Introduction. This paper examines analytical methods for calculating of loop joints in monolithic reinforced concrete structures. The main focus is on analyzing failure mechanisms that differ from classical reinforcement overlap and determining structural strength conditions.

Aim. To identify the main possible failure mechanisms of loop joints, develop an analytical model of their behavior, and propose an improved calculation methodology to ensure the reliability of connections.

Materials and methods. The study is based on an analysis of existing calculation methods as well as the results of numerical and full-scale experiments. Three main failure mechanisms are considered: local concrete crushing, failure of the concrete core between loops, and loss of reinforcement bond with concrete. A frame-bar model is proposed to describe force transmission through the concrete core.

Results. Based on the analysis of physical and numerical experiment data, as well as international experience, additions and alternative solutions to the currently adopted methodology are proposed.

Conclusions. A comparative analysis of calculation results using different methods revealed some discrepancies. For further development and refinement of analytical calculation methods for the concrete core of loop joints, continued physical and numerical experimental studies are recommended.

Introduction. In modern conditions, the design of reinforced concrete structures requires prompt processing of a large amount of regulatory data presented in text format. The task of automatization of the extraction and analysis of information from regulatory documents is becoming urgent, as it makes it possible to increase the accuracy and efficiency of design work.

Aim. Development of the information model integrating algorithms for processing regulatory documents (using the example of SP 63.13330.2018) with design systems.

Materials and methods. The Mistral language model, deployed locally through Ollama, is used to process text data. Key entities (material parameters, loads, requirements) were extracted automatically, and their relationships were visualized in a graph database. The integration of the calculation and design systems is carried out using the IFC and XML formats. The formulae are implemented (for example, the calculation of the length of the reinforcement anchoring) in Python, and the automation of reinforcement selection is carried out in the Revit environment.

Results. The application of the proposed algorithm has made it possible to automate the extraction of material parameters, design characteristics and design requirements, which significantly reduces the complexity of routine operations. The integration of the calculation model with the design environment (Revit) has provided automatic selection of reinforcement and welded meshes, contributing to increased design accuracy and reducing the likelihood of errors.

Discussion. The developed system demonstrates high efficiency in automating the processing of machine-readable regulatory documents, which leads to a reduction in design time and an improvement in the quality of construction work. Further research will be aimed at expanding the algorithm to work with other types of documents and adapting the model to specific engineering analysis tasks.

Conclusions. Machine-readable documentation formats and LLM models increase the accuracy and speed of processing of the regulatory data. Integration of the calculation and design systems via IFC/XML reduces labor costs and errors. Automation of reinforcement selection demonstrates the potential for scaling to other design stages.

Introduction. The results of studies of high-strength self-compacting cement systems with various types of aggregate are presented, that show that the reduced average density and the possibility of changing the modulus of elasticity in a wide range make high-strength lightweight concretes the preferred structural material, allowing to reduce the weight and the consumption of reinforcement of reinforced concrete structures of high-rise buildings, bridges and overpasses, as well as buildings being built in earthquake-prone regions.

Aim. Comparative assessment of the effect of the type of aggregate of dense rocks and light porous materials on the average density, strength and deformation characteristics of high-strength self-compacting cement systems – cement stone, fine-grained, heavy and light concrete.

Materials and methods. All cement systems were manufactured using modified high-strength cement stone of the same quality based on Portland cement and an organomineral modifier of the MB type in an amount of 24 % by weight of cement with a true water-binding ratio of 0.25. Aggregates of dense rocks (quartz sand, granite and basalt crushed stone) and light porous materials of artificial (expanded clay gravel) and natural (tuff crushed stone) origin were used in the production of concrete.

Results. The strength (cubic and prismatic compressive strength) and deformation (initial modulus of elasticity, Poisson ratio and maximum relative compression deformations) characteristics of six high-strength self-compacting cement systems of compressive strength classes B64–B88 with a wide range of average density (from 1842 to 2497 kg/m³) were determined using standardized and special techniques. The resistance of concrete to axial compression is in the range of 55.2–78.4 MPa and significantly exceeds the regulatory values for SP 63.13330.2018. The maximum relative deformations of high-strength concretes depend more on the volume content of cement stone than on the type of aggregate and compressive strength. The introduction of light porous aggregates into the cement system instead of aggregates from dense rocks made it possible to obtain high-strength self-compacting lightweight concretes of classes B64–B72 with an average density reduced by 17–26 % and an elastic modulus of 29.5–33.9 MPa.

Conclusions. Varying the type and volume of aggregates used makes it possible to obtain high-strength self-compacting light, fine-grained and heavy concretes of classes B60–B100 grades of average density D1800–D2500 with adjustable deformation characteristics.

Introduction. In connection with the introduction of the Amendment No. 1 to State Standard 10060-2012 "Concretes. Methods for determining frost resistance" the Institute has received an increased number of requests related to the use of various climatic automatic chambers to perform tests to determine the frost resistance of concrete. An analysis of the design solutions and the principle of operation of climate chambers presented on the Russian market has shown that in most chambers the thawing process occurs either with warm air blowing, or is implemented by incomplete immersion of sample containers in a solution of 5 % sodium chloride, i. e. it is a deviation from the regulatory requirements. It should be noted that the unit of measurement for frost resistance (i. e., the freeze-thaw cycle) is a conditional value and the use of such a unit of measurement requires testing under strictly regulated conditions. Various approaches to changing the methods of concrete testing for frost resistance, including the method of samples thawing after freezing, can lead to an unreliable assessment of the quality of concrete, that in real conditions will lead to a decrease of the safety of construction sites.

Aim. Assessment of the effect of various methods of thawing samples during the cycle of freezing and thawing according to the accelerated third method of the State Standard 10060-2012 with Amendment No. 1 on the frost resistance of concrete.

Materials and methods. The results of determining of the frost resistance of concrete according to the accelerated cooling regime of State Standard 10060-2012 with Amendment No. 1 are presented with various methods of samples thawing – under conditions of complete or incomplete immersion of sample containers in a thawing medium – a solution of 5 % sodium chloride and under conditions of blowing sample containers with warm air.

Results. Based on the results of experimental studies, the coefficients of transition (K) from the grade of concrete in terms of frost resistance, determined by thawing under conditions of incomplete immersion of sample containers in a solution of 5 % sodium chloride and blowing warm air into sample containers, to the grade of concrete, determined by the standard method of samples thawing in a bath with a solution of 5 % sodium chloride. The following average K coefficients were obtained for concretes of various grades in terms of frost resistance, respectively, for F₁200–F₁300/F₁400–F₁500: K = 0.7/0.6 when samples are thawed when sample containers are not fully immersed in a solution of 5 % sodium chloride; K = 0.8/0.9 with samples thawing under conditions of blowing samples with warm air.

Conclusions. The determination of the frost resistance of concrete by the accelerated third method with thawing after freezing sample containers in a bath with a solution of 5 % sodium chloride is optimal in terms of the most negative effect on the frost resistance of concrete. At the same time, the method of samples thawing with incomplete immersion in a solution of 5 % sodium chloride turned out to be the most "harsh". The regime of thawing of samples by blowing warm air into sample containers showed a significant variation in the determined parameters – compressive strength and mass. The coefficient of variation of the transition coefficients for this method of thawing significantly exceeds the standard value of 9 %.

Introduction. The article presents the results of determining the properties of layered porous materials selected from the depths of the structures of cultural heritage sites, which are more or less susceptible to long-term exposure to moisture. The obtained data are compared with the properties of new materials used in similar structures and other objects according to literary sources.

Aim. Identification of signs of changes in the properties of layered porous materials occurring not only in the surface layer, but also throughout the entire depth of the structure.

Materials and methods. The presented studies are based on the results of the author's tests of more than 2,500 samples of materials from 24 architectural monuments of different times and locations that are under the long-term influence of adverse operational factors.

Results. The results show that, unlike homogeneous materials, the destruction of layered systems does not occur in layers, starting from the surface, but simultaneously throughout the entire volume of the structure.

Conclusions. A significant change in the properties of materials in all studied areas shows that, unlike homogeneous materials, the destruction of layered systems does not occur in layers, but in the volume of the entire depth of the structure.

Introduction. The article is devoted to an employee of the Research Institute of Reinforced Concrete, Doctor of Technical Sciences, Professor I.G. Ludkovsky, a specialist in the field of building materials and technology, one of the founders of the scientific school in the field of reinforced concrete spatial structures. The author analyzes the versatility of the views of Isaac Grigorievich Ludkovsky, who improved and implemented many technological processes for the use of reinforced concrete on important domestic construction sites. He participated in the implementation of a new method of manufacturing of the reinforced concrete stress-reinforced pipes of large diameters, for which he was awarded the Stalin Prize (1951).

Aim. The study of Professor I.G. Ludkovsky's fruitful scientific activity in the field of reinforced concrete theory, his creation of progressive reinforced concrete spatial structures, and the addition of new facts to the scientist's scientific biography based on the study of newly discovered data.

Materials and methods. The author, having studied archival materials on a relevant topic, using retrospective, historical, typological and comparative research methods, showed certain aspects of the scientific activity of Doctor of Technical Sciences, Professor I.G. Ludkovsky, determining the degree of his active participation in the development of the theory of reinforced concrete, specifying the most significant achievements of the researcher in construction science.

Results. The article provides the first comprehensive study of Professor I.G. Ludkovsky's scientific activities in the field of concrete and reinforced concrete applications in the construction industry, and analyzes the newly discovered biographical data of the scientist in the period of 1911–1990.

Conclusions. The source base of the research has been expanded, new archival documents and materials have been introduced into scientific circulation, confirming the uniqueness of the versatile personality of Professor I.G. Ludkovsky, his outstanding achievements in construction science in the period of 1935–1990, who laid the foundations of a scientific school in the field of reinforced concrete spatial structures. The role and place of Professor I.G. Ludkovsky as a construction scientist in construction science are also determined. The article notes the great national and economic importance of the research activities of the team of scientists of the Research Institute of Concrete and Reinforced Concrete named after A.A. Gvozdev to create a new direction in construction science – stress-reinforced reinforced concrete pipes of large diameter, reinforced concrete large-span spatial structures, which significantly reduced the cost and accelerated the construction of industrial buildings, resulting in significant economic advantages nationwide.