Stirrups and ties are the thin bars wrapped around a beam's or column's main steel. They are easy to treat as minor — they are mostly 8 mm — but they are what stops a beam failing in shear and a column's main bars buckling outwards.
Beam Stirrups
Stirrups resist shear and hold the main bars in position. IS 456 limits their maximum spacing:
| Rule | Limit |
|---|---|
| Vertical stirrups | Not more than 0.75 × effective depth |
| Absolute maximum | 300 mm |
Example: a 450 mm deep beam with about 410 mm effective depth allows at most 0.75 × 410 ≈ 307 mm, so 300 mm governs. Designs commonly specify closer spacing — often 100–150 mm near supports and up to 200 mm in the middle third of the span.
Column Ties
Ties hold the longitudinal bars in place and prevent them buckling outward under load.
| Rule (IS 456) | Requirement |
|---|---|
| Pitch — least of | Least lateral dimension of column; 16 × smallest longitudinal bar diameter; 300 mm |
| Diameter | At least ¼ of largest longitudinal bar; not less than 6 mm |
Example: a 230 × 300 mm column with 12 mm main bars: the least of 230 mm, 16 × 12 = 192 mm and 300 mm is 192 mm, so ties at not more than about 190 mm. Many designs use 150 mm, with closer spacing near beam–column joints.
Why Closer Near Joints?
Shear is highest close to a beam's supports, and beam–column joints are where frames are most stressed in an earthquake. Closer stirrups and ties there resist shear and confine the concrete so it can deform without crumbling.
IS 13920 (ductile detailing) makes this mandatory in seismic zones III to V. Hyderabad is in zone II, where it is optional, but engineers often adopt its key details — 135° hooks extended 10d, closer ties in the end zones of beams and columns — because they add little cost and improve robustness.
Common Site Mistakes
| Mistake | Why it matters |
|---|---|
| Spacing wider than drawn to save steel | Reduced shear capacity |
| 90° hooks instead of 135° | Hooks can open under load |
| Ties omitted inside beam–column joints | Weakest point in the frame |
| Stirrups not tied to main bars | Cage distorts during pouring |
| Undersized stirrups | Less shear steel than designed |
The Short Version
Follow the drawing's stirrup and tie spacing, which will be at least as close as IS 456's limits — 0.75d or 300 mm in beams, the least of the column dimension, 16 bar diameters or 300 mm in columns. Keep them closer near joints, use 135° hooks, and check spacing with a tape before every pour.
