This working load limit calculator (WLL) is a specialized designed to help find the maximum safe load that can be applied to a piece of lifting or rigging equipment.
The calculator takes into account various factors such as the type of equipment, material strength, and safety factors to provide an accurate estimation of the safe working load.
Working Load Limit Calculator
| Equipment Type | Breaking Strength (lbs) | Safety Factor | Calculated WLL (lbs) | Notes |
|---|---|---|---|---|
| Chain Sling | 20,000 | 4 | 5,000 | Standard safety factor for chain slings |
| Wire Rope | 10,000 | 5 | 2,000 | Higher safety factor for added precaution |
| Synthetic Web Sling | 8,000 | 5 | 1,600 | Matches wire rope safety factor |
| Shackle | 30,000 | 6 | 5,000 | Higher safety factor for critical connection point |
| Lifting Eye Bolt | 12,000 | 5 | 2,400 | Typical safety factor for eye bolts |
| Rope (Natural Fiber) | 5,000 | 10 | 500 | Very high safety factor due to variable material properties |
| Crane Hook | 50,000 | 3 | 16,667 | Lower safety factor due to engineered design and regular inspections |
| Lever Hoist | 6,000 | 4 | 1,500 | Matches chain sling safety factor |
This is the chart of calculations using the working load limit calculation formula: WLL = Breaking Strength / Safety Factor.
- Chain Sling: With a breaking strength of 20,000 lbs and a safety factor of 4, the WLL is calculated as 5,000 lbs. This is a typical safety factor for chain slings.
- Wire Rope: We used a higher safety factor of 5, resulting in a WLL of 2,000 lbs from a breaking strength of 10,000 lbs. This higher safety factor provides an extra margin of safety.
- Synthetic Web Sling: We matched the safety factor of the wire rope (5) for consistency. With a breaking strength of 8,000 lbs, this results in a WLL of 1,600 lbs.
- Shackle: Given its critical role as a connection point, we used an even higher safety factor of 6. Despite its high breaking strength of 30,000 lbs, the WLL is a more conservative 5,000 lbs.
- Rope (Natural Fiber): Note the very high safety factor of 10 used here. This is due to the variable properties of natural fiber ropes, which can be affected by environmental conditions. This results in a much lower WLL relative to its breaking strength.
Working Load Limit Calculation Formula
The formula for calculating the working load limit is:
WLL = Breaking Strength / Safety Factor
Where:
- Breaking Strength is the maximum load that the equipment can withstand before failing
- Safety Factor is a multiplier used to account for unforeseen circumstances and provide a margin of safety
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What is working load limit?
The Working Load Limit (WLL) is defined as the maximum load that a piece of lifting equipment is designed to support under normal operating conditions.
It represents the safe limit for the equipment’s use and should never be exceeded.
Key points about WLL include:
- It is typically lower than the equipment’s breaking strength
- It takes into account safety factors and potential dynamic loads
- It is usually marked on the equipment or provided in the manufacturer’s specifications
- Exceeding the WLL can lead to equipment failure and safety hazards
Aggregate Working Load Limit
The Aggregate Working Load Limit refers to the total WLL of a lifting system that consists of multiple components. When using multiple pieces of equipment together, it’s crucial to consider the aggregate WLL to ensure the entire system remains within safe operating limits.
To calculate the Aggregate WLL:
- Identify the WLL of each component in the lifting system
- The Aggregate WLL is typically equal to the lowest WLL among all components
This approach ensures that the weakest link in the system determines the overall safe working load, maintaining a conservative safety margin.
Working Load Limit vs Breaking Strength
While often confused, Working Load Limit and Breaking Strength are two distinct concepts:
- Working Load Limit (WLL): The maximum load that can be safely applied to the equipment under normal operating conditions.
- Breaking Strength: The load at which the equipment will physically fail or break.
The key differences are:
- Safety Factor: WLL incorporates a safety factor, while breaking strength does not.
- Practical Use: WLL is used for day-to-day operations, while breaking strength is primarily a manufacturing specification.
- Risk Level: Operating at WLL is considered safe, while approaching breaking strength is extremely dangerous.
