Strain Hardening of Reinforcement in Reinforced Concrete Elements After Residual Deformations

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Abstract
The article presents a comprehensive study of the influence of strain hardening (work hardening effect) on the mechanical properties of thermally strengthened A500C reinforcement in reinforced concrete structures. The use of stepwise testing with the digital image correlation (DIC) method allowed detailed data to be obtained on local stress–strain processes, accumulation of residual plastic deformations, and changes in the yield strength of reinforcement under repeated loading. Experimental results showed that after primary overloading, the reinforcement retains significant residual deformations, which shift the stress–strain curve along the strain axis, while the elastic properties of the steel remain practically unchanged. It was found that the yield strength of the reinforcement under repeated loading increases by 10–20% due to strain hardening and partial stabilization of the dislocation structure of the crystal lattice. The interaction of reinforcement with concrete in the crack zone, including mechanical interlock and adhesion effects, was studied, contributing to local stiffness increase and actual load-bearing capacity of the elements. The proposed methodology allows quantitative assessment of the reinforcement’s residual load-bearing capacity after overloading, partial damage, or restoration, which has practical significance for reconstruction, strengthening, and modernization of reinforced concrete structures. The study results confirm the necessity of considering the work hardening effect and residual deformations when evaluating residual capacity and safety of structures, especially bridges, high-rise buildings, and objects in seismically active areas.

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