This time around, I want to again share some information with you about something other than regular pallet rack. Having received positive responses to the articles on double-deep and drive-in rack, I’m sharing information on cantilever today.
Let’s start with a definition: A cantilever is a rigid structural element, such as a beam or a plate, anchored at only one end to a (usually vertical) support. When subjected to a load, the beam or plate transfers it to the vertical support via shear stress.
Read on to learn more!
Designing a Cantilever Solution
As with every other racking storage solution, the key to success is understanding the load. Length, depth, height and weight are all important whether you’re storing furniture, steel bars, pipe, lumber or a different long and heavy item.
Step One: How Many Arms are Needed?
Preventing load deflection is what determines the number and spacing of arms. This can be quickly and inexpensively tested by placing the load over two wooden blocks representing the cantilever arms. Half the length of the load should be between the “arms” with the remaining half divided at either end as overhang, as shown below.
If you see deflection, try again with three “arms” with 1/3 of the load between the arms and 1/6 at either end as overhang. Note that the arms can have decks on top of them to eliminate deflection as well.
Step Two: Find the Arm Length
This one is easy. The length of the arm must equal or exceed the depth of the load.
Step Three: Determine the Upright Height
Like all other rack systems, the height of the units is partially determined by the facility clear height and the reach of the forklifts. Beyond that, as shown to the right, you simply add the base height, the total of the load heights to be stored, the arm thickness, and an additional 6 inches for clearance between the load and the next arm. The upright must extend at least the height of the top load above the top arm level.
NOTE: Loads placed on the base do not affect the capacity of the upright so the heaviest load should be place on the the bases.
Step Four: Calculate Arm and Upright Capacity
Here we start with the arm capacity because it will help determine the upright load. It’s pretty simple: Divide the load weight by the number of arms supporting it and you arrive at the arm capacity needed. Example: 7500 lbs load divided by three arms = 2,500 lb arm capacity.
For the upright capacity, multiple the number of arms on the system by the load on each arm. In our example, we’ll assume the three uprights shown in the first picture and the 2,500 arm load from above, giving us 30,000 lbs. Then we divide by the number of uprights to arrive at the upright capacity of 10,000 lbs. Remember that loads on the base do not contribute to this so you can exclude that load.
Step Five: Add Bracing
Cantilever brace sets provide lateral stability to the system. In other words, it prevents the system from swaying left-to-right. The length of the braces is determined by the load length and the calculations we used to determine the number of arms needed to support the load way back in step one. In that illustration we can see that our horizontal brace sets need to be 48″ long, calculated center-to-center of the uprights.
The number of horizontal braces between uprights and whether or not x-bracing is included varies by manufacturer so I can’t provide specifics here, however you should be aware that the higher the system, the more bracing is required.
More Information
I hope that this has been a helpful introduction to cantilever rack system design. If you found it valuable and would like me to expand on it, send an email to DealerSales@dakequipment.com and let me know. If there’s enough interest, I’ll turn it into a document for you and add information about double-sided systems, load stops, inclined arms and more.
I also want to remind you that there’s a preliminary design worksheet available in the Toolkit that you can download and use to get the information you need to succeed with a cantilever system.
