ACI 318-19 Section 22.5 | One-Way Shear Strength
Concrete beams resist shear forces through a combination of the concrete's intrinsic strength and steel stirrups. The new ACI 318-19 shear provisions account for the size effect in members without shear reinforcement, meaning that deeper beams are weaker per square inch than shallow beams.
Governing Formula
Variables
Quick Example
Verify reinforcement
Check if the beam has at least minimum shear reinforcement (Av ≥ Av,min). If it does not, a size effect factor modifies the equation.
Calculate concrete strength
Compute Vc using normal weight concrete (λ = 1) and zero axial load (Nu = 0).
Determine required stirrups
Calculate the required shear strength to be provided by stirrups (Vs).
When does this govern?
Size effect governing applies frequently in mat foundations, thick slabs, and transfer girders without stirrups.
Common Mistake
Using the old 2√(f'c) bw d formula for members deeper than 10" without minimal shear reinforcement, leading to severe overestimation of shear capacity.