Crack-Control Bar Spacing (ACI 318-19 24.3.2)
Max tension-bar spacing s = min(15(40000/fs) - 2.5 cc, 12(40000/fs)) for flexural crack control, fs = 2/3 fy typical. fs 40000, cover 2 in -> 10 in; more cover (3 in) tightens it to 7.5 in. A serviceability limit, not a strength check. A design aid; the engineer of record governs.
Formula and source
s1 = 15(40000/fs) - 2.5 cc; s2 = 12(40000/fs); s_max = min(s1, s2).
The ACI 318-19 24.3.2 maximum spacing of tension reinforcement for crack control, by name.
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