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.
Example
You enter
- Service steel stress fs (psi; 2/3 fy is permitted, 40,000 for Grade 60) 40000
- Clear cover cc (in) 2
You get
- s1 = 15(40000/fs) - 2.5 cc 10.0 in
- s2 = 12(40000/fs) cap 12.0 in
- S max (in) 10
Checked against published worked examples from: StructurePoint.
Details, formula, and sources
Scopefs = 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 or tables1 = 15(40000/fs) - 2.5 cc; s2 = 12(40000/fs); s_max = min(s1, s2).
Source and editionThe ACI 318-19 24.3.2 maximum spacing of tension reinforcement for crack control, by name.
Free accessACI 318 is readable free through the ACI online reading room at concrete.org; the 24.3.2 crack-control spacing provisions are in the published code.
What governsEstimate. AHJ and licensed professional govern.
API field namesfs_psi, cc_in, s1_in, s2_in, s_max_in
- Spacing limit s = min(15(40000/fs) - 2.5 cc, 12(40000/fs))ACI 318-19 24.3.2
- Service stress fs may be taken as 2/3 fyACI 318-19 24.3.2.1
- Serviceability crack-control limit, not a strength checkscope of this tile