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Notation

d_b = Nominal diameter of bar, wire, or prestressing strand, in.
f_c^'₌ specified compressive strength of concrete, psi
√fc‘ = square root of specified compressive strength of concrete, psi
f_y = specified yield strength of nonprestressed reinforcement,psi
K_tr = transverse reinforcement index, in.
l_d = development length in tension of deformed bar, deformed wire, plain and deformed welded wire reinforcement, or pretensioned strand, in.
s = center-to-center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors, in.
ψ_e = factor used to modify development length based on reinforcement coating
ψ_g = factor used to modify development length based on grade of reinforcement
ψ_s = factor used to modify development length based on reinforcement size
ψ_t = factor used to modify development length for casting location in tension
λ = modification factor to reflect the reduced mechanical properties of lightweight concrete relative to normalweight concrete of the same compressive strength

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Concrete cover for reinforcement should be in accordance with ACI Table 20.5.1.3.1. The concrete cover is measured to the outer edge of ties, stirrups, or spirals if transverse reinforcement encloses the main bars.

Cover or specified concreteis defined as the distance between the outermost surface of embedded reinforcement and the closest outer surface of the concrete.

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