Rebar Compression Development Length (ACI 318-19 25.4.9)
How deep compression dowels really go, which the tension development and hook tiles never answered: ldc = max(fy x psi_r / (50 lambda sqrt(f'c)) x db, 0.0003 fy psi_r db, 8 in). Compression development is SHORTER than tension because the bar end bears on concrete. A #8 Grade 60 dowel at 4,000 psi needs 19.0 in (the fy/sqrt(f'c) term governs); raise f'c to 8,000 psi and it stops falling at 18.0 in because the 0.0003 fy db floor takes over -- doubling the concrete strength did not shorten the dowel. Confining ties (psi_r = 0.75) drop it to 14.2 in. A design aid; the engineer of record's detailing governs.
Formula and source
ldc = max( (fy x psi_r) / (50 x lambda x sqrt(f'c)) x db , 0.0003 x fy x psi_r x db , 8 in ).
The ACI 318-19 25.4.9.2 compression development length, with the 25.4.9.3 confining-reinforcement factor psi_r = 0.75 and the 8 in minimum, by name.
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