RUBB

Our first question this month asks if there is a recognised difference between Europe and America when it comes to maximum beam deflection. The second question looks at the maximum depth of pallet overhang.

Is maximum load beam deflection different in the USA

Q. We recently converted our finished goods area to a pallet racking system from a US supplier. The racking is a teardrop system rated to hold three pallets on each horizontal pair of beams at a maximum load of 5000lbs. per pair of beams.

The manufacturer also states that a 1.7 safety factor is built in.

When loading pallets of paint on to the shelving all of the units showed some degree of deflection.

On those types of paints with a maximum weight of 1400lbs per pallet, the deflection measured approximately 1 inch. The maximum deflection allowed by the manufacturer is 0.8 of an inch.

The manufacturer has retested the remaining beams at their facility and has found no problem.

Can you indicate what the standard test method is for testing the loads, so that we can have independent tests done?

A. Any racking coming from a US supplier will almost certainly be designed to US RMI (Rack Manufacturer’s Institute) Standards which, while similar to those in Europe, are not identical.

One of the main differences is that the US Standard allows deflections of Beam Span / 180 as a maximum as opposed to Beam Span / 200 which would be the maximum allowed in Europe.

As an example, a 3600mm long beam would have a maximum deflection of 20mm under the US code and 18mm under the European codes. This is hardly a massive difference – however it is significant. The supply of racking like any other product is a competitive business and if a designer is allowed 20mm maximum deflection he will take full advantage of this in producing a cost effective product and therefore, you should expect to achieve very close to this deflection under maximum working load.

That said, you seem to be over this amount by almost 25%, and we would suggest the following: –

1) Physically weigh a sample of pallets as it would not be the first time that it was discovered that a nominal pallet load was in fact being substantially exceeded. Perhaps packing and the self weight of the pallet may not have been considered

2) It is not clear how your loading arrangement results in multiples of pallets of 1400lbs giving a total load of 5000lbs per pair of beams. If you have 3 pallets per beam this is even more worrying as you are quite a long way short of the rated loads of the beams to achieve these deflections. If you are using a 4 pallet system, then either the beams are over-loaded or you are relying on certain pallets being under maximum weight to compensate for those overweight. If the latter is the case, then we would respectfully suggest this might be the cause of the problem as all pallet racking systems are designed for a uniformly distributed load both along the beams and across them. Any deviation from this might be expected to cause problems.

3) Look carefully at your pallet design and also at the loading configuration of the paint on the pallet, together with the pallet position on the beams. As stated above, all racking is designed for uniformly distributed loading unless the users specifies otherwise. This can be a cause of deflection problems on occasions.

4) When measuring deflection it is normal to measure from a string line rather than the floor as undulations in the floor can result in significant measuring inaccuracies. Attach a string line to the uprights in the vicinity of the connector such that the line is level with the bottom flange of the beam in the unloaded condition. Load the beam and re-measure the maximum deflection, normally in the centre of the beam span.

The measurement method given above should be accurate enough to identify if there is a problem.

Should the problem still exist when you have eliminated possible causes under your own control, we would suggest that the manufacturer needs an involvement no matter how far away they are. It is very unlikely that given the time taken to ship products to the UK that the manufacturer still has samples from your batch of production made from a single delivery of steel available in his factory for test – we would respectfully suggest that proof that the remaining beams in their factory came from the same batch should be provided.

It is possible to send a pair of beams away for formal load testing at a laboratory and SEMA can provide information about local facilities that are able to carry out this work.

If you would like a local specialist racking engineer in the UK to provide specific advice on a consultancy basis, then again SEMA can provide you with some names.

Pallet Overhang

Q. Can you please advise me of the maximum depth of pallet that can be safely stored on a 900mm deep racking system? My understanding is that this is 1000mm with max overhang of 50mm front and back?

A. You are correct, assuming that you are talking about 4 way entry pallets which will give you a pallet overhang of 50mm over the front and back beams. This should then leave 100mm clearance between pallets in a back to back location when they are stored correctly.

In the event that they are stored incorrectly with the front face of the pallet flush with the beam, which occurs sometimes although it is not recommended, then this clearance will not allow the pallet to interfere with a pallet similarly located in the adjacent aisle.

We would recommend that you obtain a copy of the SEMA Code of Practice for the Use of Static Steel Pallet Racking for further guidance.

SEMA is delighted to be working with WLN on the storage Question and Answer Column which is published in WLN on a monthly basis. On the WLN website is a list of previously published columns which we hope you find useful. Please note that SEMA Users Club members also have access to a comprehensive range of additional storage related questions and answers.

www.sema.org.uk

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