Litvinov S.V.

Candidate of Engineering Sciences (Ph.D.), Associate Professor, Don State Technical University (DSTU), Russia

Study of the concordance between various concrete deformation models and experimental data for uniaxial compression cases

https://doi.org/10.58224/2618-7183-2024-7-5-6
Abstract
There are various equations describing concrete stress-strain curves, each yielding different theoretical curves. An important scientific question is achieving the best correspondence to experimental data. The Geniyev theory inherently includes equations for three components of stress and strain. In contrast, the Eurocode and the Russian Building Code equations are provided for uniaxial stress conditions. This paper presents a comparison of theoretical curves for uniaxial compression based on Eurocode equations, the Russian Building Code, and Geniyev theory with experimental results from tests on prism and cube samples. The analysis includes deviations of the maximum stress points of theoretical curves from the corresponding experimental data. Numerical analysis is provided for both stresses and strains. A distinguishing feature of this work compared to existing research on Geniyev theory equations is that they are presented in a resolute form, incorporating three parameters: concrete compressive strength, tensile strength, and the initial modulus of elasticity.
The importance of using secondary resources on the basis of industrial waste is understood by both governments of developed countries and business (production of Portland cement using ground metallurgical slag as a mineral additive at Novotroitsk, Magnitogorsk, Sterlitamak, Katav-Ivanovsk and other plants in the South Urals). The use of secondary raw materials requires the creation of technological infrastructure for processing of secondary raw materials, the costs of which can be quickly recouped due to the cheapness and availability of industrial secondary raw materials and freeing the territory from environmental pollution. In order to recoup the costs of the infrastructure, it is necessary to guarantee full compliance of the quality of pavement elements with the requirements of GOST R 59120-2021. Secondary raw materials have a great variety and laboratory analysis of the quality of pavement elements is required in order to design compositions with the best quality, satisfying all regulatory requirements. In our work the authors present the results of laboratory research and evaluation of the possibility of using clinker-free lime-slag binder based on the mineral product of soda production and metallurgical slags to strengthen and stabilize soils for their use in pavement structures in the construction of roads for various purposes and climatic zones.
It is experimentally shown that the addition of lime-slag binder in the amount of 8-10% of the dry weight of both cohesive (loamy soil, loamy sand) and non-cohesive (fine sand) soil allows to obtain reinforced soil with improved strength and elastic-deformative characteristics, which can be used instead of scarce natural crushed stone and gravel in the construction of underlying layers of pavements in the construction and reconstruction of highways. This technology can be used not only in the Russian Federation, but also in a number of other countries, including those with hot dry climates (e.g., the Republic of Egypt).
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DETERMINATION OF RHEOLOGICAL PARAMETERS OF POLYMERIC MATERIALS USING NONLINEAR OPTIMIZATION METHODS

https://doi.org/10.34031/2618-7183-2020-3-5-15-23
Abstract
The article is devoted to the problem of processing the experimental creep curves of polymers. The task is to determine their rheological characteristics from tests for any of the simplest types of deformation. The basis for the approximation of the experimental curves is the nonlinear Maxwell-Gurevich equation.
The task of finding the rheological parameters of the material is posed as a nonlinear optimization problem. The objective function is the sum of the squared deviations of the experimental values on the creep curve from the theoretical ones. Variable input parameters of the objective function are the initial relaxation viscosity and velocity modulus m*. A theoretical creep curve is constructed numerically using the fourth-order Runge-Kutta method. The nonlinear optimization problem is solved in the Matlab environment using the internal point method. The values m* and are found for which the objective function takes the minimum value.
To test the technique, the inverse problem was solved. For given values of the rheological parameters of the material, a theoretical curve of creep under bending was constructed, and the values m* and were found from it. The technique was also tested on experimental stress relaxation curves of secondary polyvinyl chloride and creep curves of polyurethane foam with a pure shear.
A higher quality approximation of experimental curves is shown in comparison with existing methods. The developed technique allows us to determine the rheological characteristics of materials from tests for bending, central tension (compression), torsion, shear, and it is enough to test only one type of deformation, and not a series, as was suggested earlier by some researchers.
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