Debra Schug, Contributing Writer
Racking systems are the cornerstone of any material handling or warehouse facility, allowing for rapid access and optimizing the vertical operational space. But, racking without the ability to actually hold product is, well, useless. As a crucial component of the storage system, decking is used to top rack load beams and shelving.
Even though decks are considered to be an accessory to industrial storage racks, there are many complicated precautions that must be adhered to in ensuring the safety of decking. This article will go over those safety measures, as well as design styles and best practices of installing decking.
Decking is typically manufactured from welded wire and has reinforcements of channels or support wires. To form a shelf surface, one or more decking sections are used. Because decks act as the load-bearing surface in a racking system, they ensure the safety of system’s support for stored material. The decking is designed to support loads of variable sizes in a rack system.
Load calculations for wire decking are computed differently than they are for an entire storage rack structure. The Racking Manufacturers Institute (RMI) publishes the ANSI MH26.2-2017: Design, Fabrication, Testing and Utilization of Welded Wire Rack Decking, which is the document that confirms wire rack decking is properly engineered for the particular application in which it is being used. RMI also recommends deck manufacturers request a buyer give specifications and load capacity ratings of a rack to ensure the decking will fit the system.
Crucial to the safety of decking is the uniformly distributed load (UDL). The official definition of UDL, as stated by RMI, is any static load that is evenly distributed over the entire surface on the rack deck; meaning the product being stored on the deck must cover the entire deck from side to side and from front to back. As it applies to storage capacity ratings, general capacity ratings are based upon a UDL stored on the deck.
An important safety point to note is that decking should only be used for the UDL storage. This is important to keep in mind to prevent workers from walking or standing on decking. Frequently, companies ask racking experts if it is safe to walk on decking, and the answer is no, because decking is not designed for holding concentrated weight or “point loading.” This means that when the deck is stepped on, it can sag and fall through the beams. Additionally, decking is not designed for human foot traffic, and the spacing of the wire mesh is often wider than a human’s foot—which can cause a trip hazard if stepped on.
Most racking systems have a “waterfall” style wire deck, which means the top deck wires overlap to run over and down the support beams. According to RMI, waterfall decks have three to four support channels that fit within the beam and support the load contained on the deck.
Another type of deck is a flush or instep deck, which fit step beams only. A step beam is a beam that provides two horizontal surfaces on which the rack decking can be placed, usually consisting of a top surface that supports the deck and a lower surface that supports the reinforcing member. A reinforcing member is a component of rack decking that helps increase its capacity rating; typical examples are channels, tubes and rods.
In this type of configuration, the deck sits flush with the top of the beams and can have formed instep waterfalls. This type of decking is best for applications requiring the rack beam face left unobstructed and being kept smooth.
The third most popular style of decking is a non-waterfall deck, which can span across the top of the front and rear load beams, but does not “waterfall” down. However, this type of deck isn’t appropriate to use with non-step beams, because the configuration is not as stable and secure as the waterfall-styles.
Best Installation Practices
Before the deck can be properly installed, it must fit perfectly with the rack to which it’s to be installed. The myriad types, sizes and designs of many different manufacturers’ racking systems can make it nearly impossible to fit decking properly without specifications. And, if the decking does not correspond with the rack’s exact dimensions, the rack might fit, but might not be safe.
Wire deck manufacturers typically ask buyers for the racking specifications before the decking is produced, which protects both the manufacturer and the customer. Another best practice is for buyers to submit the load capacity rating of the racking in order for the deck manufacturer to produce a deck designed to meet the capacity of the rack system.
According to RMI, deck capacity should take its cue from the load beams’ capacity of the rack system. In other words, if a beam pair is rated at 5,000lbs, it will require two wire decks with the capacity rating of 2,500lbs each.
All wire decks should be tested to evaluate its capacity when holding a uniformly distributed load. The purpose of this test is to allow different decking to be compared by their load carrying capacities. According to a RMI presentation at MODEX 2018 entitled “Rack Design: Resources and Frequently Asked Questions,” this test protocol is designed to have the entire load weight supported by the decking components. During this test, none of the weight should be supported by the shelf beams or anything other than the decking components.
RMI also says some type of method needs to be employed to keep the decks from falling through the beams. If the decking’s style is not designed to hold the beam, as in the case of flush or instep deck and non-waterfall deck, then the decking should be fastened to the beams or the beams should be tied to the deck to prevent the deck from dropping. Decks can be secured either using screwing, riveting or another provision to prevent beams from “spreading.”
Again, wire decking should only be used for uniformly distributed load storage. If a material handling application needs decking to handle a unique task, like highly concentrated point loading, a wire deck manufacturer and engineer should be consulted to specifically design a deck for that purpose. WMHS