Dr Murray Clarke, Structural Design Manager, Dematic, which manufactures the ColbyRACK range of storage equipment. The article previews some of the key changes in a new standard covering the design of steel storage racking systems – AS4084-2012, which was released on February 29th 2012.
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).
Improving storage system safety
Standards play a vital role in ensuring workplace safety on a day-to-day basis. 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.
It is important that all storage system users are aware of the changes and 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
The Steel Storage Racking Standard AS4084-1993 had remained unchanged for over 18 years. A period during which significant advances in storage system design and manufacture have occurred around the world.
Although a considerable amount of knowledge could be adapted from European and North American practice and racking standards, committee work updating the Australian standard still ran over several years. The standard was released for public review in September 2011. The new standard is called AS4084-2012 Steel Storage Racking.
Racking is a system, not a product
End users of storage systems invariably view the equipment as a standard “product” that either satisfies the standard or it doesn’t. Such a view would never be held in relation to buildings or bridges, each example of which is custom designed by engineers on its merits.
The same philosophy is true for steel racking systems – although the components 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 standard checks the level of load that it is required to hold, the presence or absence of seismic loads, and so on. To put it simply, compliance with AS4084-2012 is a rack-by-rack, application-dependant proposition.
That is why the role of the designer is so important. It is the designer’s task to create 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 onus of responsibility to ensure the systems are being properly used and maintained, and continue to meet the standard, falls squarely on the user.
Key changes to design philosophy
The major change contained in the new Australian standard for steel storage racking is the switch from using a “permissible stress” design philosophy to a “limit states” design approach – a move which brings Australia into 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 into line with the relevant cross-referenced companion Australian standards, including AS/NZS4600: 2005 Cold Formed Steel Structures and AS4100-1998 Steel Structures.
From a structural design perspective, the limit states approach offers advantages over the permissible stress format. It allows the designer to consider the application of different margins of safety to different types of loads (dead loads, storage loads, live loads, seismic 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.
Compared to the old standard from 1993, the new standard has the potential to result in more structurally efficient and finely tuned designs. The result is that the storage racks of today are generally lighter and cheaper than those of yesteryear, while still possessing the required minimum level of structural safety – and that’s good news for end users.
Key changes to operational requirements and end-user responsibilities
AS4084-2012 Steel Storage Racking will contain a number of important changes storage system users should be aware of:
- No changes to storage system configuration allowed without the approval of the equipment supplier or a structural engineer
- The vertical clearance requirement for pallets stored above heights of 6m has been increased from 75 mm to 100 mm. This is aimed at reducing the risk of accidental impact with beams during pallet put-away and retrieval
- The “flue space” between pallets backing on to each other has been increased by 50 mm, reducing the risk of an adjacent pallet being accidentally dislodged when storing or retrieving pallets. This increase in flue space also better accommodates the needs of insurance companies who often insist on a minimum flue space of 75 mm to allow adequate penetration of water from roof and rack-mounted sprinklers during a fire.
- A 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.
Your responsibilities: if in doubt, get it checked
As per the previous standard, storage system users should ensure their system is professionally audited every year. The reality is that many storage system users are either unaware or routinely ignore these requirements.
Recent rack collapses in NZ have shown the 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 AS4084-2012 doesn’t cover
Like the standard before it, the new steel storage racking standard is only relevant for closed-face racks such as Selective, Narrow-Aisle and Double Deep racking. It does not cover open-face racks such as Drive-In or Cantilever racking.
When designing open-face racks, designers 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. These codes 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.
Further information: Dr Murray Clarke +61 2 9486 5393 firstname.lastname@example.org
The above article is reproduced from Dematic Asia-Pacific
Dr Murray Clarke, BSc BE(Hons) PhD
Colby Storage Solutions (a division of Dematic Pty Ltd)
Member of AS4084 Committee
Associate Member of FEM Committee (Storage Racks)