The ISO/TC71/SC5 subcommittee "Simpli-fied design standard for concrete structures" with a secretariat based in Colombia includes 18 countries - full members and 20 countries with observer status. The main focus of the subcommittee is the development of standards for simplified methods of structural analysis. Currently, 4 standards have been developed and 3 are in development. There are no analogues of this subcommittee in the Russian normative document, and there is no concept of simplified calculation methods, since existing documents almost completely cover the need for normative justification of structures of any complexity. As a result of monitoring the standards of this subcommittee, interesting solutions were found that are recommended for use in updating domestic normative document.

The results of determining the density and strength of concrete based on crushed battle of ceramic bricks obtained by crushing (recycling) of substandard ceramic bricks are presented. Recycling rubble from the battle of ceramic bricks is a material (product), obtained by crushing substandard ceramic bricks, ceramic stones, fragments of brick masonry based on them, as well as concrete and ferroconcrete structures and products with fillers from the battle of ceramic bricks. It is revealed that the recycling crushed stone obtained from non-conditioned ceramic brick and ceramic stones consists of grains of brick fight of various fractions. Recycling crushed stone obtained by crushing brick masonry fragments based on ceramic bricks, ceramic stones, as well as concrete and reinforced concrete structures with aggregates from ceramic bricks, mainly consists of brick grains, mortar grains, as well as brick grains and mortar aggregated into a single conglomerate different fractions. The density of concrete based on crushed stone from the battle of ceramic bricks varies from 1810 to 1974 kg/m³. The strength of concrete based on crushed stone from the battle of ceramic bricks varies from 16.4 to 20.3 MPa.

The article presents the comparative results of determining the structural and physical-mechanical characteristics of FRP rebar, defined by standard methods and the method of non-destructive testing. Based on the results and analysis of the experience of application of non-destructive testing products from composite materials, the recommended method of acoustic guided wave testing of physical and mechanical characteristics of FRP rebar.

Modern principles for the technical assessment of building structures are developing along the path to introducing a risk-informed and probabilistic approach for the decision making related to life cycle management. Based on material degradation functions the risks of negative consequences are estimated for a lifetime, which allows us to designate optimal plans for building structures inspections. It is possible to assign, classify and locate special zones for inspection control during the life cycle, maintaining the risk of failure of the structure at the same level. At the same time, national standards are still focused on declarative forms of assessing reliability and durability, which does not allow us to make an objective prediction of the exploitation resource and its costs. In particular, it was found that many of the provisions related to the technical condition rely on subjective assessments. The article formulates the main tasks and practical recommendations for the development of existing approaches for a more objective assessment of the technical condition, control of the main characteristics of building materials and the development of the most effective strategies for managing the life cycle of structures, buildings and infrastructures.

The article systematizes and analyzes the basic methods for performing probabilistic calculations of building structures. The following methods for the approximate calculation of the safety index are investigated: the Monte Carlo method, the two-moment method (FOSM), the linearization method (FORM or AFOSM), the quadratic approximation method (SORM), and the logical-probabilistic method (LAN). On the basis of the study, a comparative analysis of the methods was performed and general recommendations on their application when performing probabilistic calculations of building structures were proposed.

The analysis of requirements of various state Standards providing weldability of reinforcing steel is carried out. The factors that ensure the weldability of the reinforcement and the strength of welded butt joints are noted. The influence of production technology and chemical composition on the weldability of reinforcement is considered. The requirements of the new GOST 34028-2016, providing weldability of rebar, replacing all other standards for hot-rolled and thermomechanical hardened reinforcement, are considered. The main changes in approaches to providing and assessing the weldability of reinforcement and strength of welded joints in modern standards and standards of the past decades are shown. The practical justification and evaluation of the requirements of GOST 34028 to ensure weldability are given. Experimental data illustrating the influence of the chemical composition and the initial strength of the reinforcement on the strength of welded joints of the reinforcement are presented. The presence of contradictions in various points of the requirements of GOST 34028 to the strength of the welded joint, as well as the innovativeness of some requirements of this GOST to the chemical composition, are marked.

The article presents the results of a brief analysis of the domestic regulatory framework, the systematization of legal, technical and methodological documents, codes of rules, standards related to the design of reinforced concrete beam-free floor slabs. A method for interpreting the results of calculation of building models performed using software systems in linear and nonlinear formulations of the problem proposed. The positive experience of the design and expertise of design solutions and construction of industrial and civil buildings made of reinforced concrete is taken into account. According to the results of work, a methodology for calculating beam-free floor slabs has been developed.

The conditions of crack formation in monolithic reinforced concrete floor slabs, in which due to shrinkage of concrete may develop significant tensile stresses at the bottom fibre of the section, are considered. The data of the checking calculations performed on the formation of cracks taking into account the shrinkage factor of concrete during the period of strength gain and reduction of the deformation modulus due to the (short-term) creep during the strength gain, as well as the formation of cracks taking into account the shrinkage factor of concrete and the actual performance of reinforcement of the floor structure, showed that at the stage of production of the slab it is possible to develop significant tensile stresses in the range from 3.6 to 5.7 MPa, which leads to the formation of cracks with a width of up to 0.42-0.65 mm in the designed reinforcement and the absence of operational loads. The nature of the theoretically predicted location of cracks in the overlap, in general, coincided with the results of their actual observations. Significant internal forces in the floor slabs over the basement, which arose as a result of the natural shrinkage of concrete, are due to the boundary conditions of (rigid) fixing along the perimeter of the slab to the basement walls, limiting their linear deformations in contrast to the "free" intermediate floor slabs. Causing the shrinkage of concrete factors are: insufficient percentage of reinforcement (structural, design) of the lower zones of the plates, taking into account the increase in the thickness of the protective layer from a = 20 mm to a = 45 mm; technological - the unbalanced composition of the concrete; production - insufficient care of concrete during the period of strength gain.

The article considers the normative and technical assurance of the process of scientific and technical support of construction. The analysis of existing documents is carried out. The related organizational issues arising before the executors of works on scientific and technical support of construction are formulated. Measures to improve the regulatory and technical framework are proposed. Scientific and technical support of construction aims to ensure the quality and safety of construction projects by applying advanced technical solutions and scientific methods of prognosis and monitoring the course of solving technical issues that arise at all stages of a project construction, but not replace a mandatory execution by the parties of the construction process requirements for quality assurance of construction works. The current regulatory and technical documentation does not allow to clearly formulate the obligation, types and volumes of work, as well as the requirements for the socalled "specialized organizations" engaged in scientific and technical support of construction. The current situation is fraught with a certain temptation for the developer to reduce costs by "optimization", i.e. the maximum formalization of scientific and technical support of construction. The purpose of the article is to draw attention to the problems of scientific and technical support of construction, as well as to invite all interested parties to the discussion and exchange of experience.

The main construction and technical properties and competitive advantages of products and structures made of monolithic foam concrete, allowing to significantly expand the scope of their application in construction, are analyzed.

The Code of Rules SP 360.1325800.2017 "Steel-fiber concrete constructions. Design Rules", which gives general rules for the calculation and design of steel fiber concrete structures, enacted. In connection with the need to accompany theoretical provisions with practical examples of calculating effective types of structures made of steel fiber concrete, it was necessary to develop methodological materials (manual) for the calculation and design of steel fiber concrete structures. The manual contains the necessary theoretical and practical recommendations, as well as examples of the calculation of the main types of steel fiber reinforced concrete and combined-reinforced (with bar reinforcement) structures of buildings and structures for various purposes. Among the examples presented are beam and slab structures of various sections, eccentrically compressed structures of rectangular and annular sections, thin-walled spatial folded structures.

Experience of application of the standard 10060-2012 "Concretes. Methods for determining frost resistance" shows that with the accumulation of experience in the application of the standard, a certain adjustment of it, is necessary. Such an adjustment can be made on the basis of the analysis of domestic and foreign experience, as well as concrete research. Based on the performed NIIZHB named after A.A. Gvozdeva research frost resistance / frost resistance of concrete obtained experimental data in the scope, allowing to specify the modes of freezing and thawing of concrete samples according to method 3 of GOST 10060.

The technological features of obtaining a cellular concrete mixture with dispersed reinforcement are considered. The optimal conditions for the formation of a cellular concrete mixture with a fibrous additive of asbestos are determined. The results of studies of rheological characteristics to determine the values of the optimal content of dispersed reinforcement of autoclaved cellular concrete from the position of molding and synchronization of the processes of swelling and setting of cellular concrete mixture are presented.. The technological scheme of organized serial production of non-autoclaved fiber foam concrete (basalt and polypropylene fiber) with the release of pilot batches of gypsum partition plates is given. The optimal content of fiber reinforcement, as well as the optimal length and diameter of the fibers in the manufacture of cellular fiber concrete in order to minimize the shrinkage deformation, are determined. The experimental data obtained as a result of studies of crack resistance of cellular fiber concrete, indicating a positive effect of dispersed reinforcement on its crack resistance due to the manifestation of shrinkage deformations. A criterion is proposed for assessing and normalizing the crack resistance of cellular fiber-reinforced concrete, due to the manifestation of shrinkage deformations, according to the crack resistance coefficient К_crc The experimental compositions of autoclaved aerated concrete (fibrogas concrete) and non-autoclaved (fiber foam concrete), as well as fibro-gas-concrete mixtures are given.

The review and analysis of fundamental scientific works in the part of problems of increase of crack resistance of cellular concrete is carried out. The topical issues of application in cellular concrete of dispersed reinforcement with mineral and polymer fiber are considered. The efficiency of fiber reinforcement of autoclaved fiber-gas concrete and non-autoclaved fiber-foam concrete is established. The experimental data obtained as a result of studies of strength and deformation characteristics, as well as crack resistance of cellular fiber concrete, which confirmed the higher strength and deformation qualities of cellular concrete with dispersed reinforcement in comparison with non-reinforced cellular concrete, as well as evidence of the positive effect of dispersed reinforcement on crack resistance and on increasing the resistance to brittle fracture. The experimental ompositions of autoclaved cellular concrete (fiber-gas concrete) and non-autoclaved (fiber-foam concrete) with strength and deformation characteristics are presented. The proposals for the design and calculation of structures from cellular concrete, in particular on the valuation of the strength characteristics (normative residual resistance tensile) are given.

Compensated shrinkage concrete is becoming more widely used in the world. One of the ways to obtain this concrete is to introduce an expanding additive during its preparation. The article provides a comparative analysis of the characteristics of mineral additives and their applicability to extenders. In Russian standards, the quality of shrinkage compensated concrete is evaluated by self-stressing (deformations of specimens hardening in dynamometric jigs). This technique is patented in the Russian Federation and is proposed for inclusion in foreign standards.