Behavior of RC Columns under Nonproportionally Varying Axial Load

Abstract

The effect of nonproportionally fluctuating axial load on the inelastic cyclic behavior of reinforced concrete (RC) columns is investigated. For this purpose, a uniaxial flexural model is developed where columns are represented with an assemblage of plane‐stress and bar elements to model the concrete and the reinforcing steel, respectively. The results indicate that under uncoupled variations in axial and lateral forces, the hysteresis curve is not of the Masing type. Furthermore, the shear force versus lateral displacement relationships demonstrate “negative energy” regions. The cause of such a phenomenon is explained in light of axial deformations. It is also shown that the phasing of the axial force has a significant effect on the response. Those properties of RC columns that are affected by this type of loading are important factors in the seismic design of RC structures. The importance of varying vertical loads on the response of bridges is demonstrated through two practical examples.