Bar Bending Schedule for Column: Complete Guide with Example, Formula & BBS Preparation

A Bar Bending Schedule (BBS) is one of the most important documents used in reinforced concrete construction. It provides complete information about the reinforcement bars required for a structural member, including bar diameter, spacing, cutting length, bend deduction, number of bars, bar shape, and total steel length.

For columns, a properly prepared BBS helps the site engineer, quantity surveyor, steel fixer, and contractor understand exactly how reinforcement is to be cut and fabricated before placing it inside the column.

In this article, we will explain Bar Bending Schedule for Column in a simple and practical way, including the important BBS terms, formulas, bend deductions, cutting length calculations, and an example based on a typical column reinforcement schedule.

What is a Bar Bending Schedule (BBS)?

A Bar Bending Schedule is a detailed tabular representation of reinforcement steel used in a concrete structure.

It normally contains information such as:

• Bar mark / member
• Structural member dimensions
• Bar diameter
• Bar spacing
• Bar shape
• Number of bars
• Cutting length
• Bend deductions
• Total reinforcement length
• Total quantity of steel

In simple words, BBS tells us what type of steel bar is required, how many bars are required, what shape they should have, and what length each bar should be cut to.

Why is BBS Important for Columns?

Columns carry loads from slabs, beams, and upper floors and transfer these loads to the foundation. Therefore, proper reinforcement detailing is extremely important.

A column BBS helps to:

1. Calculate Steel Quantity

The total length and weight of reinforcement can be calculated accurately.

2. Reduce Steel Wastage

Bars can be cut according to calculated lengths instead of cutting them randomly at site.

3. Improve Site Work

Steel fixers can easily understand the required bar sizes, shapes, and quantities.

4. Prepare Material Estimates

A BBS can be used for preparing the reinforcement steel requirement and procurement.

5. Check Reinforcement

The site engineer can compare the actual reinforcement with the approved structural drawings.

Main Components of a Column BBS

A typical column BBS contains several important columns.

For example, a schedule may include:

Types of Reinforcement Used in a Column

Column reinforcement generally consists of two major types of bars:

1. Longitudinal Bars

These are the main vertical reinforcement bars running along the height of the column.

They are designed to resist the major axial and bending forces in the column.

Common diameters may include:

• 12 mm
• 16 mm
• 20 mm
• 25 mm
• 32 mm

The actual diameter and number must always be taken from the structural design.

2. Ties / Stirrups

Ties are placed horizontally around the longitudinal bars.

Their main purposes are to:

• Hold vertical bars in position
• Provide confinement to the concrete core
• Prevent buckling of longitudinal reinforcement
• Improve column performance

Ties are commonly smaller diameter bars such as 6 mm, 8 mm or 10 mm, depending on the structural design.

Understanding a Typical Column BBS

In the provided BBS example, the schedule includes different reinforcement arrangements such as:

• Longitudinal Bars
• Square Rings
• Diamond Rings
• G.F Longitudinal Bars

The schedule also shows different bar diameters and calculated lengths.

For example, a longitudinal reinforcement item may have:

12 mm diameter × 8 bars

If the calculated cutting length of one bar is approximately 1.665 m, then:

Total Length = Number of Bars × Cutting Length

Therefore:

8 × 1.665 = 13.32 m

This is why the BBS can show a total length of approximately 13.32 m for that reinforcement item.

How to Calculate Cutting Length of a Column Bar

The cutting length depends on the shape and detailing of the reinforcement.

For a straight bar, a basic calculation may be:

Cutting Length = Required Length + Anchorage/Development Length

For a bent bar, we must also consider:

Cutting Length = Total Centre-Line Length − Bend Deductions + Required Hooks/Anchorage

The exact formula depends on the reinforcement shape and the applicable structural detailing standard.

Bend Deduction in BBS

When a reinforcement bar is bent, the theoretical lengths of the individual straight portions cannot simply be added without considering the bend geometry.

Therefore, bend deductions are applied.

A BBS may have separate columns for:

• 45° Bend
• 90° Bend
• 135° Bend
• 180° Bend

The deduction depends on the bar diameter and the applicable code/detailing method.

For example, if a bar has a bend and the calculated deduction is 36 mm, this value is incorporated into the cutting-length calculation.

Example: Column Ring Calculation

Consider a square column with an internal ring dimension of approximately 370 mm × 370 mm.

Suppose the ring reinforcement is:

• Bar diameter = 6 mm
• Number of rings = 5
• Number of similar members = 2
• Ring spacing = 150 mm C/C

The BBS should determine the cutting length of one ring based on:

1. Ring dimensions
2. Concrete cover
3. Bar diameter
4. Bend allowance/deduction
5. Hook or anchorage requirements

After determining the cutting length, the total length can be calculated as:

Total Length = Cutting Length × Total Number of Rings

If:

Total Rings = 5 × 2 = 10

then:

Total Steel Length = Cutting Length × 10

This calculated quantity can then be added to the total 6 mm reinforcement requirement.

Square Ring vs Diamond Ring

Column reinforcement may require different types of ties depending on the structural detailing.

Square Ring

A square ring surrounds the longitudinal bars and provides lateral confinement.

Diamond Ring

A diamond-shaped or additional cross-tie arrangement may be provided where required to properly restrain internal longitudinal bars.

How to Calculate Number of Rings

If the column has a specified height and the tie spacing is known, the approximate number of ties can be calculated from the reinforcement detailing.

For example:

Column Height = 3500 mm

Tie Spacing = 150 mm C/C

A simple spacing calculation would be:

3500 ÷ 150 = 23.33

However, the actual number of ties must not simply be rounded and used. The first and last tie positions, confinement zones, lap zones, and any special spacing requirements shown on the structural drawing must be considered.

This is an important point when preparing a professional BBS.

Total Number of Bars

One of the most useful columns in BBS is Total Nos.

For example:

No. of Bars = 8

No. of Members = 1

Therefore:

Total Nos. = 8 × 1 = 8 Bars

If there are 2 identical columns:

Total Nos. = 8 × 2 = 16 Bars

This calculation becomes especially useful when preparing the overall steel quantity for a project.

Total Reinforcement Length

Once the number of bars and cutting length are known:

Formula

Total Length = Total Number of Bars × Cutting Length

For example:

• Number of bars = 8
• Cutting length = 1.665 m

Therefore:

Total Length = 8 × 1.665

Total Length = 13.32 m

This is a basic calculation used throughout a BBS.

Converting Reinforcement Length into Steel Weight

For estimating steel quantity, the total length can be converted into weight.

A commonly used formula is:

Steel Weight per Meter

Weight = D² / 162

Where:

• D = Bar diameter in mm
• Weight is in kg/m

For a 12 mm bar:

Weight = 12² / 162

Weight = 0.889 kg/m approximately

If the total 12 mm bar length is 13.32 m:

Total Weight = 13.32 × 0.889

Total Weight ≈ 11.84 kg

Therefore, approximately 11.84 kg of 12 mm steel is required for that particular bar group, before considering practical wastage.

Best Practices for Preparing Column BBS

When preparing a professional Bar Bending Schedule, always follow these points:

1. Use Approved Structural Drawings

Never determine reinforcement sizes and quantities based only on assumptions.

2. Check Column Dimensions

Verify:

• Length
• Width
• Height
• Concrete cover

3. Verify Bar Diameter

Make sure the BBS diameter matches the structural drawing.

4. Check Bar Spacing

Tie/ring spacing should be carefully checked, particularly near column ends, beam-column joints, and lap zones.

5. Check Development and Lap Length

Development length and lap requirements can significantly affect cutting lengths.

6. Check Bend Details

Make sure every bend, hook, and anchorage is properly accounted for.

7. Avoid Duplicate Bars

Each bar mark should clearly identify a particular reinforcement type.

8. Check Final Steel Quantity

The diameter-wise totals should be checked before issuing the BBS for fabrication.