Blueprint Reading and Structural Drawings

Reading Plans and Structural Drawings

Chapter Introduction

Reading plans and structural drawings is a fundamental skill for any reinforcing steel worker (rebar worker) practicing the trade in Canada. Before cutting, bending, or installing a single reinforcing bar, you must be able to correctly interpret engineering drawings, specifications, and contract documents. This chapter prepares you to master the terminology, symbols, drawing conventions, and basic calculations associated with reinforced concrete plans, in accordance with the requirements of the Canada Labour Code and the standards of the Canadian Standards Association (CSA) , notably CSA A23.1 (Concrete: Constituents and Execution of Work) and CSA A23.3 (Design of Concrete Structures).

This chapter covers: types of drawings, scale and dimensions, reinforcing bar designation, welding and anchoring symbols, forming plans, reinforcing plans, general and particular specifications, as well as common exam pitfalls.

Types of Drawings in a Structural Project

A reinforced concrete construction project typically includes several graphic documents. You must be able to distinguish between them and understand their respective roles.

General Arrangement Plans and Site Plans

The general arrangement plan (or site plan) locates the building or structure relative to the site. It indicates reference grid lines, finished grades, benchmark points, and underground services. For the rebar worker, this plan is mainly used to locate work areas and verify access points.

Formwork Plans

The formwork plan shows the geometry of the concrete elements before the reinforcing steel is placed: footings, columns, beams, slabs, walls, etc. It indicates overall dimensions, top and bottom elevations, openings (blockouts), slopes, and tolerances. This is the plan on which you verify the actual dimensions of the element to be reinforced.

Reinforcing Plans (Rebar Placement Plans)

The reinforcing plan is the primary document for the rebar worker. It shows the placement, diameter, spacing, length, and shape of each reinforcing bar. It includes:

General and Particular Specifications

The specifications (contract documents) complement the drawings. They specify materials (type of steel, concrete class), tolerances, installation methods, required testing, and applicable standards. In the event of a conflict between a drawing and a specification, the specification generally takes precedence, unless otherwise indicated. Always read both.

Scales and Dimensions

Common Scales

Structural drawings are rarely drawn at a 1:1 scale. Typical scales are:

Golden rule: Never measure directly on a drawing with a ruler to determine an actual dimension. Always use the indicated dimensions. Drawings may be reduced or enlarged during printing, which distorts measurements.

Dimensioning

Dimensions are expressed in millimetres (mm) for linear measurements and in metres (m) for elevations and coordinates. Elevations are indicated relative to a vertical datum, often the finished floor level (FFL) or the geodetic elevation (m above sea level). Example: "Elev. 102.500 m" means the surface is at 102.500 m above the reference datum.

Reinforcing dimensions are given centre-to-centre or face-to-face. Bar spacing is always indicated centre-to-centre, unless otherwise noted.

Reinforcing Bar Designation

Bar Designations

In Canada, reinforcing bars are designated by a metric number corresponding to their nominal diameter in millimetres. The most common bars are:

Note: The "M" stands for "metric." The old imperial designations (#3, #4, #5, etc.) are no longer used in new projects, but you may encounter them on renovation plans. Approximate conversion: #3 ≈ 10M, #4 ≈ 15M, #5 ≈ 15M, #6 ≈ 20M, #8 ≈ 25M.

Reinforcing Steel

Reinforcing steel is specified according to CSA G30.18 (Steel Reinforcing Bars). Common grades are:

The steel must be free of harmful rust, oil, grease, or any coating that would reduce bond with the concrete. Surface rust is acceptable, but flaking rust or deep corrosion is cause for rejection.

Symbols and Abbreviations on Reinforcing Plans

Bar Symbols

Each bar is identified by a tag (or "mark") that includes:

Example of a tag: "10M @ 300" means 10M bars spaced at 300 mm centre-to-centre. "6-15M×2400" means 6 bars of 15M, each 2400 mm in total length.

Bar Shapes

Shapes are standardized according to the Reinforcing Steel Manual published by the Canadian Reinforcing Steel Institute (CRSI Canada). Common shapes are:

Standard hooks are defined by CSA A23.3. For a 10M to 20M bar, a 90° hook has an extension of 6 bar diameters (6d); for 25M bars and larger, the extension is 8 bar diameters (8d). A 180° hook has an extension of 4 bar diameters (4d) for all bars, with a minimum bend radius of 3 bar diameters (3d) for 10M to 20M bars, and 4 bar diameters (4d) for 25M bars and larger.

Common Abbreviations

Cover and Minimum Spacing

Minimum Cover

Cover is the distance between the outer surface of the reinforcing bar and the surface of the concrete. It protects the steel against corrosion and ensures force transfer. According to CSA A23.1 and CSA A23.3, minimum cover depends on exposure conditions:

Exam trap: Cover is measured from the outer surface of the bar, not from the centre of the bar. A common error is confusing cover with centre-to-centre distance.

Minimum Bar Spacing

The clear spacing between parallel bars must be at least equal to:

In practice, the minimum clear spacing is often 30 mm for 20M bars and smaller, and 40 mm for larger bars.

Reading Formwork and Reinforcing Plans

Systematic Reading Procedure

To avoid errors, follow a systematic procedure:

Example of Reading a Beam

Consider a beam B-1 with the following note: "4-25M bottom, 2-20M top, stirrups 10M @ 200, cover 40 mm".

Typical exam question: What is the total length of a 25M bar if it extends from grid line 1 to grid line 3, with a centre-to-centre distance of 6.0 m and 40 mm of cover at each end?

Answer: Bar length = centre-to-centre distance − 2 × cover = 6000 − 2 × 40 = 5920 mm. (If the bar is anchored into the supports, you must add the anchorage lengths.)

Lap Splices and Anchorages

Lap Splice Length

When two bars must be joined end-to-end, a lap splice (overlap) is used. The minimum lap splice length is specified on the plans or calculated according to CSA A23.3. It depends on the bar diameter, concrete strength, bar position (horizontal or vertical), and exposure class.

For bars in tension, the lap splice length is generally in the range of 40 to 60 bar diameters (40d to 60d). For example, for a 15M bar, a typical lap splice is 600 to 900 mm.

Practical rule: Lap splices must be staggered in adjacent sections and never all located at the same point in a zone of maximum stress.

Bar Anchorage

Anchorage is the length of bar required to transfer the tension force to the concrete. It can be achieved by:

The basic anchorage length (Ld) is calculated using the formula in CSA A23.3, but for the exam, you should mainly know that:

Welded Wire Reinforcement (Mesh)

Welded wire reinforcement (WWR) is a prefabricated reinforcing panel made of welded longitudinal and transverse wires. It is designated by a standardized nomenclature, for example "152 × 152 – MW18 × MW18":

Common designations are MW (round wire) and MWL (deformed wire). WWR is used for slabs-on-grade, walls, sidewalks, and floor slabs.

Exam trap: Welded wire reinforcement is placed with the load-carrying side (main wires) in the direction of the span. Do not confuse longitudinal and transverse wires.

Welding Symbols and Connections

Although the rebar worker does not commonly weld reinforcing steel, you must recognize welding symbols on plans, particularly for lifting anchors, inserts, and special assemblies.

Welds on reinforcing steel must conform to CSA W186 (Welding of Reinforcing Bars). Only weldable steels (Grade 400W or 500W) may be welded.

Tolerances and Inspection Standards

Placement Tolerances

Allowable tolerances for reinforcing steel placement are defined in CSA A23.1. Typical values are:

Exam rule: Cover can never be less than the specified minimum value. Negative tolerance is not permitted for cover.

Inspection and Testing

Reinforcing steel inspection is performed before concrete placement. Checkpoints include:

Pitfalls to Avoid

Here are the most frequent errors on the exam and in practice:

Summary

Quick Review Questions

Answers: 1) Formwork shows the concrete geometry, reinforcing shows the bars. 2) 75 mm. 3) 2 bars (300 / 150 = 2, but you must verify clear spacing). 4) 4500 − 2 × 40 = 4420 mm. 5) Extension of 6d = 6 × 16 = 96 mm, bend radius 3d = 48 mm. 6) CSA W186. 7) +10 mm / −0 mm. 8) Finished floor level. 9) Grade 400. 10) Because drawings may be reduced or distorted.

Normative References

These standards are available from the CSA Group (www.csagroup.org) and constitute the official references for the Red Seal exam.

This chapter has prepared you for the theoretical aspects of reading plans. In practice, practice with real plans from Canadian projects. The Red Seal exam assesses your ability to quickly and correctly interpret graphic information. Accuracy and method are your best allies.