Load Weight Plays Key Role in Keeping Crane Jobs Safe

Tue November 19, 2024
Lucy Perry – CEG CORRESPONDENT

The first step in planning a lift is to determine the weight of the load. A true understanding of load limits is critical to safe construction crane operations. Crane load limits ensure the equipment, cargo and ground crew are protected, and are why the load weight should be calculated early in the job planning process. Ultimately, it dictates every other phase of the lift project.

"Planning an overhead lift all starts with understanding the weight of the load you plan on lifting and moving," said Mike Close of Mazzella Companies. "Everything else should fall into place if you follow lifting and rigging best practices and put a lift plan together prior to any load being raised into the air."

Writing about load weight best practices for Mazzella, Close teaches a variety of simple methods to determine the weight of the load.

"You can easily identify the weight of a load without doing any type of calculations or using specially engineered load cells or dynamometers," he said.

First, and most obvious: Look at the load to see if the weight is marked.

The load may be marked clearly by the manufacturer after previous calculation.

"Look for any visual indications of load weight prior to selecting the appropriate lifting and rigging equipment," said Close. "If it's a load that you regularly lift and move through your facility … then you will already know the weight of the load."

If a crane was designed for a specific repetitive lifting application the weight of the load may have been accounted for when the crane was built.

Close said the lift planning team can refer to engineered prints or design plans specific to the load, which can indicate the final assembled weight. The planner can review a bill of lading or shipping documentation. For a transported load, weight information should be included in shipping paperwork.

"For smaller and lighter loads, you may be able to use an industrial floor scale," said Close.

These types of scales are commonly found in production areas or the shipping and receiving department of an indoor facility. The planning team should have access to the manufacturer's specifications or catalog data for the load.

The load weight may be indicated on paperwork provided by the manufacturer, on its website, or among product specs in a catalog or brochure.

Reading a Construction Crane's Load Chart

"The best way to find the load capacity of a crane is to consult its load chart," said Dustin Eusebio of BigRentz. "Crane load charts explain a crane's load capacity at different boom lengths and lift angles."

Load charts also indicate how the load capacity decreases as the boom length increases.

"You typically find load moment indicators (LMI) or rated capacity indicators (RCI) on modern cranes," said Eusebio. "These devices enhance crane safety by warning you when your load exceeds the lifting capacity suggested by the crane manufacturer."

But even if you have these features, it's essential to understand the load chart, he stressed.

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Each crane model has a unique load chart, Eusebio added, and a crane may have one or multiple load charts based on its configurations. Typically provided by the crane manufacturer, load charts are included in the operator manual, which is usually found in the cab of the machine.

"Using this chart helps you create a lift plan that is safe from start to finish," Eusebio said.

First, calculate the load radius. Most load charts will have a lift range diagram showing it. Load radius is the horizontal distance between the centerline of the crane's rotation to the load.

"The shorter the load radius, the higher the load capacity of the crane," said Eusebio.

Find the length of the boom being used and the angle it will be positioned at on the diagram. Then, find the corresponding radius at the bottom of the chart. Once load radius is determined, look across the chart to see the lifting capacity.

Load charts typically list both the crane's gross and net capacity and indicates what a machine is rated for as well as its maximum capacity.

"Load charts also contain other information that needs to be taken into account when determining your crane's lifting capacity," said Eusebio. "For example, the chart should state if capacity is calculated over the rear or front of the machine or at a 360-degree rotation."

It should also show whether the machine is stabilized by tires or has its outriggers or stabilizers down.

"Factors like these all affect a crane's net capacity, or the actual load it can lift," said Eusebio.

Also, "the lifting capacity at the rear or front of a crane is higher due to the machine's structure and weight distribution."

He stressed that if you're calculating the capacity from this position, you must make sure the boom stays here during operation or it could overload.

Ground conditions, such as the slope of the ground on which the crane will be positioned, are part of the load chart. Both ground conditions and wind speed can alter the crane's stability. Load capacity can be directed affected by crane stability.

"Also, don't forget to check the chart for the correct crane configuration, including any attachments or accessories in use," he added.

Following Rigging Best Practices

Mazzella advised that in determining load weight planners account for any other items being used below the hook such as chain, wire rope and synthetic slings.

Shackles, hooks, eye bolts, master links and any other rigging hardware, as well as lifting beams, magnets, c-hooks, vacuum lifters are used below the hook.

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The planner must determine the style sling to be used and the hitch type — vertical, basket or choker. Then they must calculate the sling angle.

Choose the correct hardware and slings for the lift based on the rating and working load limit (WLL) and inspect all rigging equipment prior to the lift.

"Any item that looks damaged, deformed or irregular in appearance should be removed from a service," said Close. "A qualified person can determine if the gear can be put back into service or should be removed from service and disposed of."

Close suggests checking proper rigging connection and technique by lifting the load a few inches off the ground to ensure no swing develops.

This minor lift also determines whether the center of gravity has been accounted for in the planning process.

He said other environmental factors can add resistance that affects the weight of the load and must be accounted for. These factors can include friction or resistance caused by a load being lifted off of a muddy surface. A load that's being dipped in and out of chemicals or other liquids; a load being lifted off of a sloped surface; or a heavy wind gust can affect load weight.

"Never lift a load off the ground any higher than you need to," said Close. "Identify possible obstructions and use a tagline when necessary to provide additional load control."

DIY Load Weight Calculating

If no load weight information has been provided to the project planners, then they'll need to calculate the weight based on the material being lifted.

There are devices on the market that provide a read-out of the load weight when it's slightly lifted off the ground, said Close.

Load cells or dynamometers are mounted in line with the crane hook, slings and hardware.

"The load is then attached to the load cell and the load cell calculates the weight of the load."

This is accomplished by measuring the force being applied to the load using a strain gauge or hydraulic or pneumatic pressure inside the device.

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"These devices can display the measured weight of the load in a variety of ways," Close said. "Some are mechanical with an analog display that utilizes a needle and dial — similar to how many bathroom or medical scales operate."

Some displays are digital. Handheld digital devices or computer software can send the read-out to an operator performing remote monitoring and diagnostics of the crane equipment.

"Another type of load cell device is a load shackle … a fully rated lifting shackle with integrated electronics and microprocessors," said Close.

These devices determine the weight of a load once it's lifted into the air. These systems also can send data to a handheld device or remote workstation.

Overload sensors built into these systems can alert the operator, safety managers, or other personnel if the crane has been overloaded. Overloads, which occur when a lift exceeds the crane's rated capacity, are prohibited according to OSHA and ASME B30 standards.

These conditions "can stress and damage the crane equipment — putting nearby employees in danger if the crane were to fail," said Close.

Following manufacturer's recommendations for load cell or dynamometer maintenance and calibration ensures compliance and accurate measurement.

Lifting Safely Is the Goal

Construction crane load limits are in place for a reason. They indicate the maximum weight a crane can safely lift, move or support.

Risks for safety hazards, crane tip-overs, deadly load drops and structural failures occur when an operator exceeds a crane's load limits.

Constant situational awareness and strict adherence to load weight are keys to a safe and successful lift. CQ