Ground Floor Design
Third Edition Concrete industrial ground floors A guide to design and construction Report of a Concrete Society Working Party Concrete Society Report TR34- Concrete industrial ground floors Third Edition 2003 IMPORTANT Errata Notification Would you please amend your copy of TR34 to correct the following:On page 50 – symbols and page 63 – Clause 9. 11. 3, change the word “percentage” to “ratio” in the definition of px and py. Concrete industrial ground floors A guide to design and construction Third Edition
Concrete industrial ground floors – A guide to design and construction Concrete Society Technical Report No. 34 Third Edition ISBN 1 904482 01 5 © The Concrete Society 1988, 1994, 2003 Published by The Concrete Society, 2003 Further copies and information about membership of The Concrete Society may be obtained from: The Concrete Society Century House, Telford Avenue Crowthorne, Berkshire RG45 6YS, UK Tel: +44 (0)1344 466007, Fax: +44(0)1344 466008 E-mail: [email protected] org. uk, www. concrete. org. uk Design and layout by Jon Webb Index compiled by Linda Sutherland Printed by Holbrooks Printers Ltd. Portsmouth, Hampshire All rights reserved. Except as permitted under current legislation no part of this work may be photocopied, stored in a retrieval system, published, performed in public, adapted, broadcast, transmitted, recorded or reproduced in any form or by any means, without the prior permission of the copyright owner. Enquiries should be addressed to The Concrete Society. The recommendations contained herein are intended only as a general guide and, before being used in connection with any report or specification, they should be reviewed with regard to the full circumstances of such use.
Ground Floor Design Essay Example
In a conventional static racking system, the full bay loading is transmitted to the slab through the baseplates at the foot of the two uprights in each frame, except for the frames at each end of the aisle where only half the full bay loading occurs. Baseplates for racking fed by pallet handling trucks are of limited plan dimensions so they do not intrude into the floor area over which the truck wheels pass or the pallets are deposited. The effective contact area with the floor is therefore limited, and most racking is provided with baseplates for fixing bolts, which are not intended to distribute load. For design purposes, the loaded area is assumed to be 100 x 100 mm, approximating to the size of the uprights of the racking.
If it is necessary to spread leg loads over a larger area the strength and stiffness of the baseplates should be checked. Typical point loads for individual racking baseplates range from 35 to 100 kN. In very high bay warehouses where highlift rail-mounted cranes are used, as shown in Figure 3. 16, point loads can approach 200 kN. Rows of racking are usually placed back-to-back, with a clearance of 250-350 mm between the inner uprights. Working aisles between the racks allow loading by fork-lift trucks or stacker cranes from either side. Loads from backto-back racking, as shown in Figure 3. 4, are usually the governing case for slab design. 13
Concrete industrial ground floors Output Input Figure 3. 6: Live storage systems. Figure 3. 4: Typical ‘back-to-back’ configuration of storage racking. Pick and deposit (P&D) stations are marshalling areas at the end of narrow aisles or very narrow aisle racking bays. They can be either marked out on the floor or form part of the racking structure; in the latter case the uprights supporting the P&D stations may carry increased loads. Mobile pallet racking (see Figure 3. 5) consists of sets of racks on mobile chassis running on floor-mounted rails. The racks are individually driven by electric motors so each aisle can be opened up as required for access to individual pallets.
Apart from the one access aisle, the whole stack is a block of high-density storage in which over 80% of the floor space can be used. an automatic latch allows the pallets to move by gravity towards the outlet end of the racking. This type of storage enables stock to be rotated on the first-in, first-out principle. The self-weight of the racking and rollers and the nature of the system may mean that the applied point loads are unequally distributed among the rack uprights. Braking will cause horizontal loads; these will depend on the particular equipment but will be much smaller than the vertical loads and are not normally considered in design.
However, the racking manufacturer should be consulted. With drive-in (and through) racking (Figure 3. 7) there is no division by aisles. The block of racking can be accessed for load storage and retrieval. Cantilever brackets attached to the racking frames support pallets. Compared to very narrow aisle (VNA) racking, 50% more of the available space can be used and the height is limited by the strength of the racking. The self-weight and configuration of the racking may mean that the applied point loads are unequally distributed among the rack uprights. Figure 3. 5: Mobile pallet racking. Laden rack stability usually limits the lift height to 11 m. The racking will apply point loads to the rails.
Depending on the stiffness and fixing arrangements of the rails, the load on the floor may be considered as a point load or a line load. If considered as a line load, approximately 150 kN/m can be expected. Acceleration and braking will cause horizontal loads; these will depend on the particular equipment but will be much smaller than the vertical loads and are not normally considered in design. However, the racking manufacturer should be consulted. Live storage systems (see Figure 3. 6), like mobile pallet racking, provide a high-density block of loads but without load selectivity. Incoming palletised loads are placed by fork-lift truck on the ‘high’ end of a downward sloping set of roller conveyors.
As loads are removed from the ‘low’ end, Figure 3. 7: Drive-in racking. Push-back racking systems (Figure 3. 8) provide a high density block of loads but with limited load selectivity. Incoming palletised loads are placed by fork-lift truck on the push-back carrier; subsequent loads are positioned on the next available carrier and used to push the previous load 14 Loadings Figure 3. 8: Push-back racking. back up a slope. Typically installations are less than four pallets in depth and are not usually higher than 6 m. Horizontal loads due to braking of the pallets are normally less than 5 kN. This type of storage works on the first-in, last-out principle.
The self-weight and configuration of the racking and carriers may mean that the applied point loads are unequally distributed among the rack uprights. Cantilever racks (Figure 3. 9) can store long loads, so they are sometimes referred to as ‘bar racks’. The racks consist of a row of uprights with arms cantilevering out on either or both sides and are often used in conjunction with sideloading fork-lift trucks. They are not usually higher than 8 m, but as they often store heavy products can be quite heavily loaded. Figure 3. 10: Mezzanine (raised platform). Figure 3. 11: Mezzanine used for access to storage, with racking below. Figure 3. 9: Cantilever racking. Mezzanines (raised platforms) Mezzanines (see Figures 3. 10 and 11) are commonly used for production, assembly and storage.
Leg loads can be in excess of 200 kN and baseplates should be designed to provide the required load-spreading capability. Additional slab reinforcement or discrete foundations may be required. Clad rack structures In clad rack structures (Figure 3. 12) the racking itself provides the structural framework for the building and Figure 3. 12: Clad rack system. supports the walls and roof. Clad rack warehouses can cover any area and be up to 45 m high. It is not possible to give typical point loads from these structures onto the floor slab as each application will depend upon the size of building, the goods to be stored as well as wind and snow loads.
Clad rack design and construction is a specialist field and expert advice should be sought. 15 Concrete industrial ground floors With this form of construction, the floor slab acts as a raft foundation to the entire structure. As the slab is constructed in the open air with no protection from the elements, surface defects are more likely. 3. 2 MATERIALS HANDLING EQUIPMENT 3. 2. 1 Introduction Materials handling equipment (MHE) is used for moving pallets and containers and for bulk products such as paper reels and timber. It is also used for order picking where individual items are collected from storage and packed for dispatch to customers or for use in nearby production facilities. All MHE generates point loads.
In order to design floors to support these loads, the maximum wheel loadings and contact areas of wheels or tyres must be known. Equipment configurations and weights vary significantly and so manufacturers should be consulted. MHE loads are dynamic, and this is a significant design consideration, see Section 9. 6. 3. 2. 2 MHE operating at floor level Pallet transporters and trailers are used at floor level for moving single or multiple pallets and for order picking. They can be controlled by pedestrians alongside or operators riding on them (Figure 3. 13). Truck capacities do not usually exceed 3 tonnes, but can be higher in specialist applications. The trucks have small load-carrying wheels (normally polyurethane) and so local load concentrations can be high.
Floor surfaces on which this equipment operates should be flat and have a good but not onerous standard of levelness. See Chapter 4 for explanations of the classification and specification of floor flatness and levelness. Joints in floors are prone to damage by the small wheels on this type of equipment. Sawn restrained-movement joints give good service provided the openings are limited in size and the joints are properly maintained, see Chapters 8 and 13. Free-movement joints are generally wider and consideration should be given to steel armouring of the joint arrises, see Section 8. 9. Where this type of equipment is used intensively, such as in food distribution, consideration may be given to ‘jointless’ slab construction, see Sections 2. 2. 2 and 8. 9.
It should, however, be noted that free-movement joints are provided at intervals of about 50 m in such floors and that these joints will be relatively wide (up to 20 mm). In such operations, the user will need to decide between more narrow joints at about 6 m intervals and fewer, wider joints. However, the armoured jointing systems that are often used in jointless construction could be provided with filler plates installed later after shrinkage of the concrete slab has taken place, allowing narrow joints to be incorporated. The operation of some types of mobile equipment can be aggressive on floor surfaces and cause abrasion and other Figure 3. 13: The small wheels on pallet trucks (such as that in the foreground) can be damaging to joints in floors. surface damage.
The main cause of damage is likely to be the scraping of pallets, particularly when they are in poor condition, across the surface when they are being picked up or deposited. This is discussed in Chapter 5. 3. 2. 3 MHE operating in free-movement areas and wide aisles Counterbalance trucks Counterbalance trucks are fork-lift trucks fitted with telescopic masts with the load carried ahead of the front (load) wheels (Figure 3. 14). They are used within buildings and externally for block stacking, in storage racking up to about 7 m high and for general materials movement. Because they approach stacking and racking face on, aisle widths for counterbalance trucks are at least 4 m. Load-carrying capacity of the trucks can be 10 tonnes or more, but in industrial buildings loads do not usually exceed 3 tonnes.
Lift heights are limited by stability and do not normally exceed 7 m. Truck tyres are either solid rubber or pneumatic. All tyres can be aggressive on dusty or wet floor surfaces. It is important to keep floors clean to avoid such conditions. Counterbalance trucks can tolerate relatively uneven surfaces and joints. See Chapter 4 for explanations of the classification and specification of floor flatness and levelness. Reach trucks Reach trucks have moving telescopic masts and transport the load in a retracted position within the truck wheelbase (Figure 1. 2). They can operate in narrow aisles up to 3 m wide and have a typical load capacity of 2 tonnes. Lift heights do not normally exceed 10-12 m.
They can be used for order picking and can also operate in free-movement areas. 16 Loadings Figure 3. 14: Counterbalance truck. Truck tyres are generally made of hard neoprene rubber with wheel diameters of 200-350 mm. The wheels are not unusually aggressive to surfaces. Floor surfaces should be flat and level with no wide, stepped or uneven joints. See Chapter 4 for explanations of the classification and specification of floor flatness and levelness. 3. 2. 4 MHE operating in very narrow aisles Front and lateral stackers These lift trucks can pick or place pallets at right angles to the direction of travel and are also known as very narrow aisle (VNA) trucks.
Operators travel at floor level or in a compartment that lifts with the forks: these are known as ‘man-down’ and ‘man-up’ trucks respectively (see Figure 3. 15). They are also used for order picking. Truck tyres are made of hard neoprene rubber. As the trucks operate on fixed paths, the wheels do not ‘scuff laterally and therefore are not unusually aggressive to surfaces. In very narrow aisles, trucks run in defined paths and so it is appropriate to measure and control the flatness in each of the tracks. Most trucks have three wheels, two on the front load axle and one drive wheel at the rear. Some have two closecoupled wheels at the rear acting as one wheel. A few trucks have four wheels with one at each ‘corner’.
When operating in the aisles, the trucks are guided by rails at the sides of the aisle or by inductive guide wires in the floor and are not directly controlled by the operator. The inclusion of inductive guide wires in the slab may affect its design thickness, see Section 9. 8. Guide wires need to be kept clear of steel reinforcement bars. Steel fibres in concrete do not normally affect guidance systems. See Sections 7. 2-7. 4. Some floor-running stackers have fixed non-retractable masts and run between top guidance rails that can also provide power to the truck through a bus-bar system. These systems are designed to provide some restraint to sideways movement of the mast to effectively stiffen it. Contrary to some expec-
Figure 3. 15: ‘Man-up’ stacker truck in a very narrow aisle warehouse. tations, these systems are not designed to compensate for inadequate floor flatness. Floor surfaces should be flat and level with no wide, stepped or uneven joints. Floors are specified with a definedmovement classification that depends on the maximum height of lift, as defined in Section 4. 4 and Table 4. 3. Stacker cranes Stacker cranes run on floor-mounted rails (Figure 3. 16). They have fixed masts with a top guidance rail and can transfer between aisles by means of special rail links. There are no onerous floor flatness requirements as the rails are set level with shims.
However, the floor should have a good overall level to datum as the racking and rails are fixed level to a datum. Limiting long-term settlement of slabs is important for stacker crane installations as changes in levels can lead to operational problems. 3. 3 CLASSIFICATION OF FLOOR LOADINGS In the review for this edition of TR 34, consideration was given to providing new advice on typical loading classifications as these are thought to have increased above those described in the widely used BRE Information Paper IP 19/87 (4). 17 Concrete industrial ground floors It was suggested that the system of classification should be revised at some time in the future following further research.
It is recognised that any such changes would require careful implementation and adequate publicity to minimise confusion in the industry. It is strongly recommended that the existing classifications should be used with caution, particularly for more heavily loaded floors with combinations of high point loads from racking and MHE. The BRE Information Paper suggests that loadings from MHE are unlikely to be critical, but this may not be the case in mixed-use floors where heavy counterbalance trucks operate or in some VNA installations where point loads from stacker trucks can be significant. The recommended approach is to design for the particular application.
The model design brief in Appendix A can be used for this purpose. Figure 3. 16: Stacker crane, running on a floor-mounted rail. 18 4 SURFACE REGULARITY 4. 1 INTRODUCTION: THE IMPORTANCE OF SURFACE REGULARITY The surface profiles of a floor need to be controlled so that departures in elevation from a theoretically perfectly flat plane are limited to an extent appropriate to the planned use of the floor. For example, high-lift materials handling equipment requires tighter control on surface regularity than a low-level factory or warehouse. Inappropriate surface regularity of a floor may result in equipment having to be operated more slowly, reducing productivity, or requiring increased maintenance.
Possible surface profiles are illustrated in Figure 4. 1. The elevational differences are emphasised for the sake of illustration: on a real floor the differences will be in the order of a few millimetres measured over a distance of several metres. Surface regularity needs to be limited in two ways. The floor should have an appropriate flatness in order to limit, for example, the bumpiness and general stability in operation of the materials handling equipment, and an appropriate levelness to ensure that the building as a whole with all its static and mobile equipment can function satisfactorily. The difference between flatness and levelness of floors is illustrated in Figure 4. 2.
It can be seen that flatness relates to variations over short distances whereas levelness relates to longer distances. These distances are not easily definable but traditionally, flatness has been controlled over a distance of 300 mm and levelness over a distance of 3 m as well as to a building’s general datum. Flatness is a function both of the elevational difference and of the rate at which elevational differences change across a floor. The terms used for defining the various aspects of surface regularity are set out in Table 4. 1. Figure 4. 3 shows examples of how some of these are derived. Level but not flat Flat but not level Figure 4 . 1 : Surface profiles.
Figure 4. 2: Flatness and levelness. Property I Property I Property II (0. 6) – (-0. 2) = 0. 8 0. 6 -0. 2 -0. 2 (-0. 2) – (-0. 2) = 0 0. 5 -0. 2 (-0. 2) – (0. 5) = -0. 7 Figure 4. 3: Examples of measurements of Property I over 300 mm and the resultant determination of change in elevational difference over a distance of 300 mm (Property II). All dimensions in m m . 19 Concrete industrial ground floors Table 4. 1: Definition of surface regularity terms. Term and definition Elevational difference The distance in height between two points. The points can be fixed at prescribed distances or they can be moving pairs of points at prescribed distances apart.
Change in elevational difference The change in the elevational difference of two moving points, at a prescribed distance apart, in response to a movement of the two points over a prescribed distance. Datum The level of the floor is controlled to datum (any level taken as a reference point for levelling). Flatness Surface regularity characteristics over a short distance, typically 300 mm. Levelness Surface regularity characteristics over a longer distance, typically 3 m, and to datum. Property Elevational differences or measurements derived from elevationa! differences that are limited for each class of floor. Property I – The elevational difference in mm between two points 300 mm apart, see also Figure 4. 3. Figure 4. 2 Section Figure 4. 3 Figure 4. 3 Figure 4. 2
Property II – To control flatness, the change in elevational difference between two consecutive measurements of elevational difference (Property I) each measured over 300 mm, see also Figure 4. 3. Property III – The elevational difference in mm between the centres of the front load wheels of materials handling equipment. Property IV – To control levelness, the elevational difference in mm between fixed points 3 m apart. MHE Materials handling equipment VNA Very narrow aisle 4. 2 FLOOR TYPES: FREE AND DEFINED MOVEMENT ically occur in factories, retail outlets, low-level storage and food distribution. They are also found alongside defined-movement areas in warehousing. In defined-movement areas, vehicles use fixed paths in very narrow aisles: they are usually associated with highlevel storage racking.