Structural Steel Erection

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:

Table 1: Typical Information on an Erection Plan

Verifying Foundations and Anchor Bolts

Anchor bolts must be verified before erection:

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:

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 rated capacity of a crane is reduced by:

Net load formula:

Net load = Rated capacity − Weight of the accessory (hook, slings, shackles)

Slings and Rigging Accessories

Slings can be made of:

Table 2: Wire Rope Sling Capacity (6×19, fibre core, safety factor 5)

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:

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:

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:

Column installation tolerances:

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:

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:

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

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:

Torque method:

The tightening torque is calculated using the formula:

T = K × D × P

Where:

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:

Inspection of Bolted Connections

Inspection must verify:

Common defects:

Welded Connections

On-Site Welding Processes

The welding processes used for site connections are:

Table 4: Comparison of Welding Processes

Types of Welds

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:

Welder Qualification

Welders must be qualified according to CSA W47.1 (Certification of Welding Companies) and CSA W47.2 (Qualification of Welders). Qualification includes:

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:

Types of temporary bracing:

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:

"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:

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

Final Checks

Before declaring the structure complete, the following checks are performed:

Documentation

The erection report must include:

Site Safety

Personal Protective Equipment (PPE)

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

Pitfalls to Avoid

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:

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