Bar Bending Schedule: Cutting Length, Hooks and Lap Rules Explained

A Bar Bending Schedule (BBS) is used to calculate the cutting length, shape, quantity and weight of reinforcement bars required for a construction project.

The cutting length of a reinforcement bar depends on its shape, diameter, bends, hooks, laps and the dimensions shown in the structural drawings.

In practical work, the exact cutting length should always be checked against the approved structural drawing and project specification.

What is a Bar Bending Schedule?

A Bar Bending Schedule is a detailed reinforcement schedule that lists the bar mark, diameter, shape, number of bars, cutting length and total weight.

A properly prepared BBS helps reduce material wastage and makes reinforcement fabrication and quantity estimation easier.

How cutting length is calculated

The basic approach is to start with the dimensions shown on the drawing and then account for bends, hooks, bend allowances and deductions according to the applicable detailing requirements.

For a straight bar, the cutting length is generally based on the required bar length shown in the drawing.

For L-shaped and crank bars, the cutting length must account for the complete developed shape rather than simply adding the visible dimensions.

Hooks and bends

Hooks are provided where required by reinforcement detailing. Their dimensions and allowances depend on the bar diameter, bend type and applicable detailing requirements.

The exact hook length should be taken from the relevant structural drawing and applicable code rather than using one universal value for every project.

Lap length

When one reinforcement bar cannot provide the required continuous length, bars may be joined using laps.

Lap length depends on factors such as bar diameter, concrete grade, steel grade, stress condition and the applicable design provisions.

A fixed lap value should therefore not be assumed for every project.

BBS quantity and steel weight

After the cutting length and number of bars are known, approximate reinforcement weight can be calculated using the commonly used relationship:

Weight per metre = d² / 162 kg/m

where d is the nominal bar diameter in millimetres.

For example, a 12 mm bar has an approximate unit weight of:

12² / 162 = 0.889 kg/m

The total weight can then be estimated by multiplying the unit weight by the total bar length.

Final check before fabrication

Before reinforcement bars are cut, the BBS should be checked against the latest approved structural drawings, bar marks, dimensions, reinforcement details and project requirements.

Engineering decisions and final reinforcement detailing should always be verified by the responsible qualified professional.