ПРИНЦИП НАЛОЖЕНИЯ ДЕФОРМАЦИЙ В ТЕОРИИ ЖЕЛЕЗОБЕТОНА

Abstract

The work substantiates the correctness of applying the principle of the overlay of deformations when deriving equations of the mechanical state of concrete that are significant in the theory of reinforced concrete in linear and nonlinear formulations. This principle consists in the summation at some point in time of partial deformations corresponding to partial increments of non-decreasing stress at successive previous points in time. Strains are represented by the sum of instantaneous strains and delayed creep strains at the moment of application. The superposition of partial creep strains is implemented according to the Boltzmann superposition principle known in the linear theory of creep - each partial increment of creep strain depends only on the magnitude and duration of the generating partial stress increment and does not depend on its other increments. When taking aging into account, postulated by this principle the mutual independence of partial increments of creep strain takes place relative to partial increments of the stress level. Representing the deformation as the sum of the initial elastic deformation and the creep deformation with a measure that takes into account the evolution of the elastic modulus leads to a different type of equation of state, which is perceived as incorrect in some publications. This perception of a different type of equation of state together with constructions, not related to the principle of the overlay of deformations, led these authors to declare that the principle of the overlay of deformations in the theory of creep is erroneous. In contrast to the traditional approach, a material (concrete, steel, wood, plastic) is considered as a combination of fractions (fibers, layers) with statistically distributed strengths. The concept of strength structure makes it possible to substantiate the principle of superimposing deformations in a nonlinear formulation. In this case, the structure of the nonlinear equation of state turns out to be identical to the structure of the linear equation. This circumstance is significant in applications, for example, when solving relaxation problems that are important for the long-term safety of building structures.