Maximum permitted spacing of stirrups in beams and ties (transverse reinforcement) in columns, per IS 456 for ordinary detailing and IS 13920 for ductile (seismic) detailing. Spacing must satisfy ALL applicable rules — pick the smallest value.
Beam Stirrups — IS 456 Cl 26.5.1.6
| Rule | Value | Applies | Note |
|---|
| Maximum spacing in plan view | 0.75 × d | Where shear stress ≤ design τc | d = effective depth |
| Absolute max spacing | 300 mm | Independent of d | Cap regardless of depth |
| Spacing in heavy shear zone | ≤ d/2 | Where shear designed | — |
| Inclined stirrups (45°) | ≤ d | Inclined bars | Less commonly used today |
| Min stirrup diameter | ≥ 6 mm | Standard beams | Some specs require 8 mm |
| Min shear reinforcement | Asv / (b × s) ≥ 0.4 / 0.87 × fy | Below this, consider unreinforced | Cl 26.5.1.6 — min Asv |
| Stirrup spacing across width | ≤ 0.75 × d | Wide beams | For multi-leg stirrups |
| First stirrup from support | ≤ 50 mm (recommended) | Construction practice | Not codified, but standard |
Beam Stirrups — IS 13920 (Ductile/Seismic)
Plastic hinge zone = 2d from face of joint
| Rule | Value | Applies | Note |
|---|
| Hoop spacing — within 2d of face | min(d/4, 8 × dlong, 100 mm) | Plastic hinge zone | Cl 6.3.5(a) |
| Hoop spacing — outside 2d | ≤ d/2 | Mid-span | Cl 6.3.5(b) |
| First hoop from joint | ≤ 50 mm | Mandatory | Cl 6.3.5(c) |
| Min hoop diameter | 8 mm (M20) / 10 mm (M25+) | Cl 6.3.5 | — |
| Hoop hook | 135° + 10 dia ext. | Mandatory ductile | 90° hook not allowed |
Column Ties — IS 456 Cl 26.5.3.2
| Rule | Value | Applies | Note |
|---|
| Maximum tie spacing — least of: | — | — | Pick smallest of 3 values |
| Least lateral dimension | ≤ b (column width) | Always | — |
| Bar diameter rule | ≤ 16 × min long bar dia | Always | — |
| Absolute max | ≤ 300 mm | Always | Cap |
| Min tie diameter | ≥ ¼ × max long bar dia AND ≥ 6 mm | Cl 26.5.3.2(c)(2) | Usually 8 mm |
| Tie at every long bar | Yes — alternate bars to be tied | Cl 26.5.3.2(c)(2) | Cross-tie if necessary |
| Helical (spiral) reinforcement | p ≥ 0.36 × (Ag/Ac − 1) × fck/fy | Cl 39.4.1 | Volumetric ratio for circular columns |
| Helical pitch — max | ≤ 75 mm OR ⅙ core dia | Cl 39.4.1 | — |
| Helical pitch — min | ≥ 25 mm OR 3 × bar dia | Cl 39.4.1 | — |
Column Ties — IS 13920 (Ductile/Seismic)
Confining zone lo = max(D, hclear/6, 450 mm) at top & bottom of column
| Rule | Value | Applies | Note |
|---|
| Tie spacing in lo zone | min(B/4, 6 × dlong, 100 mm) | Confining zone | But ≥ 75 mm |
| Tie spacing outside lo zone | ≤ ½ × least lateral dimension | Mid-height of column | Cl 7.4.6(b) |
| Cross-tie hook | 135° one end + 90°+6d other end | Allowed | Or 135° both ends |
| Spacing of cross-ties along long bar | ≤ 300 mm | Cl 7.4.4 | — |
| Special confinement at footings | Continue lo into footing | Anchorage zone | — |
Notes
• When IS 13920 applies, IS 456 spacing limits are SUPERSEDED — use the smaller of the two
• ALWAYS apply 'least of all rules' — never just pick one criterion
• Provide a hook on every tie — open ties slip under cyclic load
• First stirrup/tie must be within 50 mm of the support face (good practice)
• Tie diameter ≥ ¼ of main bar diameter is the controlling rule for thick columns
• For columns with ≥ 4% steel, all bars must be tied (no skipping alternate bars)
• Stirrup bending must use the correct hook — d2 lap is unsafe under cyclic loading
• BBS (bar bending schedule) must explicitly call out 135° hook for all seismic stirrups
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