Considering the inelasticity properties of eccentric compression columns of reinforced concrete, a uniform equivalent rigidity reduction factor is provided in specifications. As many factors affect the elastoplastic flexural rigidity of reinforced concrete columns and owing to load increase, some concrete tension zones crack, resulting in a lower flexural rigidity of concrete columns, however, the uniform equivalent rigidity coefficient cannot reflect this change rule. To investigate the change rule of flexural rigidity of reinforced concrete columns when considering the deflection second-order effect of compression columns, by testing reinforced concrete eccentric compression columns, a trilinear calculation model is established that can reflect the change rule of elastoplastic flexural rigidity of reinforced concrete columns by analyzing the relationship between bending moment and curvature. Additionally, a formula to calculate the elastoplastic flexural rigidity reduction factor of a reinforced concrete eccentric compression column is obtained via linear regression. This formula can reflect the effects of concrete cracking, axial compression ratio, eccentricity, and reinforcement ratio on the flexural rigidity of concrete columns, as well as predict the flexural rigidity reduction of existing reinforced concrete columns.
Lan et al. (Sun,) studied this question.