The structural drawing tells you what the steel should look like in the concrete. The bar bending schedule tells the bar bender how to make it, and tells you how much to buy. A good BBS reduces offcut waste, prevents shortages mid-pour and lets you check the steel order against the design.
What Does a BBS Contain?
| Column | Meaning |
|---|---|
| Member | Footing F1, column C2, beam B3, slab S1 |
| Bar mark | Identifies each bar type in the member |
| Diameter | 8, 10, 12, 16 mm etc. |
| Shape | Straight, cranked, L, stirrup — often sketched |
| Number of bars | Per member, times the number of identical members |
| Cutting length | Length of straight bar needed to make one bar |
| Total length | Number × cutting length |
| Weight | Total length × kg per metre for the diameter |
Bend Deductions and Hooks
Measured along the outside of a bent bar, the dimensions add up to more than the steel actually needed, because the bar stretches round the bend. Common site deductions:
| Bend | Deduction |
|---|---|
| 45° | 1d |
| 90° | 2d |
| 135° | 3d |
| 180° | 4d |
Hooks add length: a 180° hook on a main bar is commonly taken as 9d, and stirrups commonly end in 135° hooks extended 10d (not less than 75 mm in ductile detailing practice).
Worked Example: A Beam Stirrup
Beam 230 × 450 mm, clear cover 25 mm, 8 mm stirrups with two 135° hooks:
- Inner width a = 230 − 2 × 25 = 180 mm
- Inner depth b = 450 − 2 × 25 = 400 mm
- Perimeter = 2 × (180 + 400) = 1,160 mm
- Hooks: 2 × 10d = 2 × 80 = +160 mm
- Bend deductions: three 90° bends × 2d = 48 mm, two 135° bends × 3d = 48 mm → −96 mm
- Cutting length ≈ 1,224 mm
Weight per stirrup: 1.224 m × 0.395 kg/m = 0.48 kg. A 4 m beam with stirrups at 150 mm spacing has about 27 stirrups, or about 13 kg of 8 mm steel in stirrups alone.
Methods differ slightly between engineers in how they treat bend allowances; the BBS prepared from your drawings governs.
Main Bars: Laps and Anchorage
A main bar's cutting length includes:
- The clear span plus the length anchored into supports.
- Laps where bars are joined (often about 50d — see lap length).
- Cranks (bent-up bars) in slabs and beams, which add length.
- Hooks where specified.
From BBS to Steel Order
Add the weights by diameter across all members, then add a small allowance for cutting waste — typically 2 to 5 percent with good planning. Bars come in 12 m lengths, so planning cuts to use full bars (for example, combining a 7 m and a 5 m cut from one bar) reduces offcuts.
The Short Version
A BBS turns the drawing into cutting lengths, bending shapes and kilograms. Deduct for bends, add for hooks and laps, plan cuts around 12 m bars, and check the schedule against the drawings before the bar bender starts — it is the cheapest point to catch a mistake.
