Good detailing and bar bending schedule

Requirements for good detailing

Reinforcement detailing means the exact arrangement of bars shown on the drawings. Good detailing should:

1. Follow the code (IS 456, SP 34, and IS 13920 in seismic regions) for cover, spacing, anchorage, laps and curtailment.
2. Provide proper anchorage and development length for every bar, with hooks or bends where space is limited.
3. Keep reinforcement simple: use few bar diameters, standard shapes and regular spacing, so that it is easy to fabricate and place.
4. Avoid congestion, especially at beam-column joints, so that concrete can flow and be compacted; keep the minimum clear spacing between bars.
5. Give the specified cover (with spacers or cover blocks) for durability and fire resistance.
6. Place bars where the stresses are: tension steel on the tension face, curtailed at the correct points, with stirrups closely spaced near the supports.
7. Provide clear drawings: plan, elevation and sections with bar marks, diameters, spacing, lap positions and notes.
8. Allow for construction: bars must be capable of being placed in the sequence of erection, and lap positions and construction joints must be shown.

Bar bending schedule (BBS)

A bar bending schedule is a table prepared from the structural drawings that lists every bar of a member with its mark, diameter, shape, number, length of each bar, total length and weight. It is used for ordering, cutting, bending, fixing and checking the steel, and for estimating the quantity (and cost).

Steps:

1. Give each different bar a number (bar mark) on the drawing.
2. Find the cutting length of each bar = straight length + hook allowances - bend deductions. In usual site practice, a 45° bend deducts $1\phi$, a 90° bend $2\phi$ and a 135° bend $3\phi$, and a standard semicircular hook adds about $9\phi$ (IS 2502 practice).
3. Total length = number × length of each bar; weight = total length × unit weight, where unit weight $= \dfrac{\phi^2}{162}$ kg/m ($\phi$ in mm).

Bar | Dia | Shape    | No. | Length | Total | Weight
mark| mm  |          |     | (m)    | L (m) | (kg)
----+-----+----------+-----+--------+-------+-------
 A  | 16  | straight |  3  | 4.20   | 12.60 | 19.9
 B  | 12  | cranked  |  2  | 4.40   |  8.80 |  7.8
 C  |  8  | stirrup  | 20  | 1.10   | 22.00 |  8.7

The schedule is checked against the drawings before the steel is cut.