The plastic hinge region length is the critical parameter to determine the deformation capacity of a reinforced concrete (RC) column. The foregoing researches showed that many factores should be included to accurately access the length of plastic hinge, which could be found in the existing formulas. However, the effect of the tension shift of longitudinal rebar was not paid enough attention in these publications. In order to consider the tension shift effect, a novel model of the plastic hinge length was established based upon the equivalent principle of plastic rotation. The quasi-static tests of seven RC columns were carried out to quantify the undetermined parameters in the proposed formula. To eveluate the rationallity of the suggested model, several existing formulas were applied to calculate the plastic hinge length of the tested columns. The comparison between test and calculation shows that the proposed model can predict more accurately the hinge length of 30 columns in the literature with less discreteness than the existing formulas.

An innovative symmetrical hysteresis model for reinforced concrete (RC) rectangular hollow columns is presented. The Bouc–Wen–Baber–Noori (BWBN) model was selected to depict the inelastic restoring forces and was improved by introducing a coefficient to describe the relationship between stiffness degradation and peak displacement. Sensitivity analysis was conducted at the local and global levels to clarify the importance of each parameter in the improved BWBN model. As such, a hybrid intelligence algorithm named PSOGSA was employed to identify the parameters of the BWBN model utilizing quasi-static tests of 16 hollow columns. The empirical formulas were regressed to bridge the connection between the BWBN model and design parameters of hollow columns. The results showed that the hysteresis curves of the improved BWBN model calibrated by the PSOGSA agreed well with the measured loops. In addition, the accuracy of the empirical prediction method of hysteretic parameters was checked through comparison with other hollow members. The calibrated improved BWBN model produced more precise hysteretic responses for RC hollow columns, since the peak and residual performance levels were simultaneously considered.