Reference for Seismic Calculations

NAWL distributes an RMI certified pallet rack product the is manufactured in China. Our seismic engineering data and specifications have been tested by Seismic Inc. and all information for preliminary calculations are available through the Seismic Inc website once you register.

US Seismic Zone Map

Sheet Thickness Tolerances

RMI Certified

Pallet storage racks were created to optimize warehouse and distribution center operations. As individual storage rack manufacturers developed new and competing products, the need for design and utilization standards and their implementation by the user and producer industries became obvious.

The Rack Manufacturers Institute (RMI) was established and incorporated in 1958 to deal with industry-wide issues. Among its initial activities was development of the first edition of an RMI standard, Minimum Engineering Standards for Industrial Steel Storage Racks, which was issued in 1964. It represented the first step in developing specifications and other products designed to suit the needs of users, manufacturers, and the engineering and code-enforcement communities.

From Fema-460 – September 2005

Click to download documents below:


Roll Formed Versus Structural Racking: Key Differences

When it comes to designing, engineering and manufacturing pallet racks, RMI’s ANSI MH16.1-2012: Specification applies to both of the two main rack construction types: roll formed and structural. That’s because both are made of steel and both are more than capable of holding and storing heavy loads.

But how do you know which type is the better choice for your operation? To decide, it’s first important to understand the differences between the two types across five key areas: manufacturing process, durability, application type, configuration requirements, and cost. Here’s an exploration of each of those characteristics.

Manufacturing Process: Roll formed rack is made of sheet steel roll-formed into a structural shape. After a full roll of steel is slit into narrower widths, each section is then run through a machine outfitted with a series of rollers that progressively form the steel to create a structural shape that is later cut to length. The shapes are then bolted or welded together to create the racking columns, beams and other components. Conversely, structural rack is built from hot rolled structural steel components. The structural shape profiles (typically C, I or angle) of these components are created at the steel mill and do not need additional bending or forming to be incorporated into the rack structure. The structural steel profiles are cut to length to form racking components, including columns and beams.

Durability: Roll formed rack tends to be built from lighter, thinner material, while structural rack is usually thicker and heavier—particularly in the corners. Both offer high strength, can carry equally heavy loads and (when used properly) will provide years of safe, trouble free service. One selection consideration is that roll formed racking is more easily damaged by an impact from a forklift truck than structural rack. When impact damage occurs, roll formed rack sections are difficult to repair and return to their original shape and load bearing capacity (to mitigate the damage, a variety of accessories and rack guards can be deployed to protect the uprights). In contrast, because of its heavier construction and steel thickness, structural rack is less likely to be damaged by a forklift impact and, when damaged, can often be repaired more easily.

Application Type: Operations where there is infrequent forklift damage are well served by roll-formed racking. These include big-box warehouse and home improvement stores, as well as a wide variety of other applications where there are not typically high levels of vehicle traffic in the aisles. Conversely, facilities with significant vehicle traffic (forklifts, pallet jacks, and other material handling equipment) that frequently accesses products at multiple rack elevations may be more prone to damage from impacts, making them a good application for heavy-duty structural pallet racking. Industries like grocery, food, beverage and cold storage have mostly adopted structural racking systems in their warehouses because of their high volumes of throughput, large fleets of forklifts, and multiple daily load handling demands.

Configuration Requirements: Both roll formed and structural rack can be configured to virtually any type of storage configuration (selective, double deep, push back, and more). Because the beams click in place with limited bolted hardware, roll form is fast and easy to assemble and reconfigure, making it adaptable to changing pallet load dimensions. With its bolted connections, structural rack may take slightly more time to install, but the bolts provide a positive connection that ensures components are not dislodged by lift trucks.

Cost: Because it is constructed from lighter steel sections, roll form rack is normally less expensive than structural rack. It can also take less time to install or reconfigure, as the beams and uprights click into place via a teardrop shaped connection. Conversely, structural rack components are normally bolted together and must be tightened manually. As noted above, however, in an impact-prone operation, the return on investment in structural racking can be advantageous due to their inherent damage resistance.

Have more rack system questions? Visit RMI’s page of frequently asked questions, here.

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Why Was The R-Mark Created?

As a voluntary program for manufacturers of industrial steel storage racks and of welded wire rack decking, RMI’s R-Mark Certification helps to assure storage rack users that they have selected a product designed, engineered and made by a reputable supplier. But why was such verification necessary in the first place?

The idea for a certification came from RMI member companies in 1999, around the same time that RMI’s ANSI MH16.1-2012: Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks was first incorporated into the International Building Code (IBC) as the standard for the safe design and installation of steel storage racks. Prior to that, there were other rack design standards in the marketplace— it was difficult for potential rack buyers to determine which standard a given manufacturer followed. Therefore, RMI members created the R-Mark Certification program (although membership in the association is not a requirement for earning an R-Mark license).

To attain an R-Mark license, two independent, USA registered professional engineers—with experience and expertise in the design and application of racking systems—conduct a rigorous analysis of an applicant manufacturer’s design process. This includes verification that the testing, calculations and resulting component (rack frame, beam and decking) capacities shown in a unique design’s load table were performed in a manner consistent with the RMI/ANSI MH16.1-2012: Specification.

So the next time you see an R-Mark on an industrial steel storage rack or piece of welded wire rack decking, you can be confident that the manufacturer of those components and systems has the technical and manufacturing skills—as well as the ability—to produce products that meet RMI codes and standards.

There is a caveat, however, in that simply seeing an R-Mark applied to a component does not mean the system is safe. Rack owners must still have a qualified engineer review each application to ensure that the system design and components meet the requirements for the specific use and job site.

That’s because every rack installation is different. Load types and component structures can be constructed in a multitude of combinations. Seismic codes may or may not apply in a given location. State and local building requirements can vary from one zip code to the next. Or, a rack engineered and intended for one use might be misapplied or erroneously configured within another installation.

Ultimately, however, an R-Mark serves as an acknowledgement that the rack or decking manufacturer has the engineering skills and the manufacturing ability to produce products that meet the RMI/ANSI MH16.1-2012: Specification, and—if the project is completed under engineering supervision and the codes are properly applied—system purchasers have a high degree of assurance that their final installation will be both code-compliant and safe.

Is your industrial steel storage rack or welded wire rack decking made by an R-Mark Certified manufacturer? Find a complete listing of R-Mark certified companies here.

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Look Out Below! Rack Accessories To Prevent Product Falls

While one of the benefits to storing product on pallet rack is the increased inventory density achieved by using the overhead space of a facility, what goes up must come down. Although gravity may be an unstoppable force, the risk of products or pallets falling from rack can be significantly minimized—and the safety of personnel and equipment operating in the area maximized—with the implementation of one or more accessories.

RMI’s publication, “Considerations for the Planning and Use of Industrial Steel Storage Racks,” covers three different types of equipment that can be added to a new or existing rack structure to reduce the risk of falling pallets or merchandise. They include:

  • Load Supports Under the Pallet. To help keep pallet loads from falling through or between load beams upon which they rest, a variety of shelf-style containment accessories are available. They include drop-in, roll-in or snap-in crossbars (also called pallet support bars or safety bars); welded-wire rack decking; spaced wood boards; spaced metal channels, angles or plates; solid wood or perforated metal decking.
  • Placement Guides. To prevent pallet loads from falling off the back or sides of the rack during placement of the load into the storage system, side entry guides and load stops with set-back distances—including horizontal load stop beams, vertical column load stops and load position stops—physically block the load from advancing beyond a certain distance within the racking.
  • Barriers or Netting. To prevent loose products from sliding, overturning or toppling off a rack—particularly where rack is adjacent to walking aisles, loads are stored over work areas, or aisles or in warehouse stores open to the public—frame accessories such as flexible woven netting or rigid steel mesh barriers are attached to the rack system to prevent loads from falling and injuring people.

Further, utilize proper load containment techniques—such as stretch-wrapping, shrink-wrapping, banding, or integral-box pallets—to secure cartons or items on pallets, particularly when they are to be stored vertically in racking. In high seismic areas especially, loads should be wrapped such that the pallet can be tilted to 20 degrees without the product falling off.

Get more information and details about the different types of product fall prevention accessories in Section 3.4 of RMI’s publication, “Considerations for the Planning and Use of Industrial Steel Storage Racks,” starting on page 19.

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Protect Racks From Forklift Impacts With Variety Of Accessories

Storage racks designed to RMI’s ANSI MH16.1-2012: Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks provide excellent load-carrying properties, and will last for many years—or even decades—when properly assembled and maintained. Further, in environments where properly trained forklift drivers operate with caution and care, racks are also destined for a long lifespan.

Unfortunately, it is not uncommon for forklifts to be driven in such a way that racks are accidentally damaged. And damaged rack components can reduce the weight-carrying capability of the total storage rack system, causing a serious safety concern. To limit the potential and severity of a lift truck causing damage to storage racking, a variety of accessories and options are available. (The ANSI MH16.1-2012 specification discusses the recommended options in section 1.4.9.)

There are two areas where guarding can be applied to most effectively minimize the damage of a forklift impact:

  • At ends of rack rows (including at cross-aisles and in rack tunnel bays).
  • At the aisle-side face of the rack column.

There are multiple types of end of rack row guards. The most common types include:

  • Heavy, structural steel angles—measuring 3 inches wide x 5 inches (or more) high—with welded, formed ends that wrap around the rack columns. To attach the device, the horizontal leg of the angle is pre-punched to accept mechanical concrete anchor bolts.
  • Pipe or tube that has been formed (or welded) into an inverted U-shapes. These tubes run the full depth of the rack assembly and are factory welded to the steel base plates are anchored to the floor.
  • Free standing, industrial modular guard railing set a short distance away from the racking and is bolted to the floor. These are typically placed as close to the rack as possible in order to minimize intrusion into travel aisles.
  • Guards that attach directly to the sides of the upright frames.

Rack column protective devices for application to the aisle-side facing uprights include:

  • Free standing column protectors, which are formed steel plates that wrap around the face and sides of the rack column. To secure them, the protectors are typically factory welded to steel base plates that are anchored to the floor.
  • Steel, foam or plastic guards attach directly to the rack column with bolts, rivets or straps.

Considering adding guards to your racking? There are a few things to keep in mind as you evaluate the options.

First, the thickness of the steel used in the guard’s manufacture affects its durability—the stronger the steel, the more impacts the guard can withstand before failure. Further, look around your racking for potential installation issues. Because most rack protective devices extend into the aisles or rack bay openings in one or more directions, make sure that their doing so will not compromise existing handling clearances.

Another potential obstacle to guard installation is the position of the rack load beams, which might interfere with the guarding’s placement. Likewise, for devices that wrap around rack columns, the size of the rack column’s baseplate must be considered to avoid interference.

Of particular note, however, is that even though these protective attachments and options provide a greater degree of rack safety by limiting forklift damage, it’s also critical to address the root causes. Among them: forklift driver training and management, rack system layouts with adequate operational clearances, clean and well-lit environments, and selection of options and accessories at the time the system is specified.

Larger and/or heavier rack columns, column reinforcements and inserts, heavier upright frame bracing, and different rack column shapes can all be specified to increase the durability of the base rack system when it is initially installed. But for existing systems, the rack guards described above provide additional protection.

Looking for a complete run down of the full range of protective accessories available for racking installations? RMI’s publication, “Considerations for the Planning and Use of Industrial Steel Storage Racks,” lists more than 20 different options in section 3.4.2.

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Key Safety Considerations For Outdoor Storage Racking

Sometimes it’s more convenient—or simply necessary—to store certain items or loads outside instead of inside the four walls of a facility. And—when properly designed, engineered, installed and maintained—outdoor industrial steel storage racks offer the same degree of safety and functionality of their indoor counterparts.

Some unique considerations for outdoor applications include:

  • Galvanized versus painted finish. Check with your rack manufacturer to understand if their paint finish is designed for outdoor or humid applications. If not, a galvanized finish may be the best option to ensure that that rack will not rust or corrode over time.
  • Asphalt versus concrete slabs. Virtually all rack systems are designed under the assumption that the rack is anchored into a concrete slab with a rated design capacity. Placement of rack on asphalt or other surfaces is not recommended unless special accommodations are made. Consult your design engineer if there are any questions.
  • Design for water drainage. Depending on the configuration of the rack system, water can potentially pool, increasing the risk of corrosion and damage to the rack. Confirm that your rack’s configuration does not encourage pooling water.

Post-installation, safety considerations surrounding the use of rack installed outside include:

  • Regular Inspections. All racks, regardless of their location, should be routinely reviewed and evaluated for damage—including that caused by impacts with products or material handling equipment or by exposure to the elements.
  • Use Common Sense. Storage racks are made of steel and they can be 30-feet tall—or higher—meaning that there is potential for them to conduct electricity if struck by lightning or topple over in an unusually high wind event. If they’re outside, it’s best for personnel to stay away from them during thunderstorms or other extreme weather occurrence.

Looking for additional information on the safe use of structural steel storage rack? RMI offers guidance in its publication Considerations for the Planning and Use of Industrial Steel Storage Racks.

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Safe Spacing Matters: Pallet Load Clearance Recommendations For Storage Rack

To minimize the risk of a pallet load and/or handling equipment colliding with a rack column or another load—creating an unsafe situation—storage rack design engineers incorporate a space allowance around the widest part of the load envelope when calculating the width and height of a storage bay opening. As explained in RMI’s Considerations for the Planning and Use of Industrial Steel Storage Racks Section 2.13.2:

Too little clearance will result in damage to both the loads and the storage racks. In an effort to minimize the damage, operators will slow down the movement of the loads and greatly add to the operating costs of the warehouse. Too much clearance will waste space and increase the costs of construction, and, in some cases, the cost of the rack system.

Because the widest part of the load envelope could be the pallet, the load (if it overhangs the pallet), or a portion of a misshapen or asymmetrical load, the clearance recommendation for a single-selective bay holding two loads is typically:

  • 3 inches between the edge of the column and the edge of the widest part of the load envelope,
  • 6 inches between the two load envelopes, and
  • 6 inches between the top of the load and the bottom of the beam above it for adequate lift-off space in placement or removal.

In double-deep storage configurations, more clearance is recommended. Less clearance can be specified in push-back storage—where pallets rest on moving carts—with consideration given to the amount of overhead clearance the loads need in order to avoid interior obstructions as they travel up and down the sloped cart track.

Additionally, the National Fire Protection Association (NFPA) 13 Standard for the Installation of Sprinkler Systems requires a minimum space in the down-aisle direction between loads of 6 inches. This ensures that water can flow through the racking and better suppress a fire within the building.

Need more information on proper sizing of racks for safety? Download RMI’s Considerations for the Planning and Use of Industrial Steel Storage Racks here.

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Walking On Wire Mesh Rack Decking: Is It Safe?

Is it safe to walk on wire mesh rack decking? In a single word, the answer is “no.”

Welded wire rack decking is not engineered for pedestrian use. Because decking often supports loads weighing thousands of pounds, warehouse associates at times erroneously believe that it must be strong enough to safely support them—since they weigh much less than a pallet load. Yet, just because a piece of decking is rated for a capacity of 1,000 pounds or more, the rating is specifically calculated assuming a uniformly distributed load—a static load which is evenly distributed over the entire surface of the rack deck.

A person stepping on a deck creates a point load that puts a concentrated weight on a specific area of the decking. Since it is not designed for point loading, when stepped on the deck can buckle, bow or sag and fall through the rack beams. This can be very dangerous for an operator, potentially resulting in injury or death.

Additionally, the spacing between the wire mesh is often wider than that of a human foot, creating a trip hazard if stepped on. It is also a recommended best practice to secure decking to the rack structure with fasteners.

In summary, welded wire rack decking works very well with pallets and other types of static loads, but is not designed as—and should never be used as—a walking surface.

Looking for more details about how to properly use wire mesh rack decking? Download a copy of RMI’s publication ANSI MH26.2-2017: Design, Fabrication, Testing and Utilization of Welded Wire Rack Decking.

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Pallet Beam Deflection: How Much Is Acceptable?

When the specifications for a pallet support beam are determined by a qualified rack design engineer, the maximum amount of deflection—or bowing—permissible is included in the calculations as noted in Section 5.3 of RMI’s ANSI MH16.1-2012: Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks. The deflection limit equals the horizontal length of the beam divided by 180 (or 0.55% of the clear distance between the columns).

However, this deflection limit is not in place to ensure the structural integrity of the beam or rack. Instead, it’s to ensure that personnel interacting with and working around the rack feel safe when they see normal pallet beam deflection. In the 1960s, RMI determined that the calculation length divided by 180 quantified the point at which persons believe the situation is unsafe when deflection in pallet rack is observed.

Certain installations—particularly those that will be accessed by robotic load or pallet inserters and extractors in automated storage and retrieval systems (AS/RS)—typically specify a tighter deflection limit for load beams, such as the length of the beams divided by 240 (or 0.42%). This lesser amount of permissible deflection minimizes the risk of the automation (or the load) coming into contact with the beams during placement or removal.

Although pallet beam deflection limits have no direct bearing on rack safety, improperly placed pallet loads can cause a safety issue when removing them or the individual products or cases stacked atop the pallets. The reason is, as the beams naturally deflect under the weight of the loads (typically two per bay) the loads will tilt toward each other, getting closer toward the top. When placed improperly in the bay (asymmetrically, unevenly, or with non-uniform weight distribution) the risk that a pallet load of product will come into contact with another during load placement or removal—and potentially fall or injure a worker—is increased.

Looking for more information on load beams? Read more in RMI’s Load Beam section in its list of Frequently Asked Questions.

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Cantilevered Storage Rack Safety 101

Cantilevered rack structures are comprised primarily of a central, vertical column from which horizontal arms project perpendicularly on one or both sides, with no vertical column connecting the arms on the aisle face. Either free standing or top-tied, these racks typically store very long loads, such as building materials including piping, lumber or bar stock.

To ensure the safe design, manufacture and installation of cantilevered rack systems RMI released a new standard, ANSI MH16.3-2016, Specification for the Design, Testing and Utilization of Industrial Steel Cantilevered Storage Racks, in 2016. Applicable to cantilevered storage racks made of cold-formed or hot-rolled steel members, the standard includes guidance on cantilevered storage rack, as well as on accessories such as decked shelves, shed roofs and canopies.

As with every rack system, to ensure the safe design, manufacture and installation of cantilevered rack, it is critical to engage a professional engineer with experience in racking to evaluate a variety of factors, including: installation site, soils, anchoring, load type to be stored, handling equipment, and more.

The building’s geographic location also impacts the rack design. Seismic considerations for the rack vary depending upon the potential for damage from earthquakes in a region. Further, for applications where cantilevered rack is installed outside, the designer will take the likelihood of an extreme snow, wind, hail or other event into consideration when calculating the strength and thickness of the materials specified to construct the system. These specifications will lessen the likelihood of a system collapse should such a weather event occur.

Post-installation, safety considerations surrounding the use of cantilevered rack—whether installed indoors or outside—include:

  • Load Flexibility. Because the loads stored in cantilevered rack are typically long, they frequently sag under their own weight during placement or removal from the storage system. This may necessitate a special attachment or type of material handling equipment to provide additional support during load insertion and extraction. Alternately, the designer may elect to incorporate additional horizontal clearance within each storage position to accommodate the sag and prevent the load from colliding with the arms and weakening the structure.
  • Down-Aisle Impacts. As the operator navigates a load down-aisle (or parallel to the load access face of the rack), attention must be paid to the amount of horizontal clearance between the load in transit and the rack arms. Because there are no vertical columns on the aisle side of the rack structure, the tips of the arms are exposed. This puts them at a greater risk of a collision with a load, which could compromise their capacity and cause them to fail.

Want to learn more about cantilevered rack design, testing and use? Download RMI’s ANSI MH16.3-2016 specification.

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Protecting Workers on Rack Supported Platforms, Pick Modules

To keep workers safe when picking items stored at levels above the facility floor—such as in pick modules or on shelving within rack supported platforms—guidelines are offered in RMI’s ANSI MH16.1-2012: Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks, section 8.4, “Pick Modules and Rack Supported Platforms.” The documentation focuses on common-sense safety features and best practices, including ongoing training, to minimize the risk of worker injury as they go about their assigned tasks.

Included are requirements for posting of design loads in both rack configuration and load application drawings, as well as in conspicuous locations within the structure. It also walks through calculating the maximum limits for concentrated and uniformly distributed loads so as to not exceed the structure’s capacity, causing a potential collapse.

Additionally, components that enhance the safety of personnel working in or around the structure are required. They include:

  • Guardrails for fall protection that clearly delineate the edge of the elevated platform, and prevent a worker from accidentally stepping off it.
  • Flooring that is consistent and free of gaps or trip points that could cause a fall or a load to become jammed or obstructed. In operations with powered equipment located nearby, such as conveyor or sortation systems, electro-static dissipative (ESD) flooring is recommended.
  • Kick-plates at floor level that rise vertically from the edge of the platform, preventing a dropped object from sliding over the edge and impacting a person or material handling equipment.
  • Stair handrails, which are governed by building codes, but give personnel a solid, sturdy surface to grip or lean against as they traverse the stairs and landings that access the platform.
  • Product fall protection, such as barriers or netting, that prevents products stored high above the facility floor from falling to the ground—and potentially striking personnel or other material handling equipment—should it slip off the edge of a rack or shelf.

Seeking for more details about how to enhance worker safety on elevated platforms? The full specification begins on page 32 of ANSI MH16.1-2012.

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