Steel Structure Assembly
Introduction to Structural Assembly
Steel structure assembly is the process of assembling prefabricated structural elements (columns, beams, joists, bracing) on the jobsite to form the load-bearing framework of a building or civil engineering project. For the Red Seal exam, you must master not only lifting and assembly techniques, but also the erection sequence, dimensional tolerances, bolted and welded connections, and the temporary stability of the structure during assembly.
The reference code of practice is CSA S16 (Design of Steel Structures), as well as the Construction Safety Code (Occupational Health and Safety Regulations, Part II of the Canada Labour Code for federal sites, or applicable provincial legislation). CSA S16:19 defines the design requirements, while the CISC Erection Guide (Canadian Institute of Steel Construction) provides recommended practices for erection.
Site Planning and Preparation
Reviewing Plans and Specifications
Before any lifting operation, you must perform a thorough review of the shop drawings and erection plans. These documents indicate:
The mark number of each piece and its weight
The types of connections (bolted, welded, or hybrid)
Installation tolerances (generally ± 5 mm for column alignment)
Required camber for beams
Erection sequences recommended by the engineer
Table 1: Typical Information on an Erection Plan
| Element | Information Provided | Example |
|---|
| Column | Mark, level, orientation | C-12, Elev. +4.500 m |
| Beam | Mark, span, camber | B-34, 12.0 m, 25 mm |
| Bracing | Type, angle, connections | X-bracing, L76×76×6 |
| Floor | Slab type, thickness | Composite slab, 75 mm |
Verifying Foundations and Anchor Bolts
Anchor bolts must be verified before erection:
Position: tolerance of ± 3 mm from the theoretical layout
Projection above the concrete: per the plans
Threads: clean, undamaged, lubricated if necessary
Alignment: bolts must be perpendicular to the foundation surface
The leveling plate or base plates must be installed with an accuracy of ± 1.5 mm in elevation. Non-shrink grout is used after final column alignment.
Receiving and Storing Materials
Steel pieces are delivered by truck and must be:
Checked against the shipping list
Inspected for transport damage (deformations, cracks, corrosion)
Stored on wooden dunnage to avoid contact with the ground
Sorted by mark number to facilitate erection
Caution: Damaged pieces must be reported immediately and must never be installed without the engineer's approval.
Lifting Equipment and Accessories
Cranes and Lifting Capacity
The choice of crane depends on:
The weight of the heaviest pieces
The required reach and height
Site obstacles
The available space for crane setup
The rated capacity of a crane is reduced by:
Boom length
Boom angle
Swing and travel movements
Wind conditions (generally, operations stop beyond 40 km/h for lifting operations)
Net load formula:
Net load = Rated capacity − Weight of the accessory (hook, slings, shackles)
Slings and Rigging Accessories
Slings can be made of:
Wire rope: abrasion-resistant, but rigid
Chain: flexible, heat-resistant, but heavy
Synthetic web (nylon/polyester): lightweight, protects the steel surface, but susceptible to cuts
Table 2: Wire Rope Sling Capacity (6×19, fibre core, safety factor 5)
| Rope Diameter (mm) | Maximum Working Load (kg) |
|---|
| 10 | 1,100 |
| 13 | 1,900 |
| 16 | 2,900 |
| 19 | 4,100 |
| 22 | 5,600 |
| 25 | 7,300 |
Sling angle: The angle between the sling leg and the vertical must not exceed 60°. The tension in each leg increases as the angle decreases.
Tension in a sling leg formula:
T = (P / n) × (1 / cos θ)
Where:
T = tension in each leg (kN)
P = weight of the load (kN)
n = number of legs
θ = angle between the sling leg and the vertical
Example: 10 kN load with 2 legs at 45°:
T = (10 / 2) × (1 / cos 45°) = 5 × 1.414 = 7.07 kN
Shackles and Hooks
Shackles are classified by their safe working load (SWL) and must be checked for:
Absence of deformation (spread of the bow)
Wear on the pin
Presence of capacity markings
Lifting hooks must be equipped with a safety latch and must never be loaded on the point.
Erection Techniques
Lifting Columns
Columns are lifted using a two-leg sling attached near the center of gravity. For tall columns, a spreader bar is used to reduce the sling angle and prevent column bending.
Column erection procedure:
73.Clean the base plate and check the grout level
74.Attach the sling to the designated lifting point (often marked with a sticker)
75.Lift slowly and guide the column with tag lines
76.Position the column over the anchor bolts
77.Install nuts and washers, tighten by hand
78.Check plumbness with a level or transit
79.Tighten nuts to the specified torque (generally 70% of final torque)
80.Install temporary bracing before releasing the hook
Column installation tolerances:
Plumbness: 1/500 of the column height, maximum 25 mm
Horizontal offset: ± 5 mm from the theoretical axis
Base plate elevation: ± 3 mm
Lifting Beams
Beams are lifted with a two-leg sling attached at the ends or at marked lifting points. For long beams (> 12 m), a spreader bar is mandatory to prevent deformation.
Lifting points: Beams often have lifting holes provided in the shop. If no holes are provided, the sling must be attached at the ends, never at mid-span.
Beam erection procedure:
89.Verify the beam's camber
90.Attach the sling to the lifting points
91.Lift the beam and guide it with tag lines
92.Position the beam on seat angles or between columns
93.Install at least two bolts per connection before releasing the hook
94.Align the beam and tighten the bolts to the required torque
Safety rule: No beam shall be released from the crane hook before at least two bolts are installed and tightened in each connection.
Open Web Steel Joists
Joists are lightweight truss elements installed between main beams. They are lifted individually or in bundles depending on their weight.
Specific requirements:
Joists must be stored flat, on dunnage
Bundle lifting requires a lifting cradle to prevent deformation
Installation is generally done from an already-placed beam, using a crane or a lift
Joists must be immediately secured by welding or bolting
Bolted Connections
Types of Bolts
Bolts used in steel structures are classified according to ASTM A325 (high-strength bolts) or ASTM A490 (higher strength). In Canada, CSA G40.20 is also used for bolts.
Table 3: Structural Bolt Characteristics
| Type | Diameter (mm) | Minimum Tensile Strength (MPa) | Typical Use |
|---|
| A325 | 16 to 25 | 825 | Shear connections |
| A490 | 16 to 25 | 1,040 | High-strength connections |
| A307 | 12 to 25 | 400 | Ordinary bolts (non-structural) |
Bolt markings: A325 bolts bear the "A325" marking on the head; A490 bolts bear "A490". Corresponding nuts are marked "2H" or "DH".
Bolt Installation
Surface preparation:
Contact surfaces must be free of mill scale, rust, oil, or paint
Tightening can be done by:
Torque wrench: torque-controlled tightening
Impact wrench: rotation-controlled tightening (turn-of-nut method)
Tension control bolts: tightening by twisting off the spline end
Torque method:
The tightening torque is calculated using the formula:
T = K × D × P
Where:
T = torque (N·m)
K = friction coefficient (generally 0.20 for lubricated bolts, 0.33 for dry bolts)
D = nominal bolt diameter (m)
P = required bolt tension (N)
Example: A325 bolt, 20 mm diameter, required tension of 142 kN, K = 0.20:
T = 0.20 × 0.020 × 142,000 = 568 N·m
Turn-of-nut method:
First tighten to snug tight
Mark the bolt and nut with a reference line
Turn the nut by a specified angle (generally 1/2 turn for A325 bolts, 3/4 turn for A490)
Inspection of Bolted Connections
Inspection must verify:
The number of bolts installed (per the plans)
The type and size of bolts (correct markings)
Tightening (torque or rotation)
The presence of washers under the nut and head
Alignment of parts (no excessive gaps)
Common defects:
Bolts too short (fewer than 2 threads protruding beyond the nut)
Bolts too long (interference with other parts)
Insufficient tightening (checked by the "tap test" or by a torque wrench calibration check)
Missing or inverted washers
Welded Connections
On-Site Welding Processes
The welding processes used for site connections are:
SMAW (Shielded Metal Arc Welding): arc welding with covered electrode
FCAW (Flux Cored Arc Welding): arc welding with flux-cored wire
GMAW (Gas Metal Arc Welding): MIG/MAG welding
Table 4: Comparison of Welding Processes
| Process | Advantages | Disadvantages | Use |
|---|
| SMAW | Portable, versatile | Slow, electrodes need replacing | Small connections, repairs |
| FCAW | Fast, high quality | Heavier equipment | Main connections |
| GMAW | Fast, clean | Sensitive to wind | Shop, indoor work |
Types of Welds
Fillet weld: the most common, triangular cross-section
Groove weld: full or partial penetration
Plug weld: through a hole in one part
Fillet weld size: The leg size is specified on the plans in millimetres. The effective throat is equal to 0.707 × the weld size.
Fillet weld strength formula:
R = 0.707 × w × L × F
Where:
R = strength (N)
w = weld size (mm)
L = weld length (mm)
F = allowable strength of the weld metal (MPa)
Welder Qualification
Welders must be qualified according to CSA W47.1 (Certification of Welding Companies) and CSA W47.2 (Qualification of Welders). Qualification includes:
A practical test on a test coupon
Visual and radiographic inspection of the test weld
A valid certification for a specified period (generally 2 years)
Important: A welder qualified for the SMAW process is not automatically qualified for FCAW. Each process and each welding position requires a separate qualification.
Temporary Stability and Bracing
Temporary Bracing
During erection, the structure is not yet stable. Temporary bracing is necessary to:
Resist wind loads
Maintain column alignment
Prevent buckling of compression members
Ensure worker safety
Types of temporary bracing:
Steel cables with turnbuckles: for columns
Bracing beams in wood or steel: for floors
Shores: for long beams
Basic rule: Temporary bracing must be installed before releasing the crane hook and maintained until the permanent bracing is in place.
Erection Sequence
The erection sequence must be planned to minimize instability risks:
185.Erect the first-level columns
186.Install temporary bracing (cables or beams)
187.Erect the main beams between columns
188.Erect secondary beams and joists
189.Check alignment and plumbness
190.Tighten connections permanently
191.Proceed to the next level
"Tower" principle: Erection is generally done in vertical "bays" to create stable zones before continuing.
Stability Calculation
The stability of an unbraced column can be verified using Euler's formula:
P_critical = (π² × E × I) / (K × L)²
Where:
P_critical = critical buckling load (N)
E = modulus of elasticity of steel (200,000 MPa)
I = moment of inertia of the section (mm⁴)
K = effective length factor (1.0 for a pinned-pinned column)
L = column length (mm)
Example: W200×46 column, I = 45.5 × 10⁶ mm⁴, L = 4 m, K = 1.0:
P_critical = (π² × 200,000 × 45.5 × 10⁶) / (1.0 × 4,000)² = 5,620 kN
The actual load must be well below this critical value, with a safety factor of at least 2.
Tolerances and Quality Control
Erection Tolerances per CSA S16
Table 5: Main Erection Tolerances
| Parameter | Tolerance |
|---|
| Column plumbness | 1/500 of height, max 25 mm |
| Horizontal beam alignment | ± 5 mm |
| Beam elevation | ± 10 mm |
| Spacing between columns | ± 5 mm |
| Base plate level | ± 3 mm |
| Connection alignment | ± 2 mm |
Final Checks
Before declaring the structure complete, the following checks are performed:
General alignment: measured with a transit or laser
Bolt tightening: verified by sampling (10% minimum)
Welds: visual inspection of all welds, non-destructive testing (radiographic, ultrasonic) for critical welds
Levels: verification of beam and floor elevations
Camber: verification that beams have retained their camber after tightening
Documentation
The erection report must include:
Tolerance check results
Welder qualification certificates
Connection inspection reports
Deviations from the plans and engineer approvals
Photographs of critical areas
Site Safety
Personal Protective Equipment (PPE)
Safety hard hat with chin strap (mandatory at all times)
Safety harness with double lanyard (mandatory above 3 m)
Safety footwear with steel toe
Gloves for handling and welding
Safety glasses or face shield
Hearing protection in high-noise areas
Lifelines and Anchor Points
Horizontal lifelines must be installed on beams before erection. Anchor points must be certified for a minimum load of 22 kN (5,000 lb).
100% rule: The worker must be attached at all times when working more than 3 m above the ground, including when moving between elements.
Crane and Lifting Zone
The lifting zone must be barricaded and off-limits to unauthorized personnel
The rigger must be trained and communicate with the operator via radio or standardized hand signals
Loads must never be swung over workers
The maximum wind for lifting operations is generally 40 km/h (some cranes have lower limits)
Pitfalls to Avoid
243.Confusing A325 and A490 bolts: A490 bolts have higher strength but must not be used in connections with galvanized surfaces (risk of hydrogen-induced cracking).
244.Neglecting the sling angle: A 30° angle from the vertical increases tension by 100% compared to a vertical sling. Always use the formula T = (P/n) × (1/cos θ).
245.Forgetting temporary bracing: The structure can collapse under wind load even with light loads. Temporary bracing is mandatory from the first erected column.
246.Tightening bolts in the wrong order: Tightening must proceed from the center towards the ends of the connection to prevent distortion.
247.Ignoring plumbness tolerances: A column leaning more than 25 mm can cause excessive stresses in connections and alignment problems at upper levels.
248.Using damaged slings: A wire rope sling with broken wires (more than 6 wires over a length of 30 cm) must be removed from service immediately.
249.Confusing camber with deformation: Camber is an intentional upward curvature to compensate for deflection under load. Do not confuse it with accidental deformation.
250.Forgetting the safety factor: Sling and accessory capacities are given with a safety factor of 5 for cables, 4 for chains. Never exceed the safe working load (SWL).
251.Not checking welder qualification certificates: A welder not qualified for the process being used produces non-compliant welds that can be rejected at inspection.
252.Working without a harness: Falls are the leading cause of death on steel structure sites. The harness is mandatory from 3 m of height.
Summary
Steel structure assembly is a complex operation that requires rigorous planning, in-depth knowledge of standards and techniques, and strict adherence to safety rules.
Key points to remember for the exam:
CSA S16 is the reference standard for the design and erection of steel structures
Erection tolerances are: column plumbness 1/500 (max 25 mm), beam alignment ± 5 mm
A325 and A490 bolts are the standard structural bolts, with distinct markings
The torque method and the turn-of-nut method are the two accepted tightening methods
Fillet welds have an effective throat of 0.707 × the weld size
Temporary bracing is mandatory before releasing the crane hook
Slings must be inspected before each use and replaced if damaged
Safety is paramount: harness mandatory above 3 m, barricaded lifting zone, clear communication with the crane operator
Mastery of these concepts, combined with a good understanding of the basic calculations (tension in slings, tightening torque, critical buckling load), will allow you to pass the "Steel Structure Assembly" section of the Red Seal exam.
Normative References
CSA S16:19 — Design of Steel Structures
CSA W47.1 — Certification of Welding Companies
CSA W47.2 — Qualification of Welders
CSA G40.20 — General Requirements for Structural Steel
ASTM A325 — Standard Specification for Structural Bolts, Steel, Heat Treated
ASTM A490 — Standard Specification for High-Strength Structural Bolts, Alloy Steel
Construction Safety Code (Part II of the Canada Labour Code)
CISC Erection Guide (Canadian Institute of Steel Construction)
