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Symbols

l_d = development length in tension of deformed bar, deformed wire, plain and deformed welded wire reinforcement, or pretensioned strand, in.
d = distance from extreme fiber to centroidof longitudinal tension reinforcement, in.
λ = modification factor to reflect the reduced mechanical properties of lightweight concrete relative to normalweight concrete of the same compressive strength
d_b = nominal diameter of bar, wire, or prestressing strand, in
f^'_c = specified comprehensive strength of concrete, psi
f_yt = specified yield strength of transverse reinforcement, psi

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Stirrup legs should be extended to the compression and tension surfaces of the member as cover requirements and be anchored at both ends. To anchor shear and torsional reinforcement properly, it requires a hook or bend at the end of the reinforcement.

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• For No.5 bars and smaller and for No.6 through No.8 bars with f_yt ≤ 40 000 psi, a standard hook should use.

• For No.6 through No.8 bars with f_yt > 40 000 psi, a standard hook around a longitudinal bar plus an embedment between midheight of the member and the outside end of the hook equal to or greater than 0.014d_bf_yt / (λ(√f^’_c ). λ is given in Table 25.4.3.2.

For a No. 6, No. 7, or No. 8 stirrup with f_yt of only 40,000 psi, a standard stirrup hook around a longitudinal bar provides sufficient anchorage. The embedment should be checked for a No. 6, No. 7, or No. 8 stirrup with higher strength. A 135-degree or 180-degree hook is preferred, but a 90-degree hook may be used provided the free end of the 90-degree hook is extended to the full 12 bar diameters as required in 25.3.2.

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Except for torsion or integrity reinforcement, closed stirrups can be made using pairs of U-stirrups spliced to form a closed unit with lap lengths of at least 1.3l_d.

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