The steel framework of the Empire State Building is bolted together. The integrity of the building was not affected when a ten-ton B-52 bomber crashed into its 79th floor in 1945[/caption]
The Truth About Bolted Pallet RackIt has long been accepted on our continent that welded pallet rack is stronger and more reliable than bolted rack, but this is simply not true. Europeans have accepted bolted rack for decades, but North Americans have been slow to catch on. Due to misunderstanding and misconceptions about bolted racks’ strength and reliability, North Americans have not been so interested in this bolted product until recently. But people are finally beginning to discard their old prejudices against bolted rack, and it’s more and more becoming the rack of choice for many corporations in the US and Canada. The welded rack myth, however, is still touted by rack manufacturers and many distributors. Bolted rack is, in fact, somewhat less expensive to produce, is considerably cheaper to ship, and has other advantages which I will get to in more detail later, but there are structural advantages to bolted rack that no one talks about; and this is because almost all the North American rack manufacturers produce only welded rack. For this reason, the illusion that welded rack is superior endures.
Why bolted rack is structurally superiorThink about a building. A building constructed of steel–like a giant warehouse, or a huge retail structure (like Walmart or Home Depot) or better yet, a skyscraper. These buildings are constructed of steel posts and beams. And 90% of these posts and beams are bolted together. Not just because its more cost efficient to bolt than weld (which is true) but because a rigid structure can break. Large structures need to move. Bolted connections allow the structure to flex and give. This is how large buildings can withstand the forces of nature–from the earth shifting to high winds. A solid rigid structure is more likely to snap if it can’t “go with the flow.” The same is true for pallet rack. Strangely, many people believe that welded rack is the better choice for seismic areas, when in fact it’s the exact opposite!
Don’t just take my word for itUnfortunately, manufacturers are notorious for skewing the truth to promote their products in a good light and since I represent a manufacturer, I thought it would be a good idea to get the facts from an unbiased, real engineer not associated with our firm.* I contacted a reputable engineer who doesn’t know me from Adam (or Eve), and I asked for an interview. Ken Klimas, with Hillman and Miley Consulting Engineers in White Plains, New York was kind enough to spend some time with me discussing the misconceptions as well as the merits of bolted rack. Mr. Klimas has a BS & MS in Aerospace and Applied Mechanics from Polytechnic Institute of New York, is a licensed Professional Engineer in New York and New Jersey and has been involved in the rack industry since 1973. As a past employee of several rack manufacturers, he served as an engineering delegate to the RMI (Rack Manufacturer’s Institute) and helped author the RMI Specification. Currently, Mr. Klimas serves as one of six engineers tasked with reviewing rack manufactures product submittals for compliance with the RMI Specification and issuance of “R Mark” certification. Here is what he wrote:
Rack frames are basically vertical trusses. Classic structural analysis assumes its members and connections are subject only to axial forces, both tension and compression. Bolted frame connections present a closer analogy to this classic assumption.
The welding of bracing members to the column section introduces secondary bending forces in the frame members which are not generally considered in the frames analysis and capacity rating. Additionally, for open lipped “C” shaped column sections, bracing is usually welded only to the “lips” of the section. Forces induced in the bracing, which can be produced by rack out of plumbness, forklift impacts and seismic events, will apply bending moments to those column lips. The impact of these bending forces on the frame’s capacity is unknown and not accounted for in current rack analysis. Bolted bracing members are not attached to the column lips and will not transfer moments across the joint since connections are made with a single bolt.
Finally, if field repairs are required, bolted connections can be visually examined easily. While welded joints may appear acceptable, the connection may not be adequate and its reliability can be confirmed only with further testing.So there you have it from a racking expert–the truth about bolted pallet rack and why it’s structurally superior to welded. But even if you don’t care about that, there are plenty of other reasons to choose bolted pallet rack and they all save you money.