Rigging, Hoisting, and Crane Signaling

Rigging, Lifting, and Crane Signalling

Module Introduction

This chapter covers one of the most critical and most tested aspects of the general ironworker trade: load handling, selection and inspection of slings, and communication with the crane operator. In Canada, safety standards for lifting are governed by the Occupational Health and Safety Act of each province, but technical practices are based on national and international standards, including those from CSA (Canadian Standards Association) and ASME (American Society of Mechanical Engineers) . As an ironworker, you must master these skills not only to pass the Red Seal exam but, more importantly, to ensure your safety and that of your team on the job site.

1. Fundamental Principles of Lifting

1.1 The Centre of Gravity (CG)

The centre of gravity is the point where the entire mass of an object is considered to be concentrated. For a stable lift, the rigging must be arranged so that the centre of gravity is directly below the attachment point of the crane hook.

Moment Formula : For a load composed of two masses (m₁ and m₂) separated by a distance (d), the position of the CG relative to m₁ is:

CG = (m₂ × d) / (m₁ + m₂)

Example : A 6 m beam with a 500 kg mass at one end and a 300 kg mass at the other. CG = (300 × 6) / (500 + 300) = 1800 / 800 = 2.25 m from the 500 kg end.

1.2 Weight and Mass

On job sites, the term "weight" is often used to refer to mass. Crane load charts are expressed in kilograms (kg) or metric tonnes (t) . It is imperative to convert units correctly: 1 metric tonne = 1000 kg = 2204.6 lb.

1.3 Sling Angle and Tension

The sling angle is the angle formed between the sling leg and the horizontal. The smaller this angle, the higher the tension in each leg.

Tension per Leg Formula :

T = (P / n) × (1 / sin θ)

Where:

Table of Tension Factors (1000 kg load distributed over 2 legs) :

Golden Rule : Never use a sling angle of less than 30°. Below 30°, tension increases exponentially and can cause the sling to fail. CSA Z150 (Safety for Mobile Cranes) recommends a minimum angle of 45° for multi-leg slings.

1.4 Rated Load and Working Load Limit (WLL)

The Working Load Limit (WLL) is the maximum load that lifting equipment can support under normal conditions of use. It is determined by the manufacturer and includes a safety factor (typically 5:1 for fibre slings, 6:1 for chains, 5:1 for steel wire ropes).

The proof load is the load applied during testing (typically 2 times the WLL). The breaking load is the load at which the equipment fails.

Effective Load Formula :

EL = P × F

Where F is the correction factor (angle, mode of rigging, etc.).

2. Types of Slings and Their Applications

2.1 Steel Wire Rope Slings

Steel wire rope slings are made from stranded wire ropes. They are robust, resistant to abrasion and heat, but they are rigid and can damage fragile loads.

Inspection : Check the number of broken wires over a length of 6 diameters (6d). If 6 broken wires are visible over 6d or 12 wires over 30d, the sling must be removed from service. Corrosion, deformation (birdcaging, kinking), and wear are also reasons for rejection.

2.2 Chain Slings

Chain slings (Grade 80 or Grade 100) are used for very heavy loads, sharp edges, and high temperatures. They are flexible and can be shortened or lengthened.

Inspection : Measure the link diameter using a caliper. If wear exceeds 10% of the nominal diameter, the chain must be removed. Look for cracks, deformations, elongated links, and signs of welding.

2.3 Synthetic Fibre Slings (Webbing)

Webbing slings are lightweight, flexible, and do not damage finished surfaces. They are ideal for precast loads, formwork, and painted steel components.

Inspection : Look for cuts, tears, damaged stitching, burns, chemical stains, and illegible labels. A sling with a cut greater than 10% of its width must be removed.

2.4 Natural Fibre Slings (Manila, Hemp)

Rarely used in modern industry, they are reserved for light and temporary applications. They are sensitive to moisture and mildew.

2.5 Sling Comparison Table

3. Rigging Modes and Correction Factors

3.1 Rigging Modes

The rigging mode determines the lifting capacity of the sling. Common modes are:

3.2 Correction Factors for Rigging Modes

Note : For a 4-leg basket, the capacity is not 4 times the WLL. Due to uneven load distribution, a factor of 2.1 (or 2.0 depending on the standard) is used.

3.3 Angle Correction Factors

The sling angle directly affects the tension in each leg. The following table gives the capacity reduction factors based on the angle:

Effective Capacity Formula :

Effective capacity = WLL × Mode factor × Angle factor

Example : A 10 mm steel wire rope sling with a WLL of 1500 kg, used in a 2-leg basket with a 60° angle.

Effective capacity = 1500 × 2.0 × 0.87 = 2610 kg.

4. Lifting Accessories

4.1 Hooks

Hooks are equipped with a safety latch (or keeper) that prevents the sling from slipping off. The latch must be in good condition and functional.

4.2 Shackles

Shackles are used to connect slings to the hook or to the load. There are two main types:

Rule : The pin of a shackle must always be in place and tightened. Never replace the pin with an ordinary bolt. The load must be applied along the axis of the shackle, never from the side.

4.3 Lifting Rings and Lifting Hooks

Lifting rings (or eyes) are welded or bolted onto the components to be lifted. Lifting hooks are gripping devices used to lift plates, beams, or slabs.

4.4 Sling Hooks and Spreader Bars

A spreader bar is a rigid beam that distributes the load over multiple attachment points. It is used to lift long or wide loads without deforming them.

5. Inspection and Maintenance of Lifting Equipment

5.1 Inspection Frequency

According to CSA Z150 and CSA Z248 (Tower Cranes), inspections must be carried out:

5.2 Rejection Criteria for Steel Wire Rope Slings

5.3 Rejection Criteria for Chain Slings

5.4 Rejection Criteria for Webbing Slings

6. Signalling and Communication with the Crane Operator

6.1 The Role of the Signaller

The signaller (or rigger) is the person responsible for guiding the crane operator. They must be trained, competent, and visible at all times. They must use standardized signals that are known to the operator.

6.2 Standardized Hand Signals

Hand signals are defined by ASME B30.5 and CSA Z150. Here are the most common signals:

6.3 Radio Communication

When hand signals are not possible (distance, visibility), two-way radio is used. The signaller must:

6.4 Communication Rules

7. Lifting Calculations and Practical Examples

7.1 Calculating the Effective Load

Example 1 : A 2.5-tonne steel beam is to be lifted with a 2-leg basket sling. The sling angle is 45°. What is the tension in each leg?

T = (P / n) × (1 / sin θ) = (2500 / 2) × (1 / sin 45°) = 1250 × 1.414 = 1767.5 kg per leg.

Example 2 : A 10 mm Grade 80 chain sling has a WLL of 3200 kg. It is used in a choker hitch with a 60° angle. What is the effective capacity?

Effective capacity = WLL × Mode factor × Angle factor = 3200 × 0.75 × 0.87 = 2088 kg.

7.2 Calculating the Number of Legs Required

Example 3 : A 6-tonne load must be lifted with 16 mm steel wire rope slings (WLL = 4000 kg). The sling angle will be 60°. How many legs are required?

Capacity per leg = 4000 × 0.87 = 3480 kg.

Number of legs = 6000 / 3480 = 1.72 → Round up to 2 legs.

7.3 Calculating the Centre of Gravity

Example 4 : An 8 m beam has an 800 kg mass at 2 m from end A and a 400 kg mass at 6 m from end A. Where is the CG located?

CG = (m₁ × d₁ + m₂ × d₂) / (m₁ + m₂) = (800 × 2 + 400 × 6) / (800 + 400) = (1600 + 2400) / 1200 = 4000 / 1200 = 3.33 m from end A.

The attachment point must be at 3.33 m from end A.

8. Safety Rules and Applicable Standards

8.1 CSA Z150 Standard

CSA Z150 (Safety for Mobile Cranes) is the reference standard in Canada for mobile cranes. It covers:

8.2 CSA Z248 Standard

CSA Z248 (Tower Cranes) applies to tower cranes used on construction sites. It requires regular inspections and load testing.

8.3 CSA G4 Standard

CSA G4 (Steel Wire Rope) specifies requirements for the manufacture and use of steel wire ropes, including rejection criteria.

8.4 Canadian Electrical Code, Part I

The Canadian Electrical Code, Part I (C22.1-21) applies to electrical installations, but it is relevant to ironworkers when working near power lines. Rule 8-200 (clearances) requires a minimum distance of 3 m between the crane and power lines of less than 75 kV, and 6 m for lines over 75 kV.

8.5 General Safety Rules

Pitfalls to Avoid

Summary

Review Questions (for Self-Assessment)

Answers to Review Questions

This chapter has provided you with the essential knowledge on rigging, lifting, and crane signalling. Master these concepts, practice the calculations, and memorize the standards. Good luck with your Red Seal exam preparation!