Manual for design armocement structures developed in NIIZHB named after A.A. Gvozdev in the development of the provisions of SP 96.13330.2016 "SNiP 2.03.03–85 Armocement structures", containing general rules of calculation and design of armocement structures – thin-walled, disperse-reinforced constructions made of fine-grained concrete, as the reinforcement of which narrow thin woven, welded or braided wire steel meshes are used, evenly distributed over the cross-section of the element, usually in combination with rod or wire steel reinforcement. Armocement structures are used for spatial roofs in the form of shells and folded plates, in elements of planar roofs, floors, walls and partitions, suspended ceilings, in elements of sanitary-technical equipment, in decorative elements, etc. The manual contains the necessary theoretical and practical recommendations, as well as examples of calculating the main types of armocement and combined-reinforced (with rod reinforcement) structures of buildings and facilities for various purposes.

The paper is a review of requirements and recommendations for testing methods and ensuring frost resistance of concrete, covering data from more than 70 standards, regulatory and advisory documents. The choice of documents in the article is limited to standards and recommendations from the United States (ACI, AASHTO, ASTM), Canada (CSA, BNQ), Norway (NS-EN), Sweden (SS, SIS), Denmark (DS), Germany (DIN, ZTV, BAW), Japan (JIS), China (GB/T), and Russia (SP, GOST, SNiP), i.e. from the countries most often faced with problems of frost damage of structures. It is shown that a detailed analysis of the data and approaches accumulated in the world construction practice is required, further researches are needed to establish the correlation and relationships between different methods, taking into account different concrete compositions, the type and size of samples, freezing and thawing modes, correlation of the results of field and laboratory tests.

The research work (R & D) was carried out at the A.A. Gvozdev Research Institute of Concrete and Reinforced Concrete, one of the tasks of which was to analyze the existing methodology for calculating endurance in the current SP 63.13330.2018 from the standpoint of the changes in the regulatory and technical base in recent years. The conducted computational and theoretical studies have shown that there are some imperfections in the methodology for calculating domestic standards, the presence of which is a deterrent to its wider application. Based on the results of the research, the composition of the requirements for the endurance calculation method was formulated, which includes general provisions, calculation requirements, endurance calculation and design requirements. In the context of the specified composition of requirements, proposals were developed to supplement and update the methodology for calculating endurance, presented in SP 63.13330.2018, which include the relevant provisions for calculation and design. When developing the proposals, the provisions of the calculation methods set out in SNiP 2.03.01–84 and other regulatory documents were taken into account as much as possible. The prepared calculation proposals are expected to be included in the current regulatory documents as one of the possible options for the final calculation method.

The method of calculating the geometric dimensions of the couplings, as well as the parameters of the rolled and cut cylindrical threads of the mechanical splices of the reinforcement bars is given. The calculation method allows you to select the geometric dimensions of connecting couplings made of different grades of steel for connecting reinforcement bars of different strength classes. The article discusses the calculation method that allows you to select the parameters of mechanical splices of reinforcement bars with both rolled and cut threads, which are fundamentally different from each other in terms of manufacturing method. The methodology is based on the principles of calculating the strength of a threaded rod with a nut loaded with an axial force, which is reflected in the design scheme of forces for determining the length of the coupling and the parameters of the thread of the ends of the reinforcement bars. The calculation method consists of determining the calculated diameter of the rolled or cut thread of the reinforcing bar and selecting the parameters according to GOST 24705–2004. The length of the coupling is determined by the shear and crease stresses. The outer diameter of the couplings is determined by taking into account the safety factor for the load, which takes into account the actual strength of the reinforcement bars. Based on the results of the calculation, a formula for determining the diameter of the stamp for the stamping of the end of the reinforcement bars before performing thread cutting is proposed. Comparison of the calculation results obtained by the proposed method with the parameters of mechanical connections of reinforcement bars with cut and rolled threads of known and approved manufacturers showed satisfactory convergence. The article will be useful for engineers, designers and manufacturers of mechanical connections of the reinforcement bars.

The long-term experience of theoretical consideration and experimental evaluation of concrete fracture resistance as structured systems is discussed. Reliable experimental evaluation of concrete fracture resistance indicators is of great scientific and practical importance for solving the problems both by materials scientists and technologists (synthesis and construction of concrete structures with controlled fracture resistance, development of technological production conditions on this basis) and design engineers (taking into account the special mechanisms of deformation and destruction of modern concrete, their behavior over time). To evaluate the concrete fracture resistance indicators, the methods of obtaining complete equilibrium deformation diagrams, laser holographic interferometry of the surface strain field, determination of the critical stress intensity coefficient at normal separation, and acoustic emission were used. From the standpoint of system-structural materials science, concrete is analyzed as an inhomogeneous dissipative system characterized in the categories of accumulation, dissipation, localization and concentration of stresses in it during the work of the material under mechanical and any other loads that determine the formation of stress and strain fields at various scale levels of the structure. Under the conditions of consistent application of experimental methods of full equilibrium diagrams of deformation, acoustic emission, laser holographic interferometry,and determination of the critical stress intensity coefficient at normal separation, obtaining of quantitative estimates for groups of traditional and high-tech concretes typical in structure in the range of their compressive strength from 30 to 150 MPa is provided. The role of each of the experimental methods considered in a reliable quantitative assessment of the deformation and destruction of modern concretes is shown.

In scientific publications devoted to the theory of creep, there are doubts about the correctness of the superposition principle, which does not work during unloading. The criticized rheological equations of state are constructed for non-decreasing loading modes and it is really not correct to apply them when unloading. In addition, doubts are based on the notorious diagram σ–ε with a descending branch, which can only be constructed when measuring stresses in experiments for a given strain. When constructing rheological equations, a different diagram is used. In principle, the problem is solved in the two-component theory of creep proposed by A.A. Gvozdev and developed by K.Z. Galustov, and this finally closes the issue of the applicability of the principle. In this theory, deformations are divided into partial ones according to the principle of their reversibility. A method of such separation with the possibility of using the existing regulatory framework, which makes it possible to significantly adapt the theory to the needs of practice, is proposed.

Currently, designers are faced with the problem of calculating the strength of inclined sections of reinforced concrete columns. The problem is caused by the fact that in SP 63.13330.2018 there are no clear instructions for determining compressive stresses when calculating inclined sections by strength. This circumstance leads to the fact that at high levels of longitudinal compressive forces, the calculation of strength along inclined sections requires in some cases a sufficiently high content of transverse reinforcement, which causes a significant cost overruns of reinforcement and design difficulties. The article describes the main results of the analysis of the research conducted to assess the impact of compressive stresses on the strength of inclined sections of off-center compressed reinforced concrete elements. The issues of calculating the strength of such structures were considered, as well as the methods of domestic and foreign regulatory documents were analyzed. Based on the results of the analysis, the assessment of compliance of the methodology of current regulatory documents with the results of research was performed.