Shopfitting was first born to take weight. Then it became more about merchandising, 'discounting' that weight loading capacity is there and ok.
IT IS NOT!
CAEM is within the founders of an association of shelving fixtures manufacturer called ACAI that wanted to create UNI FEM and ISO regulations. The target is to pool between engineers about how shelving really works, and then how should it be computed and then how should it be tested. It's now 5 years we're into this process and first results will be coming during 2010.
We're all aware that weight should be 'evenly distributed' right? This makes sense. We would all think that weight is ... 'weight', regardless. IT IS NOT!
The engineers have discovered that testing shelving with (ie) bottles, is not the worse case scenario: it is proved that a weight that has a 'self structure' is putting less stress to the shelving. Differently, a loose huge water bag is a real test, because has no structure that self-help the weight. I am not an and still it is difficult to explain in easy words! Basically, if you see shelving tested with concrete blocks, bottle of waters, tiles... the guys are 'doing a favour' to their shelving. The real test is with "airbags" pushed from top, so making the weight with zero 'self-holding' help.
The above does not refer to another issue we see most times: a shelf is tested with 300kg (1300pounds) but then the blocks or the tiles are also above the brackets: even a few millimiters of weight over the brackets and not only over the suspended part of the shelf, help the numeric result dramatically.
don't forget, the real test of shelving is for RUNNING SHELVING. We see most chinese shelving manufacturers but i have to say plenty of europeans and americans sending around pictures of shelving taking a huge load, and that's how they compute their weight loading. Have a look closer: it's 1 shelving unit, with... 2 uprights and 2 bases!
the real test is the one with 5 shelving units, all wholly loaded, and your test and measurement has to be in the middle unit!
At the end of any computation and testing, a full policy of rules on safety margins is crucial. When they build bridges or towers, the engineering are obliged by law to put safety margins on the results and on their sub results (sometimes the safety factor is simple, sometime it multiplies by itself): if they need a bridge for 10 trucks, they will build it for 50 trucks. Shelving fixtures for retail merchandising has no ruling on that sense before our ACAI organization. That meaning that most manufacturers will tell you the weight at which the shelving breaks down. Some other, more serious, will cut that weight down by 30%. Some other, will cut it by 50%.
A real 'safety margin policy' suggests to use both safety margins on the weight numeric result but also limits on the deflections of materials.
my recommendation is: don't get carried away by manufacturer giving weight loadings, do always ask and ask again about it. By our experience and our analysis on most competition worldwide, very few are giving REAL weight loadings to the market.