Justification of ACI 446 Proposal for Updating ACI Code Provisions for Shear Design of Reinforced Concrete Beams

Abstract

In order to ensure adequate safety margins, the size effect for designing reinforced concrete beams against shear failure must be incorporated into American Concrete Institute (ACI) code provisions. A purely empirical approach is impossible because the available test data, mostly obtained on small beams, need to be extrapolated to much larger beams for which tests are scant or nonexistent. This paper summarizes arguments for an improved code formulation, and reviews verification by a database compiled by Joint ACI-ASCE Committee 445 which shows that the current code is unconservative for large beams. Currently, concrete design experts are debating which of several alternative formulas for size effect provides the safest extrapolation for very large beams.