No, unfortunately. And we’ll tell you why in a moment.
As a rigger and machinery mover, we obviously move big, heavy machines or pieces of equipment for our customers. This often requires us to move items across floors that may or may not have been designed to handle these types of loads. Consequently the question of floor loading capacity comes up constantly, and it comes up regardless of whether the floor in question is a slab-on-grade, an upper floor or an open grate mezzanine deck. Both you the owner, and we the rigger, need to know if the floor will support the loads we’re moving across it.
When we’re asked to quote a job or when we’re in the planning stages, we often receive information on floor loading expressed as “xx pounds per square foot load capacity”. In fact, it’s even typical for larger companies to post floor loading expressed in this fashion on different floors or areas of the plant. So when we ask questions about the supporting structure(s) or start to dig deeper, invariably someone will point out these floor loading capacity signs in the belief this is the single, critical piece of information we need to assess the ability of the floor to handle the loads. This is when we find ourselves in the common position of explaining why this won’t work. After all, at face value, it seems like it’s exactly the information needed.
When an engineer designs a building, they have to use something to calculate or specify floor loading, and “pounds per square foot” is usually it. For building design, this is normally dictated by a building code specifying a minimum required loading for different spaces such as office space, warehouse space, public assembly space, etc. So that’s what they use for design.
However, floor load capacity applies to uniformly distributed loads, not concentrated or point loads. And the total load supportable (provided it’s uniformly distributed) by a floor is a product of the total square foot x capacity per square foot. For example, a 20’ x 50’ room with a floor load capacity of 150 pounds per square (psf) foot means you have 1,000 square foot of floor space that can support 150 psf, or 15,000 pounds overall. Provided it’s uniformly distributed, of course.
The problem is, even if your total floor area can support the load, most loads aren’t uniformly distributed. Or if they were, they would need to spread across your entire floor; an impractical or impossible scenario, especially considering heavy loads with small footprints. In fact, the loads you impose on a daily basis aren’t uniformly distributed either. Take into account the following examples:
Before you ban 3,000 pound pallets or require people to shuffle across your floors with special weight distribution shoes, understand that floor structures themselves are designed to distribute those small, normal types of load concentrations expected of the design application, such as people walking across the floor. But they aren’t necessarily designed to handle the heavy loads we may need to move across your floor.
The problem is, when planning a rigging project, though we may know we exceed the floor load capacity, we don’t yet know is where the weak link is. If the weak link is the flooring, we can get around that by plating the floor or by bearing only on the floor beams. If the floor beams are the weak links, then load-spreading to grab multiple beams is the way to go. If that isn’t enough, then shoring may be necessary. And sometimes it’s not the beams, but rather the connections at the ends of the beams that are the weak links. And sometimes, it’s a combination of one or more of these things…perhaps even all of them together.
Put it all together and the answer is that there’s no easy answer. There’s no rule-of-thumb that we can use to translate a “pounds per square foot” design load into an allowable load on skates, rollers, skids or tracks. If the loads are heavy, the structure needs to be looked at. Plain and simple.
If you, as the building owner, can’t provide reliable loading data for the rigging work, the only recourse is for you or your rigger to involve an engineer knowledgeable about building design to analyze the floor structure for the loads that will be imposed during the rigging.
As the building or facility owner, if you have a new building or if you have an engineer already familiar with your building, engaging them will likely be the most cost-effective and time-efficient option. If someone unfamiliar with your structure is engaged, the biggest task might be surveying and evaluating what’s there. Once this is understood, the calculations are sometimes the easier part.
Understandably, this isn’t what most customers want to hear. But for those projects where floor loading is a concern, there simply is no shortcut and ignoring it can be catastrophic. For all of us. As your rigger, we’ll help you through this process or we can perform this process for you if you want us to. We’re here to help you. And you can count on us to not perform any work or approach any project in a manner that presents risks to anyone’s health and welfare, or to your property or ours.
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