FAQs


Please refer to our FAQ Disclaimer for important information.

What is RMI?

"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.

What is the R-mark?

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.

How do I obtain copies of the ANSI/RMI Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks and the ANSI/RMI Specification for Welded Wire Rack Decking? Does the RMI have a web-site?

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.mhi.org/rmi.

Where can somebody find information on how to plan for and the uses of Industrial Storage Rack?

The Rack Manufacturers Institute published a document titled “Considerations for the Planning and Use of Industrial Steel Storage Racks” in 2012. This document covers such topics as Planning, Purchasing Consideration, Installation, Use and Inspection and Maintenance of storage rack.

The safe and efficient use of racked storage facilities depends on a number of factors. It is with these factors in mind that the document was written. It was prepared to give advice to the warehouse operator, who may not be a specialist in technical matters, or in the detail design related to the storage facility.

Users should be diligent in creating safe and effective systems. The implementation of safe and effective systems will help avoid injury to persons and property. Safety should always be the number one priority in the use of any system.

Storage systems using pallets, pallet racking and mechanical handling equipment, will contribute best to safety objectives when well designed, diligently maintained and used carefully, as intended. A copy of the document can be purchased at http://www.mhi.org/rmi.

How do I obtain copies of the ANSI/RMI Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks and the ANSI/RMI Specification for Welded Wire Rack Decking? Does the RMI have a web-site?

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.mhi.org/rmi.

What are the Standard Industrial Classification (SIC) and North American Industry Classification System (NAICS) Code for Storage Racks and related items?

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:

ProductsNAICS Code SIC Code
Rack Accessories33715EYYW2542300
Drive In/Drive Through33715E1112542341
Cantilever33715E121 2542343
Portable Racks / Frames 33715E1312542345
Stacker Racks33715E1412542347
All Other (incl Conventional)33715E1512542349

What were the changes to ANSI MH16.1-2008 that resulted in ANSI MH16.1-2012?

The 2012 RMI Specification was modified in the following areas:

  • In Sections 2.1 and 2.2 the load combinations were modified to include the redundancy factor and seismic product load coefficient.
  • Section 2.6.2.1 was added explaining the redundancy factor.
  • The seismic maps in Section 2.6.3.2 were updated.
  • Information on the Seismic Design Categories utilized by the building code was added in Section 2.6.3.3.
  • Section 2.6.4 regarding Connection Rotational Capacity was updated.
  • Section 2.6.6 was added on the seismic separation between rack and the building columns in Seismic Design Category D and higher.
  • The section on Beam-to-column connections was moved from Section 7 and added to Section 5, which deals with beam design.
  • Section 5.5 was added on Pallet Supports.
  • The maximum considered earthquake base rotation in Section 7.1.3 (formerly Section 7.2.3) was better defined.
  • Section 7.2 on Slab and Subgrade Evaluation was added.
  • Section 7.3 on Anchor Bolts was added.
  • Section 9.6.11 on Evaluation of Test Results was added.

Why should I purchase racks that conform to the ANSI/RMI Specifications?

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.

Should I buy used racks?

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.

Where can I find more information about industrial metal shelving?

More information about industrial metal shelving may be found on the Storage Manufacturers Association web site – www.MHI.org/SMA.

How do I obtain copies of the ANSI/RMI Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks and the ANSI/RMI Specification for Welded Wire Rack Decking? Does the RMI have a web-site?

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.mhi.org/rmi.

What were the changes to ANSI MH16.1-2008 that resulted in ANSI MH16.1-2012?

The 2012 RMI Specification was modified in the following areas:

  • In Sections 2.1 and 2.2 the load combinations were modified to include the redundancy factor and seismic product load coefficient.
  • Section 2.6.2.1 was added explaining the redundancy factor.
  • The seismic maps in Section 2.6.3.2 were updated.
  • Information on the Seismic Design Categories utilized by the building code was added in Section 2.6.3.3.
  • Section 2.6.4 regarding Connection Rotational Capacity was updated.
  • Section 2.6.6 was added on the seismic separation between rack and the building columns in Seismic Design Category D and higher.
  • The section on Beam-to-column connections was moved from Section 7 and added to Section 5, which deals with beam design.
  • Section 5.5 was added on Pallet Supports.
  • The maximum considered earthquake base rotation in Section 7.1.3 (formerly Section 7.2.3) was better defined.
  • Section 7.2 on Slab and Subgrade Evaluation was added.
  • Section 7.3 on Anchor Bolts was added.
  • Section 9.6.11 on Evaluation of Test Results was added.

Are all tests outlined in section 9 of the RMI specification mandatory?

No, all tests are not mandatory; however, the MH16.1-2012 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.

What should I know about height-to-depth ratio of single rows of rack?

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.

How far out-of out plumb can my racks be before I should fix them?

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.

Should I tie single rows of rack to the wall?

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.

Does it matter which direction the upright diagonal braces run on a typical selective rack installation?

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.

Can upright bracing be left out to create "window" openings?

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.

Click here to view a list of anchoring issues.

Why should I install load plaques?

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.

If I do need a permit, what materials are normally required from the rack supplier and from the owner? Is there a cost for this?

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.

If I do need a permit, what materials are normally required from the rack supplier and from the owner? Is there a cost for this?

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.

Is there an NFPA fire safety code regarding racking or wire decking?

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

When a portion of a current rack structure is repaired, is it required to bring the unrepaired sections of the rack up to current ANSI/RMI specifications?

The RMI/ANSI MH 16.1 is the best technical storage rack design resource available today. It may be desirable to have the whole rack system evaluated to this standard.

Repairs to any structural element of an existing rack structure should comply with the requirements of the RMI/ANSI specifications for new construction. Existing structural elements of a rack structure that do not require repair and are not adversely affected by the repair of other structural elements may not be required to comply with the ANSI/RMI requirements for new structures. It might be prudent to contact the local building department to determine if a new review is necessary.

Additional information regarding damaged rack can be found in the “Guideline for the Assessment and Repair or Replacement of Damaged Rack” published by the Rack Manufacturers Institute. A copy can be purchased at http://www.mhi.org/rmi/.

What should I do if I want to reconfigure my load beam elevations?

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.

If more rack is added to an existing rack system, is the new rack required to be designed according to the current ANSI/RMI specifications?

New rack should always be designed in accordance with the current ANSI//RMI specifications. However, any existing rack that is unaffected by the addition of the new rack does not have to be modified to bring it up to the current specifications. If the new rack will affect the design of the existing portion, the whole affected part of the system must be reviewed for compliance with the current design specifications.

IBC-2012 code reference: Chapter 34, Section 3403.1.

When a portion of a current rack structure is repaired, is it required to bring the unrepaired sections of the rack up to current ANSI/RMI specifications?

The RMI/ANSI MH 16.1 is the best technical storage rack design resource available today. It may be desirable to have the whole rack system evaluated to this standard.

Repairs to any structural element of an existing rack structure should comply with the requirements of the RMI/ANSI specifications for new construction. Existing structural elements of a rack structure that do not require repair and are not adversely affected by the repair of other structural elements may not be required to comply with the ANSI/RMI requirements for new structures. It might be prudent to contact the local building department to determine if a new review is necessary.

Is it permissible to add frame extensions to the tops of upright frames to increase the height of existing pallet storage rack frames?

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 beam 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.

What is the best loading protocol for a pallet rack?

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.

Why is it important to provide the rack designer with the average load per shelf as well as the maximum load per shelf for the rack structure?

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.

What constitutes a UDL (Uniformly Distributed Load) and how does it apply to storage capacity ratings?

The definition of UDL: Any static load which is evenly distributed over the entire surface on the rack deck. (Ref MH26.2). This means that the product being stored on the deck must cover the entire deck from side to side and front to back. General capacity ratings are based upon a UDL stored on the deck.

What is a concentrated or point load?

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).

What should I do if I think there may be a structural problem with my rack system?

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.

Does it matter if rack frame braces are damaged?

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.

Additional information regarding damaged rack can be found in the “Guideline for the Assessment and Repair or Replacement of Damaged Rack” published by the Rack Manufacturers Institute. A copy can be purchased at http://www.mhi.org/rmi/.

What is an acceptable repair of a damaged rack component?

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.

Additional information regarding damaged rack can be found in the “Guideline for the Assessment and Repair or Replacement of Damaged Rack” published by the Rack Manufacturers Institute. A copy can be purchased at http://www.mhi.org/rmi/.

How much pallet beam deflection is acceptable?

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).

What is the requirement for beam connector locking devices for uplift force?

ANSI/RMI MH 16.1 Section 5.4.2 requires a locking device that prevents disengagement of the shelf beam when subjected to a 1000 lbs vertical uplift force. It is important that the locking devices be properly installed and remain engaged.

How do I know that my beam to column connection is properly installed in accordance with the manufacturer’s instructions?

A properly installed beam-to-column connection, with an engaged locking device, will not become dislodged when subjected to a minor upward force (less than 1,000 lbs). Every manufacturer of storage racks has one or more unique beam-to-column connections. The detailed requirements of the assembly of the connection and the connection strength and stiffness are the result of each individual manufacturer’s testing of that connection. The installation and maintenance of the rack, including the beam-to-column connection should be in accordance with that manufacturer’s instructions. This might be shown on the project specific Load Application and Rack Configuration drawing or detailed manufacturer’s literature.

Should storage rack be periodically inspected?

(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.

Are there any safety considerations for personnel accessing the area under the racking?

Section 8.4.5. of the RMI/ANSI MH 16.1 Specification and Commentary requires “The owner should specify to the designer any locations where operations may require horizontal or vertical safety barriers. These barriers shall prevent product from falling into those areas.”

What is a tunnel bay and what are some of the special considerations?

A tunnel bay is a storage rack bay that has the lower beam levels removed to allow people or lift equipment to pass through the rack in the direction that is perpendicular to the storage rack aisles for the purpose of egress, and also to provide more efficient travel distance to stored loads. The person preparing the rack layout should work closely with the rack user to determine the most optimum locations for tunnel bays. Longer systems may require more than one tunnel bay location.

Special consideration should be taken for tunnel bays that are placed at the ends of the rows, because special design of the frame may be required to allow for the longer unbraced column length. Tunnel bay frames are often reinforced or equipped with protective devices, because they are more vulnerable to damage from cross-traffic or turning vehicles. The clear height of tunnel bays should be adequate to allow for the vehicle to pass through safely. Tunnel bays are often wider than standard bays. The first shelf level of tunnel bays is often protected by wire decks or other guarding.

What is a pick-module?

A pick-module is a rack structure comprised primarily of vertical frames and horizontal beams, typically having one or more platform levels of selective, case-flow, or pallet-flow bays feeding into a central pick aisle(s) supported by the rack structure. Pick modules are used by authorized or trained personnel only, and are not open to the general public.

In pick modules, where can I find the requirements for the stairway system, including handrail and guardrail?

The pick module stairs, handrails and guardrails are required to comply with ANSI MH16.1, which is the referenced standard for storage rack in the building code. These structures are not open to the public and are only to be used by authorized and trained order pick personnel and, therefore, have specific storage rack design requirements.

The ANSI/RMI Specification may be purchased from RMI in their website www.MHI.org/RMI.

Should I tie single rows of rack to the wall?

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.

Why may it be necessary to increase the horizontal clearance between rack members and building structure in Seismic Design Category D and above?

Horizontal separation is required in the RMI/ANSI MH 16.1 – 2012 Specification Section 2.6.6 and recommended in the RMI Considerations for the Planning and Use of Industrial Steel Storage Racks Section 2.15, for the more active seismic regions, because the structures will sway differently during this ground motion. It is desirable to minimize the potential of these two structures from bumping into one another during this ground shaking.

What constitutes a UDL (Uniformly Distributed Load) and how does it apply to storage capacity ratings?

The definition of UDL: Any static load which is evenly distributed over the entire surface on the rack deck. (Ref MH26.2). This means that the product being stored on the deck must cover the entire deck from side to side and front to back. General capacity ratings are based upon a UDL stored on the deck.

How do I obtain copies of the ANSI/RMI Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks and the ANSI/RMI Specification for Welded Wire Rack Decking? Does the RMI have a web-site?

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.mhi.org/rmi.

What are the most common types of wire decks?

(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.

Why do you need the rack / beam specification to properly apply wire decks?

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.

Must the decking be secured to the beams?

There should be a method provided to keep the decks from falling thru the beams. For decks not designed to capture the beam, an alternate securing method is recommended to prevent the deck from falling thru. Methods of securing decks include, but are not limited to, screwing, riveting or some other provision to prevent beams from spreading under load. The deck manufacturer in conjunction with the rack manufacturer can provide specific details.

Should someone stand or walk on a deck?

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).

Can storage rack be installed on floors (surfaces) other than concrete?

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.

What information should I know about the floor slab and the soil subgrade and why is this important?

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.

What is the required floor flatness for a rack system?

The RMI Specification does not provide requirements for floor flatness or levelness. Section 1.4.11 of the 2012 RMI Specification explains the out-of-plumb and out-of-straight limits of rack columns. If a warehouse floor has flatness or levelness irregularities that result in out-of-plumbness or out-of-straightness of a rack column, this is commonly remedied by the use of shims. Section 7.1.4 of the 2012 RMI Specification explains the requirements for shims.

In today’s construction practices, when specifying and measuring the surface flatness (roughness, wash boarding, or bumpiness) and levelness (tilt, pitch, or slope) of a poured concrete floor, the F-numbering system is used in lieu of the former straightedge (⅛-of-an-inch-in-10-feet) method. The F-numbering system was developed by the Edward W. Face Company in conjunction with the ACI Committee 117. By profiling the floor surface, both a flatness value, FF, and a levelness value, FL, can be determined. More information about the F-Number System can be found at http://faceco.com/40q.html.

It is recommended that an owner consult with the manufacturers of their VNA trucks, AGV’s, reach trucks, etc, in order to determine the required flatness and levelness of the concrete slab in their warehouse.

Why should pallet racks be anchored?

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.

What size anchors should I use?

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.

Do all the holes in the baseplate require anchors?

Not necessarily. Racks must always be anchored to the floor as shown on the Load Application and Rack Configuration drawings. The RMI Specification requires at least one anchor per column. The rack manufacturer will often provide extra holes in the base plate as alternate holes that can be used in case floor reinforcing interference is encountered when drilling the floor.

Do I need column protectors? What kind?

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).

Why should I install load plaques?

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.

How do I obtain copies of the ANSI/RMI Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks and the ANSI/RMI Specification for Welded Wire Rack Decking? Does the RMI have a web-site?

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.mhi.org/rmi.

How do I know if my rack system will require a design review to account for seismic forces?

Areas in Seismic Design Category B and above face the potential of earthquakes to varying degrees, magnitudes, and probabilities. Areas in Seismic Design Category A do not have enough seismic activity to warrant a design check for that loading case. 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).

What happened to the old seismic zones (0 to 4)?

The zone designations are no longer used. This occurred with the introduction of the International Building Code in 2000 which affected the ANSI/RMI MH 16.1 Specification.

The old UBC seismic zones (0 to 4) were based upon the seismic ground motion, corresponding to a certain probability of occurrence within a zone. Therefore, all structures within a zone were designed for the same requirements.

What is currently used by the building codes to designate seismicity in lieu of the seismic zones?

The building codes use what is now referred to as Seismic Design Categories (SDC), which range from A to F, and are a function of the seismic hazard at the site, the type of buildings (or occupancies) built at the site and the soil data at the site, and is more representative of the site seismic characteristics. The Seismic Design Categories have been in existence since 2000. The building codes design manuals and the ANSI/RMI MH16.1 all utilize the Seismic Design Categories in their seismic design.

How do I find the Site Coefficients and Seismicity factors required for the seismic design of my storage racks?

There is a United States Geological Survey (USGS) website available, for free, that will provide the seismic design parameters based on the site location. This web site may be found at – http://earthquake.usgs.gov/designmaps/us/application.php.

The Specification utilizes spectral response seismic design maps that reflect seismic hazards on the basis of contours. These maps were developed by the USGS.

What is the importance of knowing the soil classification?

The soil classification will affect the design of the storage rack.

For example, the importance of knowing the soil information is as follows: Given, SS = 0.2 and S1 = 0.08, if the soil is Site Class A or B, then the Seismic Design Category is A, and seismic design is not required. If the Soil is Site Class C or D (Site Class D is the default required to be used if the actual Site Class is not known), then the Seismic Design Category is B where seismic design is required.

Why may it be necessary to increase the horizontal clearance between rack members and building structure in Seismic Design Category D and above?

Horizontal separation is required in the RMI/ANSI MH 16.1 – 2012 Specification Section 2.6.6 and recommended in the RMI Considerations for the Planning and Use of Industrial Steel Storage Racks Section 2.15, for the more active seismic regions, because the structures will sway differently during this ground motion. It is desirable to minimize the potential of these two structures from bumping into one another during this ground shaking.

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