Kumar IronUpdated
In this guide
Why the straight length is not the cut length
When you bend a bar, the outer face stretches and the inner face shortens. If you add the outside dimensions of a stirrup together, you get a number that is too long. The fix is to subtract a small amount at every bend. These are called bend deductions, and they depend on the bar diameter d and the bend angle.
Standard bend deductions
| Bend angle | Deduction per bend |
|---|---|
| 45 degrees | 1 d |
| 90 degrees | 2 d |
| 135 degrees | 3 d |
| 180 degrees | 4 d |
These are the widely used shop floor values. They are close enough for ordering steel. Your engineer or detailer may use a slightly different method for the final schedule.
Worked example: a rectangular stirrup
Take a 8 mm stirrup for a 230 x 300 mm beam with 25 mm clear cover. Inside the cover, the stirrup outline is 230 minus 50 = 180 mm wide and 300 minus 50 = 250 mm deep.
- Perimeter: 2 x (180 + 250) = 860 mm.
- Two hooks at 135 degrees, each with a straight extension. The drawing usually gives about 6 to 10 times the bar diameter. Take 10d = 80 mm each, so 160 mm for both.
- Four 90 degree corners: 4 x 2d = 4 x 16 = 64 mm. Two 135 degree hook bends: 2 x 3d = 2 x 24 = 48 mm. Total deduction 112 mm.
- Cut length = 860 + 160 minus 112 = 908 mm. Round to 910 mm.
For 60 stirrups this is 54.6 m of bar, or about 21.6 kg using 0.395 kg per metre. Add a small allowance for waste when ordering.
Hooks, cranks and bent up bars
- End hooks on main bars are given on the drawing. Do not shorten them to save steel, because they are part of the anchorage.
- Cranked bars in a slab or beam have two 45 degree bends. Add the extra slant length and deduct 1d per bend.
- Stirrup spacing is usually closer near supports. A bar schedule shows each zone, so count stirrups zone by zone.
Do not rebend or heat TMT bars
Bend bars cold, on a proper bending table, and only once. Bending, straightening and bending again at the same spot weakens the bar. Heating TMT bars to bend them destroys the strength gained in manufacture. See our guide on welding and heating TMT bars.
Frequently asked questions
- How do I find the cut length of a stirrup?
- Add the outline perimeter inside the cover, add the two hook extensions, then subtract the bend deductions. A 90 degree bend deducts 2d and a 135 degree bend deducts 3d.
- How long should a stirrup hook be?
- Follow the drawing. Seismic detailing usually asks for a 135 degree hook with an extension of 6 to 10 times the bar diameter, and not less than 65 mm.
- Can bars be bent on site?
- Yes, cold, on a bending table or with a proper bender, to the radius the engineer specifies. Do not heat them.