Vol 20, No 5 (2024)

The relevant problem of concrete strength in the near-reinforcement zone is solved as a problem of volumetric stress-strain state with the “closure” of output integral parameters of this zone on the framework of the whole reinforced concrete element, synthesizing hypotheses and dependencies of various disciplines of solid mechanics, including fracture mechanics. The model of reinforced concrete element takes into account Vl.I. Kolchunov’s effect of reinforced concrete, which describes the mechanism of formation and development of transverse and longitudinal cracks. In this respect, generalized hypotheses of linear and shear strains for warping and gradients of relative mutual displacements of reinforcement and concrete are adopted. New functionals of reinforced concrete are constructed, which are consistent with the physical interpretations of the strength of cross-sections of bar elements in near-reinforcement zones. Constitutive equations for the concrete matrix, which models zones between transverse cracks, are written. The displacement components for the nearreinforcement zone in relation to the crack opening width at the “concrete-reinforcement” contact interface in transverse, longitudinal and radial cracks, respectively, are found. The use of the adopted assumptions and a multi-level calculation approach for the near-reinforcement region brings the model significantly closer to a real evaluation of the physical phenomena.

Bridge structures are often subjected to extreme conditions such as rough weather, earthquakes, impacts from traffic accidents, and even blasts. Such extreme loads can cause damage to the anchorage zones as a result of high stress concentration and can lead to cable loss. Such extreme loads can cause dam-age to the anchorage zones as a result of a highstress concentration and can lead to cable loss. One of the main targets of this study is to develop an analytical method that increases our understanding of the behavior of long-span cable-supported bridges in the case of the failure of one or several cables,through this method, a formula can be deduced to calculate dynamic amplification factor (DAF) more accurately, which could be useful for academic research. In this study, a parallel-load bearing system is considered as a conceptual model of long-span cable-supported bridges. The objective is to investigate the structural robustness of long-span cablesupported bridges in a cable-loss scenario. The conceptual model consists of a beam suspended from cables (tension elements). A simplified model is intentionally selected to make the analytical approach easier. If examining the simplified model shows a certain phenomenon, a similar phenomenon in more sophisticated models can also be expected. The study considers multiple cable failures and employs an analytical approach, developing an approximation function for stress magnification factor in cable break scenarios, using least squares method. The proposed approximation function is accurate and less than 5% error-free in all tested systems, except for minor β values, and increasing β reduces stress magnifica-tion factor. The parameter β influences the calculation of the cable load. For systems with high β values, smaller design loads are necessary, allowing long-span cable-stayed bridges to be segmented into zones with varying β values. This approach enables the determination of minimum design loads for each zone, ultimately reducing cable design costs in cases of cable loss.

Shallow shells of double curvature are often used as elements of building structures and are subjected to various external effects, including dynamic periodic loads. The paper proposes to extend the previously proposed approach to modeling the process of deformation of thin shells to a class of problems with periodic effects. A mathematical model is used based on the Timoshenko - Reissner hypotheses, taking into account transverse shears, geometric nonlinearity and rotational inertia. The calculation algorithm is based on the method of L.V. Kantorovich and the Rosenbrock method for solving rigid ODE systems. The calculations are performed in Maple. Dynamic responses are obtained for an isotropic shallow shell of double curvature at different frequency values, and vertical displacement fields are shown at peak values of the oscillation amplitude.

The possibility of using computational methods to take into account the service life, nonlinearity and rheology of deformation of the materials used and potential corrosion damage of various reinforced concrete structural elements already at the design stage, which will allow to determine cross-sectional dimensions and assign the required grades of concrete and reinforcement, is studied. The considered process of long-term deformation of reinforced concrete under varying external load conditions is based on the integral estimation method of deformation resistance, which relies on the use of integral deformation modulus. A method for calculating a reinforced concrete frame on a soil base in aggressive environment under the conditions of rheological deformation has been developed, which reflects the real operation of structural elements under the combined influence of force and non-force factors based on the modern phenomenological theory of deformation of an elastic creeping body. Long-term operation of a reinforced concrete frame on a soil base, taking into account corrosion damage, is evaluated. An example calculation of a reinforced concrete frame of a building on a soil base is given for various operation periods and the presence of corrosion damage. It is shown that damage due to exposure of reinforced concrete structures can affect the strength of the material, change the calculation models, redistribute stresses in the cross-sections of the structure and also lead to other consequences that reduce the design life of buildings.

The research object is the natural resonance frequencies of the buildings of the Ural Branch of the Russian Academy of Sciences (UB RAS) located in Ekaterinburg and their distribution at observation points. The method of spectral ratios (HVSR or the Nakamura method), which allows hidden construction defects to be identified, is applied to analyze the resonance characteristics. Periodic monitoring of technical condition allows to calculate and evaluate changes in dynamic characteristics over time. Equal values of the amplitude extrema of the spectral ratio curve and uniform distribution of the values throughout the building indicate a normal operational state of the structure. The presence of abnormally high values at some points may be due to hidden defects and requires additional study. A method for calculating vulnerability coefficient is demonstrated. According to the results of annual monitoring (since 2017), the stable state of the Institute of Geophysics building of UB RAS is demonstrated, and a comparison with resonant frequencies obtained from the standard project (Institute of Geology & Geochemistry of UB RAS) is presented. This article presents a method for assessing seismic stability by calculating horizontal acceleration ( ) at observation points. Acceleration is calculated at the maximum possible seismic event in the studied region (44 cm/s²). The possible maximum acceleration is calculated, taking into account the characteristics of the soil, for the observation point with the highest , = 30.6 cm/s², which corresponds to an earthquake intensity of 5.6.

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