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Seismic Separation and the Pallet Rack Layout

In the last five years, seismic separation in racking layouts has become increasingly enforced and a section on seismic separation has been written into the 2012 RMI specification. Seismic separation is the required horizontal distance between the building columns or walls and the racking components. To compute the seismic separation requirement for a rack project in an elevated seismic risk area, the seismic displacements of the rack and the building need to be known or calculated. Once these values are determined, the required seismic separation can be computed. These separation distances will be different for the down-aisle and the cross-aisle direction of the rack and may have more impact on warehouse design in areas with higher ground accelerations.

The required seismic separation will usually be greater than a typical rack layout would allow for a distance from the building walls or columns to the rack. Most engineers allow as much aisle space possible to help forklifts maneuver the warehouse. In higher seismic areas, the building officials may require that the layout be changed so the required separation distances can be established. This can have a significant effect on the rack layout and may cause problems when the rack user has to increase flue space and reduce forklift aisles. Back spacers may also fall too close to frame lines in the down-aisle direction and have to be re-sized or adjusted. A typical proposed layout may only have 2-3 inches between the building column and the rear pallet rack beam but when the seismic separation is computed, it can be up to 12 inches or more. The warehouse layout can be drastically different from the original design once these values are considered and pallet placement locations are usually impacted.

What is the purpose of these requirements?
The purpose is to avoid the collision between the rack structure and the building structure in the event of an earthquake. Because the rack and the building will both move independently during the earthquake, both must be considered in the calculation.

What should be done initially?
The rack user should be warned about this potential issue and that the requirement may cause the layout to be altered once the final design is complete and the separation requirements are determined. The building owner will need to try to find out what the seismic drift of the building is in each direction. If this value is not available, there are default values in the RMI Specification that can be applied. The rack engineer will calculate the amplified seismic drift of the rack in the cross-aisle and the down-aisle directions. The racking layout will then be adjusted to include the new values of separation.

In the end, bay configurations will need to accommodate the movement of the pallet rack and the building during an earthquake, so working seismic separation into the equation as early as possible may stop the headaches of a complete layout change before the project is too far along.

Baseplate… Size Matters

Why upgrade from the Standard Baseplate?

Seismic baseplates are larger, thicker and have additional anchoring holes for options when rebar impedes the installation of anchor bolts.

Most rack companies offer a very small and thin baseplate (1/8” x 3” x 5”) as their standard baseplate with standard pallet racking components. This is what you may get for your frame if you are in a low seismic risk area where a larger baseplate is not needed for seismic resistance and there is no request made for a more substantial baseplate. The purpose of this blog post is to outline the importance of the baseplate and to help the rack user understand that it may be a wise decision to consider an upgrade from the standard simple baseplate, even in low seismic applications.

The baseplate is important because:

  • It distributes the column load to the floor slab. The larger and thicker the baseplate is, the less stress (PSI) is exerted on the slab.
  • It provides rotational restraint at the base of the column. Added rotational restraint at the base can significantly increase the actual capacity of the frame from the “pinned base” condition.
  • It transfers any uplift force that may exist (from seismic or other overturning effects) to the anchor bolts.
  • In the event of a fork-lift impact, it transfers the load from the column to the anchors and works to keep the column in its position, rather than being displaced. A second anchor in the aisle side column can also be beneficial to prevent the column from “spinning” if impacted.
  • It helps to prevent a collapse from progressing to the whole row if there is an incident where a fork-truck takes out a column.

An upgraded baseplate will result in improvement in all items, one through five above. The main argument against a heavier baseplate is cost, but when the total frame weight and cost are considered, the percent change by a baseplate upgrade is really surprisingly minimal. A standard 1/8” x 3” x 5” baseplate may weigh 0.6# as compared to a 3/8” x 5” x 7” baseplate weight of 3.7#, so upgrading to the 3/8” baseplate only adds 6.2# to the frame weight. If the frame weighs 200#, the difference is about 3% of the frame weight and an even lower percentage of the total project cost. Many rack users later regret not selecting this small upgrade to their rack purchase.


Why Choose Cold-Formed T-Bolt Pallet Rack?

UNARCO offers a variety of optional rack styles to satisfy a large variation of storage rack project requirements. The two most common types of rack are:

1.) Cold-formed storage rack (generally with boltless connections)
2.) Hot-rolled structural rack (generally with bolted connections)

There is another option offered by UNARCO that is really the best of both worlds, cold-formed T-Bolt rack, which uses a 2-bolt connector. It has the benefits and equal strength of the structural bolted connector with the economy and paint aesthetics of cold-formed rack.
Probably the two biggest arguments that customers will raise against bolted connectors are:

1.) Higher initial installation cost
2.) Having to use tools to remove a beam

There are some important things to consider regarding the first argument. First, most racks are only installed one time, but the rack has to function for the life of the structure. The bolts on the bolted connector need to be properly tightened but require no auxiliary beam locking devices that can become non-functional or broken, requiring the whole beam to be replaced. The bolts are far stronger than the locking devices provided on boltless beams. Bolted connectors provide a clamping force between the face of the column and the inside face of the connector that adds rigidity and structural resistance. This type of clamping pressure is not present for many boltless connectors commonly found on interchangeable pallet rack.

Moving a beam that is boltless may require blows with a hammer while holding the lock due to settling of the floor and the pallet rack system. Boltless rack connectors often require special care or visual inspection to be sure that pins are properly engaged and the connectors are properly seated. A boltless beam can appear to be properly installed, but have pins that are not really engaged in the column holes, which could result in the beam becoming disengaged and dropping a pallet.

Another advantage of bolted racks is that the installer can achieve a more plumb installation. If there are any irregularities (rack or floor), the pins are less forgiving and the proper seating of boltless connectors can cause twist in the assembly that is hard to remedy in the field. There is more flexibility for plumbing the rack with a bolted connection.

The need for tools should not be a huge concern because the ½” diameter bolt requires a ¾” wrench, readily available, as it is the size of a car lug nut.  Many other components of the rack system such as back connectors, crossbars, anchors, etc. require additional tools to be present on-site.

The 2-bolt T-Bolt connection for a rack beam allows the customer to gain all of the benefits of the rigid structural bolted rack connection without having to accept some of the disadvantages of buying structural rack. Photos of the 2-bolt T-Bolt connections can be found on UNARCO’s website: http://www.unarcorack.com/photos/pallet-rack-photos/

Note: UNARCO manufactures the single-bolt (bolt-tab) T-Bolt connector for light or very short applications, but recommends the 2-bolt connectors for fork-truck pallet racks of medium height (greater than twelve feet) or taller.


Closed Tube Column vs. Open C-Shape Column

UNARCO offers a closed tubular column section and an open C-shape column section for uprights. We are often asked by customers “Which column section is stronger?” and “Why are both sections offered?”

The closed tubular column is a stronger and more efficient column section than the open C-shape. The closed tube geometry is considered a better design because, in addition to flexural buckling and local buckling, the open C-shape section is subject to some buckling modes that the closed tube will not experience as modes of failure. These modes diminish the capacity of the column. Three of these are shown below with some quick sketches to help illustrate.

1.) Torsional-Flexural Buckling:Torsional-Flexural

2.) Non-Symmetric Distortional Buckling: Non-Symmetric
One flange “in” and one flange “out”

3. Symmetric Distortional Buckling:Symetrical-inSymetrical-out
Flanges “in” or “out”

The C-shape is much more sensitive to the location of the frame braces than the closed section so the C-shape section usually requires shorter frame brace panels near the lower part of the frame.

The answer to the second question as to why C-shapes are used is that the open columns are less expensive to roll and often a more than adequate design for most standard warehouse rack designs. The closed tube section has to be formed into a tube and seam welded at the end of the rolling process adding more steel to the strip width and an extra manufacturing process. In some cases the tubular design can be calculated to include a lighter gauge material because of its geometry and might be a more cost-effective solution. In other applications, a C-section upright may be more than adequate and a smarter, more economical choice.

In short, no two rack jobs are the same and both open and closed section uprights allow customers to decide which design fits their application best and is the most cost-effective.

Homemade Pallet Rack Repair – Please Don’t!

It is safe to say that if you have pallet rack in a warehouse where product is moving on forklifts or pallet jacks, you have lower level pallet rack damage.  In my travels around the country I have seen many different types of rack repair.  Some repair kits seem almost over-designed for the application and I definitely do not have a problem with that.  However, some “homemade designs” by local fab shops are welded and bolted nightmares.  Pallet rack repair kits are not to be taken lightly.  It is important that the replacement parts attached are, at a minimum, the same gauge steel as the damaged parts they are replacing and also compatible design.  I have seen custom sloped-leg replacement rack repair kits with a little too much slope and welded straight-leg repairs with high-stacking shims to help level out a repair kit that is improperly sized.  Pallet rack damage is bad enough, but far too often warehouses compound the problem with mismatched repair kits doubling the danger.

Repair kits should always be ordered from authorized dealers or the manufacturer.  If you are in doubt, always contact the pallet rack manufacturer.  Most rack companies fabricate pallet rack repair kits from their own standard components that can be welded or bolted.  Either a welded design or a bolted design will work, but the bolted option is generally a less complicated installation.   The harsh fumes from welding on-site can lead to OSHA violations and fire safety issues.   If you are having local companies take steel scraps and make a repair kit, it is likely not the same steel chemistry or design as the existing upright.  Money and time saved now will cost you more in the long run.

The pallet rack repair kit design and fabrication is not the only concerning matter I have witnessed.  Some of the installations were dangerous as well.  It is imperative that the kit not only fit properly but be installed by a trained technician.  Do not let just anyone cut your racking system and install new parts.  If you do not have a list of qualified rack repair installers you can contact the manufacturer.  You do not want employees or anyone installing pallet rack repair kits who do not have training and experience.  Again, your problems can go from bad to worse if unskilled people are cutting apart your existing racking system without unloading it and then trying to put homemade, fabricated parts in its place.  If you have never seen how quickly damaged pallet rack can come down or you don’t understand how important it is to maintain the integrity of your racking system, there are hundreds of horror stories and even some videos on YouTube of falling rack.

Pallet Rack Bottom Beams – Can We Remove to Double Stack Pallets?


Our rack engineers are often asked by rack users if it is safe to remove bottom beam levels in a pallet rack system to store double-stacked pallets on the floor.  UNARCO informs users that this practice is not safe because the capacity of the frame is dramatically decreased.  Without hesitation, the rack user then asks, “How about if we just remove the beam in every other bay?  Then we still have the same column span.”

The answer to this question is, “No!”  The reason the answer is No lies in the fact that when every other beam is removed, one of the fundamental assumptions that is used to compute the frame table capacity value is undermined.  The rack frame capacity tables are developed with the assumption that a column span is framed by two beam connections at the top and either a base plate or two beam connections at the bottom.  When every other beam is removed, half of the top-span restraint of the column is gone and the frame model is no longer valid which voids the frame table capacity value.  The practice of removing every other lower beam span in a pallet rack system is no safer that removing every other first story beam in a multi-story building.

Straddle Protectors – Original or Retrofit, A good idea.

Possibly the biggest and most regrettable mistake rack users make is to overlook the damage that the outrigger of a forklift truck can do to a pallet rack column.  We see many cases where a significant percentage of warehouse aisle columns have been severely damaged due to forklift “bumps” during the first year.  No matter how high your forklift driver accuracy is, history tells a consistent story of column damage from outrigger abuse even in some of the safest warehouses in America.

The best time to consider this issue and avoid this mistake is when you purchase the pallet rack and plan your warehouse layout.  There are many ways to address this problem and probably the most obvious method would be to make sure the aisles and bays are wide enough to accommodate normal forklift activity.  Because of site constraints, it is not always possible to keep the uprights out of harm’s way and we recommend that you add a “straddle” or outrigger guard on the aisle columns for extra insurance.    Another simple precaution that prevents front column twist when the outrigger grazes the front column is to add a second anchor bolt.  If the column is allowed to twist, damage to the column above the straddle protector can occur and easily defeat the purpose of the guard.  It is not too late to check existing rack and make sure all anchors are installed properly and install an additional anchor on aisle upright columns.

You may be thinking, “I wish I had read this blog BEFORE I bought my pallet rack.”  If this is the case, there are many ways to address this problem even after the rack is installed.  Probably the best method is to add bolt-on, retrofit straddles that can do the job.  A few dollars per column for a retrofit guard is a whole lot better than the cost of a repair piece or the replacement price of an upright frame.  The straddle protector retrofit guards are easy to install with no disruption to warehouse operation.   It is always a good idea to be proactive when it comes to warehouse safety and maintaining the pallet rack is as important as the initial design.  If the current rack does not have proper equipment to ward off forklift damage, it may be a good time to address the abuse caused by daily operations and install some type of column protection.


As a pallet rack manufacturer, we are constantly asked to design rack systems of every magnitude. We have a large number of people who send in orders which would seemingly not require any engineering. However, there is one simple design principle that rack purchasers often overlook. Probably the easiest principle of pallet rack design in a complicated world of equations spanning from Phi and Lx is the height to depth ratio rule. The RMI defines the height to depth ratio for a single row of pallet rack to be “the ratio of the distance from the floor to the top beam level divided by the depth of the frame.” For the junior rack engineers out there, this simply means that a 24” deep upright should not have a top beam level higher than 144” (six times the depth). This easy fifth grade ratio computation is a welcome and simple approach to keep pallet rack from toppling over but is not as publicized as it should be.

UNARCO Blog Welcome

With over fifty years of manufacturing experience, UNARCO Material Handling has partnered with the best and brightest companies in nearly every industry. The UNARCO Blog is intended to help pallet rack and warehouse storage users benefit from topics ranging from seismic design, to codes, to rack safety.

Our engineering and manufacturing teams have worked with the majority of the current Fortune 500 list and helped develop some of the most advanced distribution networks in America. We are launching this blog to communicate on a number of topics in the world of pallet rack and warehouse storage solutions and weigh in with our views. After fifty successful years and as an industry leader, our views should be of some relevance in helping our past, present and future partners.

Please feel free to comment or suggest additional topics that you would like to add in future updates.