|SEMA - Codes|
by Alan Moule
Unfortunately, the subject we are about to discuss next will require us to backtrack somewhat. You have already heard a great deal about various racking systems, and their pros & cons, but we need to return to the history of racking in general, and I trust that I will not be repeating too much of what you have heard from our other very capable speakers.
The overall concept of "unit load handling" as it is commonly referred to developed almost entirely during the 2nd World War. The vast quantities of supplies and munitions needing to be stored and moved often half way across the world created a logistics challenge unprecedented in previous history
The concept of handling a large number of small items as one unit is not new, and the general idea of the pallet is probably as old as the pyramids. It was the powered forklift truck that finally enabled the handling and movement of the huge tonnages that today we take for granted.
Almost simultaneously with the pallet and the FLT came the need for what we now normally refer to as pallet racking that is a structure enabling us to support one pallet load above another in an orderly and efficient manner, rather than simply dumping them on the floor.
Seeing a business opportunity, every Tom, Dick & Harry immediately started producing so-called pallet racking to supply this new need.
Initially these racks would have been grossly over designed, welded up from commercially available standard steel sections.
It wasnt long however before the market pressures of price and competition led to cost cutting in material content, and coupled to the need for adjustability, cleverly designed "systems" entered the picture. The problem was that anybody could design, market, and install their own so-called system, with the assurance to the end-user that it would work! Which is to say that it would perform its function and safely . . . .
There were no standards by which to qualify this claim, and no guarantees.
After a while, the qualified and reputable manufacturers that had developed sound systems disillusioned by the short-term success of imitators and chancers banded together to establish a united front. This would entail the setting out of stringent standards and guidelines to control integrity within their chosen industry but it took organisation, and it wasnt until the 1960s that SEMA was formed.
Perhaps the first thing to consider is the bottom item on the screen - Terms & Descriptions of Storage Equipment, whereby the terminology to be used throughout SEMA discussions and publications was defined so that everyone understood each other!
For instance vertical support members were posts, posts assembled with diagonal bracing members were frames, horizontal support members were beams or rails respectively (depending on system) etc.
Otherwise the main types of papers produced by SEMA are known as either guidelines or Codes of Practice, and these are listed on the screen.
It should be made quite clear that none of these guides or codes are in any way mandatory or enforceable legally or otherwise even in their country of origin. They are intended to establish
"good practice" with the purpose of protecting both the customer, and the standards of their own industry. In SA we have mostly voluntarily elected to follow these codes because
Those we are most concerned with for todays discussion are:
Design of Static Racking
This defines the way in which the overall system, and its component parts are designed. Issues of rigidity & stability or "sway", adjustability, accidental dislodgement of beams, etc are discussed, as well as the way in which loadability is determined and this is obviously crucial to all racking, since the customers loading needs will always vary according to circumstance.
The codes are not concerned with the quality of steel used which is invariably cold formed sheet, either hot or cold rolled since this varies extensively. The important thing is to KNOW the steel most importantly its specific tensile strength normally expressed in Mpa.
From a known Mpa, using calculations described but pretty much standard engineering formulae, the loading on a specific section can be determined. (Today we have clever PC programs such as Procon to do this for us in seconds even to the extent of using "models")
Posts/frames need to support vertical loads, while beams support loads horizontally. In the latter case especially, deflection (since steel is an "elastic" product, and bends under stress) is taken into account as well as ultimate, or cripple, loading.
After the theoretical calculations have been done, it is vital that empirical testing be carried out to confirm these. Beams for instance have to be progressively loaded until they bend to a point of no return (called the yield point), and then on to collapse.
These tests also determine safety factors which is another vital factor laid down in the Codes.
Use of Static Pallet Racking
This refers more specifically to specific customer application, as well as correct installation. Handling equipment, pallet type, operating conditions, clearances, floor fixings, maintenance, and damages inspection, all receive detailed attention.
Erection Tolerances for Static Racking
Tolerances for component manufacture, and for damage concerns, are covered by previous codes, but verticality, alignment, and deflections, are covered here in a lot more detail stemming largely from the increasing sophistication of operating equipment.
Standards perfectly acceptable for 3m high forklifts are not good enough for 9m high reach-trucks, let alone narrow-aisle, or Turret-trucks, while automated and crane applications need virtually Panasonic standards of "zero tolerance"!
The publication "Truck/Racking Interface" covers this aspect even further.
The overall collection of documents is large (not huge or unmanageable), but I have been asked not to dwell on too much detail.
More important is to consider the potential implications of non-conformance. Inferior product design, poor quality Raw materials (steel), careless installation, over-stated loading claims, or over-stated safety factors, are all issues of great concern to the end-user since the results can be collapse with costly damages, or even fatal, results!
Despite this, and the fact that customers are consistently seduced by low price offerings from the numerous "fly-by-night" suppliers that abound in our industry, there are remarkably few serious incidents brought about by non-conformance.
Oh, yes, they do happen, but the supplier is usually able to talk his way out of repercussions, in the same was as he conned the customer in the first place!
Which is just as well, since few of them will be carrying adequate liability insurance to cover the claims - which can be pretty substantial.
In sequence of severity, the major things that go wrong can be summarised:-
However, it must be pointed out that 90% of frame problems arise from impacts by handling equipment.
An FLT accidentally bumping the rack, normally near the base, weakens it considerably sometimes to the point where it is no longer safe.
An FLT crashing into a post can cripple it to collapse then the whole rack, even the whole system can come down like a pack of cards!This can be prevented by:
* adequate training for operators;
* correct spec for aisle widths;
* periodic and structured safety checks and reporting;
* repairs where required - by original supplier!
What I as a rack manufacturer, and we, as the Institute of Materials Handling, would like to see in SA is regulation, (incl ultimately legislation) using Codes of Practice, for this industry.
Martin Bailey of National Council has prepared a draft for such a Code under the Institute banner, but we have a long way to go before it is finalised and accepted.
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