Deflection of Reinforced Concrete Flexural Members with Axial Load

Deflection of reinforced concrete flexural members (beams and slabs) is typically computed with an effective moment of inertia I-e that accounts for tension carried by the concrete between cracks (tension stiffening) and the variation of stiffness along the member length. The ACI 318-19 Building Code Requirements for Structural Concrete has adopted an expression for I-e different from the expression used for the past fifty years or so by earlier editions of ACI 318 and other codes and standards. CSA A23.3-19 Design of Concrete Structures and S6-19 Canadian Highway Bridge Design Code are both considering adoption of the new expression used by ACI 318-19 for reinforced concrete. This paper extends the approach used to develop the new expression for I-e to compute deflection for flexural members with axial load. The approach is applicable to flexural members with low axial load such as load bearing walls and can be extended to compute deflection of columns and prestressed members that are cracked under service load.