A pallet rack upright that is leaning (out-of-plumb) or bowed (out-of-straight) beyond a certain point will have a significantly reduced capacity, making it unsafe and at risk of collapse.
Nolwazi (in accordance with the SEMA erection tolerance for static racking) defines the severity of these two conditions as follows:
- Out-of-Plumb Ratio– Maximum out-of-plumb upright perpendicular to the plane of the upright and maximum out-of-plumb upright in the plane of the upright frame.
- Out-of-Straight Ratio– Maximum imperfection of upright with regard to the theoretical longitudinal upright axes x or y.
The higher the ratio, the more likely a rack is to fail. Recognizing this, SEMA: Guide to erection tolerances for static racking limits the ratio for both out-of-plumb and out-of-straight (measured prior to loading) to 1/500 and 1/1000.
The limits are intended to prevent excessive bows or dogleg conditions that may exist in a rack upright. For example, an upright could be plumb from top to bottom, but have an excessive bow (out-of-straight) in the middle. Alternately, a 6-meter-tall column that could be out-of-plumb 10mm from top to bottom, which would be acceptable unless the entire out-of-plumb condition is solely between the floor and the top level, referred to as a dogleg (commonly caused by a fork truck impact).
Other causes of out-of-plumb and out-of-straight conditions include beam height adjustments or alterations, the type of connection used, bolts that weren’t sufficiently tightened during the installation, or impacts with machinery or pallets as loads are moved to and from the racking.
The best practice to ensure a safe installation is to inspect the racking regularly with tools such as a plumb bob, long level or laser line to determine if uprights are leaning or bowed. Remediation of the condition includes first unloading the rack, then loosen the column bolts in order to straighten them, then re-tighten bolts. Beam connectors should also be inspected to ensure that the lean has not caused them to bend or otherwise deform.
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