. This allows us to characterize the obtained approximating functions as theoretical models of good quality. Proposed equations was compared with other methods and static load test results. 10.18720/MCE.97.4 bearing capacity cast-in-place piles design claystone sandstone mechanical properties https://engstroy.spbstu.ru/article/2020.97.4/

RAR RUS 9705-9705 Bryansk State University of Engineering and Technology Serpik Igor iserpik@online.debryansk.ru Bryansk State University of Engineering and Technology Tarasova Natalya tarasova_natalie@mail.ru

Bryansk, Russia

Optimisation of steel trusses with a choice of multi-stage prestressing conditions This paper presents a methodology for optimisation of flat steel trusses with a system of high-strength tie bars, for each of which the possibility of multiple pre-stresses is provided. Pre-stress is one of the most effective ways to increase the carrying capacity of steel trusses with minimum material costs. Besides, a significant effect, according to the literature data, can be achieved by alternating stages of pre-stresses and payloads. At the same time, algorithms for designing such objects while choosing a sequence of force actions still need to be worked out. The problem of minimising the truss cost is considered taking into account strength, stiffness, and stability constraints. A search has been specified for the sequence of alternating the stages of pre-stress and the application of portions of useful loads, pre-stress forces, bar profiles, and cable cross-section area values. Multiple allowable scenarios of force impacts on a redundant template are used. It is acceptable to indicate the load absence condition in such template in some positions. A possibility has been implemented for the cable system to set a redundant topology which is controlled by including the ability to select negligible cross-section areas. As a result, the mathematical statement of the problem is reduced to discrete parametrical optimisation. A scheme of genetic algorithm is implemented with a mixed approach to the mutation operator in order to find efficient solutions. A methodology has been developed to calculate the stress-strain state of steel frameworks pre-stressed using high-strength cables in a single computational process to efficiently check for compliance with the problem constraints. The performance of the suggested procedure of the optimum search has been illustrated by the example of a steel arch truss. A possibility to use bars made of round pipes together with high-strength tie bars was provided. The efficient parameters of the framework and force impact modes have been determined. The expediency of alternating impacts caused by pre-stresses of cables and application of useful load parts is confirmed. The approach proposed will significantly increase the possibility of obtaining cost-effective design solutions for steel trusses. 10.18720/MCE.97.5 steel trusses multiple pre-stresses optimisation genetic algorithm strength stiffness stability https://engstroy.spbstu.ru/article/2020.97.5/

RAR RUS 9706-9706 57200287767 Siberian Federal University Koyankin Alexandr KoyankinAA@mail.ru 12795222600 Novosibirsk state University of architecture and construction Mitasov Valery mitassovv@mail.ru Stress-strain state of the precast monolithic bent element The features of the stress-strain state of a precast monolithic bent element (beam) arising as a result of its phased installation and loading are considered and experimentally investigated. At the first stage, the load is perceived only by the precast part of the beam made of heavy concrete, and at the second stage, monolithic lightweight concrete (expanded clay concrete) is included in the process of deformation and perception of the external load. There were two factors that served as motivation for these experimental studies: − Real precast monolithic structure, mounted on the construction site, in the absence of special structural measures (temporary mounting racks, brackets, etc.) is included in the deformation process in stages, first being the prefabricated part, followed by the monolithic one. This point is in no way reflected in the regulatory documents for design; − Insufficient study of the influence of the phased installation on the stress-strain state of the precast monolithic bent element leads to a biased assessment of its performance. Experimental studies of the stress-strain state of the precast monolithic bent element are performed, taking into account the installation process and the stepwise inclusion of the precast and then monolithic parts in the deformation process. At that, the precast part is made of heavy concrete, and monolithic-of light concrete (expanded clay concrete). The influence of the following factors on the stress-strain state of precast monolithic structures is investigated and studied: the value of pre-loading of the precast part at the first stage; the stages of installation and loading; the height of the monolithic part of the concrete. As a result of conducted research, the new data concerning features of formation of the stress-strain state of the precast monolithic element are received. The positive influence of phase loading and higher height of the monolithic part on the stress-strain state of the precast monolithic structure is revealed. In this case, the insignificant influence of the value of pre-loading of the precast part is determined. 10.18720/MCE.97.6 reinforced concrete compressive strength cracks tensile strength reinforcement experimental investigations precast monolithic structures https://engstroy.spbstu.ru/article/2020.97.6/

RAR RUS 9707-9707 0000-0002-9850-6565 Department of Civil Engineering, Semnan Branch, Islamic Azad University Akhavan Salmassi Mehran m.akhavan.s@stu.semnaniau.ac.ir

Semnan, Iran

0000-0001-7802-2013 Semnan University Kheyroddin Ali kheyroddin@semnan.ac.ir

Semnan, Iran

0000-0003-4867-631X Department of Civil Engineering, Semnan Branch, Islamic Azad University Hemmati Ali ali.hemmati@semnaniau.ac.ir

Semnan, Iran

Seismic behavior of end walls in RC tall buildings with torsional irregularity Many factors affect tall buildings under the influence of earthquake forces. According to the conducted studies, more tensions have been observed in the end wings of shear walls. The end shear wall is used to reduce tensions and to improve the performance of shear walls in tall buildings. In this study, 10-story, 30-story and 50-story concrete buildings with square plans were modeled and two cases of the moment-resisting frame with shear wall and moment-resisting frame with end shear wall, which were under the influence of earthquake and linear static analysis have been investigated. In this analysis, the buildings were torsioned and the results of the analysis showed that the values of the drifts, roof displacement and first period in the structure with the end wall are about 50 % percent less than of that of the building without the end wall, also, On the other hand, with the presence of the end wall in structure the ratio (∆max/∆avg) is more than 1.2, so, the use of the end wall led to a more appropriate behavior of warping in comparison to concrete square frames with no end walls. 10.18720/MCE.97.7 end wall shear wall tall buildings linear static analysis warping https://engstroy.spbstu.ru/article/2020.97.7/

RAR RUS 9708-9708 6504446571 0000-0001-6981-7420 Jordan University of Science and Technology Al-Rousan Rajai rzalrousan@just.edu.jo

Irbid, Jordan

Behavior of CFRP strengthened columns damaged by thermal shock  In the last two decades, using of Carbon Fiber Reinforced Polymers (CFRP) in strengthening of deficient reinforced concrete structural elements has been increased due to their ease of installation, low invasiveness, high corrosion resistance, and high strength to weight ratio. Strengthening damage structures is a relatively new technique. This paper presents a nonlinear finite element analysis (NLFEA) results of reinforced concrete columns confined externally with carbon fiber reinforced polymers (CFRP) subjected to thermal shock impact. After reasonable validation of NLFEA with the experimental test results of companion columns, NLFEA was expanded to provide a parametric study of eighteen columns that correlates the ultimate axial stress of CFRP-confined RC columns to number of CFRP layers and damaged thermal shock. Thermal shock has a significant impact on the behavior of CFRP-confined circular RC columns. The increase in ductility is directly related to a decrease of compressive strength due to thermal shock. Also, the confinement effectiveness in terms of ultimate load was decreased with the increase in concrete compressive strength (un-damaged). The influence of the number of CFRP layers on the ductility, energy absorption, and ultimate load improvement percentage is significant. There will be no further significant increase in the ductility and ultimate load of the column after a certain volumetric ratio, while significant increase in its stiffness continues to occur. 10.18720/MCE.97.8 reinforced concrete thermal shock structural strength axial strength fiber reinforced polymer nonlinear finite element analysis https://engstroy.spbstu.ru/article/2020.97.8/

RAR RUS 9709-9709 0000-0001-9282-3255 Peter the Great St. Petersburg Polytechnic University Egorov Denis egorov.dv@edu.spbstu.ru

St. Petersburg, Russia

57194431559 0000-0003-4992-2084 Peter the Great Saint Petersburg Polytechnic University Galyamichev Alexander galyamichev@yandex.ru

Polytechnicheskay, 29

57209803918 0000-0002-6056-5498 Peter the Great Saint Petersburg Polytechnic University Gerasimova Ekaterina katyageras17@gmail.com

St. Petersburg, Russia

6508223358 Riga Technical University Serdjuks Dmitrijs Dmitrijs.Serdjuks@rtu.lv

1 Kalku Street, Riga LV-1658, Latvia

Stress-strain state of fiber cement cladding within curtain wall system This article presents the experimental methodology and results of laboratory tests and numerical modeling in order to determine the values of bearing capacity and stiffness of fiber cement board (FCB) within a frame of curtain wall system. The performance of a panel as a part of a system is taken into account for evaluation of the stress-strain state of a cladding. An analysis included 2 stages: an experimental study of a full-size fragment of a curtain wall system with fiber cement cladding and its numerical simulation by means of finite element method (FEM). The dependences of the deflection of the panel on a value of uniformly distributed load were obtained, and the experimental results converged with numerical calculation. The maximum values of the uniformly distributed (simulating wind impact) loads acting on the panel under which the panel satisfies the requirements stated by Ultimate and Serviceability Limit States were calculated also. It can be concluded that onset of Ultimate Limit State is characterized by appearance of cracks due to the stresses in the panel exceeding the value of flexural strength in the area of fastening to curtain wall frame. The results demonstrated that the stress-strain state of the cladding depends on the structural scheme of the supporting frame of the curtain wall system and its rigidity, therefore it is recommended to perform tests on the cladding in conjunction with the supporting frame. 10.18720/MCE.97.9 composite materials cements fiber reinforced materials bending strength facades finite element method https://engstroy.spbstu.ru/article/2020.97.9/

RAR RUS 9710-9710 0000-0002-3641-7540 Riga Technical University Prozuments Aleksejs aleksejs.prozuments@rtu.lv

Riga, Latvia

AAV-2280-2020 48361113100 0000-0001-9004-7889 Riga Technical University Borodinecs Anatolijs anatolijs.borodinecs@rtu.lv

Riga, Latvia

0000-0002-7812-3540 Riga Technical University Zemitis Jurgis jurgis.zemitis@rtu.lv

1 Kalku Street, Riga LV-1658, Latvia

Peter the Great St. Petersburg Polytechnic University Strelets Kseniya kstrelets@mail.ru

29 Politechnicheskaya St., St. Petersburg, 195251, Russia

The effect of the air duct tightness on the stability of the indoor air parameters The present study aimed to determine the impact of a gradual and lineal increase of the air duct leakage factor on various indoor air stability parameters in ventilation systems across the following scenarios: 1) air leakage effect on the air pressure and volume; 2) air leakage effect on the indoor air parameters when the ductwork passes through an uninsulated and unheated premise. A galvanized steel air duct was used for the air leakage measurement sessions, and orifices were cut in the duct before each subsequent measurement session, thus, consecutively decreasing the air tightness factor of the duct over the measurement sessions. The results indicated that the ductwork air tightness affects the stability of the air parameters such as air temperature, relative humidity and CO2 concentration, however, up until certain point, the impact was either non-detectable or negligible. The transition in the behavior of the air stability parameters occurred in line with the introduction of orifices 4→5, resulting in perceptible effects on air pressure, volume etc. Although, this factor may be attributed to the errors caused by low instrument sensitivity or by relatively small number and size of the orifices, authors suggest that minor air duct leakage such as presented in this study may result in the disruption of air stability parameters, which in certain instances is critical. 10.18720/MCE.97.10 air duct tightness air quality ventilation HVAC energy efficiency https://engstroy.spbstu.ru/article/2020.97.10/

RAR RUS 9711-9711 6602444316 LLC Research and Production Company “SCAD Soft” Perelmuter Anatoliy avp@scadsoft.com

Kiev, Ukraine

Assessment of the tornado impact on the Chernobyl new safe confinement All the nuclear facility structures must be analyzed for tornado loads. This analysis was per-formed when designing the New Safe Confinement over the ruined Chernobyl power unit (NSC ChNPP). The standard methods of tornado analysis could not be applied due to its large size and geometric shape. Therefore, it was necessary to develop new calculation methods. The paper provides detailed information on the performed calculations and describes the conservative assumptions made when there was not enough information. The purpose of this paper is to analyze the gained experience of performing such an analysis of this unique structure, which may be of some interest. The following two complex problems are considered: • establishing the design tornado parameters; • developing an engineering methodology for the tornado analysis. Moreover, questions are formulated that should be clarified when carrying out similar designs. 10.18720/MCE.97.11 design-basis tornado wind speed Fujita scale Rankine combined vortex model nuclear plant https://engstroy.spbstu.ru/article/2020.97.11/

RAR RUS 9712-9712 57195684636 0000-0001-8800-2657 Voronezh State Technical University Slavcheva Galina gslavcheva@yandex.ru Voronezh State Technical University Artamonova Olga ol_artam@rambler.ru Voronezh State University of Architecture and Civil Engineering Shvedova Maria marishwedowa@mail.ru

Voronesh, Russia

0000-0002-9251-1419 Karaganda State Technical University Khan Maxim han_maks@mail.ru

Karaganda, Republic of Kazakhstan

Clinkerless slag-silica binder: hydration process and hardening kinetics (part 2) In part 1 of the studies, it was shown the results of the implementation of the “top–down” nanotechnological principle to obtain clinkerless binder with a high content of microsilica, activated during grinding what allowed to increase their hydraulic activity. Part 2 of the studies have been implemented in order to ensure the possibility of using of clinkerless slag-silica binder, modified by complex additive of SiO2 nanoparticles in combination with a plasticizer (“bottom–up” nanotechnological principle), as a hydraulic binder. For nanotechnological activation the solution of nano-additives, synthesized by the sol–gel process, is used. Experimental results of changes phase composition and microstructure of clinkerless slag-silica binder during hydration and structuration processes; flocculation and hardening kinetics are presented. The laser granulometry method, dynamic light scattering and transmission electron microscopy were used to estimate the particle size of original components. XRD – method, scanning electron microscope were used to estimate phase composition and morphology of the clinkerless binder’s hydration product. The flocculation was evaluated by the penetrometric method. The hardening kinetics was evaluated by the mechanical tests after 1, 3, 7, 14, 28 day of curing. As a result, the distinctive features of the main periods of heterogeneous processes of structure formation of the nano-activated clinkerless slag-silica binder are revealed at the different stages of hardening. It was established that the “bottom – up” nanotechnological principle, implemented through the introduction of SiO2 – nanoparticles into binder paste allows to increase the hydraulic activity of slag due to the catalytic role of nanoparticles and their chemical interaction with slag minerals. As a result, the strength of the of clinkerless slag-silica binder was 35.8 MPa, and it’s setting and hardening rates corresponds to the speed of these processes for Portland cement under normal temperature-humidity conditions. 10.18720/MCE.97.12 clinkerless binder complex nanoadditive nanosilica hydration phase composition flocculation hardening compressive strength https://engstroy.spbstu.ru/article/2020.97.12/