Stressed-deformed condition of concrete When unloading after preliminary compression Based on its structural theory
Abstract
During the operation stage, long-term applied compressive stresses take place in the structures of reinforced concrete elements. Their assessment is based on the strength and deformation characteristics of the concrete constituents and have phenomenological dependences. Proceeding from this, the authors studied the stress-strain state of concrete during unloading after a preliminary long-term compression based on its structural theory.
On the basis of the analysis, an idealized structural diagram was adopted that looked like a staggered arrangement of the aggregate in the cement matrix. At the same time, the prerequisites for a nonlinear relationship between stresses σηtτ and the creep characteristic φηtτ and a linear relationship between the secant modulus of total deformations which takes into account creep deformations and the initial level of long-term stresses ητ at a fixed time t-τ for a cement stone were accepted (solution).
Based of these assumptions, the stress-strain state of concrete is considered at zero stress in the cement stone (mortar). For this state, the secant modulus values for the cement stone and concrete deformation were obtained in each section of the structural diagram. In these sections, the stress in concrete and aggregate was determined during unloading with the relative level of compression ητ in the absence of stress in the cement stone.
The deformations secant modulus value for the entire concrete element was obtained in the absence of stress in the cement stone and relative deformations
The intrinsic stress-strain state in concrete with complete unloading and the absence of unloading cracks along the cement stone is also considered.
The concrete and cement stone deformations secant modulus at full unloading is determined from the conditions for solving the system of equations of deformations equilibrium and compatibility for each of the sections in the idealized scheme, and the entire concrete section at full unloading after the long compression.
Based on the obtained dependencies, the intrinsic stress state in concrete was determined, that is, tensile stress in cement stone, , stress in the aggregate, and deformations during unloading . The scalar values of the given parameters for different levels of preliminary reduction are given.
