You may be wondering how much weight can be added to pallet racking and how to calculate storage racking capacity. Engineers and designers determine pallet racking load limits by evaluating the structural load carrying capacity of each racking system component. Taken together, each component contributes to the integrity of the rack, which is how they determine rack capacity.
Determining warehouse racking capacity is a mathematical exercise, not a theoretical examination. Engineers are pragmatic people who follow known information, such as validated tables that specify known weight limits for rack components based on their physical dimensions and metallurgical composition. Based on available information, they know how to calculate pallet racking load capacities.
It’ s fairly simple, in theory, to figure out how to determine rack capacity. Just calculate the maximum weight of a combined pallet load and then resize the decks, beams, columns, supports and base plates to exceed the expected limits. Sizing rack components is always intended to reach a level beyond any realistic possibility that you will exceed the known weight capacity of the rack system.
There is more to it than that, however, in practice. Each rack component manufacturer and supplier provides a design weight limit for each piece free of charge. The trick is to make sure that each rack component is compatible with its adjacent partner, rather than being a weak link situation.
The four-step method used by racking experts to determine the maximum load.
1. Calculating Upright Capacity
If there is one component of your racking system that is most critical to proper calculation, it is your uprights. In the racking business, you’ll also hear about upright frames. These components support the weight of the entire system, which is collected from the loaded pallets, set on the deck, sent across the beams and through the uprights to the earth.
There are two weight classifications for uprights to absorb and transfer. Each weight type increases the overall capacity that your uprights need to support. In engineering terms, these are the two loads that occur in a pallet racking system as they move along the uprights.
Static load: This load itself consists of the static weight of the racking system. It includes the total gravitational pressure exerted by the unloaded deck, beams, brackets and the columns themselves. Your racking capacity must maintain itself, but your system must also safely support your loaded pallets.
Live Cargo: The pallets you load are a fluid commodity. Sometimes your racks are at maximum capacity and there is no extra space. At other times, your pallets go in and out of the warehouse, off and on the racks. A loaded pallet is called a live pallet. While the weight of your rack components never changes, your pallet loads do, which is why your rack capacity rating must exceed the maximum amount of live and dead load that puts stress on your system.
2. Calculating Beam Capacity
The key information you need to know about beams is that there is a strength or load capacity ratio between length and depth. Beam width has little effect on the size of the rack assembly. However, the depth is critical. Why? Because gravity acts on the loaded rack beam.
The beam experiences compression, which is the downward force exerted by the live load. The beam also compensates for the tension that extends from the center of the load or point and runs along the beam toward the lateral transverse and transfers the weight to its upright attachment point.
When you adjust the beam capacity, your rule of thumb is the longer the beam, the deeper it needs to be. A 96-inch rack beam with a depth of 3.5 inches, for example, can carry up to 4,044 pounds per pair. If the depth of this eight-foot-long beam is increased to 4.3 inches, the pair can now support 6,111 pounds. Further, the maximum weight capacity of a 144-inch beam length is only 3,000 pounds, but if you increase the depth of the 144-inch long beam to six feet, it will now hold 7,820 pounds per pair.
Your maximum beam capacity determines how large of a column your system will need. Calculating a racking system starts with knowing the maximum weight you expect the pallet to hold. Then, determine the size of the beam pair based on the beam length or “bay clearance entry” distance. Once you know these parameters, you can match the upright frame size and load capacity to the beams.
As you can see, beams are the backbone of a strong and reliable racking system for your individual warehouse needs. Beams need to be strong enough and must be used under many changing conditions. However, you can expect your rack beams to flex a little under load, which engineers call deflection in normal conditions.
3. Rated bending or deflection of pallet rack beams
Rack beam manufacturers use high grade steel for all components including decks, uprights, base plates and cross members. You should not experience bending and flexing with columns or plates, but your horizontal beams can bend or deflect. This phenomenon is natural in engineering.
Rack beams deflect or bend because they are partially flexible. This means they will sag slightly under compression and tension. This component of the beam design is nothing to worry about. It is part of their intended design.
Engineers specify standard rack beam deflection rates within acceptable safety standards. Bow, sag or deflection is 0.55% of the horizontal run of the beam. The maximum allowable deflection is obtained by dividing the beam span by 180.
Some rack manufacturers specify tighter deflection tolerances for certain applications. Under robotic conditions such as automated store and retrieve systems, the deflection percentage is only 0.42. With automated systems, human operators are less likely to catch beams that are overstressed and designers err on the side of caution.
Engineers typically specify load factors and reactions to compensate for the maximum chance of stress fatigue or failure. Interestingly, the deflection rating is primarily designed to alert warehouse workers to load conditions and to be aware of deflected beams when they are found. It ensures that workers are aware of the safety limits of the loader frame and avoid applying any excessive weight to the beams or other components.
4. Calculating Deck Capacity
Pallet rack decks or platforms are used as horizontal stabilizers to distribute pallet loads evenly across the beams and down through the uprights. Loaded pallets are often uneven in their direct weight distribution and properly designed decks compensate for high and low weight transfer contacts. The following are two load classifications that engineers consider when calculating the maximum pallet rack weight capacity.
Uniform Loads: Uniform loads distribute weight evenly from one surface to another. They are static and dispersed under equal pressure. An example of this is a properly loaded rack deck that transfers weight uniformly across the cross members.
Point Loads: Point loads are uneven concentrations of weight. They are inconsistent weight transfers where one part of the contact surface has a higher pressure than another part. A good example of a point load is a pallet sled, which collects the total weight of the pallet and then transfers the load to a highly concentrated area of the deck or beam.
Not all warehouse racking systems use decks. Some systems place the edges of the pallets directly on the beams or uprights. Working without a deck is the obvious case for point loading, and your undecked racking system requires careful weight calculations to be sturdy and secure.
How much weight can pallet racking handle?
Your pallet racking system must be sufficient to support the maximum weight you can possibly apply. It is wise to extend the manufacturer’s rated capacity one step beyond your imagined storage capacity. Computer racking capacity is obviously a safe rather than sorry situation.
However, it may be possible to overestimate your rack size and weight capacity. Overkill incurs unnecessary costs and costs too much for little or no return. Oversized racking systems are also bulkier and take up valuable warehouse storage space.
The easiest way to determine how much weight a pallet system can handle is to consult an expert. A professional who specializes in warehouse racking design will know exactly what you need. A reputable and experienced supplier of racking components will work with you to assess your needs. They are the most qualified to calculate a safe, reliable and economical pallet racking system that will serve your facility for many years.
Further Reading:
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Daily maintenance of pallet racking
Advantages of mobile shelving in auto parts storage
Post time: Feb-14-2022