A Report on the SEMA Code of Practice for the Design of Static Racking

Safety In Numbers

One of two no-nonsense guides to safe storage from Redirack

SAFETY IN NUMBERSDoes your pallet racking meet the

SEMA code?

Published by Redirack in the interests of storage safety

Redirack Limited, Wharf Road, Kilnhurst, Mexborough, South Yorkshire. S64 5SU.Tel: +44 (0) 1709 584 711 Fax: +44 (0) 1709 589 821 Web: www.redirack.co.uk

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CONTENTSIntroduction Page iii

Say what you want - know what you are getting 1The vital exchange of information between customer and supplier.

Is it strong enough? 3Material specifi cations, safe loadings and structural confi guration.

Elbow room! 5Recommended operating clearances.

Leaning towers 7Racking installation tolerances.

Keep it true 9Racking installation stability.

One lady owner... 11Racking installation, operation and maintenance.

Whoa! 13The use of pallet backstops.

Which pallet, which rack? 15Recommended pallet locations for racks and pallets of different sizes.

Conclusion 17

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INTRODUCTIONWhat's wrong with British Standards?

If you mean the British Standards that form the authoritative yardstick for the design, manufacture and production of so many British products - there’s nothing wrong with them.

The catch is that the determination of such detailed standards just can’t be rushed. And in the case of the storage business, product design and development moves fast. Today, any storage equipment manufacturer worth his salt sticks closely to BS449. That’s the standard for structural steel employed in the building industry generally.

However, the Standard can offer only general rules relating to the design of steel structures. Complex structures require particular care and more specifi c guidelines governing design and testing have been introduced via the Storage Equipment Manufacturers Association (SEMA), in the form of the Code of Practice for the Design of Static Racking.

Happily, the storage business has a good safety record. In an effort to maintain that record, SEMA have taken a close look at every aspect of static pallet racking, and in addition produced a guide to help the user of racking understand its limitations - Code of Practice for the Use of Static Racking.

That’s what this booklet is about. It covers each of the key points in that Code of Practice. It explains how they relate to the specifi cation and use of all kinds of static rack. It’ll help you choose, and use, your racking installation effectively and confi dently. And the fi rst thing you need for a good relationship with your racking is - confi dence.

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SAY WHAT YOU WANT-KNOW WHAT YOU'RE GETTINGIn the old days, when there was only one type, one brand of rack on the market, buying was easy. You either bought it or you didn’t. You located it wherever there was space, and stored on it whatever fi tted.Today, things are different. There are all kinds of rack style, all kinds of brands. You get the benefi t of a wide choice, but you also get the problem of making your choice. Given the very specialised nature of your own requirements (and that includes cost and effi ciency, as well as the shape of your warehouse), and all the apparent solutions, selecting the right rack will take time. And unless everyone’s clear about what you’re trying to achieve - mistakes will be inevitable.So, say what you want your racking to do for you, and say how you’re going to use it. Then, get your supplier to tell you exactly what he’s offering you. In detail.Here’s the kind of information SEMA suggest you supply, and the kind of information you should be given:

PROVISION OF INFORMATION

BY THE CUSTOMER

Before the user purchases racking equipment, it is important that adequate information is provided to the supplier. Details that should be asked for by your supplier include:

PalletsType, size, construction and load carrying capacity. For drive-in and drive-through racking installations, quality and type maybe critical. Direction of fork entry must be specifi ed.

Unit LoadWeight (including weight of pallet), overall dimensions, and stability of load.

Pallet Handling EquipmentType, capacity, maximum lift height and minimum practical operating aisle. For drive-in and drive-through racking installations, physical dimensions of handling equipment may be critical.

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Storage AreaDimensions, obstructions, fl oor type (suspended or ground bearing), fl oor surface (levelness), loading capacity, fi xing facilities, access and egress and goods fl ow within the storage area.

GeneralType of goods to be stored, frequency of movement and fi re protection requirements.

PROVISION OF INFORMATION BY THE SUPPLIERThe user should be provided with information regarding the technical limitations of the use of the racking in either load carrying capacity or re-arrangement of the racking. The supplier should also provide a plaque measuring not less than 125mm deep by 250mm wide on which the maximum permissible unit loads, for that confi guration of racking, should be displayed. This should be fi xed in a prominent position in the warehouse. Plaques or identifying systems should be changed if the arrangement of beams or frames is modifi ed.

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IS IT STRONG ENOUGH?In any rack installation, there are two kinds of strength you need to consider.

The fi rst is the strength of the raw materials used to make the rack. Being told that ‘it’s eighth-inch thick, isn’t it..' just isn’t good enough. British Standards can be applied in this instance, and you should fi nd out if the materials in your rack conform. Here are the SEMA recommendations for material specifi cations:

Materials shall comply with one of the following, whichever is appropriate.

1. Hot Rolled Steel Sections to BS 4360: 1972 Specifi cation for Weldable Structural Steels.

2. Cold Formed Sections fr9m hot rolled strip to BS 1449: Part I: 1983 Specifi cation for Steel Plate Sheet and Strip.

3. For steel strip and cold-reduced strip with guaranteed minimum mechanical properties. no quality control testing by the rack manufacturer is necessary.

4. For steel strip and cold-reduced strip without guaranteed minimum mechanical properties, quality control testing shall be carried out as follows:

The rack manufacturer shall make the following quality control tests on each 15000kg of unguaranteed material:i) one bend test to BS 1639: 1964ii) one tensile test to BS 18: Part 3: 1971

A statistical analysis shall be carried outon 100 such tests and a minimum 0.2% proof stress shall be calculated which shall be defi ned as the mean 0.2% proof stress minus 1.64 standard deviations. This calculated minimum value shall be used in all calculations as the minimum specifi ed yield stress Ys.

5. Steels not listed in the above standards are not excluded provided that they conform to the chemical and mechanical requirements of one of the listed standards, or other published standards which establish their properties and structural suitability. They should also be subjected by either the steel producer or the rack manufacturer to analyses. tests and other controls to the extent and in the manner prescribed above.

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The second (quite different) strength you need to consider is that of the assembled rack installation. You can’t tell the strength of a rack by kicking it. Flexing and bending is normal in most racks - but you can’t judge the safe limits by eye. You must fi nd out from your supplier just how restrictive the safe design of your rack will be. Because what’s good for timber pallets may be no good for post pallets. Because, depending on the beam centres, under one set of circumstances a pair of beams could have one ton capacity, whereas under other circumstances the same pair of beams may only have a ¾ ton capacity. If those warnings make you wish you’d never thought of racking in the fi rst place, don’t worry. If you and your supplier follow the SEMA recommendations, you’ll end up with a very safe rack that does just what you want

SAFE RACK LOADING CONDITIONS AND STRUCTURAL CONFIGURATIONS OF BEAMS AND FRAMESBeamsBeams are designed on the basis of the load being a uniformly distributed load (UDL) over the whole length of the beams. Manufacturers usually state the safe UDL which can be supported by a pair of beams. For timber pallets supported

directly by a pair of beams the UDL condition is usually met. For post pallets, pallets with skids etc, the beam is subjected to a series of concentrated point loads. These conditions of loading can result in higher stresses and/or defl ections and the manufacturer’s advice should be sought on the beam size to be used. Beam defl ections should not exceed a two hundredths (1/200) of the span, e.g.13.25mm on a clear span between uprights of 2650mm. With some types of handling equipment this defl ection limit may be too high. Physical alterations to beams, such as welding on additional bearers or cleats etc., should not be done without the advice of the manufacturer. Also, changes of use from timber pallets to post pallets should not take place without the advice of the manufacturer.FramesFrames consisting of pairs of uprights braced together are designed on the basis of fairly complex rules which govern both the strength and stability of the installation as a whole.Generally, manufacturers state a minimum frame load capacity based on a multi-bay, multi-beam level situation. This is an upper safe limit which should not be exceeded under any circumstances, but the load which a frame can support under a given set of circumstances is governed by three main factors:(i) The spacing of the beams. The further

apart the beams are spaced vertically the lower is the upright load carrying capacity.

(ii) The beam size and number of beam levels in a bay.

(iii) The number of bays in the rack length. Factors (i) and (ii) govern the overall stability of a rack. There are special design rules governing frame loads for single bay and/or single beam level racks (e.g. raised storage areas). Adjustment or removal of beams may change the strength and stability of a rack and should not be done without checking with the manufacturer for advice. Also, physical alterations to uprights or bracingshould not be made without reference to the manufacturer.

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ELBOW ROOM!Warehouse and storage space costs a lot of money, especially when you’ve fi nished heating it, lighting it, insuring it and mending the roof where the rain comes in.So an effi cient storage system makes use of every available cubic foot of space, and it’s planned to save time, energy and cost. A balance must be struck between the type and number of pallet-loads to be stored, and the nature of the rack needed to store them. Another balance must be struck between the amount of space given to actual stored goods, and the amount of maneuvering space needed for different kinds of truck.Complicated? Certainly. But the SEMA Code of Practice helps simplify the business a great deal:

OPERATING CLEARANCES

1. Palletised Goods Relative to Racking The location of pallets within racking installations depends on the type of pallet under consideration. Timber pallets come in two basic styles (for the purposes of rack planning): 2-way and 4-way entry. Details of pallet location features for these two types on end elevation are shown on page 15. 2-way entry single sided, and wing type pallets are not normally suitable for use with drive-in racking installations.

Stillages and other caged pallets usually require the provision of additional accessories to ensure safe location within the racking. It is usual for such pallets to be stored within the depth of the frames. Location of pallets when viewed on the front elevation of the rack is shown on page 16. For this consideration, all types of pallets are applicable. Horizontal clearances refer to either the pallet or goods where these overhang the pallet.

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Vertical clearances should be increased as the height of the rack increases, to facilitate easier location of the pallet at higher levels.This recommendation can, however, be overruled when an order-picker type of truck is to be used (when the operator is elevated to picking levels), or with a truck with automatic height selection.

2. Aisle and Gangway Relative to TruckThe forklift truck is the major factor which infl uences the minimum operating aisle.In general, there are two types of truck, which should be considered separately:1. Those requiring 90” turns within aisles,

to load and off load.2. Those which remain parallel to the

aisle and having forks operating at 90” to the direction of travel.

Ignoring pedestrian operated trucks of all other trucks in group 1. above, counter balance trucks require the widest aisles, with reach trucks requiring the narrowest.With all types in this group, the aisle width will also be infl uenced by the size of the pallet being handled. Similarly there are two types of truck covered in group 2. Both types usually operate in aisles only a little wider than the trucks themselves. Because of this feature an independent means of guiding is normally required.In all cases, the truck manufacturers’recommendations should be followed in determining aisle dimensions. Gangway clearances are usually less of a problem with the exception, perhaps, of certaintrucks included within group 2. For instance, a narrow aisle truck which can only pick from one face of the aisle would require to leave

the aisle and turn through 180” to return and pick from the opposite face of the aisle. Thus, the gangway would need to be wide enough to allow for this.Here again reference should be made to manufacturers’ minimum recommendations.

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LEANING TOWERSIt’s true to say that you’ll never see a rack installation looking like the Leaning Tower of Pisa. Racks are either vertical, or they’re fl at on the ground underneath a lot of squashed goods.

It’s cheaper to have an upright rack - and there are a number of things you and your supplier can do to get one. For instance, depending on the height of the rack, it may be fi xed to the fl oor, or built back-to-back against another rack. Or, perhaps, braced to the ceiling. Certainly, it’s not enough to stand a rack in place and hope. Even the best truck drivers bump a beam occasionally, and you’d need a micrometer to position each pallet with its Centre of Mass plumb over the rack’s Centre of Stability. A small investment during assembly of a rack can save a lot of grief later. For a stable rack, SEMA make some basic requirements very clear.

Stability

The main factors effecting the stability of racking installations are the height-to-depth ratio and the requirement for racks to be fi xed to the fl oor. Free standing racks (i.e. not fi xed to the fl oor) are not normally to be recommended where fork lift trucks are in use.The height of a rack for the purposes of assessing height-to-depth ratios shall be the height of the top of the topmost loaded beam. The depth of rack shall be the overall depth of the rack frame. Where racks are joined together back-to-back to form double sided racks. the depth of the rack shall be the overall depth of the two frames and the space between, provided the frames are joined together with run spacers which are not more than 2.5 metres vertically apart.

Minimum requirements for fi xing to the fl oor should be as follows: 1. Where height/depth ratio does not

exceed 6:1 and racks are subjected to gravity loads only, plus incidental horizontal forces from loading and offl oading of beams, perimeter uprights only need to be fi xed to the fl oor.

2. Where height/depth ratio does exceed 6:1 but does not exceed 10:1 and where racks are subjected to gravity loads only, plus incidental horizontal forces from loading and off-loading of beams, all uprights must be fi xed to the fl oor.

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The fi xings referred to should be applied through the base plate of the upright and be capable of safely resisting the anticipated horizontal shear and vertical tensile forces. Where single sided racks exceed a height to depth ratio of 10:1 but do not exceed 20:1, each frame should be restrained by connections to other substantial structures capable of providing the support necessary. This provision will be met if the single sided rack frame is connected at the top to the top of a double sided rack frame. For more specifi c details or for information on applications where racks are subjected to specifi c horizontal forces such as cranes or trucks which have mast-steady devices the advice of the supplier should be sought.Drive-in and drive-through racks should always be considered as special cases and be designed accordingly by the supplier, particular importance being placed on the fl oor fi xings.

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KEEP IT TRUERacking installations have a unique ability to highlight the minutest inconsistencies in fl oor levels. When it comes to building a rack, you’ll suddenly fi nd that the fl oor you thought was like a billiard table is more like the Himalayas.Is the only answer an expensive, purpose-built marble fl oor? Not necessarily. There aren’t many fl oors that are too lumpy or too skewed for a well-designed rack installation. You’ll just need to make sure your supplier knows exactly where you want the rack sited. If the location really is too bad, he’ll be the fi rst to tell you. If (more likely) it’s the average wonky fl oor, make sure the rack is supported on purpose-designed shims - not folded fag-packets.

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If you’ve yet to tell your supplier that your fl oor resembles the south slope of the Seven Stones Reef - break it to him gently, and show him this extract from the SEMA Code of Practice:

INSTALLATION TOLERANCESFor conventional pallet racking the only tolerance which is critical is the vertical alignment of frames. The normal tolerance allows a maximum out-of-plumb of the racking of+ 1 in 500. Where fl oors are too irregular and give rise to greater degrees of tolerance, shims must be fi tted to correct vertical mis-alignment. Racking installations involving narrow aisle trucks or

order pickers may require a more accurate vertical alignment and close tolerances on longitudinal alignment, beam and locations and beam defl ections. Such requirements should be agreed between the user and the racking and truck manufacturers. Cross aisle fl oor level differences must be small and the truck manufacturers’ recommendations on acceptable fl oor tolerances must be obtained.

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ONE LADYOWNER...It’s doubtful that there’s a real market for ‘used pallet racking: no matter how carefully it’s been driven.But there certainly are advantages in applying some basic principles to the everyday use of your racking. And a proper maintenance programme can pay dividends, too.Maintenance? That’s something reserved for vehicles and machines, you say. Yet it applies to racking, all the same. After all, a well-used installation does a lot of hard work, and can have quite a rough life, even in the course of normal operation. A little bit of care and attention will keep your racking more than good-looking - it’ll help keep it safe.The SEMA Code of Practice spells out just what sort of things are involved in caring for your rack:

The purpose of this section of the Code is to stress the importance of ensuring that the racking installation continues to be both serviceable and safe. The fi rst factor to be conscious of is that, for economy, racking components are produced from light gauge sections and this naturally limits the amount of abuse which can be absorbed without impairing recognised levels of safety.

Certain user industries are particularly prone to abusive damage involving the racking. Such conditions occur where high turnaround and rapid movement of goods form the main activity, particularly where reach and counterbalance trucks are used in overwide aisles. Unit loads and pallets in poor condition can also be a hazard, whilst fl oor cleanliness, operator skill level and condition of the fork lift trucks have a considerable infl uence on the ability to maintain a safe racking installation. The user should be prepared to discuss such factors with the supplier, and where

hazardous situations are identifi ed, these can usually be accommodated.

If all the foregoing has received due consideration, it still remains the responsi bility of the user to maintain the racking in reasonable condition. This is best achieved by driver training and regular inspections of the racking. Inspections should be seen as planned maintenance and carried out on a regular basis.

Warehouse staff should be encouraged to report any damage incurred, however minor, so that its effect on safety can be immediately assessed.

Damage Requiring Replacement

1. That which signifi cantly changes the original cross-sectional profi le of any main-load-bearing member.

2. That which signifi cantly deforms the straightness of any main-load-bearing members.

OPERATION AND MAINTENANCE

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3. That which signifi cantly weakens jointed members through weld breakages or failure of bolts.

4. Damaged or wrong type of pallets.

Hazards Requiring Attention

1. Mis-alignment of racks.2. Incorrect location of beam connectors. 3. Looseness of fi xings.4. Dislodgement of accessories.5. Spillage of goods.6. Greasy, slippery fl oors.7. Fork lift truck defi ciencies.8. Checking that beam connector locks are

present and working.Racking manufacturers will be able to help the user in identifying the defi ciencies referred to in 1 and 2 above and, if required, advise on the frequency of the inspections.

Rack Protection

Where necessary, steps should be taken to protect corner uprights from being struck by fork lift trucks and other vehicles. A fi rst line of defence should be incorporated, sue as column guards or guide rails, which prevent the truck getting too close to the main racking structure. Column protection in other areas likely to incur damage should also be considered.

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WHOA!All of us are prone to going ‘a bit too far’ now and again. But, in doing so, few of us can do as much expensive damage as the poor truck driver, when he shoves a pallet out of the far side of a rack. For that reason, you’ll sometimes come across pallet backstops, which prevent a pallet being pushed through the rack.

Sadly, a backstop won’t always stop a driver pushing a pallet too far. And then, he doesn’t just push the pallet over - he pushes the rack, too. And if one rack goes over, then. . .

Ultimately, the decision on pallet backstops is yours. But heed this section on the SEMA Code of Practice:

There are many arguments for and against the use of pallet backstops attached to the racking structure. They are not generally recommended because of the danger of structural damage. If racking layouts are correctly designed to give adequate (75 mm minimum - see page 16) clearance between back to back pallets or loads or alternatively between a pallet or load and any other obstructions at the back of a rack, then backstops are unnecessary for a trained driver to deposit a pallet correctly and safely, i.e. if the front edge of the pallet is placed in its prescribed position relative to the front supporting beam, then the back face will automatically clear any

obstructions if the load or pallet is of the size and type for which it is designed. If backstops are provided then they should be designed for either:

a) A specifi c load or thrust which can be regulated, i.e. such as can be provided for by slide through forks or tables with a slipping clutch as a means of regulating the thrust.

b) As a replaceable warning device which will give way without structural damage to any important rack members.

PALLET BACKSTOPS

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WHICH PALLET-WHICH RACK?

PALLET LOCATIONS END ELEVATION

2 WAY ENTRY

4 WAY ENTRY

Width of frames, clearance between back-to-back loads, pallet overhang, height clearances. These are all key considerations in planning a rack. Fortunately, the SEMA Code of Practice provides an easy way of calculating the necessary dimensions. They’re tried and tested recommendations, and you should be surprised if your supplier suggests anything different. If he does, and he hasn’t got a convincing reason for doing so - use these tables to work it out for him. . .

x - overall depth of pallety - dimension over outside of beamsz - clearance between back to back

pallets or loads

x y z

750 600 100

900 700 100

1000 750 150

1200 900 150

z

Typical Dimensions:

x y z

750 700 75

900 800 75

1000 900 100

1200 1100 100

Typical Dimensions:

y

x

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PALLET LOCATIONS FRONT ELEVATION

Typical Dimensions:

b

a a a

Beam Height is the dimension from fl oor to top of beama - clearance between adjacent pallets or

loads, and pallet/load and upright.b - clearance between underside of beam

and top of load or pallet where no automatic height selection is used.

BEAMHEIGHT a b

3000 75 75

6000 75 100

9000 100 125

12000 100 150

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CONCLUSIONWithout getting into some very technical areas, and some very detailed material, this is about as far as we can go.

At worst, you’re now armed with a little more knowledge about static racking than most people. At best, you’ll be able to work together with your racking supplier - and your racking itself - to gain the enormous benefi ts that result from a professionally designed and built racking installation.

It should be remembered that choosing the right pallet racking installation, and the right storage and materials handling in general, is very important to any organisation. According to the recent DOE report (“Materials Handling Costs. A new look at manufacture”), storage and materials handling costs British industry around £8 billion per annum. In engineering and related industries, for example, storage and materials handling makes up 12% of conversion costs. £90 million a year could be saved in these industries alone. So, given the equipment is right for the job, storage and materials handling can be an excellent area for investment.

Despite our rather informal presentation, the complete SEMA Codes of Practice are truly valuable working documents and ought to be on every engineer’s shelf. The information contained is the result of many years’ experience, gained by a great many storage equipment manufacturing companies.

If you’d like a copy of the complete Codes, write to:

The Storage Equipment Manufacturers’ Association, The National Metalforming Centre47 Birmingham RoadWest BromwichB70 6PY

Published by Redirack Limited, 1978, amended 1988 and 2007Extracts from Code of Practice for the Design of Static Racking (1980) and the Code of Practice for the Use of Static Racking (1979) by kind permission of the Storage Equipment Manufacturers Association (SEMA)

Redirack Limited, Wharf Road, Kilnhurst, Mexborough, South Yorkshire. S64 5SU.Tel: +44 (0) 1709 584 711 Fax: +44 (0) 1709 589 821 Web: www.redirack.co.uk