RESEARCH ON BENDING STIFFNESS DEGRADATION OF PRESTRESSED CONCRETE BEAMS CONSIDERING SIZE EFFECT

Based on the development law of fatigue damage of concrete and the section stiffness damage model, the crack propagation of ordinary rebars and prestressed rebars after being subjected to fatigue loads was considered. The damage elastic modulus and nonlinear damage accumulation criteria were used to describe concrete damage, and the effective cross-sectional area was used to reflect the fatigue damage of steel bars. The correction factor of size effect was introduced to further deduce the calculation model of the stiffness degradation of the prestressed concrete beam after being subjected to fatigue damage. The accuracy of the stiffness degradation model was verified by analyzing the experimental research results of prestressed concrete beams in different sizes under cyclically multi-level variable-amplitude loads. The test results showed that the stiffness degradation of prestressed concrete beams and the development of concrete damage under the multi-stage variable-amplitude loading test had similar laws; the calculation results of stiffness by the theoretical deduction formulas had a little deviation from the experimental results.