Bending and shape codes
Link (stirrup) cutting length from member size, shape 51 or 63
- where
- link outside dimension along the member depth (mm)
- member depth (mm)
- nominal cover to the link (mm)
- link outside dimension along the member width (mm)
- member width (mm)
- hook length: entered, or BS 8666 minimum end projection for links (mm)
- minimum scheduling radius (mm)
- link bar diameter (mm)
- total mass of links (kg)
- number of links
- cutting length of the selected shape (mm)
Explain this equation
Works out the cutting length and weight of closed rectangular links for a beam or column from the member size, cover and link bar size.
A and B are the outside dimensions of the link: the member depth h and width b less the cover c to the link at each face. C is the hook length, set to the BS 8666 minimum for links unless you enter one. r is the minimum bend radius, d the link diameter, n the number of links and M their total mass.
Shape 51 goes round the four sides with a hook at each end, so the length is twice A + B + C less an allowance for its five bends. Shape 63 laps along the B side, so B appears three times and the deduction covers six bends. The weight uses d²/162 kg/m.
Sense check: a 300 × 500 mm beam with 25 mm cover and 10 mm links with 100 mm hooks gives 1500 mm per link, about 0.93 kg.
Watch out: take the cover to the link, not to the main bars, or every link comes out too big.
Works out the cutting length of a closed rectangular link for a beam or column from the member size, cover and link bar size, using the BS 8666 shape 51 or 63 formula.
Enter your values to see the result.
Good to know
A and B are the outside dimensions of the link: the member depth and width less the cover to the link on each side. With the hook left at 0, C is set to the BS 8666:2020 minimum end projection for links with bends under 150° (for example 130 mm for a 10 mm bar and 155 mm for 12 mm), which gives the shortest permissible link. Use the number of bars calculator with the link spacing to get the number of links in a member.
Common mistake
Taking A and B as the member size, or deducting cover to the main bars instead of cover to the link, so the links come out too big and the cover is lost.
Limits
Rectangular links of one bar size at the BS 8666 minimum radius. Hooks shorter than the table minimum cannot be bent reliably. Seismic or torsion links may need longer hooks set by the designer.
Sources
- BS 8666:2020 Scheduling, dimensioning, cutting and bending of steel reinforcement for concrete. Specification (Table 2 minimum radii and end projections; Table 5 standard shapes and length formulae)
- Coen Steel, Shape Codes BS 8666:2020 (total length formula for each shape code)
- Collins Reinforcements, BS 8666 shape codes (dimension rules: free dimensions in brackets, A and end legs not less than P; minimised links 51 and 63)
- KB Rebar, BS 8666:2020 shape codes sheet (Table 2: r, M, P, links P, hook diameter q = 3d + 2r rounded up to 5 mm)
- RebarCalcPro, BS 8666 shape code 51 worked example (300 × 500 beam, 25 mm cover, H10 link, C = 100 mm, r = 20 mm: L = 1500 mm)
- IStructE / The Concrete Centre, Standard method of detailing structural concrete (4th edition)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Always work to the engineer’s drawings and bending schedules, BS 8666, BS EN 1992, BS EN 1090-2, BS 5531/the BCSA National Structural Steelwork Specification and manufacturers’ data. Lifting must be planned under LOLER by a competent person.