Stiffness of RC columns with hollow section

Abstract

During the past few decades, hollow section reinforced concrete columns have become especially popular in bridge pier construction in seismic areas. As compared with solid piers, their desired strength-to-mass ratio and stiffness-to-mass ratio, as well as the reduction in mass contribution of the column to seismic response are preferred. However, the seismic behavior, especially in terms of its effective stiffness, was not fully explored. Thus, this project aimed to investigate the shear and flexural behavior of hollow section reinforced concrete columns and propose an empirical equation to predict the effective stiffness. In particular, an accurate and reliable OpenSees model was proposed and validated against experimental data. It was then used to conduct parametric studies regarding the effect of various parameters on the flexural stiffness of hollow section columns. The parameters analyzed involved hollow section ratio, yield strength of longitudinal reinforcement, longitudinal reinforcement ratio and axial load ratio. It was observed that the latter three parameters play significant roles in flexural stiffness. The shear stiffness component was studied in details and an equation was proposed based upon the continuum truss model for cracked elastic shear stiffness with constant crack angles. The shear and flexural stiffness of forty-eight specimens were combined to introduce an empirical equation predicting the effective stiffness for hollow section reinforced concrete columns.