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:


Learn More About Rack Installation And Safety Inspections In RMI’s New Video

The responsibility for safe industrial steel storage rack ownership and usage does not end at installation. Instead, it’s an ongoing process that includes several elements—including regular, routine inspections—to ensure a safe workplace. To help both potential and current end users and owners gain a better understanding of proper rack installation and inspections, RMI has produced and released a new video.

Running for four minutes, the video details the potential issues that can arise from a poor installation, and why it is critical to follow the manufacturer’s load application and rack configuration (LARC) drawings and installation guidelines. Other installation best practices that minimize the risk of failure include:

Further, the video reviews the minimum recommended safety inspection frequency of once a year. Operations should consider inspecting racks more frequently if their facility has: high traffic volumes around end aisles and transfer aisles; lighter-duty racking systems that are more prone to damage; or areas with a history of damage that are more likely to be damaged again. Inspections should occur after a collision or seismic event, and should always be performed under the guidance of a qualified rack system engineer.

Likewise, the video notes that rack inspections are not solely the responsibility of a single person, but rather of everyone who works in the facility. All personnel should continuously keep an eye out for damage or other issues and notify management of such occurrences immediately. The key steps of performing a thorough rack safety inspection are also detailed.

This video is the second in a planned series of industrial steel storage rack videos; the next one will focus on best practices in rack maintenance and repair.

For more details about why your facility should consider scheduling rack safety inspections more frequently, click here.

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Point Versus Uniformly Distributed Loads: Understand The Difference

When placing loads of equal weight in storage racks, it’s important to remember that all pallets or loads are not created equal. Some pallets are designed with multiple boards—or stringers—spanning the bottom surface; others have a foot in each corner. Unusually shaped loads like steel coils or rolls of paper can also create problems. The pallet’s bottom construction contributes greatly to whether the load is uniformly distributed or resting atop specific points. That means the distribution of the load weight can be different, depending on the type of pallet underneath it or the specific type of product being stored on the rack system.

When placed in steel storage racks, a uniformly distributed load is one whose weight is evenly distributed over the entire surface of the rack’s beams or deck. A point load is a one with its weight significantly concentrated in one (or more) places on the rack’s beams or decks. For example, a steel coil stored directly on a rack beam can create a very concentrated point load; even if the steel coil weighs the same as a palletized load, the load beam will likely have to be heavier duty. (There’s also a third type of load distribution: a line load, which has only two or three boards across its bottom, which creates a more even distribution of weight than a point load, but less even distribution than a uniformly distributed load).

So what does this mean for rack safety? Placing a point load within a steel storage rack that has been designed solely to support uniformly distributed loads could cause one of two situations: excessive beam or deck deflection and/or failure.

Beam Deflection: When a rack design engineer determines the specifications for a pallet support beam, the maximum amount of permissible deflection—or bowing—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 (i.e. L/180). The safety risk arises if a point load is placed on a beam that has been engineered only to bear the weight of uniformly distributed loads. That’s because the concentration could cause the beam to deflect beyond its maximum allowable amount, leading to possible failure and potentially causing the load to fall.

Decking Failure: Typically made of welded wire with reinforcing channels, or corrugated steel, decking is often placed on pallet rack beams to span the distance between them. While this provides additional support for the pallet load, unless the decking has been properly engineered to accommodate point loads—as specified in RMI’s ANSI MH26.2-2017: Design, Fabrication, Testing and Utilization of Welded Wire Rack Decking—the concentrated point load could cause it to fail and the load to fall.

To ensure the safest pallet rack design, therefore, a qualified design engineer must be advised of the types of loads and the pallets upon which they will be placed for storage. In applications where multiple types of pallets may be stored within the same racking structure, the system should be engineered to support point loads as the most conservative—and safest—approach.

Have more steel storage rack questions? Get answers from RMI’s list of Frequently Asked Questions.

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What’s Height-To-Depth Ratio, And Why Is It Important?

To significantly minimize the risk of a single row of standard steel storage rack from becoming unstable and overturning due to a seismic event, wind or forklift impact, Section 8.1 of RMI’s ANSI MH16.1-2012: Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks advises evaluating its height-to-depth (HTD) ratio.

In simple terms, the HTD ratio describes the ratio between how tall the rack is compared with how wide it is at its base. A rack that is 10 feet tall and 10 feet wide (a 1-1 HTD Ratio) will be much more stable (less likely to fall over) than a rack that is 10 feet tall and 1 foot wide (a 10-1 HTD ratio). To calculate the HTD ratio, divide the measured height of the pallet rack from the floor to the top surface of the highest load-supporting beam level by the depth of the frame. (The depth should to be measured at floor level, from the outside of the front column to the outside of the back column.)

If the calculated HTD ratio is 6 to 1 (or less), the rack base plates can be secured to the floor with normal anchoring. However, if the HTD ratio exceeds 6 to 1, the anchors and the base plates should be designed to resist an overturning force of 350 pounds applied to the uppermost beam level.

If it is determined that the HTD ratio is greater than 8 to 1, the Specification recommends that racks be stabilized using overhead, or cross-aisle, ties as an additional safety measure. These extend across the aisle to connect two frames together at the top for additional support and to minimize the risk of overturning. (Additionally, when overhead ties are needed, the frame heights are frequently further extended so as to avoid being hit by a load during placement or removal from the top pallet position of the rack.) If anchoring is used for racks of this high ratio, an engineer must certify the anchors’ design.

The HTD ratio specifications apply to both roll-formed and structural rack in a standard, single-row configuration (not back-to-back). Racks in a back-to-back configuration require the proper type and quantity of row spacers to secure the two frames together. If unsure, contact an engineer. A rack system designed with sloping or offset legs are subject to different engineering calculations and analysis. Slope leg or offset leg frames are not to be used in a single row application without an engineer certifying the design.

Looking for more insight into rack specifications? Download a copy of ANSI MH16.1-2012: Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks.

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Don’t Forget To Check Permitting Requirements For Your Proposed Rack Systems

Whether planning for a new rack system in a new location, or a new rack system in an existing location, the system cannot be installed until all applicable building codes have been satisfied. Further, a building permit must be issued for a particular system design that meets geographic location requirements while supporting the user’s load application. The local Authority Having Jurisdiction (AHJ) or building official will first need to verify that all code provisions will be satisfied before issuing a building permit and will issue a certificate of occupancy (CO) upon completion of the rack installation.

As for the basis of the permits themselves, many U.S. jurisdictions (but not all) utilize the 2015 International Building Code (IBC)—developed by the International Code Council—as their standard. The IBC references RMI’s ANSI MH16.1-2012: Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks in section 2209.1 as the standard for safe design and installation of steel storage racks. Likewise, the National Fire Protection Association references the same specification in the NFPA 5000 Building Construction and Safety Code. Key areas of inspection can include verification of proper anchorage of the racks to the floor, field welding, proper flue spaces are maintained between the racks and between the products being stored, and egress distances.

Many projects are delayed by not addressing fire safety requirements during the planning process. In many cases fire protection requirements will significantly impact the design of the rack system, as well as what can be stored in it. The permit and inspection verify that a facility’s sprinkler system and racking are properly designed and will work together effectively, as per the NFPA 13 design standard for sprinkler system installation and the International Code Council (ICC) International Fire Code (IFC) regulations. IFC Section 2302 covers permits for High Piled Storage, which is defined as storage of combustible material in closely packed piles, or combustible materials on pallets, in racks or on shelves where the top of storage is more than 12 feet high.

In order to ensure a smooth project and to minimize surprises, it is a good idea to contact the local building and planning department ahead of time. This allows a facility owner to gain a better understanding of the requirements, costs and the typical timeline for plan review, permit processing, inspections, and completed project approval.

RMI offers published guidelines for operations to review before undertaking a rack project. Get your copy of Considerations for the Planning and Use of Industrial Steel Storage Racks today.

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Making A Tight Beam-To-Column Connection

To ensure that a pallet rack beam does not separate from an upright rack column as a result of either an impact or seismic event, RMI’s ANSI MH16.1-2012: Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks specifies how a steel storage rack manufacturer should calculate the number of engaged locking mechanisms (such as pins, bolts, or other devices that resist disengagement).

In general, the more pins or bolts used to connect a beam to a column (typically ranging from two to four), the tighter the connection. This yields higher load capacity, as well as greater resistance to both vertical and lateral (or horizontal) forces. In high seismic zones, for example, racking should be engineered to not only hold a pallet load securely, but also to withstand the side-to-side motion caused by an earthquake. This ensures the rack system can withstand lateral forces and minimizes the chance of collapse.

Specific to racking systems loaded by forklift, Section 5.4 in MH16.1-2012 covers beam-to-column connections, noting:

Except for movable-shelf racks, beams subject to machine loading shall have connection locking devices (or bolts) capable of resisting an upward force of 1,000 pounds (453.6 kilograms) per connection without failure or disengagement.

Section 2.6.4 provides guidelines for determining the maximum rotational capacity of a beam-to-column connection in a seismic zone.

Every storage rack manufacturer utilizes one or more unique beam-to-column connections. The assembly requirements for both the connection and its strength and stiffness result from the manufacturer’s testing. As detailed in section 2.4.1 of the ANSI MH16.1-2012: Specification, three different tests can be applied when determining the proper number of beam-to-column connections to create the strongest structure:

Cantilever Test (Section 9.4.1) – Conducted to determine the beam-to-column connection’s moment capacity. Set-up includes one column segment and one beam segment connected to each another with a load applied downwardly in the plane of the frame at the cantilever end of the beam segment.

Portal Test (Section 9.4.2) – Another test to determine the beam-to-column connection’s ability to resist force and its rotational rigidity. Specifically, this test is used to obtain a joint spring constant needed for semi-rigid frame analysis. It utilizes two column segments connected by a single beam in between—creating a portal frame. The load is applied both laterally in the plane and to the corner of the portal frame in the direction parallel to the beam segment.

Cyclic Test (Section 9.6) – Specifically designed and conducted to determine the beam-to-column connection’s earthquake force resistance, inelastic rotational capacity and rotational stiffness, as well as its energy-dissipation properties, this test subjects the connections to cyclic (repeated) loading conditions. The test set-up creates a double cantilever, with two beam segments connected to a single column, and applies the load to the end of the beams in an alternating fashion.

Based on the results of the tests, the rack manufacturer will include specific beam-to-column connection instructions on the installation’s Load Application and Rack Configuration drawing.

Want to learn more about beam-to-column connections? Section 5.4 of the ANSI MH16.1-2012: Specification includes more details.

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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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