Chepurnenko A.S.

Doctor of Engineering Sciences (Advanced Doctor), Professor, Don State Technical University, Department «Structural Mechanics and Theory of Structures», Russia

Processing of nonlinear concrete creep curves using nonlinear optimization methods

https://doi.org/10.58224/2618-7183-2024-7-1-2
Abstract
The article proposes a method for determining the rheological parameters of concrete based on creep curves at various stress levels using the theory of V.M. Bondarenko. Using the proposed methodology, the experimental data presented in the work of A.V. Yashin is processed. The problem of searching for rheological parameters is posed as a nonlinear optimization problem. The sum of squared deviations of the experimental values of creep strains from the theoretical ones is minimized. The interior point method is used as a nonlinear optimization method. Four different expressions for the creep measure are considered, including the creep measure by N.Kh. Harutyunyan, creep measure by A.G. Tamrazyan, a creep measure in the form of a sum of two exponentials, and McHenry’s creep measure. It has been shown that the best agreement with experimental data is provided by the McHenry’s creep measure. An expression has been selected for the nonlinearity function, which describes the nonlinear relationship between stresses and creep strains. It is shown that the instantaneous nonlinearity of deformation and the nonlinearity that manifests itself over time cannot be described by a single function.
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Optimization of Rectangular and Box Sections in Oblique Bending and Eccentric Compression

https://doi.org/10.58224/2618-7183-2023-6-5-2
Abstract
The article presents a solution to the problem of finding the optimal ratio of the height of the cross-section to the width for a rectangular and box-shaped section in the case of oblique bending and eccentric compression. Optimization is performed according to the strength criterion, and for the case of oblique bending of a rectangular beam, a solution was also obtained from the condition of a minimum full deflection. For a rectangular section, the solution is made analytically, and for a box section, numerically using the MATLAB environment and the Optimization Toolbox package. As a numerical method of nonlinear optimization, the interior point method is used. To simplify the solution, the box section is assumed to be thin-walled, i.e. it is assumed that the wall thickness is significantly less than the height and width of the cross section. An estimate of the error of such an assumption is also performed. It has been established that in the case of oblique bending of a rectangular beam, when optimizing according to the strength criterion, the optimal ratio of the cross-sectional height to width is equal to the cotangent of the angle between the force plane and the vertical axis, and when optimizing according to the rigidity criterion, it is the square root of the cotangent of this angle. In the case of eccentric compression of a rectangular beam with eccentricities in two planes, the optimal ratio of the height of the cross section to the width is equal to the ratio of the eccentricity along the vertical and horizontal axes. For a box-shaped section, graphs of the change in optimal parameters depending on the angle between the force plane and the vertical axis in the case of oblique bending, as well as depending on the ratio of eccentricities along the axes in the case of eccentric compression, are plotted.
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