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For over 65 years, North America has resisted the worldwide concept of steel rack construction. Until 2001, the United States was an entirely pro-weld country. A decade later, only a slight shift has been made to combat the misinformation about bolted’s benefits. The tried and true method in the States has always been to utilize the welded side bracing of selective upright columns, primarily on the perception that welded steel is stronger, more reliable and cost less to install. Welded products arrive in an end-user’s facility assembled, and therefore must be sturdier and invulnerable to damage. Contrarily, the stigma against bolted rack has long existed that if a product has bolts, it is only a matter of time before those bolts come undone. Neither belief is true. However slowly, businesses are discovering the benefits of bolted rack. In the face of a struggling economy, the U.S. is looking for an alternative to the industry standard; anything that will improve efficiency and increase profits.
The conventional wisdom across all nations has long been that if rack does what it is designed to do, customers won’t care how the frame was constructed. Reliability and affordability is king, which leaves the customer to determine which is the more affordable construction and if it does what it is designed to do?
Structural Differences
The differences between the two racks are subtle enough that manufacturers on both sides have gotten away with making misleading claims without ever having to account for them. The largest difference lies in the rack connections; whether the uprights and beams are connected by bolts or by welds. Beam diagonals are the most visually obvious difference between the two styles of rack connectors. Welded strut patterns generally avoid connecting two struts on the same part of the upright. Often with the k-bracing or wind-bracing of the bolted systems, two diagonal struts will share the same bolted hole in the upright. The reason for this is simply because a weld covering two different connections isn’t as strong as a weld covering one. A bolt, however, can handle two connections. “The differences in structure don’t just come down to beam diagonals, the posts are different,” explained Linda Demke, the CEO at Interlake Mecalux, one of the few companies manufacturing both welded and bolted product. Bolted posts were designed using the metric system, while welded products were not, one of the reasons the post sizes for bolted rack are slightly larger. “There is no advantage or disadvantage,” Demke says. “They’re just different.”
Assembly Differences
One of the oldest knocks against bolted connections is that a third-party is in charge of assembling them. The assumption being that a third party runs a higher risk of assembling the rack incorrectly. Rarely, if ever, is bolted rack maintenance pawned off on a party not pre-approved by the manufacturer or distributor. Many companies have trusted stocking distributors at the ready, carrying its knocked down product. By doing this, the bolted rack manufacturers save on shipping costs, maximizing the containers in which the product is shipped. This gives these distributors the ability to service the market with whatever size installation may be necessary, making bolted rack the ideal for smaller applications in which selective racking is to be utilized. It’s far more cost-effective to ship bolted systems than welded ones because the structure can be broken down, requiring less space on the truck, which means more sections of bolted rack – almost twice the weight of welded – can be shipped at a single time. Then once the rack reaches its destination, its assembly requires little more than a pair of sawhorses.
Knocked Down, Drag-Out
Unquestionably, racks take abuse. Being hit with forklifts, constantly storing and removing pallets and various other human errors all add to the wear and tear of a shelving unit, and the inevitability of repairs. But repairing a bolted rack is generally easier and quicker than a welded unit. “Selling bolted to a welded market is all about serviceability,” Demke says, adding that in most cases, “it is easier to service a bolted frame if it’s damaged.” With a welded pallet rack, the damaged piece needs to be torched or cut off. The loads are then removed (which would happen with bolted rack, too) and replaced with a repair kit often comprised of – ironically – bolted frame. And while not having to remove beams is nice, it doesn’t add to the overall efficiency of the repair process, as most facilities disallow repairs to welded rack during work hours because it is necessary to shut down an aisle or existing area during the cutting process.
Another misperception of bolted rack is that, without constant attention, the nuts will unthread from the bolt and the structure will fall. This was the false refrain singled out above all others by Greg Hajdus, a structural engineer with Interlake Mecalux. “I’ve heard many times that if you have bolted frame, every once in a while you will have to go in and tighten the bolts,” Hajdus says, “but that’s not true. When you’ve got bolted frame, when it’s assembled correctly, you don’t have to do anything with it. Ever.”
Even after being given time and space to perform the repair, the weld may still be faulty. It may have been undercut, given too much or too little heat, or a lack of added flux core; all of which are human errors common to bad welds and broken rack. The problems with repairing welded rack and worrying about welder fluency don’t exist with bolted selective shelving. Every bolted piece is machine manufactured and passed through strict quality testing. Additionally, the restraint provided by bolts and welds differs. Welding a brace provides it with a certain amount of end restraint. The more end restraint, the more the carrying capacity of the rack. Reducing the brace’s buckling length enhances the restraint, however if a weld – often applied by a human – is faulty, the rack’s capacity could be reduced to as little as zero, perhaps without the end-user realizing it. The same results would occur for a bolted rack with faulty connections as with a welded rack, but the risk of it happening is so much lower. Bolted frames have well-defined and highly controlled buckling length. In short, if a bolt is missing, you’ll see it. If a weld is bad, you probably won’t. Miguel Lopez, an area market manager for Interlake Mecalux and one of the first to regularly sell bolted rack in the United States, agrees. “The quality of the welded connection is always somewhere between excellent to non-existent,” Lopez says. “But you have to test it.” If repairs are necessary, a warehouse’s maintenance engineer can take care of them immediately with an adjustable wrench and socket set. Bolted rack may cost more to install, but customers save on the back end by not having to cover the costs of certified welders and on the front end by saving on the shipment of the parts. Likewise though, if a weld breaks, the shelving’s structural integrity is in jeopardy. Bolted units are safeguarded against such a catastrophe, even in the unlikely incident of a nut and washer coming off a bolt, the unit will still hold because the bolt is in place. However, all Interlake Mecalux bolted selective shelving units bolts have serrated nuts, ensuring that this does not occur. May it be welded or bolted rack, regular warehouse maintenance is still needed to ensure safety. One doesn’t bring their car to a mechanic and ask for every bolt to be torqued down, so the fear of a bolted selective rack coming apart is a moot point.
Even the type of steel – whether it is galvanized or not galvanized – illustrates bolted rack’s superiority. Galvanized steel does not rust and therefore meets the regulatory codes for pharmaceutical and food industries. Galvanized steel however is more difficult to weld than bolted’s hole punch because the zinc coating gives off toxic fumes and weakens the coating’s integrity. Even if coated frames have been safely welded, the steel still needs a second dip to restore the coating; an unnecessary step with bolted rack. Because of these factors, many of the parts are welded together first, then coated. Doing this creates difficulty in coating unexposed surfaces.
There has been a subtle shift in the market as major corporations like Wal-Mart, Target, CVS and Home Depot have all installed European-manufactured AS/RS systems structured around bolted rack – a small-but-substantial step in bringing such rack into the North American mainstream. That mainstream isn’t likely to turn its back on welded anytime soon. There will always be a market for welded. But a shared marketplace in which each customer’s budget, timeframe and storage are evaluated, is on the horizon, a vision long overdue for warehouse owners interested in the best deal instead of the standard one.