Concrete Reinforcing (Rebar) Placement

Placement of Reinforcing Steel (Rebar)

Introduction to Rebar Placement

Rebar placement, or reinforcing steel installation, is the process of positioning, assembling, and securing steel reinforcing bars in formwork before concrete placement. For the structural/ornamental ironworker, this task represents a significant portion of work on civil engineering, building, and bridge projects. The Red Seal exam requires complete mastery of installation techniques, tolerances, laps, and the requirements of the National Building Code of Canada (NBC) and standards CSA A23.1 (Concrete: Constituents and Execution of Work) and CSA A23.2 (Test Methods for Concrete).

Rebar placement is not simply a mechanical installation: it determines the load-bearing capacity, durability, and structural safety of the project. A poorly positioned bar, insufficient lap, or inadequate concrete cover can lead to cracking, corrosion, and in extreme cases, structural failure.

Roles and Responsibilities of the Ironworker in Rebar Placement

The ironworker is responsible for:

Reading and interpreting reinforcing drawings (rebar placement plans) and specifications.

Preparing, cutting, and bending reinforcing bars according to specifications.

Installing reinforcing steel in formwork, foundations, columns, beams, slabs, and walls.

Placing bar supports (chairs) to ensure the required concrete cover.

Assembling bars by tying or welding, according to specifications.

Verifying work compliance with allowable tolerances.

Types of Reinforcing Steel and Material Properties

Steel Reinforcing Bars

Reinforcing bars are designated by their nominal diameter in millimetres (or in inches on older drawings). In Canada, bars conform to CSA G30.18 (Steel Reinforcing Bars for Concrete). The most common grades are:

Grade	Yield Strength (fy)	Ultimate Strength (fu)
300R	300 MPa	500 MPa
400R	400 MPa	540 MPa
500R	500 MPa	650 MPa

Bars are identified by raised marks: grade, steel type, and manufacturer. The ironworker must be able to recognize these marks to avoid confusion on site.

Welded Wire Mesh

Welded wire mesh (welded wire reinforcement) is used for slabs, walls, and pavements. It is manufactured according to CSA G30.5 and is designated by a code such as 152 × 152 – MW 30 × MW 30, where 152 is the spacing in millimetres and MW 30 is the cross-sectional area of the wire in mm².

Other Reinforcing Elements

Tie wires: annealed steel wire used for tying.

Bar supports (chairs): plastic, concrete, or metal elements that maintain concrete cover.

Mechanical couplers: devices used to join bars without laps.

Prestressing reinforcement: strands or cables under tension (rarely handled by the structural ironworker, but good to know).

Reading Rebar Placement Drawings

Rebar placement drawings indicate:

Bar diameter and spacing (e.g., 15M @ 300 mm).

Bar lengths, bends, and hooks.

Required laps.

Positions (top bar, bottom bar, skin bar).

Special reinforcement zones (openings, corners, joints).

The metric bar designation follows this format: the number (10, 15, 20, 25, 30, 35, 45, 55) followed by the letter M. The number corresponds to the nominal diameter in millimetres (approximate). For example, a 20M bar has a nominal diameter of 19.5 mm and a cross-sectional area of 300 mm².

Common Symbols on Drawings

Symbol	Meaning
Ø	Diameter
@	Spacing (e.g., @ 300 = every 300 mm)
L	Total bar length
A	Cross-sectional area
fy	Specified yield strength
Cover	Distance between the concrete surface and the outer surface of the reinforcement

Concrete Cover and Tolerances

Concrete cover is the minimum distance between the surface of the reinforcement and the surface of the concrete. It protects the steel against corrosion and ensures stress transfer. Minimum cover values are specified in the NBC (Article 4.3.3.1) and CSA A23.1 (Article 4.3.2).

Element	Minimum Cover (mm)
Concrete cast against the ground	75
Concrete exposed to weather (walls, beams)	50
Concrete not exposed (interior)	30
Slabs on grade	75
Exposed columns	50
Foundations	75

Placement tolerances are also critical. According to CSA A23.1, allowable tolerances are:

Bar position: ± 15 mm (or ± 1/6 of the spacing, whichever is greater).

Concrete cover: -10 mm (never less than the minimum), +15 mm.

Bar spacing: ± 15 mm.

Stirrup height: ± 10 mm.

Important: The negative tolerance on concrete cover is more restrictive than the positive tolerance, because insufficient cover compromises durability.

Cutting and Bending Bars

Bar bending must comply with minimum bend radii to avoid cracking the steel. Values are given in CSA A23.1 (Article 7.3.4) and depend on bar diameter and bend type.

Minimum Bend Radii

Bar Diameter	Minimum Radius (standard hook)
10M to 20M	3 × diameter
25M to 35M	4 × diameter
45M and larger	5 × diameter

Standard hooks (90° and 180° hooks) are used for bar anchorage. A standard 90° hook has a straight extension of 12 × diameter after the bend; a 180° hook has an extension of 4 × diameter (minimum).

Common Bend Types

90° hook: used for anchorage in beams and columns.

180° hook: used for tension bars.

Stirrup: closed or open tie, bent at 90° or 135°.

U-bend: used for shrinkage joints or anchorage.

Bending is done cold, using a hydraulic or manual bender. It is prohibited to heat bars for bending, as this alters the mechanical properties of the steel.

Laps and Anchorages

Reinforcing bars are delivered in standard lengths (6 m, 12 m, 18 m). When the required length exceeds the available length, laps (overlaps) or mechanical couplers must be provided.

Lap Length

The lap length depends on:

Bar diameter.

Concrete quality (compressive strength, f'c).

Bar position (top or bottom bar).

Spacing between bars.

Exposure class (interior, exterior, aggressive environment).

The basic formula for tension lap length is given in the NBC (Article 4.3.7) and CSA A23.1. For 30 MPa concrete and a 15M bar, the typical lap length is approximately 450 mm (30 × diameter). For a 25M bar, it is approximately 750 mm (30 × diameter).

Rule of thumb: The minimum lap length is 300 mm, and it must never be less than 30 × diameter for tension bars.

Lap Positioning

Laps must be staggered to avoid concentrating weaknesses in the same section.

In any given section, the percentage of lapped bars must not exceed 50% (unless drawings indicate otherwise).

Laps in zones of maximum moment (mid-span of beams) should be avoided where possible.

Bar Anchorage

Anchorage is the transfer of forces from the steel to the concrete through bond. The anchorage length (or development length) is the distance required to transfer the full bar stress to the concrete. It is generally longer than the lap length.

Supports and Chairs

Bar supports (chairs) hold bars at the correct height and ensure concrete cover. They are classified by type and material:

Support Type	Material	Application
Concrete chair	Precast concrete	Slabs on grade, foundations
Plastic chair	Polypropylene	Walls, slabs, columns
Metal chair	Galvanized steel	Thick slabs, heavy structures
Wheel chair	Plastic	Slabs on grade, mesh
U-chair	Plastic	Vertical bars

Supports must be spaced to prevent bar sagging under their own weight and the weight of fresh concrete. Maximum support spacing is generally 1.0 m for horizontal bars and 1.2 m for vertical bars.

Tying and Assembly

Bar tying is done with annealed steel wire (16 or 18 gauge). Knots must be tight but not overly so, to avoid damaging the steel. Common tie types include:

Simple tie: for horizontal bars on supports.

Cross tie: for bar intersections.

Figure-eight tie: for vertical bars.

Chain tie: for welded wire mesh.

Tie spacing is generally 600 mm for horizontal bars and 900 mm for vertical bars. In seismic zones, spacing is reduced to 300 mm.

Placement in Structural Elements

Foundations

Foundation reinforcement is placed on concrete chairs (75 mm cover).

Bars are arranged in a grid, with bottom bars perpendicular to top bars.

Laps must be staggered, and corner bars must be bent at 90° for anchorage.

Columns

Longitudinal reinforcement (vertical bars) is held by ties spaced according to the drawings.

Ties must be closed and anchored with 135° hooks in seismic zones.

Tie spacing is tighter at the ends (critical zones) and wider at the centre.

Beams

Longitudinal bars are placed in two layers (top bars and bottom bars).

Stirrups are spaced closer near the supports and wider at the centre.

Skin bars are added on the side faces to control cracking.

Slabs

Reinforcement is placed in a grid, with bottom bars running in the direction of the main span.

Welded wire mesh is placed on wheel chairs.

Openings (holes, sleeves) require additional reinforcing bars around the perimeter.

Walls

Vertical and horizontal reinforcement is placed in a grid, with tie bars for double walls.

Retaining walls have different reinforcement at the base and the top.

Tolerances and Quality Control

Quality control of rebar placement includes:

Verification of bar diameters and lengths.

Verification of spacings and laps.

Verification of concrete cover (using a cover meter after placement).

Verification of the verticality and horizontality of the reinforcement.

Allowable tolerances are specified in CSA A23.1 (Article 7.4). The ironworker must know these tolerances and know how to apply them on site.

Practical Calculations for the Ironworker

Calculating the Number of Bars

For a 6 m × 4 m slab with 15M bars @ 300 mm in both directions:

Number of bars in the length direction: (6000 / 300) + 1 = 21 bars.

Number of bars in the width direction: (4000 / 300) + 1 = 14.33 → round up to 15 bars.

Total: 21 + 15 = 36 bars.

Calculating Total Length

Each bar must extend 25 mm beyond each end (for cover). Length of one longitudinal bar: 6000 + 50 = 6050 mm. Total length: 21 × 6050 = 127,050 mm = 127.05 m.

Calculating Weight

The weight of a reinforcing bar is approximately 0.00616 × d² (where d is the diameter in mm) in kg/m. For a 15M bar (15 mm diameter): 0.00616 × 225 = 1.386 kg/m. For 127 m: 127 × 1.386 ≈ 176 kg.

Safety on Site

Rebar placement presents specific hazards:

Puncture hazards: bar ends must be protected with caps or bent over.

Fall hazards: working on elevated reinforcement requires harnesses and lifelines.

Overload hazards: stacked bars can collapse; they must be stored on stable supports.

Electrical hazards: reinforcing bars are conductive; minimum distances from power lines must be respected (see Canadian Electrical Code, Part I (CE Code), Chapter V, Rule 8-200).

Applicable Standards and Codes

The ironworker must know the following standards:

NBC (National Building Code of Canada): Articles 4.3.1 to 4.3.8 for reinforced concrete.

CSA A23.1: Concrete: Constituents and Execution of Work (Articles 7.1 to 7.5 for reinforcement).

CSA G30.18: Steel Reinforcing Bars for Concrete.

CSA G30.5: Welded Steel Wire Mesh for Concrete.

CSA S16: Design of Steel Structures (for connections with structural steel).

Common Mistakes to Avoid

Confusing steel grades: a 400R bar cannot replace a 500R bar without engineer approval.

Neglecting concrete cover: insufficient cover is the leading cause of reinforcement corrosion.

Placing laps in zones of maximum moment: this weakens the structure.

Forgetting bar supports: bars sag and cover becomes insufficient.

Bending bars hot: this alters the steel properties and is prohibited.

Not checking the drawings: rebar placement drawings are complex; a reading error can lead to major non-conformance.

Using inappropriate tie wire: wire must be annealed steel, never stainless steel (unless specified).

Ignoring seismic zones: tie and lap requirements are stricter in seismic zones (NBC, Appendix C).

Summary

Rebar placement is a critical operation that determines the safety and durability of reinforced concrete structures.

Reinforcing bars are designated by their nominal diameter (10M to 55M) and grade (300R, 400R, 500R).

Minimum concrete cover ranges from 30 mm (interior) to 75 mm (concrete against the ground).

Laps must be at least 300 mm and staggered.

Bar supports are essential for maintaining cover and bar position.

Placement tolerances are ± 15 mm for position and -10 mm / +15 mm for cover.

Reference standards are the NBC (Article 4.3) and CSA A23.1 (Article 7).

Safety is paramount: protect bar ends, use harnesses, respect electrical clearances.

The ironworker must know how to read drawings, calculate quantities, and verify work conformance.

Common Mistakes to Avoid (Exam Reminder)

153.Do not confuse cover and lap: cover is the distance to the concrete; lap is the overlap of bars.

154.Do not forget negative tolerances: cover can never be less than the minimum, even with tolerance.

155.Do not ignore seismic requirements: 135° hooks are mandatory in seismic zones for ties.

156.Do not use rusty or damaged bars: excessive rust reduces bond to concrete.

157.Do not cut bars without authorization: any modification to the drawings must be approved by the engineer.

158.Do not neglect laps in columns: laps must be staggered (never all at the same level).

159.Do not forget skin bars: they are required for deep beams (over 900 mm).

160.Do not confuse spacings: a 300 mm spacing means centre-to-centre, not edge-to-edge.

161.Do not use wooden supports: they decompose and leave voids in the concrete.

162.Do not skip the final inspection: before concrete placement, the ironworker must inspect their work and correct any non-conformance.

This chapter covers the essential knowledge required for the Red Seal exam in rebar placement. Hands-on site practice, careful reading of drawings, and knowledge of the standards are the keys to success. Good luck with your preparation!