Location of Balance Points on Design and Actual P–M Interaction Curve for RC Sections

Abstract

The axial force–bending moment (P–M) interaction curve is a graphical representation of sectional capacity of a uniaxial eccentrically loaded reinforced concrete (RC) member. On the P–M curve, balance point represents simultaneous achievement of limit states of both concrete and reinforcing steel. Although locations of balance points are commonly used for demarcating under-reinforced and over-reinforced regimes of behavior of RC columns, these are not studied from the point of view of actual behavior. In the present study, first P–M curves are generated as per the actual stress–strain curves of concrete (considering the confinement action) and reinforcing steel for different sizes of column section. The balance points are located on the actual P–M curves based on the definition of limit states of concrete and reinforcement. The locations of balance points on the actual P–M curves are reviewed to determine whether the design balance points give an upper bound or lower bound of the under-reinforced range of behavior.