Safety In Numbers

Safety In Numbers
A Report on the SEMA Code of Practice for the Design of Static Racking
One of two no-nonsense guides to safe
storage from Redirack
SAFETY IN NUMBERS
Does 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
CONTENTS
Introduction
Say what you want - know what you are getting
Page iii
1
The vital exchange of information between
customer and supplier.
Is it strong enough?
3
Material specifications, safe loadings and
structural configuration.
Elbow room!
5
Recommended operating clearances.
Leaning towers
7
Racking installation tolerances.
Keep it true
9
Racking installation stability.
One lady owner...
11
Racking installation, operation and maintenance.
Whoa!
13
The use of pallet backstops.
Which pallet, which rack?
15
Recommended pallet locations for racks and
pallets of different sizes.
Conclusion
ii
17
INTRODUCTION
What'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 specific 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 specification and use of all kinds of static rack. It’ll help
you choose, and use, your racking installation effectively and
confidently. And the first thing you need for a good relationship
with your racking is - confidence.
iii
SAY WHAT YOU WANTKNOW WHAT YOU'RE GETTING
In 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 fitted.
Today, things are different. There are all kinds of rack style, all
kinds of brands. You get the benefit 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 efficiency, 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:
Pallets
Type, 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 specified.
1
Unit Load
Weight (including weight of pallet), overall
dimensions, and stability of load.
Pallet Handling Equipment
Type, 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.
Storage Area
Dimensions, obstructions, floor type (suspended or ground
bearing), floor surface (levelness), loading capacity, fixing
facilities, access and egress and goods flow within the storage
area.
General
Type of goods to be stored, frequency of movement and fire
protection requirements.
PROVISION OF INFORMATION BY THE SUPPLIER
The 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 configuration of racking, should
be displayed. This should be fixed in a
prominent position in the warehouse.
Plaques or identifying systems should be
changed if the arrangement of
beams or frames is modified.
2
IS IT STRONG ENOUGH?
In any rack installation, there are two kinds of strength you need
to consider.
The first 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 find out if the materials in your rack conform. Here are the
SEMA recommendations for material specifications:
Materials shall comply with one of the
following, whichever is appropriate.
1. Hot Rolled Steel Sections to BS 4360:
1972 Specification for Weldable
Structural Steels.
2. Cold Formed Sections fr9m hot
rolled strip to BS 1449: Part I: 1983
Specification 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: 1964
ii) one tensile test to BS 18: Part 3: 1971
A statistical analysis shall be carried out
on 100 such tests and a minimum 0.2%
proof stress shall be calculated which shall
be defined 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 specified
yield stress Ys.
3
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.
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 find 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 first 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 FRAMES
Beams
Beams 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 deflections and the
manufacturer’s advice should be sought on
the beam size to be used. Beam deflections
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 deflection
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.
Frames
Frames 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 multibay, 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 bracing
should not be made without reference to
the manufacturer.
4
ELBOW ROOM!
Warehouse and storage space costs a lot of money, especially
when you’ve finished heating it, lighting it, insuring it and
mending the roof where the rain comes in.
So an efficient 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.
5
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 Truck
The forklift truck is the major factor which
influences 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,
counterbalance trucks require the widest
aisles, with reach trucks requiring the
narrowest.
With all types in this group, the aisle width
will also be influenced 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 certain
trucks 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.
6
LEANING TOWERS
It’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 flat
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 fixed to the floor,
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-todepth ratio and the requirement for racks
to be fixed to the floor. Free standing
racks (i.e. not fixed to the floor) 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.
7
Minimum requirements for fixing to the
floor 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
offloading of beams, perimeter
uprights only need to be fixed to the
floor.
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 fixed to
the floor.
The fixings 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 specific details or for information on
applications where racks are subjected to
specific 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 floor fixings.
8
KEEP IT TRUE
Racking installations have a unique ability to highlight the
minutest inconsistencies in floor levels. When it comes to building
a rack, you’ll suddenly find that the floor you thought was like a
billiard table is more like the Himalayas.
Is the only answer an expensive, purpose-built marble floor? Not
necessarily. There aren’t many floors 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 first to tell you.
If (more likely) it’s the average wonky floor, make sure the rack is
supported on purpose-designed shims - not folded fag-packets.
9
If you’ve yet to tell your supplier that your floor 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 TOLERANCES
For 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 floors are
too irregular and give rise to greater
degrees of tolerance, shims must be fitted
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 deflections. Such requirements
should be agreed between the user and
the racking and truck manufacturers.
Crossaisle floor level differences must
be small and the truck manufacturers’
recommendations on acceptable floor
tolerances must be obtained.
10
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 goodlooking - 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:
OPERATION AND MAINTENANCE
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 first 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 floor cleanliness, operator skill level
and condition of the fork lift trucks have
a considerable influence on the ability
to maintain a safe racking installation.
The user should be prepared to discuss
such factors with the supplier, and where
11
hazardous situations are identified, these
can usually be accommodated.
If all the foregoing has received
due consideration, it still remains the
responsibility 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 significantly changes the
original cross-sectional profile of any
main-load-bearing member.
2. That which significantly deforms the
straightness of any main-load-bearing
members.
3. That which significantly 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 fixings.
4. Dislodgement of accessories.
5. Spillage of goods.
6. Greasy, slippery floors.
7. Fork lift truck deficiencies.
8. Checking that beam connector locks are
present and working.
Racking manufacturers will be able to help
the user in identifying the deficiencies
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 first
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.
12
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:
PALLET BACKSTOPS
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
13
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 specific 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.
14
WHICH PALLET-WHICH RACK?
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
y
z
PALLET LOCATIONS
END ELEVATION
2 WAY ENTRY
Typical Dimensions:
x
y
z
750
600
100
900
700
100
1000
750
150
1200
900
150
4 WAY ENTRY
Typical Dimensions:
x
y
z
750
700
75
900
800
75
1000
900
100
1200
1100
100
x - overall depth of pallet
y - dimension over outside of beams
z - clearance between back to back
pallets or loads
15
PALLET LOCATIONS
FRONT ELEVATION
Typical Dimensions:
BEAM
HEIGHT
a
3000
75
75
6000
75
100
9000
100
125
12000
100
150
b
Beam Height is the dimension from floor to
top of beam
a - 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.
b
a
a
a
16
CONCLUSION
Without 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 benefits 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 Centre
47 Birmingham Road
West Bromwich
B70 6PY
17
Published by Redirack Limited, 1978, amended 1988 and 2007
Extracts 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