Mobile elevating work platforms (MEWPs) and telehandlers are often used on ground conditions that can vary greatly from site to site—from undeveloped terrain one day to finished floors the next. To best prepare on-site crews for working on different types of surfaces, project planners need to pay attention to two specs: 1) floor load capacity and 2) machine ground bearing pressure.
Floor load capacity is measured in pounds per square foot (psf). Machine ground bearing pressure is measured in pounds per square inch (psi). There is not a direct conversion between floor load capacity and ground bearing pressure.
Because these specs seem similar, it is not uncommon for crews to use the two terms interchangeably, but they are not the same.
FLOOR LOAD CAPACITY
Floor load (also referred to as floor pressure) is the total weight capacity that a floor can sustain in a given area.
Why is it important? Because any machine used on a jobsite is only as strong as the ground or surface the machine is working on. For example, floors are engineered and constructed to only handle a certain amount of load. If this load is exceeded, there is an increased risk of compromising the structure and damaging the floor—which comes with costly consequences. So, before work begins, it is critical to know if the ground or surface can support a machine’s weight during work and travel.
Also, it’s important to know that the floor’s load capacity may change over time, depending on the materials its constructed with, its age, and the environment. For example, if a machine is working on a freshly poured concrete slab, that slab will have a lower floor load capacity than a fully cured slab. Or, if a machine is working on fully compacted earth, like a site that’s been heavily graded for a new road or building construction, that surface will have a higher capacity than softer, looser dirt conditions, like what would be found in someone’s yard.
Before operating, it’s important to always check the allowable capacity of the surfaces, including floors, bridges, etc. Also, figure out if the machine could potentially damage the surface during operation, such as leaving ruts in the soil or scuffs on the concrete. Whenever possible, operators should consult with a structural engineer or other qualified people to know as much as possible about jobsite surfaces where work will be done.
Where can you find information on a floor’s load capacity? Project managers should check with the project’s structural and/or architectural engineer to find a floor load capacity specification. Either of these professionals will be able to assess the project site and make the necessary calculations needed to determine this critically important measurement.
GROUND BEARING PRESSURE
Ground bearing pressure is the amount of pressure exerted on the ground by a machine’s tires, tracks, and/or outriggers.
Why is it important? Because as a machine is working, it is not just the machine’s weight that tests the floor’s strength but also the amount of stress applied to the ground or surface by the machine during work and travel. Too much stress on a floor may start with small, seemingly harmless cracks, but over time, it can contribute to failure, leading to collapses or cave-ins—which can lead to hazardous situations for people and property.
The machine’s contact area and orientation will significantly influence this specification. For example, increasing the size of the contact area of the machine on the ground (i.e., its footprint), to its weight, will decrease the ground pressure. Lower ground pressures are recommended for working in fragile ecosystems, such as extremely soft turf, like sugar sand, or on extremely delicate flooring, like ceramic tile. Decreasing the ground pressure also increases the machine’s flotation, which allows it to travel better over soft terrain.
To be even more precise in knowing how much strain a machine is exerting on the floor, it is important to also become familiar with some other terminology, in addition to the ground-bearing pressure, such as:
- Maximum Machine Weight: The machine’s weight in its heaviest configuration, excluding accessories.
- Maximum Platform Capacity (rated load): The maximum allowable weight in the platform, excluding accessories.
- Maximum Load: The maximum load supported while the machine is in its working configuration, supporting its rated load.
- Maximum Ground Bearing Pressure: The maximum pressure exerted while the machine is in its working configuration and supporting its rated load.
- Where can you find these specs for MEWPs and telehandlers? Project managers should reference OEM-approved equipment spec sheets for machine details, including ground bearing pressure, weight, rated load capacity and maximum load.
BEFORE YOU BEGIN TO WORK
If knowing the floor’s load capacity and the machine’s ground bearing pressure is extremely important to successfully plan a project, then conducting a workplace inspection before project start-up is critically important to successfully execute a project.
Precautions to avoid all hazards in the work area must be taken before and during the operation of any machine, including anomalies in a floor that aren’t of the same capacity as the typical floor such as access panels, masked cavities under a surface, tunnels under sidewalks, septic tanks in yards, and so on.
Workplace inspections can help identify these hazards by:
Checking the operating surfaces for holes, bumps, drop-offs, obstructions, debris, concealed holes, and other potential hazards.
Making sure that the ground conditions are adequate to support the maximum tire load (indicated on the tire load decals on the machine’s chassis, adjacent to each wheel). It is important to not travel on unsupported surfaces.
Examining the work area for hazardous locations. The machine should not be operated in hazardous environments unless approved by the OEM for that purpose.
CLOSING THOUGHT
To ensure equipment are operating safely, knowing the floor load capacity and ground bearing pressure is a best practice.
For More Information:
Content provided by Provided by JLG Product Safety & Reliability. For more, visit jlg.com.
Modern Contractor Solutions, February 2023
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