Higher and heavier racking
September 1st 2006

Kevin Mallinson, sales manager of Stow UK considers the racking system issues involved in storing higher and heavier loads.

Commercial pressures to reduce warehousing costs by optimising space has driven a trend for higher storage facilities holding heavier loads. Over the last 3-4 years builders have raised warehouse eaves heights to 14 metres, while forklift truck suppliers now offer reach trucks lifting up to 12 metres and narrow aisle machines attaining heights of 13.5 metres. This has produced a growing population of sheds using simple warehousing techniques, such as wide aisle and narrow aisle, to store 70,000 pallets or more.

Set with a challenge of efficiently storing such a large number of pallets a company would be well advised to talk to suppliers of forklift trucks and racking regarding how high the building needs to be and how much load can be stored because, particularly when it comes to racking, there are a number of significant issues to consider when it comes to going higher and heavier.

Going up For heavier loads on standard racking of 4-5 pallets high, some manufacturers gain a little bit more capacity out of the frame by moving from a single fixing on the floor to a double bolt fixing to provide greater rigidity and therefore greater capacity out of the frame. Others, such as Stow UK, will vary the pitch of the bracing; putting more diagonal braces into the system increases the capacity of the frame.

However, as racking systems get taller and heavier, the size and duty of the upright as well as the range of upright available becomes more crucial. When an upright is fixed at the floor and a beam is fixed at height, to what degree the upright can bend both left or right will determine the load capacity of a racking system.

This is particularly so for drive-in racking, where higher racking will require wider uprights not to simply increase load capacity but to reduce deflection under increased loads. Suppliers offering a wide range of uprights will have greater design flexibility.

The number of uprights used in a racking system can be optimised thanks to a trend towards longer beams that provide room for three pallets on a pair of beams between uprights rather than two.

Three standard pallets across a pair of beams can increase the cost effectiveness of a warehouse; providing the flexibility to hold four of the increasingly common Euro pallets if required.

Floor strength and flatness Taller and heavier racking however increases the load on a floor slab. So this is another major calculation to take into account. The floor specification must be checked as should the floor tolerance requirement for the lift trucks being used.

Safety Higher and heavier racking must consider safety in worst case operating scenarios into account. For example, racks need to conform to a height to depth ratio of 10 to 1. A double run of racking, will usually be deemed to have a 2 metre depth and in practice wide aisle or narrow aisle racking will not go above 20 metres. However a single 1000 mm deep run on the outside of a scheme may go beyond 10 metres high and will therefore need to be tied back to prevent the rack from toppling due to miss-use.

Automation summit Today's automated solutions are also getting higher, with crane installations going up to 32-33 metres. Of course, the taller the uprights, the more they will be affected by factors such as slenderness ratios. However, top end uprights today can reach 40 metres, which means they will comfortably handle the loads placed on a 33 metre rack. It also allows cost effective racking schemes employing fewer uprights to be designed.

Choosing the supplier Tony Lock, managing director Stow UK maintains that customers and specifiers should: "Look for a racking manufacturer that can offer the right advice other than just purely supplying racking, such as ensuring that the scheme works in collaboration with the correct lift trucks. As well as having a wide product range the supplier should also provide a comprehensive project management capability and be able to both manufacture and install a system to the necessary tolerances. This overall capability becomes more crucial the higher and heavier the racking system gets."