| Primary value | 150 mm c / c (typical) (code limit: min(0.75 d, 300 mm) — IS 13920 hinge: min(d/4, 8ϕ, 100 mm)) |
| Applies to | Two-legged vertical stirrups in simply-supported and continuous beams · Beams designed to IS 456 (non-seismic) |
| Exceptions | Inclined / bent-up stirrups → min(0.5 d, 300 mm) |
| IS 13920 — plastic hinge zone (within 2 d of support) → min(d/4, 8 × smallest long. bar dia, 100 mm) | |
| IS 13920 — outside plastic hinge zone → min(d/2) | |
| Minimum stirrup diameter → 6 mm (8 mm preferred for Fe500) | |
| Measured as | Centre-to-centre spacing measured along the longitudinal axis of the beam. d = effective depth (overall depth minus cover minus half longitudinal bar diameter). |
| Source | IS 456 — Clause 26.5.1.5, 26.5.1.6 ✓ Verified |
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Stirrup spacing controls shear failure mode and confines the longitudinal bars against buckling. The 0.75d limit ensures that any 45° shear crack crosses at least one stirrup. In seismic zones, the d/4 limit at plastic hinge zones is what gives ductile beams their post-yield rotation capacity.
Most residential beams have 8 mm stirrups at 150 mm c/c throughout — well below the 0.75d limit and conservative against shear. In seismic Zone IV/V, the plastic hinge zone tightens to 75–100 mm spacing for the first 2d from each support.