Vol 19, No 9 (2024)
Construction system design and layout planning. Construction mechanics. Bases and foundations, underground structures
Resistance of compressed elements with small eccentricity taking into account actual height of the compressed concrete zone
Abstract
Introduction. The load-bearing capacity of normal sections of eccentrically compressed reinforced concrete structures at small eccentricities, according to current regulatory documents, is determined taking into account the linear approximation of the nonlinear dependence of stresses in tensile reinforcement on the height of the compressed zone. This approach is largely simplified and in some cases leads to an unreasonable overestimation of the bearing capacity of elements. The aim of the study is to obtain analytically the most universal and accurate dependence for determining the height of the compressed zone of concrete, the stresses in tensile reinforcement and, as a result, to clarify the value of the maximum bearing capacity of the normal section of eccentrically compressed elements during destruction of the compressed zone in concrete. Objectives of the research: analytical obtaining the dependence for the height of the compressed zone of concrete in the section in the limit state; comparison of the obtained load-bearing capacity, taking into account the obtained dependence, with the simplest dependence adopted in regulatory documents, as well as with the results of calculations using a nonlinear deformation model; determination of the degree of unreasonable overestimation of the bearing capacity of eccentrically compressed reinforced concrete structures with small eccentricities in current regulatory documents.Materials and methods. The main methods used in the modern theory of concrete and reinforced concrete strength were adopted.Results. The analytical expression for the height of the compressed zone is obtained based on the simplified three-linear diagram of the deformation of concrete under compression. Reasonable refinement of the height of the compressed zone makes it possible to achieve maximum convergence with the results of calculations using a nonlinear deformation model without the use of iterative approaches to solving the problem.Conclusions. The proposed dependencies make it possible to determine the actual stress-strain state in normal sections of eccentrically compressed reinforced concrete elements under the action of small eccentricities of application of the longitudinal compressive force in the limit state.
Vestnik MGSU. 2024;19(9):1435-1443
1435-1443
Method of reliability coefficients with adjustable values for steel structures design
Abstract
Introduction. The method of reliability coefficients with fixed values (declared in regulatory documents) is used as a basic method of limit state verification. However, there is a more general formulation of the semi-probabilistic method, within which the specificity of the design (e.g. information on the variability of actual dimensions, material properties, etc.) and the specificity of the location (e.g. information about climatic loads) can be taken into account more accurately. This method is referred to as the modified (adjustable) partial factor method.Materials and methods. The paper is aimed at the development of the method of reliability coefficients with adjustable values for the design of steel structures and the scientific justification of the parameters of this method. The methodological formulation of this method is based on determining the design values of the basic variables based on the distribution function for a given quantile. In this case, the quantile of the distribution is calculated using the sensitivity coefficients of the basic variables of the first-order reliability method and the target value of the reliability index.Results. The study describes in a general formulation a method of reliability coefficients with adjustable values for the design of steel structures, which allows explicitly taking into account the target reliability level and variability of the basic variables. In the course of the study, the scientific substantiation of the sensitivity coefficients of the basic variables based on the first-order reliability method was performed and instructions on the purpose of probabilistic models of random variables were presented.Conclusions. The analysis of the generalized function of the limiting state of the steel element by the probabilistic method showed that the sensitivity coefficients change significantly with the change in the loading parameter (characterizing the ratio of variable loads to the total), while it changes slightly depending on the type of variable load itself. Sensitivity coefficients can be assumed based on graphs or simplified dependencies presented in this study. Conservatively, the sensitivity coefficient values for the bearing capacity of the steel element can be assumed to be 0.6, for constant loading –0.4 and for variable loading –0.9.
Vestnik MGSU. 2024;19(9):1444-1453
1444-1453
Resistance to progressive collapse of monolithic frames of buildings at localized damage of nodes from push-through
Abstract
Introduction. When designing buildings and structures it is necessary to ensure mechanical safety throughout the life cycle of the object. During the operation of buildings, situations arise in which monolithic load-bearing structures acquire defects in the area of the slab-column connection (SCC) in girderless slabs. These are, first of all, cracks caused by bending of slabs and slab pushing through by columns. The problem of taking into account the operation of structures with regard to such data of local damages in emergency situations is not sufficiently studied. In a number of cases the loss of bearing capacity of nodes is of brittle nature, which is not allowed by normative documents, as it can lead to progressive, including avalanche-like, destruction of neighboring elements.Materials and methods. The bearing capacity of elements and the degree of resistance to progressive failure of a 9-storey monolithic girderless frame under different scenarios of initial local damages are determined. Three levels of such damage are introduced, and the slab and column connection nodes are modeled by volumetric finite elements. Verification of the computational model is performed experimentally by in-situ pushover tests of the SCC under central load application. Simulia Abaqus software package is used for the purpose of calculations. The CDP model is used for modelling of concrete deformations, and bilinear diagrams with hardening are used for modelling of reinforcement deformations.Results. Experimental data on the deformations of the slab-column connection under longitudinal force loading and realization of the push-through mode are obtained. Taking into account the selected damage levels and experimental data, calculations of the monolithic frame with different damage scenarios in the investigated nodes are carried out. The nature of force redistribution for frames with different levels of such damage and the degree of their danger in the realization of progressive failure are established.Conclusions. It is determined that damages in the nodes of column and girderless slabs interfaces can lead to redistribution of forces and changes in the character of slab operation. These changes can initiate progressive failure in emergency situations in case of structural solutions of nodes with two-sided and three-sided design contours in terms of CP 63.13330 for push-through calculations. Additional design justification is required for such nodes.
Vestnik MGSU. 2024;19(9):1454-1468
1454-1468
Deformation approach to the calculation of compressive strength of steel-reinforced concrete elements
Abstract
Introduction. Compressed steel-reinforced concrete structures, due to the requirements of reduced cross-sectional dimensions for vertical load-bearing structures with high strength and rigidity of structures, as well as their fire resistance, are widely used throughout the world in the construction of high-rise buildings, entertainment structures, etc. Methods for their calculation are constantly being improved. The deformation approach to calculation makes it possible to obtain the parameters of their stress-strain state (SSS) at any stage of deformation under load, to take into account physical nonlinearity of the materials and the loading stages.Materials and methods. The selection of compressed steel-reinforced concrete elements for the theoretical study was made according to the data published in open sources. A cross-sectional model was compiled, taking into account the joint work of concrete, rigid and flexible reinforcement, and their deformation diagrams, taking into account physical nonlinearity. A criterion for the destruction of the cross section of a steel-reinforced concrete element without limiting the limiting deformations of materials under compression is proposed.Results. The prerequisites for using the deformation approach to the calculation of steel-reinforced concrete elements are formulated. Two stages of their operation are considered: under the action of forced shrinkage deformations during concrete hardening and subsequent loading. Using examples of the accepted specimen of compressed steel-reinforced concrete elements, the advantages of the deformation approach in their calculation are shown.Conclusions. The deformation approach to calculation makes it possible to obtain the SSS parameters of compressed steel-reinforced concrete elements of arbitrary cross-section shape with different distribution of reinforcement over the cross-section, to take into account the nonlinearity of deformation of materials, concrete shrinkage. The proposed criterion for the destruction of compressed steel-reinforced concrete elements allows to take into account the redistribution of forces between concrete, rigid and flexible reinforcement to full extent.
Vestnik MGSU. 2024;19(9):1469-1483
1469-1483
Experimental studies of the influence of deformations in nodal joints on the stress-strain state in a full-scale support made of MIC-C
Abstract
Introduction. Deformations in bolted joints of elements in theoretical studies were taken into account by introducing linear deformation modules of elements instead of elasticity modules. The necessity to take into account the deformability of the interfaces is due to the fact that rigid nodes of rod structures are actually deformable, while hinged ones are able to perceive moments. The pliability of bolted joints leads to increase in the total deformations of structural structures by 40 % and change in the forces in the elements by up to 30 %. In some cases, the forces in the elements change the sign.Materials and methods. The experiment was carried out with the assistance of Bridge Crew No. 81 on a full-scale design of an auxiliary support for the semi-mounted assembly of the bridge span structure, coordinated with the Central Research Institute and Glavmoststroy. The vertical load on the support was created by the weight of the bridge superstructure being mounted, the horizontal load was created using a cable attached to a C-100 bulldozer tractor. Cable tension control with a bulldozer was performed with a dynamometer. Relative deformations were measured using beacons drilled into the body of the elements using a strainmeter with a base of 505 mm and a division price of 0.01 mm. The displacements in the bolted joints of the elements were measured with a strainmeter with a base of 125 mm.Results. The experimental force values obtained in the presence of displacements in the joints of the auxiliary support are quite close to the calculation results according to the proposed method. The average value of the ratio of experimental forces in the elements, taking into account displacements in the joints, to the values of theoretical forces without displacements (according to the hinge scheme) and to the values of theoretical forces, taking into account displacements in bolted joints, according to the proposed methodology, are 0.84 and 1.05, respectively. The average relative change in forces caused by displacements in the joints of the elements is 48 % for braces and 18 % for racks.Conclusions. It is shown that the experimental values of the forces in the elements are close to their calculated values determined by the calculated modules of linear deformation. At the same time, the magnitude of the forces differs significantly from their values obtained by calculation without taking into account the displacements in the elements.
Vestnik MGSU. 2024;19(9):1484-1493
1484-1493
Development of the calculation methodology of cross-beam foundation on the sloping base complicated by karst and sinkhole processes
Abstract
Introduction. A calculation scheme of karst sinkhole in karst territories using the results of laboratory experimental studies is developed, which makes it possible to determine the shape and size of karst sinkhole depending on the karst cavity dimeter (radius), its depth, the base slope angle and the angle of internal friction of soils composing the slope.Materials and methods. The method of calculation of normal contact stresses in the sloping soil base under the bottom of the cross-beam foundation during the formation of karst sinkholes is given, considering three main cases of karst cavity location in the slope massif with the most unfavourable location of the karst cavity relative to the cross-beam foundation structures.Results. The analytical dependence allowing to determine the theoretical value of the design value of the diameter Lc of the cavity in the sloping base is obtained, as well as to establish the main design dependences for determining the normal contact stresses, which allow to estimate the changes in the VAT parameters of the cross-beam foundation operation after the cavity vault collapse and formation of a complex shape of the collapse funnel.Conclusions. The developed methodology is convenient to use for qualitative assessment of design solutions in the design of cross-beam foundations on a sloping base in karst-prone areas. The obtained variant design values of the main VAT parameters according to the proposed methodology will allow to apply rational design solutions in design.
Vestnik MGSU. 2024;19(9):1494-1504
1494-1504
A review of the world experience in full-scale testing of existing reinforced concrete structures
Abstract
Introduction. Domestic and foreign experience of full-scale tests is analyzed. The retrospective of development of standards for conducting full-scale tests in Russia and the USSR is presented. The review of the world regulatory documents regarding the requirements for conducting full-scale tests of structures is carried out, which showed insufficient research of this question both in our country and abroad. The obtained review can be the basis for the development of the national standard of the Russian Federation for conducting full-scale tests.Materials and methods. Analytical review.Results. The state of the issue and the application of stress tests (full-scale tests) in our country, as well as in Germany, the USA, Italy, Canada, Australia, Switzerland and other countries are shown. The minimum requirements for the target test load during testing, the loading mode and acceptance criteria for the experimental assessment of the load-bearing capacity of existing load-bearing structures specified in various standards are given. Specialized criteria for the acceptance of load-bearing structures, such as the permanency ratio and deviation from linearity index, mentioned in individual standards, are analyzed.Conclusions. The similarity of common approaches and the lack of unified requirements for conducting this type of research and evaluating their results are noted. The necessity to develop a national standard of the Russian Federation for full-scale tests of erected reinforced concrete structures is considered.
Vestnik MGSU. 2024;19(9):1505-1520
1505-1520
Construction material engineering
Sound-absorbing properties of porous glass ceramics from zeolite-containing rocks
Abstract
Introduction. Sound-absorbing systems are widely used in construction, reconstruction, repair of industrial and civil facilities, as well as in mechanical engineering. The most affordable and widely used systems are those using porous materials. The influence of the type, size, nature of pores, as well as phase composition of porous glass-ceramic samples obtained from zeolite-containing rocks on its sound-absorbing properties was established.Materials and methods. The results of experimental studies were obtained by the impedance method, as well as by methods of X-ray phase analysis, light microscopy, X-ray microtomography, etc.Results. Porous glass-ceramic materials with average density grades D250 and D300, compressive strength class B3.5, thermal conductivity coefficient from 0.066 to 0.079 W/m∙°C and recommended maximum application temperature up to +850 °C were investigated. The total porosity of the tested specimens of glass-ceramic materials was from 87.7 to 90.1 %, and the number of open pores from to 18.3 %. The sound-absorbing properties of porous glass-ceramic specimens are directly dependent on the open porosity of the material. With an increase of this indicator from 4.5 to 18.3 %, the sound absorption coefficient of the material increased 1.5–2 times, depending on the range of sound frequencies.Conclusions. Porous glass ceramics obtained from zeolite-containing rocks have good physical and mechanical properties and a high application temperature (at least +850 °C), and with a high open porosity index, it can be recommended for application as sound-absorbing materials in construction and mechanical engineering facilities.
Vestnik MGSU. 2024;19(9):1521-1529
1521-1529
Hydraulics. Geotechnique. Hydrotechnical construction
Influence of the coefficient of non-uniformity of expansion of clay soil specimen on mechanical characteristics
Abstract
Introduction. Determination of strength and deformation characteristics of soils composing the soil mass is the key process of calculation and design of structures of all types. High accuracy in determining mechanical characteristics plays a huge role at every stage of project development. Triaxial compression units are one of the most popular and widely used devices for laboratory research, as this type of testing allows you to reproduce the stress-strain state of the soil mass and determine its mechanical characteristics most accurately.Materials and methods. Experimental studies were performed on clay soil specimens (sandy loam, loam, clay) in a triaxial compression device in a consolidated-drained mode in order to study the effect of the coefficient of non-uniformity of expansion of the soil specimen on its mechanical properties.Results. Analyzing the data of experimental studies, it was found that the coefficient of non-uniformity of expansion of specimen b has a significant effect on the obtained values of the mechanical characteristics of clay soil, namely: the values of the angle of internal friction in the medium increased by 5 %; the values of specific adhesion increased by 4.4 % on average. However, it should be noted that despite the increase in the strength characteristics of the tested soil specimens, the exclusion of the coefficient b from the treatment process led to a decrease in the values of the secant deformation modulus at 50 % strength E50 by an average of 4.5 %.Conclusions. The obtained overestimated values of strength characteristics φ, c and underestimated values of deformation characteristics E50 are not critical, however, to increase the accuracy of calculations performed based on the results obtained as a result of in-house processing of laboratory test specimens, the coefficient of uneven expansion b of the specimen should be taken into account.
Vestnik MGSU. 2024;19(9):1530-1540
1530-1540
Engineering systems in construction
Hot water treatment in autonomous heat supply systems with several water intake points
Abstract
Introduction. Improving the energy efficiency of HVAC equipment makes the greatest contribution to reducing the man-made impact on the environment. The peculiarities of using gas heaters for several hot water disassembly points are related to the comfort of hot water consumption. Two points are included in this concept. The delay in the start time of hot water supply from the moment the tap is opened and the fluctuation of hot water temperature when several water intake points are used at random at the same time. The aim of the study is to investigate the operating modes of hot water of gas heaters, to determine the influence of algorithms for modulation of thermal power and thermal inertia of heat exchangers on the change in the temperature of hot water supply with the simultaneous use of two water intake points.Materials and methods. The study was carried out on the research stand of the “ARDERIA” plant. Objects of research — Gas Instantaneous Water Heater with Thermal Power Modulation Ariston FAST EVO ONT C 14, Arderia D24 and Arderia D24 Atmo wall-mounted gas boilers.Results. The coefficients of thermal inertia of the heat exchangers of the studied specimens, the value of temperature change at the main point of water intake (shower) during periodic connection and disconnection of the tap in the kitchen were determined. Comparisons of the thermal power modulation algorithms of the specimens under consideration are given.Conclusions. Operation of autonomous hot water supply systems with several water intake points leads to water temperature fluctuations with a range of up to 10 °C. Water temperature equalization time is up to one and a half minutes. The solution to the issue of ensuring a given comfortable level of water temperature is achieved by organizing the consumption of hot water and cold water in accordance with the level of priority of water consumption at various water intake points, the use of buffer heat tanks or heat generators with a large range of heat power regulation and reduced thermal inertia of heat exchangers.
Vestnik MGSU. 2024;19(9):1541-1549
1541-1549
Technology and organization of construction. Economics and management in construction
Assessment of economic efficiency of artificial intelligence application in construction: the choice of the optimal method
Abstract
Introduction. The review of existing ideas of artificial intelligence implementation in the construction industry is carried out. On the basis of the studied data the applicability of the technologies was analyzed and their economic efficiency was evaluated, as well as the feasibility of investment in potential projects was substantiated. Construction is a fundamental area of human life, in which the use of information technology innovations, especially artificial intelligence should be associated with a balanced decision and thorough testing. For this reason, it is required to choose the most appropriate method to evaluate the feasibility of implementation. By the chosen method it is possible to reveal the possibilities of a new project and to correlate it with all costs and risks.Materials and methods. Russian and foreign studies, Internet resources and conference materials were studied. As a result, the current trends of technologies of artificial intelligence application in construction were found. The integrated method allowed to consider technologies from the point of view of ideology, reality of embodiment, practical application and economic feasibility. The method of scoring of projects was applied and the list of technologies was compiled. This list includes technologies that are favourable for application and promising for development. Multilevel study of the selected projects was carried out according to the system modelling approach.Results. Based on the results of the study, conclusions are made about the best method for assessing the economic efficiency of innovative projects based on artificial intelligence, which are applicable to the construction industry. The theoretical model is aimed at considering the project as a process of cause-and-effect relationships. This project reveals the list of necessary steps and their sequence.Conclusions. This study on the effectiveness of the implementation of AI in construction of some ideas revealed an optimal and sufficiently informative method of assessing the economic efficiency of projects, as well as the degree of relevance and compliance with the interests and needs of the construction industry. A list of recommendations for the process of implementation of a new project with the use of artificial intelligence is presented. A vector for further research in the field of practical calculations of efficiency and forecasting is proposed.
Vestnik MGSU. 2024;19(9):1550-1561
1550-1561
Methodology of evaluating of factors affecting the efficiency of construction project implementation by general contracting organization in Fit-out direction
Abstract
Introduction. The demand for interior design services (Fit-out) in Russia began to grow actively in recent years, so the research in this area, aimed at improving the efficiency of project implementation, is relevant. Despite the relevance of this direction in our country, in the scientific community the topic of interior design (Fit-out) is touched upon only in the field of BIM modelling. The stages of research on revealing the dependence of the choice of organizational and technological solutions by general contracting organization on the terms of construction project implementation in the direction of Fit-out are presented.Materials and methods. Literary sources, scientific publications, Internet resources were studied. The analysis of design and estimate, production, organizational and technological, executive, tender, financial and reporting and other documentation, with which the studied factors affecting the efficiency of construction project implementation by general contracting organization in the direction of Fit-out are connected, is carried out.Results. The dependence of the identified factors and the analyzed documentation is determined. The performance criterion — the period of realization of the construction project Fit-out is established. As a tool for assessing the efficiency of construction project realization “Complex indicator of efficiency of construction project Fit-out” is accepted. The formed system will be the basis for the development of a methodology for determining the efficiency of construction project implementation by the general contracting organization in the direction of Fit-out.Conclusions. Completed projects are required to be evaluated for achievement of the company’s objectives and quality of work. These evaluations can serve as feedback for future projects and for process improvement. In addition, these evaluations can be used to make adjustments to organizational, technological and management decisions during the construction process to achieve goals.
Vestnik MGSU. 2024;19(9):1562-1569
1562-1569