Reading Engineering Drawings and Bar Bending Schedules (BBS)

Module 2: Reading Engineering Drawings and Bar Bending Schedules (BBS) 

1. Understanding Construction Drawings

Construction drawings (also called structural drawings or reinforcement detail drawings) are blueprints that guide steel fixers in placing reinforcement correctly. These drawings include symbols, dimensions, and specifications to ensure structural integrity.

Key Elements of Reinforcement Drawings

• Structural Layouts: Shows the position of beams, columns, slabs, and foundations.

• Rebar Symbols & Markings:

• Lines with numbers (e.g., "T12-200") → Rebar type (T12) and spacing (200mm).

• Hooks, bends, and stirrups → Indicated with specific symbols (e.g., 90° or 135° hooks).

• Sectional Views: Displays cross-sections of structural elements to show rebar layering.

• Notes & Specifications: Includes concrete cover requirements, lap lengths, and special instructions.

2. Bar Bending Schedules (BBS)

A Bar Bending Schedule (BBS) is a detailed table that lists all reinforcement bars needed for a structure, including their shapes, lengths, and quantities.

How to Interpret a BBS

A typical BBS includes:

• Bar Mark (e.g., "B1") → Unique identifier for each bar type.

• Bar Diameter (e.g., "12mm") → Thickness of the rebar.

• Shape Code (e.g., "A, B, C") → Standard bending shapes (defined in BS 8666 or other codes).

• Cutting Length → Total length of the bar before bending.

• Bend Dimensions → Measurements for hooks, stirrups, and overlaps.

• Number of Bars → Quantity needed for the project.

Calculating Cutting Lengths and Bend Allowances

• Cutting Length = Straight Length + Bend Length – Bend Deduction

• Bend Deduction accounts for the extra length taken up by bends.

• Example: A 90° bend on a 12mm bar may require an additional length (bend allowance) as per standards.

3. Practical Exercise: Sketching Simple Reinforcement Layouts

Exercise Steps

1. Study a Basic Drawing: Review a simple beam or slab reinforcement layout.

2. Identify Key Components:

• Main Bars (Bottom/Top Reinforcement)

• Stirrups/Links (Shear Reinforcement)

• Lap Splices & Development Lengths

3. Sketch the Reinforcement:

• Draw elevation and cross-section views.

• Label bar sizes, spacing, and bending details.

4. Cross-Check with BBS: Ensure the sketch matches the Bar Bending Schedule.

Common Mistakes to Avoid

• Misreading bar spacing (e.g., "T12-200" means 12mm bars at 200mm centers).

• Ignoring lap lengths (required where bars overlap).

• Incorrect bend angles (e.g., 135° hooks in seismic zones vs. 90° in normal conditions).

Conclusion

This module equips trainees with the ability to read engineering drawings, interpret BBS, and perform basic reinforcement sketching—essential skills for accurate steel fixing. Mastery of these concepts ensures correct reinforcement placement, reducing errors and structural risks.

Next Steps:

• Hands-on practice with real construction drawings.

• Advanced bending calculations (e.g., helical stirrups in columns).