For our first question this month we look at Point Loads on Mezzanine floors and then we have a look at the differences between Racking and shelving.
Point Loading
Q. Would it be possible to tell me what the point loading is for a mezzanine floor with a 4.8kn/m maximum load? Could you also tell me if there is somewhere I can find the specifications for mezzanine floors?
A. Point loads on mezzanines are an area that has been the downfall of many a designer over the years.
Point loadings are rarely point loadings and might more reasonably be referred to as patch loadings i.e. high intensity loads over a small defined area that can act for a short or long duration. This small area can vary considerably as can the duration and magnitude of the load depending on the usage of the system.
It is necessary to look very carefully at the proposed usage of the mezzanine and to try to anticipate what the loads might be.
For instance if there is a pallet gate specified it might be reasonable to expect that a hand pallet truck might be in use and then it will be necessary to calculate the load distribution of the pallet between the wheels of the truck and the size of wheels involved so that a contact area and an imposed load can be established.
If a truck or a trolley is in use than this might cause a fairly intermittent load as the equipment is moved around or alternatively the user might choose to park fully loaded trolleys on the mezzanine for several months! These two situations can have different consequences depending on the decking material used.
It is not unusual for mezzanines to be fitted with shelving which sits on the mezzanine floor itself. Again it is necessary to define what the capacity of the shelving will be and size of base plates of the shelving system as well as the load that can be expected on each upright.
In summary a complex issue that requires a formal agreement on what is required between the User and the Supplier. Once this specification is agreed and supplied a load notice defining the use for which the mezzanine has been designed should be provided and displayed on each installation so that future Users are aware of the limitations of the system.
Some general guidance might be available in BS EN 1991 series on loadings however general guidance is exactly that!
Bespoke racking needs testing
Q. We have some racking that was fabricated on site several years ago, however we have no SWL notices applied to this. It has been ignored in the past and we would like to rectify the situation by having a structural engineer visit, calculate and advise.
The racking is constructed from rolled steel “u” section and welded together. Unfortunately we have no COC or test records for either the steel used or the welding wire/rods.
A. The problem here is that you appear to have a only a small quantity of bespoke racking loaded with fairly heavy press tools. It is quite likely that it has carried the current imposed loads perfectly satisfactory for many years however as you say there is no record of either material quality, welding procedure or probably even what the intention in terms of load carrying capacity was when it was originally fabricated. If nothing was changed it could likely go one carrying this load for the foreseeable future however it is very difficult to prove this.
Any company of chartered civil and structural engineers could in theory carry out calculations to arrive at a carrying capacity however they would likely have to make some fairly fundamental assumptions when doing this or would have to destroy part of the rack in order to carry out a tensile test on the steel and perhaps a strength test on the welded joints.
This would destroy part of the rack though would tell you what carrying capacity the destroyed rack had though it might not be totally accurate in identifying the capacity of the untested ones which they might surmise were made from the same materials and by the same operators as all the others.
Perhaps there is a need to carefully look at insurance policy terms and conditions in such circumstances. In order to do a combination of tests and calculations which would justify the definition of a load carrying capacity a considerable amount of work would have to be done and unless you have a significant amount of this racking a scrap and replace proposal might be ta much cheaper option.
Most of the suppliers of Warehouse racking will have within their range a heavy duty version for this kind of application and should have no problem in designing a series or racks from standard components where as well as the benefit that they will warrant the carrying capacity that you specify there is also the ease of purchasing a replacement component if something should be accidentally damaged
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