15 Industrial storage buildings Jolyon Drury, updated with advice from Stephen George & partners
KEY POINTS: Modern warehouses need the height to use mechanical aids at maximum efficiency Scales have increased massively; a ‘big shed’ now is ten times the size of the largest building only 20 years ago
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Contents 1 Introduction 2 Identification of warehouse and storage types 3 Preliminary decisions 4 Height, area and type of handling system 5 Storage method 6 Disposition of the racking 7 Relationship of storage method, mechanical handling equipment and building height 8 Outline specification 9 Security 10 Handling equipment 11 Fire precautions 12 Bibliography
CI/SFB 284 UDC 725.35
3 PRELIMINARY DECISIONS The initial decision about what type of building is required will involve a choice between these three types, dependent on the client organisation’s needs. Such a study is generally undertaken in cooperation with a specialist consultant. Other factors to be considered at the pre-design stage are: 1 The orientation of the loading bays and the heavy vehicle marshalling areas. Future expansion must be taken into account. 2 The orientation of the goods sorting and load accumulation areas which must be related to the disposition of the storage area, i.e. block stacks or racking and loading bays. 3 Will the required bulk of the building be acceptable in terms of planning consent? 4 Are the existing roads suitable to meet increased demand? 5 Is there public transport for operatives? 6 Are there night operating restrictions which will entail special features to muffle night noise? Can this be catered for by any design measures/configurations?
1 INTRODUCTION Few industrial storage buildings are designed to make a profit (steel stockholders and cash and carry stores are exceptions); the majority perform the function of a valve or pipeline, limiting the supply of a product to suit demand, to stabilise prices and allow steady and economic manufacture within fluctuating market conditions. Industrial storage is therefore a service at a cost that must be minimised. The payback period most frequently chosen for such a building is 25 years. During that time, it is likely that the storage method will need to change at least three times, and that the type of goods handled will change even more frequently. Flexibility for expansion and manner of use are therefore important design considerations. Large distribution buildings are now even larger than they have ever been. Twenty-five years ago, a large industrial ‘shed’ contained approximately 100 000 ft2 of space. Industrial storage buildings are now being constructed 10 times that size. At the time of writing, industrial storage buildings cost approximately £32 per square foot to build (£336 per square metre). This price regime and changes to building regulations (Part L in particular) may well make the purchase and reinvention (through recladding, etc.) of an existing building unviable, i.e. it would be cost effective to construct a new building.
2 IDENTIFICATION OF WAREHOUSE AND STORAGE TYPES The three main types are: between manufacture and the market, 15.1. • Transit similar to a transit unit, but accepts a wide variety • Distribution: of goods from a number of manufacturers, sorts them into orders
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and distributes them to a number of outlets, 15.2. A components warehouse for a factory performs a similar function. Repository: a warehouse used for stockholding, either as a service (e.g. a furniture repository) or within a company (e.g. a cold store), 15.3.
15.1 Relationships in warehouse for transit between manufacturer and market 15-1
15-2
Industrial storage buildings Table I Typical internal clear heights for storage areas Minimum clear internal height (m)
Type of storage
5–5.5
Minimum-cost low-rise block stacking warehouse. Suitable for light industrial factory use Minimum for any industrial storage building combining racking and block stacking When narrow-aisle trucks are used Fully automatic, computer-controlled warehouses and stacker cranes are to be used
7.5 9þ 15–30
Clearance for structural memvers, sprinklers, lighting must be added to obtain overall height of buildings
Table II Classification of materials for handling and storage as unit loads
15.2 Relationships in distribution warehouse
Description
Examples
Storage method
Materials not strong enough to withstand crushing – not suitable as integral unit load
Automobile components, On pallet in rack made-up textiles, electrical appliance components, manufacturing chemists’ sundries, light engineering products, glassware
Materials strong enough to Casks and drums, sawn withstand crushing – suitable for and machined timber, sheet materials unit loads
On pallet, or selfpalletised and block stowed
Irregular-shaped materials, strong in themselves suitably packed into unit loads
Goods in cases, creates or cartons
On post pallets and stacked, on pallets in rack or self palletised
Bagged materials which form a flat surface under load
Grain, powder and similar On pallet and block stowed
Bagged materials which do not Forgings, moulded or form a flat surface under load or machined parts, nuts and bolts will not take pressure
On pallet in rack
Large irregular loose materials
Moulded plastics; sheet metal pressings
On post pallets and stacked
Small irregular loose materials
Machined and moulded parts, pressings, forgings
In cage pallets and stacked
Materials hot from production process
Castings and forgings
On post pallets and stacked
Materials too long to be handled Steel sections, tubes, other than by side loader or timber boom
Horizontally in tube or bar racks
Materials strong enough to withstand crushing but subject to damage
Partly machined automotive parts, painted finished materials, books
Steel box pallets with special partitions
Perishable goods
Frozen meat, vegetables, drink
Cartons, soft packs pallets, box pallets, etc.
15.3 Relationships in a stockholding warehouse. The bulk stock area is dominant 4 HEIGHT, AREA AND TYPE OF HANDLING SYSTEM The most economical way of gaining volume for storage is to use height – Table I; this affects the choice of the handling system to be employed. Typical structures are shown in 15.4. Consider also: type of unit load to be handled and the physical character• The istic of the goods – crushability, durability, the type of unit loads
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that will be assembled after sorting (Table II). The speed of turnover. This will determine what storage method is the most efficient. The position of the construction and movement joints within a concrete floor. Generally, columns should be hidden within the racking, as should the floor joints. Access widths should suit the
selected loading mechanisms and racking should not obscure exits. In a portal frame construction, columns are typically set at 32.2 m centres. A grid of 8.2 m can accommodate two dock levellers.
5 STORAGE METHOD Storage methods (see Tables III–V) include: 1 Very fast throughput involving a limited number of products: block stacking, 15.5, rather than racking. First in, first out, or first in, last out configuration, depending on the shelf life of the goods. 2 A wider variety of goods, but still with fast turnover: drive-in racking, 15.6, or ‘live’ (roll-through) storage, 15.7. Pallets are placed into racking up to four positions deep, with the pallets’
a Generic service yard section and elevation 15.4 Examples of typical structures (continued over)
b Modern ‘big box’ warehousing – 520 × 170 m industrial storage unit for ProLogis by Stephen George & Partners. The unit contains 78 loading bays on its northern and southern sides, with 5000 m2 of office space
15.4 Continued
Industrial storage buildings
15-5
Table III Mechanical handling
Cubic space utilisation (%) Effective use of installation capacity (%) Accessibility of unit loads (%) Order picking (%) Speed of throughput Load crushing Stability of load Ease of relocation Speed of installation Rotation of stock
Block stacking
Post pallets
Drive-in racking
Beam pallet racking
Gravity live storage
Powered mobile racking
100 75 10 Poor Fastest Bad Poor Not applicable Not applicable Poor
90 75 10 30 Good Nil Fair Not applicable Not applicable Poor
65 75 30 30 Poor Nil Good Fair Good Poor
35–50 100 100 100 Good Nil Good Good Fastest Good
80 70 30 30 Good Some Fair Difficult Fair Excellent
80 100 100 100 Quite good Nil Good Difficult Slowest Good
Table IV Manual handling
Cubic space utilisation (%) Effective use in installation capacity (%) Accessibility of goods Ease of relocation Load range (kN/m2) Speed of picking Speed of installation Rotation of stock
Long-span Shelving
Tiered shelving
Raised storage area
Cantilever shelving
Lightweight live storage
Fir tree racking
45 95
45 95
80 50
50 100
65 70
25 70
Good Good 2–9.5 Good Very good Very good
Good Fair 2–9.5 Fair Good Good
Poor Difficult 2.8–11 Poor Fair Poor
Good Fair 2–4.7 Good Fair Very good
Excellent Very difficult Up to 0.2 kN/m run of track Very good Slowest Excellent
Good Best 2.6–4.4 kN/arm Good Fastest Very good
Table V Load mounting Load mounting
Type of load Heavy unstable load
Special cradle with/without pallet Standard pallet Flat board pallet þ decking supports Direct mounting on timber panels Drum supports Post pallets cage/bin Coil supports Skips/skeds With skids
Flat cards/sheets
Sacked/ bagged loads
Small unit loads
Drums Reels Barrels
Coils
Casks
Bales
Textile Raw materials
edges resting on runners attached to the rack’s uprights. First in, last out. Live racking involves inclined storage lanes. For heavy pallets and shock-sensitive goods, braking and separating equipment can be incorporated.
3 Pallet racking, 15.8 and 15.9. For a wide variety of goods, the speed of throughput decreases. Pallet racking is the solution with a large variety of products, brands or pack sizes. Each pallet is normally allotted a unique position in the racking.
15-6
Industrial storage buildings
15.5 Method of block stacking for stock rotation. Where cartons are being stacked on pallets, a height of three pallets is the normal maximum
15.7 Roll-through racking
15.8 Pallet racking
15.6 Drive-in racking for fork-lift. A maximum depth of six pallets, with fluorescent lighting in the racking structure. Four-pallet depth is preferable
6 DISPOSITION OF THE RACKING There are two common alternatives: The rack is oriented at 90 to the order assembly areas, with the • fast turnover stock in the bays nearest to it or complete racking face is oriented along one side of the • One order assembly area and reserved for very fast-moving stock.
7 RELATIONSHIP OF STORAGE METHOD, MECHANICAL HANDLING EQUIPMENT AND BUILDING HEIGHT The effect of handling equipment on warehouse section is shown in 15.10–15.13. These factors depend on site conditions: 1 For very constricted sites where a large volume of goods needs to be held high-bay, automated warehouses can prove the most economical solution. Such warehouses have been built up to 30 m high, the racking being used as the roof and wall cladding supporting structure. Handling machines run on fixed tracks, 15.13 and 15.14. 2 For medium- and large-scale installations where full automation is not justified, storage areas up to 12 m high allow free-standing racking (bolted to the floor) with aisle widths marginally wider
than the largest pallet, 15.15. ‘Narrow-aisle trucks’ used in this type of plant are free path machines based on fork-lift technology, 15.16. 3 Where the cost of high-bay stacking and high-lift machinery is not justified, fork-lifts and reach trucks are used, 15.17. Reach trucks are suitable for conventional pallet weights (1 – 1.5 tonnes) over flat floors. They can lift to 9 m and operate in aisles of about 2.8 m. A fork-lift truck can carry heavier loads but requires aisles of 3.2–4 m width, 15.18. Heavier trucks are required to lift greater heights and tend to require a greater aisle width. 4 Mobile racking where pallet racking is mounted on mobile bases and rests face to face may be suitable where storage is to be installed in an existing structure or where the site is limited in area and the turnover of products comparatively low. It is costly to install and the floor slab has to accept double the normal distributed load.
8 OUTLINE SPECIFICATION 8.01 Storage area Pitched roofs, though strong on first cost, waste storage volume and run the risk of being damaged by handling equipment: Three factors favour the flat or low pitch roof type: column pitch can be wide, 15.17 and 15.18. • The They more adaptable to a change of use or changes dictated • by newareprocesses. are more suitable for the installation of services such as • They cooled air.
Industrial storage buildings
15.9 Construction of pallet racking
15.10 Section through small warehouse for fork-lift operation
15.11 Section through large warehouse for fork-lift or reach truck operation
15.12 Section through warehouse for narrow aisle truck operation. Floor tolerance 3 mm in 3 m run
15-7
15-8
Industrial storage buildings
15.13 Section through warehouse for stacker crane handling (left) and steel stockholding with side loader (right)
a Order picker
b Stacker crane
15.14 Dimensions of:
15.16 Relationship to structure of narrow-aisle truck aisles
15.17 Relationship to structure of reach truck aisles
15.15 Free path stacker/order picker with elevating cab, fixed mast and rotating fork. The four-post mast gives extra stability. Out of the aisle can also be used as a fork-lift truck. The free lift on the fork carriage also allows differential movement between the pallet and the picking platform. Minimum building height 2.2 m above top lifting level
Industrial storage buildings
15-9
15.18 Relationship to structure of fork-lift truck aisles. Note: 16100 mm span is common to fork-lift and reach truck requirements
8.02 Order picking and assembly Space demanded will vary with the type of business involved and the method of order assembly, in turn generated by the method of despatch and transport. For instance, a brewery warehouse may despatch whole pallet loads, 15.7, but a pharmaceutical warehouse may handle and assemble a very large number of small items. Therefore, it may require a large area for order assembly, 15.19–15.21.
8.03 Loading bay and load accumulation area The loading bay is the critical link between the storage and distribution system, 15.22. It usually combines inward and despatch movements. It must provide sufficient space for: goods to be checked off; • incoming unit load devices to be removed; and • empty • despatch loads to be accumulated
15.19 Second level order picking, typically used for food distribution and supermarket replenishment. The operative fills a roll pallet or cage from the pallet on the floor and the shelf above it
15.20 Reach truck aisle for second-level order picking
15.21 Stacker aisles for order picking: a Pulling from lower levels – replenished by stacker truck (15.25) b Alternating pick-up and replenishment aisles c Multi-level alternative aisles, replenished by narrow aisle truck
15-10
Industrial storage buildings
a Where available
b Where depth is limited 15.22 Combined arrival/despatch loading bays A full vehicle length (12 m) should be allowed as the zone behind the loading dock. 8.04 Office and amenity areas Large warehouses can employ more than 100 order-picking staff (mainly female) each shift. Extensive washing and changing facilities will be required. Also space for operatives to rest and smoke outside the storage area. See BS 6465-1:2006 (which supercedes BS 6465-1:1994) for full details of sanitary installations. Clients and developers generally prefer the office element of a distribution building to face the main entrance to the site, leaving loading/unloading at the rear. If this means, offices facing south (taking advantage of sunshine) it may mean fixing brise soleil to the fac¸ade. 8.05 Equipment maintenance areas Most mechanical handling equipment for internal use is batterypowered electric. The batteries need charging at night or after shifts of about 12 h. Requirements for maintenance areas are:
water supply; • a1 distilled tonne hoisting tackle for removing batteries; • fume extraction; and • acid-resistant floor. • Major services and repairs tend to be done off site.
9 SECURITY Warehouses are, by definition, prone to theft. Most thefts are carried out during working hours. This can be minimised by ensuring that: is no direct access from loading bays to the warehouse, • There especially through the order-picking zone, without supervision. from office accommodation to the warehouse should be • Access visible from the office area. changing rooms, showers (necessary in cold stores) and • The WCs should not have direct access from the warehouse, and
Industrial storage buildings 15-11
equally, should not be accessible from outside. Visiting drivers should have segregated WC facilities. If small, valuable goods are involved, a search room may be required. Operatives’ parking should be well separated from heavy vehicles’ parking and away from the loading area.
10 HANDLING EQUIPMENT Goods handling systems are now highly specialised and only their general layout falls into the architectural remit. Computerised and robotic handling systems, controlled from a central database, can represent half the build cost. Some typical handling equipment is shown in 15.23–15.27.
11 FIRE PRECAUTIONS It is worth remembering that the goods stored within a building may be worth more than the building itself. Therefore, it may be worth considering the protection of the goods rather than the building – indeed, this may be a crucial part of the operator’s business plan. Compartmentalisation and the judicious arrangement of sprinklers may need to be considered. Table 12 of Approved Document B (Fire Safety), which came into effect April 2007, provides details about compartment sizes. If a building is fitted with sprinklers throughout, there is no need to compartmentalise; if a decision has been taken to dispense with sprinklers, then buildings must be compartmentalised. Each compartment must be no larger than 20 000 cubic metres and no higher than 18 m. In high bay buildings (up to 35 m), automatic sprinkler systems must be installed. Note: the more sophisticated and more sequential the sprinkler system, the less potential water damage.
15.23 Manual pallet truck. For use inside the warehouse building up orders, loading vehicles on raised docks or with tail-lifts, general pallet handling. Increasingly used in retail premises for handling bulk goods. Capacity up to 1500 kg generally and for short-distance travel (operatives soon tire when pushing heavy loads any distance). Forklengths available 0.8–1.6 m, widths from 460 to 680 mm. Heights: lowered 83 mm, raised 203 mm. Pallet width should be 150 mm over fork (typical length is 1.06 m for a 1.2 m pallet). Where gangways are narrow and stability is important, a heavy truck should be used with maximum width between forks. This device will turn in its own length but needs additional clearance for overhangs. Normally, it requires level floors to operate satisfactorily, but large wheels in nylon or with solid rubber tyres plus articulating axles are available for use in older buildings; although instability may occur. Steel wheels are available but are less popular. Where loading ramps are used, pallet trucks with brakes should be used. Adaptors are available for use as a stillage truck
15.24 Powered pallet truck. For internal transfer, loading vehicles on docks, order build-up, transporting roll pallets to load assembly position. For use with all types of pallet and cages. Capacity 1800–3000 kg, forklengths 0.75–1.8 m, speeds up to 3.6 km/h running light, widths up to 850 mm, usually 760 mm. Long forks available to carry three roll pallets at once. Special forks for drums and paper rolls. Will turn in its own length but needs additional clearance for overhangs. Some have 200 turn on the single power steering wheel. Aisle width depends on forklength: a (90 stacking aisle) ¼ 1840 mm (truck þ 1 m pallet) b (intersecting aisle) ¼ 1570 mm Turning circle 1.78 m radius with 960 mm long forks. This device requires level floors and a three-phase charging point. It can manage ramps up to 10%. Some larger-capacity units can also be ridden on, and can tow non-powered pallet trucks if long distances are involved
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15.25 Power travel and lift pedestrian-controlled stacker truck. When travelling the pallet rests on the stacker frame which has travel wheels. Power lifting is independent of the travel frame, and is directly into the rack. Only suitable for short travel distances. Lifting range up to 3.6 m. Can be supplied with attachments. Capacity up to 1500 kg at 600 mm centres, straddle width 0.86–1.3 m, travel speed up to 4.8 km/h laden. Will turn with full load on 2.1 m aisle
15-12
Industrial storage buildings
a Two-way entry pallet
b Four-way entry pallet
c Post pallet
15.26 Types of pallet
15.27 Plan of typical palletising machine. Top right is buffer track required for slower shrink wrapper 12 BIBLIOGRAPHY Jolyon Drury and Peter Falconer, Buildings for Industrial Storage and Distribution, Elsevier 2003 (2nd edition) Ju¨rgen Adam, Katharina Hausmann, Frank Ju¨ttner, Industrial Buildings: A Design Manual. Birkha¨user, 2004 Approved Document B – Volume 2 – Buildings other than dwellinghouses (2006 Edition). Obtainable as a downloadable PDF from www.planningportal.gov.uk
Approved Document L2A: Conservation of fuel and power (New buildings other than dwellings) (2006 edition). Obtainable as a downloadable PDF from www.planningportal.gov.uk