The article presents the results of an experimental study of the effect of loading speed on the deformation and strength characteristics of concrete of class B45 under central compression. 15 prisms measuring 100×100×400 mm, divided into three series according to the loading speed, were tested. Regression dependences are constructed, correlation coefficients (up to 0.9975) and determination coefficients (up to 0.9950) are determined, confirming the high degree of consistency of the models with experimental data. It is established that an increase in the loading rate contributes to an increase in strength and a decrease in the magnitude of the marginal relative deformation of concrete. The obtained dependences can be used as an experimental basis for constructing a nonlinear deformation method for calculating bent and non-centrally compressed reinforced concrete structures made of concrete of the class under consideration (B45), subject to static and high-speed impacts.

Keywords: experiment, concrete samples, high-speed loading, central compression, statistical processing of results, least squares method, regression curve

The paper presents an analysis of experimental data reflecting the influence of the loading rate on the strength and deformation characteristics of concrete of class B25 under conditions of central compression. 12 prismatic samples with dimensions of 100×100×400 mm, distributed in three series with different load application rates, were prepared and tested for the study. Statistical data processing, including analysis of variances and the construction of regression models, allowed not only to predict the behavior of concrete under various loading conditions, but also to confirm the theoretical prerequisites associated with the dynamic hardening of the material. The high values of the correlation coefficients (up to 0.9943) and determination (up to 0.9922), as well as the Fisher criterion, which significantly exceeds the tabular thresholds, characterize the high reliability of the results obtained, indicating an increase in concrete strength with an increase in loading speed and a simultaneous decrease in its deformability. The derived dependences can serve as an experimental basis for the development of a nonlinear deformation method for calculating bent and non-centrally compressed reinforced concrete structures made of concrete of this class (B25), subject to short-term impacts, including classical static loads, as well as dynamic loads of medium duration, characteristic of the operating conditions of structures under the influence of factors such as the movement of overhead cranes along crane beams or the passage of fire trucks along the overpass. The results obtained contribute to a more accurate consideration of dynamic effects in the design and calculation of reinforced concrete structures operated in such conditions.

Keywords: experiment, concrete samples, central compression, loading rate, strength, marginal relative deformations, dynamic hardening, correlation and regression analysis

The article discusses modern approaches to the calculation of embedded parts using the most common computing systems in the design environment. The main purpose of the work is a comparative analysis of the stress-strain state of the support plates and anchor rods when calculating in various computing complexes in order to obtain the most reliable and complete results necessary for the designer to ensure reliability when designing components of building structures. In addition to the above, the article focuses on ensuring the rigidity of the support plates, in case of compliance with which, the nodal structural element is able to withstand a single impulse impact.

Keywords: computing complexes, embedded parts, calculation methods, calculation situations, dynamic coefficient, strength indicators

The article discusses modern methods for protecting load-bearing structures from progressive collapse, as well as methods for their calculation in extreme conditions, in order to ensure the safety of buildings and structures, reduce material damage and minimize human casualties as a result of emergency situations. The main purpose of the work is to identify the imperfections of existing methods for calculating building structures against progressive collapse, regarding multi-storey residential complexes, which are characterized by girderless frames, which have significant architectural advantages, as well as revealing the inaccuracies of empirical formulas used in practice for determining the coefficients of dynamic strengthening in tension and compression, which entails a calculation that does not correspond to the actual work of structures.

Keywords: beamless frame, progressive collapse, protection measures, calculations, dynamic coefficient, dynamic strengthening coefficient