Dr Murray Clarke, Structural Design Manager of Dematic, previews some of the key changes in a new standard, AS4804-2012 covering the design of steel storage racking systems.
Improving storage system safety
The new Australian standard covering steel racking systems will bring Australia up to date with the latest international knowledge and experience in the design of storage systems and cold-formed steel structures.
Standards play a vital role in ensuring workplace safety on a day-to-day basis, making it essential for all storage system users to be aware of the changes, their responsibilities under the new standard, and what they should be asking their supplier to ensure they meet the new requirements.
Why the standard is being updated
During a period when significant advances in storage system design and manufacture occurred around the world, the Steel Storage Racking Standard AS4804-1993 had remained unchanged for over 18 years.
The new standard is called AS4084-2012 Steel Storage Racking and incorporates several European and North American practice and racking standards.
Racking is a system, not a product
Although components of steel racking systems may well be standard components, the issue of compliance with the standard depends on how these standard components are interconnected to make a system, the level of load that it is required to hold and the presence or absence of seismic loads among other factors.
Compliance with AS4084-2012 is a rack-by-rack, application-dependant proposition with the designer entrusted with the task of creating steel racking systems that are fit for purpose, meet the user’s requirements and budget, and provide acceptable safety margins to ensure safe, long-term operation.
However, when it comes to day-to-day operation, the user is still responsible for ensuring the systems are being properly used and maintained.
Key changes to design philosophy
A switch from using a ‘permissible stress’ design philosophy to a ‘limit states’ design approach is one of key changes of the new Australian standard for steel storage racking, bringing Australia in line with most of the advanced rack designs codes in the world, including the European racking standard EN15512: 2009 and the Rack Manufacturers Institute Specification from North America.
It also brings the standard in line with the relevant cross-referenced companion Australian standards, including AS/NZS4600: 2005 Cold Formed Steel Structures and AS4100-1998 Steel Structures.
Advantages from a structural design perspective of the limit states approach includes enabling the designer to consider the application of different margins of safety to different types of loads to facilitate design optimisation, while guaranteeing a prescribed level of safety across different combinations of loads.
Limit states design also provides the designer with greater insight as to how the structure will behave in the event of an overload that approaches the true collapse load of the system.
Other significant changes in the new standard include vastly expanded and improved testing provisions including statistical evaluation, and the inclusion of advanced methods of structural analysis and finite element analysis.
The new standard has the potential to result in more structurally efficient and finely tuned designs with modern storage racks being lighter and cheaper than previous models while still possessing the required minimum level of structural safety.
Key changes to operational requirements and end-user responsibilities:
- No changes to storage system configuration allowed without the approval of the equipment supplier or structural engineer
- Vertical clearance requirement for pallets stored above heights of 6m has been increased from 75mm to 100mm to reduce the risk of accidental impact with beams during pallet put-away and retrieval
- Flue space between pallets backing on to each other has been increased by 50mm, reducing the risk of an adjacent pallet being accidentally dislodged when storing or retrieving pallets. Higher flue space also better accommodates the needs of insurance companies who often insist on a minimum flue space of 75mm to allow adequate penetration of water from roof and rack-mounted sprinklers during a fire
- Minimum of two ground anchors must be used per baseplate on racks where forklifts are used
- Minor changes to rack load signage whereby the dimension from ground to first beam level, and from first to second beam level must be noted explicitly on signs
Responsibilities of storage system users:
- Users must ensure their system is professionally audited every year
- Importance of regular system audits to identify existing rack damage that could compromise performance during a seismic event or overloading of the structure
- Failure to conduct annual audits could expose users to litigation and potential penalties should an incident occur
What AS4808-2012 doesn’t cover
The new steel storage racking standard is only relevant for closed-face racks such as Selective, Narrow-Aisle and Double Deep racking systems, and does not cover open-face racks such as Drive-In or Cantilever racking systems.
Designers of open-face racks will need to seek guidance from other international standards and codes such as FEM 10.2.07 for drive-in racking and FEM 10.2.09 for cantilever racking, which can be used in conjunction with AS/NZS4600-2005 Cold Formed Steel Structures to obtain structurally sound racking designs consistent with world’s best practice.
Dr Clarke is a member of the Standards Australia committee for steel storage racking and represents Dematic at the European Racking Federation (ERF) technical meetings. The ERF is a division of the widely known European industry body FEM (Fédération Européenne de la Manutention).