Model for the Plastic Region in Slender RC Columns with Nonlinear Moment and Stiffness Profiles

This paper presents a nonlinear inelastic solution for the length of the critical plastic region in the case of nonlinear moment profiles along RC bridge columns. A new analytical expression for the length of the plastic region capturing the combined effects that column slenderness, second-order P-δ moments, and the reduced postyield flexural stiffness have on the spread of plasticity over the column length is proposed. Variable flexural stiffness along the column height was also considered. Experimental results from three slender RC bridge columns with aspect ratios (shear span to diameter) greater than 10 were used to verify the analytical solution. Moreover, the results from the proposed solution were compared against previous models and it was found that the presented nonlinear inelastic solution offers better performance over linear and nonlinear elastic solutions for predicting the length of the plastic region and how it is affected by geometric nonlinearities and P-δ moments.