This month we begin with a question on Cantilever racking and what the degree of acceptable fall back is. Next we consider testing or replacing racking as an option when the SWL is unknown and can’t be found.
Cantilever racking and fall back
Q. We have recently had some cantilever racking manufactured and installed and the arms have a 1 degree fall back on them. I want it to be that this is sufficient due to the fact that we are loading the racking with rolls of wrap that can weigh anything from 200kg to 400kg per roll and I wouldn’t want them to roll off injuring someone.
A. It is difficult to comment where we do not know the basis of the design or what was agreed in the contract between the user and manufacturer so there is little that can be said with certainty.
However the current SEMA code for the design of Cantilever racking states that “under full working load the arm should not deflect below the horizontal (clause 3.2.2).” I know some would interpret this to mean that the tip of the arm would not deflect below the heel of the arm where it is connected to the upright. Under load however this will mean that the end of the arm will droop slightly and as you describe the matter there might be a slight tendency for goods to roll to the end of the arm. SEMA interpret this requirement to mean that no part of the arm shall be below the horizontal when measured with a small spirit level at any part of the arm while under full working load. This would take account of any upright and base deflection as well, as these also both affect the overall deflection of the arm which does make this all very complex. Some manufacturers will incline the arm upwards to overcome this effect however the amount of the pre-set that is placed in the design will depend on the flexibility of the arm. A very flexible arm will need a lot of pre-set and vice versa so there is no absolute requirement here.
Racking or shelving
Q. What is the difference between Racking and Shelving?
A. A key difference between racking and shelving is that shelving is almost always loaded by hand and the weight of the individual goods carried is comparatively low (typically less than 25kg), furthermore the total weight carried in a bay of shelving will typically be less than 4t.
Racking is typically loaded by machine (forklift truck or crane) and the unit loads carried are typically heavy i.e. many hundreds of kg; pallet weights exceeding 1t are common. The weight of goods carried in a bay of racking can exceed 40t in extreme circumstances. Racking is typically, therefore, a heavier duty system than shelving utilising larger members and thicker material. If a racking structure has some sort of flat surface (decking, panels etc.) positioned on the beams then (with appropriate design) it is possible to use a racking structure as shelving. It is impossible to safely use a shelving structure as racking i.e. storing pallets etc.
SEMA defines racking as:
A skeleton framework of fixed or adjustable design to support loads generally without the use of shelves. The term racking is usually qualified e.g. Pallet Racking, Tyre Racking, Drum Racking etc.
Adjustable pallet racking is defined as:
A system of upright frames that are connected by horizontal beams to provide pallet storage levels, which can be adjusted vertically. SEMA defines Shelving as: A series of load carrying surfaces (shelves) supported by upright frames
The above definitions are taken from the SEMA Terms and Definitions code, see the following link http://tinyurl.com/hwwaa8g
Unfortunately many people are not particularly precise in the use of these terms and will interchange them; which can lead to confusion. SEMA is delighted to be working with WLN on the storage Question and Answer Column. On the WLN website is a list of previously published columns.
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