"RMI" are the initials of The Rack Manufacturers Institute. The Rack Manufacturers Institute is an independent, incorporated trade association formed in 1958 and affiliated with the Material Handling Industry. The membership of the RMI is made up of companies which produce the vast majority of industrial storage racks installed in USA. The RMI promotes the safe design and use of storage racks and related structural systems such as Welded Wire Rack Decking through research, testing, preparation of specifications, educational programs, and meetings. The RMI is the American National Standards Institute (ANSI) accredited developer of storage rack standards and administers the R-Mark Certification Program.

In 1997 the RMI issued a new specification for storage rack (later updated to become the 2002 edition and more recently adopted by American National Standard ANSI MH 16.1-2004). Shortly thereafter, RMI created the R-Mark Certification Program as a way for storage rack users and customers to clearly identify that rack frame and beam capacities shown in a load table were calculated in accordance with the new standard. A way of identifying special projects that were designed in accordance with the new specification was also established.

To satisfy these requirements the RMI developed a program by which any rack manufacturer, member or nonmember, could submit a standard set of data and information about their racks, testing information and sample calculations for review. The RMI facilitated the submittal of this information to two randomly selected, independent, pre-qualified, storage rack design engineers for their review and approval that the testing, calculations and resulting component capacities were in accordance with the 1997 RMI Specification (since updated to the 2002 Edition and more recently adopted by American National Standard ANSI MH 16.1-2004).

The RMI then issued a seal (the R-Mark) that the rack company can use on published capacity charts and, in conjunction with a Professional Engineer’s seal, on special designs to indicate that the components and design are in accordance with the RMI Specification.

Copies of the most recent edition of the ANSI/RMI Specification For The Design, Testing and Utilization of Industrial Steel Storage Racks, Commentary, ANSI/RMI Specification for Welded Wire Rack Decking and other useful information are available directly from the Rack Manufacturers Institute (704-676-1190), from any of the member companies or from the RMI website at www.mhia.org/rmi.

Beginning in the late 1930’s, Federal economic statistics for USA were collected and organized using the Standard Industrial Classification (SIC) System. In 1997, the SIC system was replaced by the North American Industry Classification System (NAICS) to normalize data-capture between USA, Canada and Mexico.

SIC and NAICS codes for racks and related items:

Wire decking is a decking system used on pallet rack shelves. Its purpose is to provide additional support for stored materials, as well as, becoming a safety net for unstable loads. Wire decking is fabricated from welded-wire mesh, and generally has reinforcements in the form of channels or support wires. Wire decks are supported by the rack beams at the front and rear and the strength and stiffness of the wire deck system provides support for the load between the beams. Decking designs vary greatly depending on the application. Wire thickness, grid pattern and number of channels all have an effect on performance. Wire decking is unique to other types of shelving not only in appearance but also in performance. Because wire decks are made of steel, their integrity, capacity and performance remain constant. The advantages of wire mesh decks include safety, greater capacities, their ability to allow light, air, debris and water (very important in some states due to fire codes) to pass through the decks.

Wire decking is a decking system used on pallet rack shelves. Its purpose is to provide additional support for stored materials, as well as, becoming a safety net for unstable loads. Wire decking is fabricated from welded-wire mesh, and generally has reinforcements in the form of channels or support wires. Wire decks are supported by the rack beams at the front and rear and the strength and stiffness of the wire deck system provides support for the load between the beams. Decking designs vary greatly depending on the application. Wire thickness, grid pattern and number of channels all have an effect on performance. Wire decking is unique to other types of shelving not only in appearance but also in performance. Because wire decks are made of steel, their integrity, capacity and performance remain constant. The advantages of wire mesh decks include safety, greater capacities, their ability to allow light, air, debris and water (very important in some states due to fire codes) to pass through the decks.

The definitions are as follows:
Concentrated Load - any static load which is not uniformly distributed over the entire surface of the decking section. (Ref MH26.2 - 2004)
Point Load - any static load that is concentrated to particular points on the deck. (ie. A container with four small feet (point load) versus a container with two runner bars running the entire length of the container (concentrated load).

Racks that do not conform to the ANSI/RMI Specifications may not be as safe as racks that conform to the specification. The Rack Manufacturer’s Specification is the only recognized U.S. specification for the design, testing and utilization of industrial steel storage racks. If there should ever be an accident or other incident involving the storage racks, a responsible rack user may want to show that its racks have been designed to meet this recognized standard.

Racks that do not conform to the ANSI/RMI Specifications may not be as safe as racks that conform to the specification. The Rack Manufacturer’s Specification is the only recognized U.S. specification for the design, testing and utilization of industrial steel storage racks. If there should ever be an accident or other incident involving the storage racks, a responsible rack user may want to show that its racks have been designed to meet this recognized standard.

The RMI recommends purchasing racks that clearly meet the requirements of the ANSI/RMI Specification.

It is the responsibility of the owner to make sure that the new or existing floor slab in the building will support the loads that are imposed on it by storage racks, fork trucks and any other equipment that may be present. The owner should consult with a qualified engineer who is able to evaluate the existing floor or design a new floor once the intended use of the building has been established and the expected loading on the floor has been determined.

The data required for designing a floor system or for evaluating an existing floor system should include information about the soil sub-grade. At a minimum, the designer typically needs the bearing capacity of the soil sub-grade expressed in pounds per square foot and the stiffness of the sub-grade (also known as the sub-grade modulus) expressed in pounds per cubic inch. Additional data such as the soil type may also be needed to evaluate slabs so that the soil site classification can be determined. This soil site classification can have a significant effect on the design of storage racks for earthquake resistance. This information should be given to the rack engineer and the building engineer, who is analyzing the floor slab.

The necessary slab data may include the strength of the concrete (compressive yield strength in pounds per square inch), the slab thickness, the strength and spacing of the steel reinforcement in the slab, the levelness and flatness of the floor, the joint locations, any other irregularities that may be present in the floor slab, and more. This data should also be given to the rack engineer and the building engineer who is analyzing the floor slab.

It will be beneficial to the owner to provide all of the information on the slab and the sub-grade because doing so could reduce the chance of having problems with the slab or rack structure and could result in a more economical rack and floor slab design for new construction. In many cases the building engineer may communicate directly with the rack engineer at the request of the owner. The rack engineer may give the building engineer the loads imposed by the rack, and there can be agreement on items such as the base plate size and the anchor bolt locations. Often the location of the rack anchor bolts can be coordinated with rebar placement in the floor to reduce or eliminate interference.

The use of average load is only appropriate for the determination of the seismic down-aisle horizontal force. The use of average load is not to be used for static design.

For the down aisle seismic design, the RMI Specification allows the designer to use the average load to determine the horizontal seismic forces for the rack analysis. This can result in economy by preventing the down aisle seismic analysis from becoming overly conservative. The RMI Specification allows the average load to be used for computation of these horizontal forces because at the time of a seismic event only the loads that are actually in the rack at the time of the event will participate in swaying the racks.

The RMI Specification does not permit the use of the average load for computation of cross-aisle seismic forces because there could be an accumulation of heavier loads in one bay.

The user and designer are reminded that for the rack design, once the horizontal seismic forces are determined, the RMI Specification requires the racks to be designed for these forces in combination with the maximum gravity loads. The loads are to be combined using the appropriate load combinations.

Rack structural systems, not unlike building structures, are often subject to the building code review and permitting process. The pertinent building code is usually required by a municipality, county, or state. Most building codes which have been adopted and are being enforced include rack structures - e. g., the International Building Code, the NFPA, and the earlier UBC, BOCA, and SBC model codes. Those provisions often include the requirement of a local building permit. Occasionally, local requirements may differ slightly from the more generally-applied national and international building codes. The user should determine from local authorities which building code is applied and should report that information to the rack manufacturer.

The materials required for a building permit normally include the details of the proposed rack system and its use, the various loads for which it has been designed, the “calculations” from an engineering analysis accomplished and “sealed” by a registered design professional, demonstrating the structural integrity of the proposed system and its conformance with all applicable building code provisions, details of the fabrication and installation processes, information about the building in which the rack system will be housed and used. The building information may include relevant information about the characteristics of the floor slab, the below-slab soils, and about the building structure if connections to the building are proposed. Typically the owner works with the rack supplier to assemble and process this information through the permitting process. There may be costs associated with the development and processing of this information through the local permitting process and for a building permit itself. The magnitude of these costs and how they are shared are matters of negotiation between the owner and the rack supplier and may relate to the size, complexity, and site-specific requirements of particular projects.

Rack structural systems, not unlike buildings, are often subject to the building code review and permitting process. Most communities face the potential of earthquakes to varying degrees, magnitudes, and probabilities. Particular seismic requirements are site-specific, and the user should bring to the attention of the rack manufacturer the specific local requirements, including applicable building codes, the specific installation location, any knowledge of the supporting concrete slab, and any information about the below-slab soils and their properties. Rack systems should be designed, manufactured, installed, and used in accordance with the site-specific requirements of the site; these requirements may include seismic effects and may also include the characteristics of the building in which the rack system is housed. (See also, ANSI/RMI, Specification section 2.7, and Commentary section 2.7). To find the requirements for your job site contact the local building authority.

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. Normal anchoring as is used for double rows is usually adequate for racks whose ratio is 6 to 1 or less. If the height to depth ratio exceeds 6 to 1, the anchors and the base plates should be designed to resist overturning. The ANSI/RMI Specification in section 8.1 provides for the anchorage to resist an overturning force of 350# applied at the topmost shelf level (to an empty rack). If the LRFD method of design is used, this force should be treated as a live load and multiplied by 1.6.

If the height to depth ratio exceeds 8 to 1, the racks should be stabilized using overhead ties. If anchoring is used for this extreme case, the design of the anchors must be certified by an engineer. All of these ratios and requirements are for a typical rack frame. If a set back leg or slope leg upright were to move the center of gravity from the frame’s midpoint, these ratio limits do not apply, and a rack engineer should approve the configuration. Slope or setback legs should generally be avoided in single rows.

It is generally not a good idea to tie racks to the wall because forces from the building can be transferred to the racks and because forces from the racks can be transferred to the building, although wall ties are sometimes used in low seismic areas. If wall ties are used, there must be proper coordination between the building engineer and the rack engineer to ensure that the ties and any transmitted forces will not damage the rack or the building structures. The connection to the wall must be capable of transferring the required forces, and the connectors must be compatible with the wall material. The seismic analysis of the rack and the building being tied together is extremely complex, and the connection is best avoided. If the height to depth ratio is such that a single row needs extra stability, heavy- duty anchor patterns with larger base plates or cross aisle tie configurations could be used rather than wall ties.

Load plaques serve as a constant reminder of the rated load capacity of the rack. Plaques may also serve as a record of the rack’s manufacturer. The ANSI/RMI Specification states that rack installations should display load plaques. Building and safety inspectors may require that plaques be installed.

Yes, ANSI standard MH26.2 - 2004 and can be purchased through www.MHIA.org.

Yes, NFPA 13: Installation of Sprinkler Systems, 2007 edition and can be purchased through www.NFPA.org.

No, all tests are not mandatory; however, the MH16.1-2008 Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks Section 4.1.3.1 does require that stub column tests be done as detailed in Section 9.2 to determine the Q value of perforated rack columns. This is required because the effect of the holes on the column strength is difficult to determine analytically. Additionally, in Seismic Design Category D and above, a connection cyclical test as specified in Section 9.6 is required.

The remaining tests in Section 9 are optional tests that may be used to evaluate the effects of components on the overall behavior. This section also states that the tests can be used when there are factors affecting the design of the racks that are difficult to account for analytically. When rational analytical methods can be used, these other tests are not required.

The ANSI/RMI Specification requires that all rack columns should be anchored. This means that both the aisle column and the interior or rear columns must be anchored on all frames according to the instructions from the manufacturer and applies to all rack frames all the time. If there is a specific application where the racks can’t be anchored, the user should get permission from the manufacturer’s engineer to waive the requirement. Anchors are required to resist many forces at the base of the columns and to maintain the position of the rack column.

The rack manufacturer should be able to provide the information on the proper quantity and size of anchors for the installation of its rack frame. This information should accompany installation instructions or on installation drawings. A ½” diameter anchor with the proper embedment depth is commonly the anchor bolt used for medium sized pallet racks in non-seismic areas. If there is any uncertainty as to the anchoring requirement, the rack user or installer should contact the designer or the manufacturer regarding the anchoring requirement for that specific application.

Some lightweight storage rack applications may be installed on surfaces other than concrete such as wood decking, bar grating or other materials, but a qualified design engineer must review the means for anchoring or attaching. The rack user should provide a qualified design engineer with the necessary loads and configuration, and any other information that is required, to evaluate the ability of the floor system to support the rack column loads and the method for attaching or anchoring the rack.

The ANSI/RMI Specification shows the maximum out-of-plumb ratio for a loaded rack column as 1/2” per 10 feet of height. Columns whose out-of-plumb ratio exceeds this limit must be unloaded and re-plumbed. Any damaged parts must be repaired or replaced. This ratio could be used for straightness also. In other words, the out-of-straightness limit between any two points on a column should not exceed 0.05” per foot of length (1/2” per 10 feet).

An out-of-plumb or out-of-straight condition will reduce the capacity of a rack column. The reduction can be significant. A rack that is out-of-plumb from top to bottom or a rack column that is not straight is likely to become further out-of-plumb or out-of-straight when it is loaded.

The out-of-straight limit is given to prevent excessive “bows” or “dogleg” conditions that may exist in a rack column. A column could be plumb from top to bottom but have an unacceptable bow at mid-height (see figure (a)), or a 20 ft. high column could be out 1” from top to bottom, which could be acceptable using a simple top-to-bottom out-of-plumb measurement, but the entire out-of-plumb could be between the floor and the 5 ft. level (see figure (b)). This dogleg condition would be very harmful. This condition could be caused by fork truck impact. The column could have a sine wave shape and be out of straight as shown in figure(c). A column could also become bent and exceed this limit (see figure (d)). As re-written the specification now prevents these situations from being acceptable if they exceed the 0.05" per foot out of straight limit.

At normal design working loads, beams are typically designed to accommodate vertical deflections that do not exceed 1/180 (or 0.55 percent) of the horizontal beam length as measured with respect to the ends of the beams. Some users may specify a lesser-deflection requirement for visual appearance or cosmetic purposes. Still other users with systems intended to use more precise automated storage and retrieval equipment may specify a lesser-deflection requirement. (See ANSI/RMI Specification section 5.3, Commentary section 5.3).

Column protectors are often used to protect rack columns from possible collision damage in traffic aisles of rack storage systems. The nature of column protection may depend on the particular rack system and the vehicles which are used to service it. With inattentive operation, columns may be struck by man-operated forklift trucks directly or by over-hanging loads being carried by those vehicles.

It is not always feasible to build, install, and operate rack systems that are immune to such dynamic operational abuse. Column-protectors, fenders, bumpers, or deflectors are often installed in front of each exposed rack column to attempt to keep such misuse from damaging the rack columns; aisle guides may also be used to attempt to keep a man-operated forklift from going astray; or reinforcement may be added to the exposed aisle-side columns with additional column sections, other reinforcing steel or other materials to improve their impact resistance. Automated or wire-guided vehicle systems are normally constrained on their intended path and are thus less likely to damage traffic-aisle rack columns. Users should consult their rack supplier about the various available protections, considerations, and options. (See ANSI/RMI, Specification section 1.4.9 and Commentary section 1.4.9).

Pallet racks are originally designed for configurations requested by the owner. These configurations are shown on the Load Application and Rack Configuration Drawings supplied to the owner. Changing the racks to a configuration that was not considered in the design may create an unsafe condition. A qualified engineer should review any change to the bay configuration that is different from the original design configurations.

The RMI Specification states, “Upon any visible damage, the pertinent portions of the rack shall be unloaded immediately by the user and the damaged portion shall be adequately repaired or replaced.” If the damage were to re-occur, the application of the racks should be reviewed to see if modifications could be made to lessen the severity or the frequency of the damage. Forklift driver training is essential.

Yes. The rack frame bracing consists of horizontal and/or diagonal members that join the front column to the rear column. These members are very carefully designed by the rack manufacturer to stabilize the rack frame in the cross-aisle direction and to support each of the individual columns, also, in the cross-aisle direction. Any damage to these components could jeopardize the stability of the frames and could degrade the strength of the column.

If a frame brace is damaged, the first priority should be to immediately unload the area supported by the damaged component and to prevent placement of loads into that area. In the case of the frame braces, it may be the bays on either side of the upright which are damaged.

Contact the manufacturer’s representative for an engineering evaluation of the effects of the damage to the structural integrity of the rack, of the damage. Only after such an evaluation, after repairs if necessary are competently completed, and after approval of the work is done should the rack section be returned to service.

The detail used to make an acceptable repair should be designed or reviewed by a qualified design engineer and installed by people who are qualified to make the repair. The rack repair should be reviewed for compliance to the ANSI/RMI MH 16.1 Specification. A good repair will result in a structural member or connection that is at least as strong as the original.

When welding is prescribed, the welders must be certified for the types of welded joint required.

If there are any concerns about structural problems with the storage rack system, the first priority must be to safely and immediately unload the area supported by the damaged component and to prevent loads from being placed into that area. Then, the manufacturer’s representative should be contacted for an engineering evaluation of the problem. If the manufacturer cannot be identified, an independent engineer, experienced in the design of storage racks, should be retained for an evaluation.

All storage rack systems are designed for the specified load in any location, and it is commonly assumed by the designer that the rack system will be loaded and unloaded in a random fashion during its lifetime. With that said, an appropriate approach to fully load a pallet rack is to start at the bottom middle of the rack row and to work outwards and upwards.

Research has shown that a generally appropriate protocol for loading a rack system is to store the heaviest product on the floor or lower levels toward the middle of the rack and then to work outward to the ends of the rows and then upward. Due to inventory systems and control, this may not always be possible, but it is often the most appropriate loading method for a given structure.

If the reason for extending the height of the pallet rack upright frames involves a change in the existing beam elevations or the addition of one or more bean levels, the design configuration of the rack is being changed. Prior to making any such changes to the configuration or loads, the original and proposed rack design should be reviewed by the original manufacturer or by a qualified design professional.

All rack components and connections must be checked with the new loads and the revised configuration to ensure that all the requirements of the ANSI/RMI Specification are satisfied for the new configuration and loads. The splice connection used must adequately transfer all loads from the frame extension to the existing frame. The frame extension must have proper bracing and be compatible with the beams or other components that will connect to it for the new configuration. In some cases individual column extensions may be acceptable. If the rack configuration or load change is made and the extensions are added, it may be necessary to revise or replace the information on the load plaques and the rack application drawings.

If the reason for extending the frames is for non-structural purposes, the design review may not be required. If the racks are being extended to add cross-aisle ties for any reason, the design should be reviewed because the cross-aisle design model of the racks will be altered. If the racks are being extended for the purpose of tying the racks to the building, the design should be reviewed and the building design engineer must approve the connections. Any rack frames that are damaged must be properly repaired or replaced before the extensions are added.

It is important to install the frames oriented as the manufacturer recommends. However, there may be cases that the orientations are not identified as important design considerations.

When the orientation of the frames is not design critical the diagonal brace orientation in the bottom upright panels run from lower front to upper rear so that the diagonal braces go into tension should the base portion of the aisle column be damaged. This orientation also means that the aisle column usually has both a horizontal and a diagonal brace coming into the base portion of the aisle column for extra stiffness.

The other thought is to have the diagonal braces in the bottom upright panels run from upper front to lower rear so that the diagonal braces won’t be damaged or their welds broken if the base portion of the aisle post is damaged. The choice is basically a matter of personal preference. There are no studies which prove that one is better than the other and both cases have excellent track records.

To minimize damage to the aisle posts, your rack supplier will often recommend heavy-duty bottom braces, deflector angles, backer posts, post protectors, or some combination thereof.

Upright bracing members can be omitted to create openings. However, this should be included in the initial design and fabrication by the rack manufacturers.

It is also possible to retrofit existing uprights with openings. However, this is a substantial structural change to the uprights and must be reviewed by a qualified design professional. Removal of bracing may also require modifications to the surrounding bracing, columns, or both.

No, wire decking is not designed to be walked or stood upon. Walking and/or standing on a wire deck creates both dynamic (moving and varying) and concentrated loads. Wire decking is designed and assigned a load carrying capacity based on carrying uniformly distributed, static loads. While there is a safety factor designed and built into wire decking, dynamic and concentrated loading as a result of standing or walking on a wire deck is a use which falls outside its intended purpose. In addition, the surface of a wire mesh deck is flexible and irregular and the open areas within the mesh may cause a person to trip. Furthermore, when subjected to lateral motion decks may slide upon the supporting rack beams or tip upward and become dislodged when loaded in a concentrated fashion on the outer extremities (beyond the outermost support members).

Wire decks are intended as an accessory to pallet rack. The dimensions of the wire deck must correspond with the rack upon which the decks are to be installed. There are a relatively large number of different rack manufacturers and a wide variety of beam styles and designs. If the dimensions are wrong, the wire deck may not fit on the rack or may fit but be unsafe. Generally wire deck manufacturers require a buyer to submit dimensional specification of the rack prior to production. This protects both the manufacturer and the buyer and assures that there is agreement upon precisely how the wire decks are to be utilized.

It is also a best practice to supply the wire deck manufacturer with the load capacity rating of the rack system so that the wire deck can be designed and built to meet or exceed the capacity of the rack system. Short of that the system is only strong as its weakest link. Generally speaking the deck capacity is specified to mirror that of the load beams of the rack system, for example a beam pair rated at 5,000 lbs. will require two wire decks rated at 2,500 lbs. each.

(a) The most common type of wire deck is a waterfall style. The waterfall is the overlapping of the top deck wires running over and down the face of the support beams, resembling a waterfall. They usually have three to four support members or channels designed to fit within the step of the beam and support the load resting upon the deck. A waterfall deck for a box or structural beam is the same as above with the exception that the support members or channels are flattened or flared at the ends where they rest on the top of the rack beam.

(b) Another popular type of wire deck, similar to the above, is a flush or instep deck fitting step beams only. This deck sets on the step ledge between the beams, flush with the top of the beams. It can be flat or have formed instep waterfalls. The purpose of the design is to avoid any potential snag points and to leave the rack beam face unobstructed.*

(c) Also available is a non-waterfall deck that may span across the top of the front and rear load beams but does not waterfall down. This style of deck is not recommended for non-step beams due to the configuration being unstable.*

* When applying types (b) and (c) above, it is recommended that the decks be fastened to the beams or the beams tied to prevent beam spread which could result in the deck dropping.

(a) The storage rack system owner should establish and implement a program of regularly scheduled storage rack system inspections. The inspections should be performed by a qualified person familiar with the storage rack design and installation requirements retained or employed by the storage rack system owner.

Storage rack should be inspected periodically to check for any damage or abuse and immediately after any event that occurs that may result in damage to the rack. The frequency of inspections should be up to the discretion of the owner, depending on the conditions of use. As a minimum, inspections should be performed annually. The inspection schedule and results of the inspection should be documented and retained.