Our first question this month is asking for advice on Attachment of Racking and our second is about Cantilever Racking & Fall Back.
Attachment of Racking
Q. Please can you advise if it is acceptable (indeed wise) to attach racking to a wall in addition to the floor. I have looked at the guidance for installation of racking and cannot find any advice in this respect.
A. First of all we would comment that most racking manufacturers have components such as wall ties available in their range and these provide a level of extra security when used correctly. Normally these are used on single sided runs of racking backing onto a warehouse wall or other structure.
They are not universally specified as there is often a reluctance on the part of the building designer to accept onto his building structure any loading from the racking no matter how small. A climate of litigation and the professional indemnity insurance of the building designer lead him to be reluctant to accept the risk of absorbing loads for which he is not being paid a fee. He will often therefore decline to confirm that his building is suitable for connection to the racking which will need to remain as a self-supporting structure.
Where possible connecting to the building provides a small degree of restraint to the end frame such that in the event of a major truck rack collision taking out the front upright of the rack the frame is held in the vertical for a few milliseconds rather than rotating into and across the aisle and falling into the adjacent rack which can cause this to collapse in turn leading to a progressive collapse over a larger area. Where a relatively weak connection exists to the wall or building structure the frame will be held in the vertical long enough for load to be transferred from the damaged front upright to the rear upright via the frame bracing causing that in turn to collapse. This will the result in a vertical collapse and at that point the wall tie will tear out of the wall as the rack and goods sink vertically downwards. This is a preferable failure compared with the rotational one and will with a degree of good luck be restricted to a couple of bays in the run concerned.
This is in effect the same reason that run spacers are used in back to back racking.
The contra argument is of course that if the wall tie is too strong there is the possibility that the wall itself will be destroyed in the collapse and if there is the possibility to people working on the other side of the wall concerned then this might not be a very good idea. Modern block walls are not particularly strong however neither are they items that anyone would want to fall on themselves.
The answer to your questions therefor is “that it all depends” and all we can suggest in such circumstances that a risk assessment be carried out before contemplating such an course of action and if it seems a sensible thing to do then the building designer needs to be consulted and only with the agreement of all concerned should it be done.
Cantilever Racking & 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 both of these also 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.
If you have a query send it to us and we will do our best to have it answered.
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