Title: Comparison of Existing Approaches for Computing Deflection of Reinforced Concrete
Author(s): Peter H. Bischoff
Publication: Structural Journal
Appears on pages(s): 231-240
Keywords: beams; deflection; effective moment of inertia; minimum thickness; slabs
This paper evaluates the approach adopted by ACI 318-19 for computing deflection of reinforced concrete. Comparison is made with the European approach and Branson’s approach used in previous editions of ACI 318. The adopted approach uses a rational expression for the effective moment of inertia, Ie, with a reduced cracking moment that gives greater values of computed deflection for lightly reinforced slabs. The impact of this change on member stiffness and minimum thickness requirements related to immediate and long-term deflection limits for serviceability is evaluated for beams and one-way slabs. Appropriate limits for maximum service load and member span are provided for slabs, and more stringent requirements are needed for minimum thickness of beams. Information about two-way slabs is also provided.