How to Calculate the Weight of a Load Before an Overhead ...

How to Calculate the Weight of a Load Before an Overhead Lift

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One of the very first things you should do before lifting a load is to determine its total weight. This should be done during the initial planning stages, as every aspect of the overhead lift must account for this weight, including:

• Equipment/type of crane being used for the lift
• Type of lifting slings, rigging hardware, and/or below-the-hook devices being used
• Type of sling hitch and sling angle

The complete weight of the load must include every piece of lifting gear involved in the lift, such as:

• Hook block
• Ropes
• Lifting beams
• Shackles, hoist rings, and other hardware
• Lifting slings

There are several different methods you can use to determine the weight of the load, which we will cover in more depth in this article.

Simple Methods to Determine the Weight of a Load

There are many ways to easily identify the weight of a load without performing calculations or using specially-engineered load cells or dynamometers.

Look at the Load to See if the Weight is Marked

The load may be marked with the weight by the manufacturer or may have been previously calculated and marked. Look for any visual indications of load weight before selecting the appropriate lifting and rigging equipment.

Load Familiarity

If it’s a load that you regularly lift and move through your facility—like a steel coil or a bundle of pipes or lumber—then you will already know the load's weight. Often, your overhead crane was designed with a duty cycle and capacity specifically for that repetitive lifting application, so the load's weight was considered when the crane was built.

Refer to Engineered Prints or Design Plans

Product prints or engineered drawings of the load may indicate the final assembled weight.

Review Bill of Lading or Shipping Documentation

If the load was shipped or transported to your facility or job site, there should be some type of weight information included in the shipping paperwork you received.

Use an Industrial Scale

For smaller and lighter loads, you may be able to use an industrial floor scale commonly found in production areas or the shipping and receiving department of a facility.

Refer to the Manufacturer’s Specifications or Catalog Data

If the load is a product or piece of machinery, the weight of the load may be indicated on:

• Paperwork provided by the manufacturer
• Information on the manufacturer or distributor’s website
• Product specifications in a catalog or product brochure

Calculating the Weight of a Load

If no load weight information has been provided, you will need to calculate the load's weight. In this section, we’ll provide some basic calculations for calculating the weight of different sized loads of varying material types.

Step 1: Determine the Volume of the Load

Rectangle/Square: Volume = Length x Width x Height

Hollow Cylinder: Volume = 3.14 x Length x Wall Thickness x (Diameter – Wall Thickness)

Complex Shapes: In some instances, imagine the whole object is enclosed in a rectangle and then calculate the volume of that rectangle. Or, break the object into two or more smaller rectangles and then calculate the weight of each part and add them together.

Step 2: Determine the Material You’ll Be Lifting

The table below can be used for approximate weight values of common loads and materials:

Step 3: Determine the Weight of the Object

Multiply the approximate pounds per cubic foot of the material by the calculated volume of the load to get the weight of the object or load.

Example #1: Block of Aluminum

Here’s how you would calculate the load weight of a block of aluminum that is 6 feet long, 3 feet wide, and 4 feet tall:

Volume = Length x Width x Height

Volume = 6 feet x 3 feet x 4 feet

Volume = 72 cubic feet

Aluminum weighs 165 pounds per cubic foot (based on the numbers from the table above). Based on this information, you would perform the following calculation:

Block weight = 72 cubic feet x 165 pounds per cubic foot

Block weight = 11,880 lbs. / 5.94 tons

Example #2: Steel Pipe

Here’s how you would calculate the load weight of a hollow steel pipe that is 8 feet long, with a 3-foot outside diameter, and a wall thickness of 1.5 inches:

Volume = 3.14 x Length x Wall Thickness x (Diameter – Wall Thickness)

Volume = 3.14 x 8 feet x 1.5 inches x (3 feet – 1.5 inches)

Convert inches to feet (1.5 inches = 0.125 feet)

Volume = 3.14 x 8 feet x 0.125 feet x (3 feet – 0.125 feet)

Volume = 3.14 x 8 feet x 0.125 feet x 2.875 feet

Volume = 9.03 cubic feet

Steel weighs 480 pounds per cubic foot (based on numbers from the table above). Based on this information, you would perform the following calculation:

Steel tube weight = 9.03 cubic feet x 480 pounds per cubic foot

Steel tube weight = 4,334 lbs. / 2.17 tons

Example 3: Complex Shapes

Here’s how you would calculate the load weight of an irregularly shaped object made out of concrete. First, separate the object into rectangles and then calculate the weight of each section individually and then combine them, as shown below:

Volume1 (Top) = 4 feet x 2 feet x 3 feet

Volume1 = 24 cubic feet

Volume2 (Bottom) = 9 feet x 2 feet x 3 feet

Volume2 = 54 cubic feet

Total Volume = Volume1 (24 cubic feet) + Volume2 (54 cubic feet)

Total Volume = 78 cubic feet

Concrete weighs 150 pounds per cubic foot (based on numbers from the table above). Based on this information, you would perform the following calculation:

Complex concrete shape = 78 cubic feet x 150 pounds per cubic foot

Complex concrete shape = 11,700 lbs. / 5.85 tons

Using Load Cells or Dynamometers to Determine Load Weight

Other devices can be included in the rigging that will provide the operator with a read-out and determination of the load weight when it’s lifted slightly off the ground. These devices, called load cells or dynamometers, are mounted in line with the crane hook, slings, and hardware. The load is then attached to the load cell, which calculates the load weight by measuring the force being applied to it using a strain gauge, hydraulic, or pneumatic pressure inside the device.

These devices can display the measured load weight in various ways. Some are mechanical with an analog display that utilizes a needle and dial—similar to how many bathroom or medical scales operate. Others have digital displays right on the device itself, and some even work with handheld digital devices or computer software to send the readout to an operator who may be performing remote monitoring and diagnostics of the crane equipment.

Another type of load cell device is a load shackle, which is essentially a fully-rated lifting shackle with integrated electronics and microprocessors to determine the weight of a load once lifted into the air. These types of devices also send data to a handheld device or remote workstation.

Many load cells and dynamometers come with overload sensors that alert the operator, safety managers, or other designated personnel if the crane has been overloaded. An overload occurs when a lift exceeds the crane’s rated capacity. Overloads are prohibited according to OSHA and ASME B30 standards and can stress and damage the crane equipment—putting nearby employees in danger if the crane were to fail.

When using load cells or dynamometers, always refer to the manufacturer’s recommendations for scheduled maintenance and calibration to ensure your device is in compliance and continues to provide accurate measurements.

Wrapping it Up

Planning an overhead lift begins with understanding the weight of the load you plan on lifting and moving. Everything else should fall into place if you follow lifting and rigging best practices and put a lift plan together before any load is raised into the air.

Some of these rigging best practices include:

• Always determine the weight of the load and account for any other items being used below-the-hook when calculating or determining total load weight. This includes:
  • Chain slings, wire rope slings, and synthetic slings
  • Shackles, hooks, eye bolts, master links, and any other rigging hardware
  • Lifting beams, magnets, c-hooks, vacuum lifters, or other below-the-hook devices
• Determine the style sling you’ll be using (chain, wire rope, or synthetic) and hitch type (vertical, basket, or choker). Calculate the sling angle. Choose the correct hardware and slings for the lift based on the rating and working load limit (WLL).
• Inspect all rigging equipment before any overhead lift. Any item that looks damaged, deformed, or irregular in appearance should be removed from service, and a qualified person can determine if the gear can be put back into service or should be removed from service and disposed of.
• Proper rigging connection and technique should be checked by lifting the load a few inches off the ground to ensure no swing develops and that the load is completely secure and the center of gravity has been accounted for.
• Additional environmental factors can add resistance that affects the weight of the load and must be accounted for. Some examples include:
  • Friction or resistance caused by a load being lifted off a muddy surface, or a load that’s being dipped in and out of chemicals or other liquids
  • A load being lifted off a sloped surface
  • Heavy winds/wind gusts
• Never lift a load off the ground any higher than you need to, identify possible obstructions, and use a tagline when necessary to provide additional load control.

At Mazzella Companies, we can provide a lifting and rigging consultation to ensure you're using best practices for rigging, lifting, and moving a load through your facility. We also offer classroom training for your employees, and we sell a variety of lifting and rigging products, including:

• Overhead cranes
• Hoists and hoist parts
• Alloy chain, wire rope, and synthetic slings
• Rigging hardware
• Load cells and dynamometers

If you need assistance in putting a lift plan together, need rigging training for your employees, or want to schedule a site assessment of your rigging equipment and practices, please contact us today to speak with a Lifting Specialist.

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