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Rigging Essentials: Mastering Load Evaluation for Modern Lifts

In the critical world of rigging, accurate load evaluation is paramount. Riggers need to know a load's weight, center of gravity (CG), and other key factors to ensure a safe and successful lift.

Beyond Guesswork: How to Determine Load Weight

Guessing a load's weight is a recipe for disaster. Here's a prioritized list for accurate weight determination:

  • Load Markings: Inspect the load for weight markings, ensuring they represent the entire load and not just a single component.
  • Documentation: Check shipping papers, manifests, or bills of lading for weight information.
  • Weight Certificates: Contact the load's source (supplier or manufacturer) for certified weight documentation.
  • Load Drawings: Review accompanying load drawings for weight listings.
  • Truck Scales: If the load is still on a vehicle with known tare weight, weigh it using truck scales.
  • Material Weight Tables: For regular shapes (like rolled steel sections), calculate weight using material weight tables.
  • Identical Components: For identical loads (e.g., bundled pipes), weigh one and multiply for total weight.
  • Volume Calculation: As a last resort, estimate weight based on volume (length x width x height) and material density using a weight table (be aware of potential density variations).

Understanding the Center of Gravity (CG): Key to Lift Stability

The load's CG heavily influences balance and stability during the lift. Ideally, the load should remain level when lifted. This requires positioning the hoisting equipment's hook directly above the CG. Lifting points (lugs, eyes) should be used whenever available.

Stability and Load Shape:

Stability refers to a load's resistance to rotation around its CG. Loads with a small base and high CG are more prone to tipping. A load is inherently stable if the attachment point is above the CG. Even stable loads can become unstable due to wind or hoisting dynamics.

Load Nature: Shape, Material, and Temperature

The load's shape, material, and temperature all influence sling selection. Loads with sharp corners or high temperatures might require chain slings for better grip. Conversely, polished or delicate surfaces might benefit from round synthetic fiber slings. Always evaluate the need for edge protection to safeguard both the load and the sling.

 Weight 
MaterialPounds per cu. ft.Kilograms per cu. m.
Aluminum1702,700
Brass5008,500
Brick1252,100
Coal941,450
Copper5558,800
Concrete1502,400
Iron/Steel5007,700
Lead71011,200
Oil50800
Paper561,120
Water631,000
Wood50800

 


Note: The values in this table are average and may vary depending on the specific class or grade of the indicated material.