Our first question concerns the aftermath of an inspection where the rating of beams and purlins has been requested. Then for our second question we look at the minimum space required between long span shelving.to allow correct picking.
Purlin ratings for Mezzanine floors
Q. We have had an inspection carried out and the weight capacities have been given, we now have the mezzanine floor suppliers disputing what has been reported and it all seems to be down to the beam / purlin ratings. I am looking for some information myself about the different sizes and loadings etc.
A. The purlins are likely to come from a specialist supplier in either zed section or lipped C section shapes though sometimes more exotic shapes are used. The strengths will be defined by both the section size (mainly the depth of section) but also the material used in making the section. This can vary in thickness and also in material from Z250 which is a galvanised material with a minimum yield of 250 Newtons to Z350 which is obviously substantially stronger at 350 Newtons and in some extreme cases material either stronger or weaker than these general limits may be used.
Sometimes the manufacturer marks the purlins so the material can be identified however if not then there is no alternative but to go to the manufacturer assuming they can be identified and ask for their specification and a set of load tables. The major manufacturers usually make some software available for their clients to use so once you have identified who the manufacturer is this should not be a problem.
As far as beams are concerned the same applies as there are usually several weights / linear metre for the same nominal size of beam each with its own carrying capacity and in addition high strength steel can sometimes be available. Usually the lightest section in grade 43 steel is used however the supplier would need to confirm this.
Your mezzanine floor supplier should have all this information to hand and should be able to justify what has been done in the original design. Mistakes are rare, however do happen from time to time and we would have thought that it would be in everyone’s best interest to bottom out whether this problem identified by your Inspector is real or otherwise.
Ultimately if you cannot get agreement between parties you may have to obtain the services of a Consulting Chartered Structural Engineer to act as arbiter by carrying out an independent design check.
Minimum Row Space?
Q. We would like to erect several rows of shelving and are unsure on what the minimum space / distance should be between rows of long span shelving to comfortably allow someone to be able to pick from both sides.
A. The answer is it all depends on the particular circumstances and I am afraid you have all the information on that one. For instance if you are picking into a trolley then the aisle needs to be wide enough as a minimum for two trolleys to pass unless you are planning a one-way system when perhaps this would work as long as the aisles were not too long as overtaking would not be possible with two pickers within the same aisle! If there are few pickers then this may not be a problem.
We note you appear to be to be an automotive company and there may be some irregular shaped items like windscreens, body panels and exhausts that require careful handling to get them into and out of the rack as well as batteries that are very heavy and with some of the bigger ones might even need two people to handle them.
Sometimes it is worthwhile to build a prototype two bays opposite each other in a spare area which can then be loaded with what is judged to be the more difficult items and carry out a practical appraisal to see how items can be loaded into the rack and unloaded to picking trolleys. The bays can be moved apart or closer together replicating various aisle widths options until an optimum distance is established for how you intend to operate. This highlights the problems areas which might even mean special handling equipment, but also clarifies the mind as to where heavy objects ‘must’ be stored for easy handling.
Involving future operators of the system in this evaluation also ensures a minimum of grumbles about a new storage system when it goes live and sometimes such people come up with some neat solutions to potential problems.
SEMA Technical Enquiries If you have a query send it to us and we will do our best to have it answered by one of our experts.
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