Our first question this month asks for assistance on the Rules and Regulations with fitting stop beams and our second question asks for the maximum overhang on racking.
Back Stops
Q. A customer has asked me are there any rules or regulations with fitting back stop beams and do SEMA insist these be fitted or is it customer choice?
A. Backstops come in two varieties, ‘safety backstops’ and ’buffering backstops’ both of which need careful consideration in the initial layout of the racking. The safety backstop is located 50mm behind the normal placement point of the pallet so in theory should only be hit in a significant accident. It is allowed therefore to be installed on the assumption that the racking frame can deal with this impact force as an overstress in the material without the need to specifically design for it which would be the case if regular impacts were involved.
The consequences of this however are that there has to be 50mm clear in front of the backstop beam between it and the pallet and the beam itself may be anything from 50 to 100mm wide so the central flue in back to back situations needs to be designed much wider. This rarely happens in practice and the backstop is fitted in whatever space is available and is therefore hit on a regular basis, becoming a ‘buffering’ backstop and usually does not last long.
With the ‘buffering’ backstop the design anticipates regular impacts by incorporating these forces into the design of the rack structure and therefore increasing the size and strength of the upright backstop to upright fixings, floor fixings, and frame bracing. This means the forces have to be included in the original design of the rack and it cannot be added as a postinstallation. This is how it should be done, however it is almost always ignored on cost grounds which leads on to ongoing arguments between customer and supplier where a customer wishes to know why the design was not strong enough to resist serious damage.
SEMA have for many years recommended against these items as in our view they encourage bad driving techniques on the part of the truck driver who will use the backstop as a ‘stop’ for his truck rather than using his judgement and the brakes on the truck! When we have discussed these issues with our continental manufacturing colleagues they admit they have all these problems in Europe however as they are very popular, they argue that they have to give the customer what he wants so continue to use them and accept the flak generated as a result!
Maximum Overhang
Q. We currently have racking that is 900mm deep, which is not suitable for storing 1200mm deep Euro pallets as they rest on the pallet runners rather than the pallet blocks when placed on the beams, with a current 150mm overhang front and rear. This creates a point load on the pallet runner, not what the runner is intended for I believe. When I’ve looked through the SEMA guidelines it refers to a maximum overhang of 50ml also.
I’ve been given 3 options to resolve and wondered which could be categorised as compliant with the guidelines.
1. Place timber panel decks fully covering the location that are 1100ml deep and sit in the current racking structure. The finished pallet will then go on top with a 50ml overhang over the board. The decking boards themselves will overhang the racking structure by 100ml also.
2. Place decking boards/steel mesh decks 900mm deep in the existing structure. I’ve been informed this will convert the point load to a UDL, bringing 75% of the runner and the middle block into supported load. I am informed that when conversion to UDL the overhang issue does not afford a problem?
3. Take down all the rack and reconfigure to 1100mm deep to be suitable for the pallets stored.
A. We think the three options you have provided could all work; however having not seen this installation it is very difficult to be positive on this. Probably the main thing to watch is that with this amount of overhang you are not closing your aisle width down to the extent those operations become difficult due to lack of clearance.
Plainly option 3 is the best option however it is also likely to be the most expensive in terms of cost and disruption.
Option 1 and 2 are dependent on having sufficient space in the back to back ‘flue’ such that the pallets can be misplaced by operators as undoubtedly they will be, without hitting and displacing the pallet in the row behind.
Steel mesh decks in option 2 come in all kinds of strengths and capacities. We note the comment about converting point loads to UDL and would need to be convinced on this, which would depend on the particular type and capacity of the mesh deck provided as well as on the quality of the pallets in use. Given the large amount of overhang that would be present at front and back beams it would also be a challenge to the FLT operators to achieve consistent accurate positioning of the pallets. This would be our least preferred solution.
Sorry we are not able to be more precise however having not seen the installation we hope the above thoughts are of assistance.
SEMA has a code of practice on load notices www.sema.org.uk/ page.asp?node=2
The HSE publication HSG76 also gives guidance www.hse.gov.uk/ pubns/books/hsg76.htm.
SEMA
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