Services Co-ordination with Structural Beams · 2012-08-21 · from Arup also contributed. ......

InterfaceEngineering

Publications is aCo-Construct

initiativesupported by

Services Co-ordinationwith Structural Beams

Guidance for a defect-free interface

By Sally Mitchell, Martin Heywood, and Glenn Hawkins

What is Co-Construct?Co-Construct is a network of five leading construction research and informationorganisations - Concrete Society, BSRIA, CIRIA, TRADA and SCI - who areworking together to produce a single point of communication for constructionprofessionals.

BSRIA covers all aspects of mechanical and electrical services in buildings,including heating, air conditioning, and ventilation. Its services to industry includeinformation, collaborative research, consultancy, testing and certification. It also hasa worldwide market research and intelligence group, and offers hire calibration andsale of instruments to the industry.

The Construction Industry Research and Information Association (CIRIA )works with the construction industry to develop and implement best practice,leading to better performance. CIRIA's independence and wide membership basemakes it uniquely placed to bring together all parties with an interest in improvingperformance.

The Concrete Society is renowned for providing impartial information andtechnical reports on concrete specification and best practice. The Society operatesan independent advisory service and offers networking through its regions andclubs.

The Steel Construction Institute (SCI) is an independent, international, member-based organisation with a mission to develop and promote the effective use of steelin construction. SCI specialises in providing advanced internet-based solutions forthe construction industry.

TRADA provides timber information, research and consultancy for theconstruction industry. The fully confidential range of expert services extends fromstrategic planning and market analysis through to product development, technicaladvice, training and publications.

For more information on Co-Construct visit www.construction.co.uk.

Services Co-ordination with Structural BeamsCopyright of all material in this publication rests with The Steel ConstructionInstitute and BSRIA. Guidance appearing in the yellow text boxes is copyright TheSteel Construction Institute, while all guidance in blue text boxes is copyrightBSRIA.

Authors: Martin Heywood is with The Steel Construction Institute. Sally Mitchelland Glenn Hawkins are with BSRIA. Roderic Bunn from BSRIA and Chris Twinnfrom Arup also contributed.

All photographs and illustrations in this publication were provided by BSRIA andThe Steel Construction Institute.

This publication was part-funded by the Department of Trade and Industry underthe Partners In Innovation (PII) collaborative research programme. The viewsexpressed in this publication are not necessarily those of the DTI. Final editorialcontrol and publishing responsibility of this publication rested with BSRIA.

©BSRIA/SCI IEP2/2003 December 2003 ISBN 0 86022 634 4 Printed by The Chameleon Press Ltd

All rights reserved. No part of this publication may be reproduced, stored in aretrieval system, or transmitted in any form or by any means electronic or mechanicalincluding photocopying, recording or otherwise without prior written permission ofthe publisher.

An Interface Engineering Publication 2

What are Interface Engineering Publications?Interface Engineering Publications (IEP) are a series of guides that aim tobridge the gaps in technical knowledge at the interfaces between constructionpackages. The publications involve reformating existing professionalknowledge, developed independently by Co-Construct members, into a singlesource of guidance.

The objective of IEPs are to reduce failures on site, to create greaterunderstanding of shared processes by clients, designers and contractors, and toimprove construction quality and the in-use performance of building systems.

Services Co-ordination with Structural Beams was jointly researched,edited and produced by BSRIA and The Steel Construction Institute in orderto provide comprehensive guidance in a single publication. All the informationhas been drawn from current research and existing publications, and cross-referenced with the latest regulatory requirements.

For more information on Co-Construct visit www.construction.co.uk.

Co-Constructc/o BSRIA, Old Bracknell Lane West, Bracknell, Berkshire, RG12 7AH, UKTel: +44 (0)1344 426511www.construction.co.uk

1SERVICES CO-ORDINATION WITH STRUCTURAL BEAMS

The office boom of the early 1980s led to many innovations: facadeengineering, myriad forms of air conditioning, and many new designs ofsteel structures. Trendsetting developers discovered that the choice ofstructural beam had a fundamental effect on the efficiency and speed ofconstruction. By running services through holes in structural beams – anddesigning those beams with services distribution in mind – developerswere able to reduce storey heights, increase lettable area, and save on thecost of the external envelope.

However, real reductions in capital cost only accrue from properly co-ordinated design, where the structure and services are designed inharmony, and where the policy of integration is followed through toinstallation. For less well co-ordinated projects, the theoretical savings canbe more than wiped out by lack of detailed co-ordination. The resultingproblems can only be solved through costly improvisation by sitecontractors.

This guide, the second in a series called Interface EngineeringPublications, aims to provide guidance on the best ways to engineer theinterface between structural design and services distribution. BSRIA andThe Steel Construction Institute (SCI) have pooled their technicalknowledge to provide structural and services engineers with consistent,interlocking advice.

The publication largely contains material repackaged from existingBSRIA and SCI guidance. Details of the original publications, relevantEuropean and British Standards and other references for further readingare provided at the end of this publication.

Much of the guidance in this publication concentrates on the technicalaspects of a well co-ordinated design. It argues that structural engineersmust invite their services colleagues to take part in option analysis, todesign the beam openings to cater for the favoured services systems, andto help resolve the inevitable conflicts that occur in ceiling voids. The riskfrom not doing so will be increased time or cost overruns duringinstallation, largely caused by the need to adapt ductwork and pipework,and to provide additional fittings required to make services go together.

The key message is that structural design must not be carried out inisolation from the design of the building services. All parties to the designprocess should make it clear to the client – and the client’s representatives– that savings will only be achieved if services are installed so they willperform properly, and in a manner that enables them to be maintained.

Roderic Bunn, BSRIAMartin Heywood, The Steel Construction Institute

December 2003

Introduction

2 SERVICES CO-ORDINATION WITH STRUCTURAL BEAMS

Contents

Introduction 1

Early design decisions 4First steps in designIntegrating the services

Beam options 4Types of structural beam

Isolated web openingsCellular beamsLattice girdersTapered beamsStub girdersCastellated beams

Building services options 10The technology

Mechanical servicesElectrical servicesTypical ceiling mounted building servicesLocal systems

Services scheme design 12Services information needed

Design inputsTerminal unit issuesAdvantages of circular ducts

Deflection information needed

Structural detailed design 14Structural design issues

Isolated web openingsCellular and castellated beamsTapered beams

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Services detailed design 16Services design issues

General design information neededPlant sizing issuesDuctwork sizing and selection issuesDuctwork requirements

Structural fire protection 20Structural design issues

Cement or gypsum-based materialsBoards and blanketsIntumescent coatings

Services and fire protection 22Fire protection issues

Integrating fire dampers

Services installation 24Key installation issues

Services running parallel to beamsDepth restrictions

Standards and further reading 30

Glossary 31

How to use this guide

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Key mechanical watchpoints

� Essential mechanical engineeringmessages from the guide

Key structural watchpoints

� Essential structural messages fromthe guide

See also

Links to m&e sectionsLinks to structural sectionsLinks common to both sections

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Standards for structural and m&e design

Further reading to support this guide

Glossary for terms and definitions

Advice about the structural requirements ofrunning services through structural beamswill be found in yellow-tinted boxes.Comments marked by � link to mechanicalengineering sections listed under see also.Comments marked by denote a linkcommon to both specialisms.

Advice about the mechanical engineeringrequirements of running services throughstructural beams will be found in blue-tintedboxes. Comments marked by � link tostructural sections listed under see also.Comments marked by denote a linkcommon to both specialisms.


Building structure is often designed between the client, the architect and the structuralengineer, but the services engineer also has a key role to play. If savings in construction materials andinstallation cost are to be achieved, along with a well integrated services installation, then the structuralengineer must obtain guidance from the building services engineer on the dimensional nature of theproposed services design, and the preferred routes of those services.

Early design decisions

First steps in design

A clients’ guide to

Early on in the design of a building, thestructural engineer and architect have to makeimportant decisions regarding the layout ofthe structural frame. Although the total cost ofthe structural steelwork in a typicalcommercial building is less than 10% of thetotal capital cost, these decisions can have asignificant effect on building whole-life cost.

The design of the steel frame should beconsidered as part of the overall buildingdesign. When selecting a beam and columnlayout, the structural engineer needs to takeaccount of the present and futurerequirements for unobstructed floor space, thetype of floor system to be used, the effect ofthe structural layout on the overall buildingheight, the proposed layout of the buildingservices, and the level of flexibility required,such as cutting additional services risers.

Beam span and layoutThe structural engineer should aim for long

span solutions in order to minimise thenumber of columns and maximise theunobstructed floor space. This providesflexibility for the design of the internal layoutand allows for future changes of use.

The exact span between the columns shouldbe selected to suit the architectural grid, sothat the locations of the structural memberscoincide with the spacing of the partitions,ceilings and, in some cases, fixed items offurniture. The architectural grid typically hasintervals of 0�6 m, in which case suitable beamspans would be 3�6 m, 6�0 m, 7�2 m, 9�0 m etc.

Having decided on the column locations,the structural engineer must then decide onthe arrangement of primary and secondarybeams to transfer the loads from the floor tothe columns (figure 1).

The use of secondary beams is oftennecessary because the spacing of the columnsusually exceeds the maximum span of thefloor decking units.

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See also

Services Detailed Design, page 16Table 1, page 11Figure 9, page 12

Standards on page 30

Further reading on page 30

Glossary on page 32

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Mechanical engineering issues

Structural issues

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Although the total cost of thestructural steelwork in a typicalcommercial building is less than10% of the total capital cost of thebuilding. The structural engineercan have a significant effect on thewhole-life cost of the building

Explain to the client that savings ininstallation time and cost willaccrue from the structural andservices engineers workingtogether in an integrated approach

Savings will accrue from matchingthe size and shape of the beamopenings to the dimensional andperformance requirements of thebuilding services; standardisationshould be a priority


Storey heightIt is often advantageous to reduce storeyheight in order to minimise the cost of thecladding, or to comply with planningrestrictions on the overall height of thebuilding. This requires the careful selection ofbeam members and consideration of servicesintegration into the structure.

If the beams are arranged such that thesecondary beams span further than theprimary beams (figure 1), it is sometimespossible to use primary and secondary beamsof a similar depth. This approach minimisesthe depth of the steelwork, but might preventthe services from being passed through thebeam webs, resulting in a need for a separateservices zone beneath the beams.

If a beam layout is chosen that requiresdeep primary beams and shallow secondarybeams, the depth of the steelwork will begreater, but it should be possible to passservices through the webs of the primarybeams and under the secondary beams. Theminimum storey height does not thereforealways correspond to the minimum beamdepth.

The services engineer has the choice ofpassing the services beneath the beams in aseparate services zone, or locating themwithin the depth of the beams. It is essentialthat the building services engineer andstructural engineer discuss the options earlyon in the design process and work closely toarrive at the best integrated solution.

If it is decided to pass the services throughthe beam webs, the services engineer mustprovide data on the number, size and spacingof the required holes so that the beams canbe fabricated accordingly. Failure to do socould lead to expensive alterations on site.

Integrating the building servicesFigure 1: A typical layout for primaryand secondary beams. ©The SteelConstruction Institute (SCI). See alsoFigure 11, page 16.

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Beam options 1A clients’ guide to

Several different types of steel beam are usedin building construction. These have specificattributes that aid the horizontal distributionof building services (figure 2). These beamtypes are generally classified as:� Universal beams or plate girders with webopenings� Cellular beams� Castellated beams� Stub girders� Tapered beams� Trusses or lattice girders

Isolated web openingsWhere relatively few services are required topass through the beam, isolated holes maybe cut in the webs of beams.

Relatively large openings can usually beprovided without the need for strengthening,provided that there is sufficient shearresistance in the remaining web. These holeswill often be cut to meet the specificrequirements of the building services.

While isolated, tailor-made openingsmight seem ideal to the building servicesdesigner, the option limits the future scopefor alteration of the services layout, forexample when the building is refurbished.

Cellular beamsWhere the requirements for buildingservices are uncertain, or likely to changeduring the life of the structure, the cellularbeam may be a more versatile alternative toisolated web openings.

Cellular beams contain many regularlyspaced circular holes along the entire lengthof the beam and are produced by specialistmanufacturers in a range of depths (figure 3).They permit an aesthetically pleasingsolution for situations where the beams areexposed, are structurally efficient andprovide plenty of scope for future changes tothe services layout.

Manufacturers provide a specialist designservice for sizing the depths and hole sizes.

A full understanding of the different types of structural beam, and the services that can runthrough them, is necessary for a proper option-appraisal process. The choice of structural beam willbe influenced by a range of construction issues, but when it comes to optimising the services distribution,every person involved in the design process needs to appreciate the cost and performance benefits ofintegrating the beam design with the services design.

Types of structural beam

Figure 3: Fabricatedbeams with circular and

rectangular web openings.

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See also

Glossary, page 32Figure 11, page 16Figure 12, page 18Services Installation, page 24Figure 4, page 8Table 3, page 15



Glossary on page 32


Structural issues

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Figure 2: Different types of steel beams suitable for integrating with buildingservices. ©The Steel Construction Institute.

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Key m&e watchpoints

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Designers should considerprioritising the design andinstallation of building services.For example:� Sanitary drainage has veryspecific fall requirements� More duct fittings will increasepressure losses, fan duty andrunning costs; the same is true ofpipework fittings� Moving installed cables toaccommodate later services willincur re-installation costs� Long sprinkler pipework runswill increase the required pumpduty

When sizing services to gothrough a beam aperture, theapertures must be large enough toallow for beam fire protection andinsulation around the services (airhandling ductwork can haveinsulation 25-75 mm thick) and toenable ease of installation

Services such as hot waterdistribution pipework will expandwhen in use. Check that thisexpansion can be accommodated

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Notched beam Composite slab

End of beam notched toallow for main ducts

Secondary servicesunder beam

Ceiling

Shear connectors

Possible duct position Alternative shape

Tapered beam

Stub girder

Openings

Lattice beam

Typical diagonals

Cellular beam

500 mm diameter holesat 750 mm centres

Lattice girder

100 by 200 mmmaximum

300 mm diametermaximum

Typical diagonals

Diameter usuallybetween 240 - 300 mm

Castellated beam


A clients’ guide to

Castellated beamsA castellated beam is a beam with equallyspaced hexagonal openings over all or mostof its length (it is common to use infill platesat beam supports). The beam is formed bycutting a rolled-steel joist along the web in azig-zag shape. The crests of the cuts are thenwelded together.

Although rarely used today in newconstruction, castellated beams have beenused extensively in the past and will regularlybe encountered by building servicesengineers working on refurbishment projects(figure 4).

Stub girdersA stub girder is a special form of Vierendeelgirder, consisting of a universal column (UC)section as a bottom chord and a concrete slabas a top chord (figure 5).

Intermittent short lengths of a standardsteel section, connected by shear studs to theconcrete slab and welded to the bottomchord, act as vertical web members.

Tapered beamsAs an alternative to rolled sections, fabricatedsteel sections produced from flat plate can beused. This provides the option of varying thedepth of the beam along its length toproduce a structurally more efficient solution.

Depth may be reduced at the ends of thebeam, depending on the required shearresistance. This saves weight of steel, butmore importantly, releases space below thebeam for service distributions. Thus areasonably-sized zone is created in whichlarge services may be accommodated adjacentto the columns. However, this can push mainduct runs to the edge of the slab which willcause a conflict with perimeter air grilles,usually needed to ventilate cellular offices.

Lattice girdersThe use of lattice girders (or trusses) for longspans is a well-established alternative torolled or fabricated steel sections. Latticegirders can be manufactured from tees, anglesor hollow sections and are usually welded

Figure 4: A typical castellated beam assembly, formed by cuttingand re-welding standard universal beams. ©The SteelConstruction Institute.

Beam options 2

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Figure 5: Stub girders consist of a universal column section as abottom chord and a concrete slab as a top chord. ©The SteelConstruction Institute.

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See also

Figure 24, page 29Figure 16, page 25Figure 16, page 25Figure 12, page 18



Glossary on page 32


Structural issues


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Cellular beams: Cellular beamsfeature regular rows of circularopenings which offer flexible,(though not necessarily optimal)routes for services

Castellated beams: More likelyto be encountered on arefurbishment project, castellatedsteel sections feature regularrows of hexagonal apertures, butdo not normally provide scope fordifferent sizes and shapes ofservices

Stub girders: Stub girders forgood flexibility for servicesdistribution, particularly forrectangular ductwork and inproviding scope for future re-servicing

Tapered beams: Tapered beamsgive the structural engineer thegreatest freedom in the selectionof section size. These beams mayhave straight tapers or be semi-tapered (figure 2), and aid thelocation of services at the beamends

Lattice girders: Lattice girdersoffer great opportunity forallowing services to pass through,although the full width of theopening is only available forservices at particular locations

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Figure 6: A typical lattice girder prior to the application of fireprotection. ©BSRIA.

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Figure 7: A standard universal beam cut with rectangularapertures. A symmetrical layout such as this gives wide scope forservices distribution, though not necessarily optimal. Note thehorizontal stiffeners above and below the openings. ©SCI.

together (figure 6).The spaces that are formed between the

individual elements that make up the trussoffer many opportunities for passing servicesthrough the beam, allowing flexibility in thelayout of the building services and futurealterations. However, the triangular shape ofthe opening means that the full width of theopening is only available for services atcertain locations, restricting the size of theservices that can be passed through the beam.

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Building services optionsA clients’ guide to

The technology

There are various building services systems that traverse ceiling voids. The one thing theyhave in common is the need for space. Clients and structural engineers need to have an appreciation ofthe various systems and their basic characteristics. It is also important to understand how a decision madefor structural reasons might affect the nature of the building services, and how those building serviceswould be designed and installed as a consequence.

Mechanical servicesMechanical building services that commonlytraverse ceiling voids include:� Supply and extract ductwork serving amechanical or full air conditioning system� Heating and cooling pipework, andcondensation pipework (serving from anyceiling-mounted cooling devices such as fancoils or direct expansion refrigerant coils)� Fire suppression pipework; water-based forserving sprinklers, or gaseous pipeworkdistribution for gas discharge systems� Refrigerant pipework for variable flowrefrigerant systems (VRF), and split systemscomprising indoor and outdoor components� Ancillary devices serving the above systems,including ductwork and pipework suspensionsystems hangers, valves on pipework, andaccess doors on ductwork.

Many of the latter affect space allocation andcan influence the freedom of servicesdistribution depending on the space availableand the intensity of the servicing.

Electrical servicesElectrical services include:� Power cables� Communications cabling for datacommunications and telephones� Building management system signal cables,linking to in-ceiling devices such as thermostats,fan coils and luminaires� Power cables for lighting� Fire protection system cables� Security cabling for closed circuit television,and access control entry systems� Ancillary devices, such as cable tray, supportmechanisms, and terminal devices such asbuilding management system controllers.

The latter may not necessarily be integral tothe unit to which the cables connect, and could

impinge on space otherwise set aside foraccess to ductwork, for example.

Cables can be run on trays or in conduitwhere several cables need to follow the samepath. Sometimes power cables are put inseparate trays or conduit to the communicationscables in order to prevent electricalinterference. Although most power cables tendto run in the floor void, power will still berequired in the ceiling void for lighting, and topower fan coils and associated controls.

Typical ceiling-mounted building servicesThe largest and most common types of buildingservices are those serving a mechanicalventilation system or a full air conditioningsystem with terminal units. These fall intocategories: centralised air systems, partiallycentralised air and water systems, and localsystem. Table 1 lists nominal dimensions.

Centralised systems involve constant volumeor variable volume systems, each of whichhave specific ductwork and pipeworkrequirements. Partially centralised systemsinclude fan coils, chilled beams, chilled ceilingpanels, and room-based heat pumps. Figure 8illustrates some general requirements.

Constant volume systems provide temperedventilation air at a fixed rate through ductworkto devices such as fan coils and chilled beams.These units handle the primary heating andcooling requirements of the space.

Variable air volume systems (often calledVAV) are more complex. VAV is an airconditioning system where the ducted air notonly provides room ventilation (at a variable ratedepending on demands) but also handles spacecooling and heating needs.

When the ventilation air is the cooling andheating medium, larger ductwork is required tocope with the peak air volumes. This can be a

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Figure 11, page 16



Glossary on page 31

Key m&e watchpoints

See also

The services engineer shouldprovide the structural engineerwith basic dimensions of typicalceiling-void services to aid thechoice of beam (Table 1).

Refer to manufacturer’sdimensional information andconstantly revisit the spacerequirements

Ensure that early consideration isgiven to the need to segregateelectrical services fromcommunications cabling

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limiting factor when the ductwork is beingthreaded through beams.

Both constant volume and VAV systemsneed for good co-ordination with cellularbeams. Poor co-ordination will preventconstant volume and VAV systems fromdelivering good ventilation and temperaturecontrol.

Local systemsLocal systems are not served by centralisedplant, and are mostly cooling devices servingspecific zones in a building. Some recirculateroom air without any fresh air makeup, otherscan be ducted to an air handling unit locatedelsewhere in the building.

Local systems include split air conditioningunits (commonly called splits) and variablerefrigerant flow systems (VRF). These devicesare served by refrigerant pipework.

Figure 8: A schematic showing a centralised VAV system with afan coil system. Fan coils require separate hydraulic circuits, andVAV systems are served by large primary ductwork with smallersecondary ducted connections to terminal units. ©BSRIA.

Occupied floors

VAVterminalunits

Ductwork and air handling unit

Boilers

Chiller

Fan coilunits

Centralised plant area

Smaller duct for fresh air only

Table 1: Space needs of typical ceiling-void services. ©BSRIA.

Note that the dimensions in Table 1 are nominal –accurate dimensions should be obtained from thepreferred system suppliers.

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Services scheme designIssues to address during

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Services information needed

The scheme design stage is where all parties in the design process will discuss the options.The choice of structural system will have a fundamental effect on floor to ceiling heights and ceiling voiddepth, and thereby the services installation. The services designer needs to make it very clear that any spacesavings will only be beneficial to the client if the services can be installed in a way that enables them toperform to specification, and be maintainable during operation.

Design inputs� Architectural drawings for all zones� Client brief and desired ventilation and/orair conditioning strategy� Building orientation and shading� Details of the structural frame and beams� Space plan and layout� Floor to ceiling heights� Use and occupancy of spaces� Desired internal design condition� Internal zoning and building layout� Locations of fire compartments, includingthe floor and ceiling voids� Nominal zones for additional meetingrooms, communication rooms and kitchenareas that may require additional servicing.The services engineer should obtaininformation on the total deflection of thestructural beams before and after the servicesare installed (dead load and imposed loads).

Terminal unit issuesThe actual size of any ductwork of terminalunits will vary according to the number ofunits and the load imposed on the space it isserving. Sizes and connection layouts mayalso vary between different manufacturers forsimilar rated units. Figures for the amount ofdepth or clear space in a ceiling or floor voidfor various terminal units, derived fromBSRIA BG 14/2003 Rules of Thumb, are:� Variable air volume: 350-750 mm� Variable refrigeration flow: 450 mm� Recessed chilled beams: 350-450 mm� Surface chilled beams: 250 mm� Chilled ceilings: 250 mm� Fan coils: 450 mm� Ducted air system: 450 mm.

Advantages of circular ductsOne advantage of using circular duct instead

of rectangular duct is the overall reducedsystem resistance which in turn has an affecton the fan size and associated installation/running costs. There are also other advantagesto using circular ducts, such as being able tocut the duct lengths to size on site.

If a building has cellular beams, thensquare or circular or flat oval duct can beused. Circular duct will provide a lowerresistance compared to a square duct throughcellular beams, although insulation and fireprotection will reduce the space available forthe duct.

When designing duct services throughcomposite beams there will be restrictions onthe maximum duct size that can fit throughthe beam. This will obviously be influencedby the type of beam and the size/shape ofthe holes. With these constraints it isimportant to check the options available thatwill best suit the application.

Figure 9: If the beams in the building have rectangular holes, thenflat oval ducts may be an option. Alternatively, a single rectangularduct or two square ducts (such as supply and extract) may bechosen depending on cost and availability. If the services engineer believes this option would provide acost and performance benefit for the client, then the structuralengineer needs to be made aware of these benefits when thebuilding structure is being designed. It may be possible to cut flat-oval apertures in the beams to cater for this services distribution.

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Structural issues

Deflection information needed

All beams deflect when loaded and anallowance must be made for such deflectionwhen designing and installing building services.

Initially, the beam will deflect due to its self-weight and the weight of the concrete slab (thedead load). This loading is carried by the steelbeam and the deflection will therefore be afunction of the stiffness of the beam.

As this deflection occurs before the servicesare installed, services designers andcontractors need to be aware that the beamsthrough which their services pass might notbe horizontal or at the same level along thelength of the building at the time the servicesare installed.

In some cases, beams can be precambered tooffset the effects of dead load. Where this isnot possible, the services should be supported ina way that allows the levels to be adjusted.

The added load of the services will cause thebeam to deflect further. With compositeconstruction, the weight of the services will beresisted by the beam and slab acting together,and so the deflections are likely to be small.

Deflection also occurs in service due toimposed (live) loads from occupancy of thebuilding and partitions, fixtures and fittings.BS 5950-1: 2000 Structural use of steelwork inbuilding recommends limits for calculateddeflections due to imposed loads (Table 2).For long span beams a maximum deflection of60 mm is generally specified.

Where services are supported by beams, theyshould be able to withstand deflections equal tothese limits. Where services pass freelythrough holes in beam apertures, there shouldbe sufficient clearance between the edge ofthe hole and the service to allow for beammovement. Services designs must take intoaccount the total deflection (dead load plusimposed loads).

Table 2: BS 5950-1: 2000 limits for calculated deflections dueto imposed loads.

An allowance must be made forbeam deflection when buildingservices are intended to passthrough or under beams

Deflection must be anticipated byboth the structural and buildingservices engineers to avoid costlyre-routing and modification ofservices during installation

Services engineers must providethe permissable degree ofdeviation between the centres ofapertures in a series of perforatedbeams destined for a run ofservices

Obtain information on thedeflection characteristics of thestructural beams under pre-servicing and post-servicingconditions

Services must be able to copewith the deflection of the totalload on the structure (dead loadand live loads)

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Structural detailed designIssues to address during

Structural design issues

The scheme design stage is where all parties in the design process will discuss the options.It is not unusual for the architect’s design to have been already accepted by the client, leaving the engineersto propose solutions. It is vital that the specialists able to shed most light on co-ordination issues areinvolved in discussions: for structure that means the supplier of the cellular beams, and for services, theventilation system suppliers and the ductwork contractor. This will necessitate early tendering.

The following structural design information isrequired at the scheme design stage. All partiesneed to agree the consistent use ofterminology.

Isolated web openingsWhen locating rectangular openings in thewebs of composite beams, the followingguidelines should be considered:� Openings should not be located closer thantwo times the beam depth D from the support,or 10% of the span, whichever is greater.� For uniformally loaded beams, the bestlocation for any opening is between one fifthand one third of the span from a support.� For beams subject to point loads, the bestposition of the openings depends on therelative importance of moment and shear alongthe beam, but normally openings are placedclose to the mid-span.� Rectangular openings should not be lessthan the beam depth (D) apart.� Rectangular unstiffened openings shouldnot generally be deeper than 0�6 D, nor longerthan 1�5 D. The shear resistance and instabilityof the web should be checked.� Rectangular stiffened openings should notbe deeper than 0�7 D, nor longer than 2�0 D.� Stiffeners in the form of horizontal platesshould be welded above and below the opening.� Point loads should not be applied at lessthan D from the side of the adjacent beamopening.

Cellular and castellated beamsCastellated beams formed from structuralsections have an overall depth D 50% greaterthan the parent beam. Standard castellationscomprise hexagonal holes of maximum depth0�67 D at 0�72 D centres.

For cellular beams, it is possible to have a

1 wide range of opening and beam sizes (Table3). Circular openings can be created withdiameters of 0�6 to 0�8 times the final beamdepth, and at spacings of 1�1 to 1�5 times theopening diameter. A typical span/depth ratiowould be 20. As with castellated beams, theloss of the beam web reduces its bending andshear strength.

In some cases, openings may be enlargedby removing the web post separating twoadjacent openings. This can be achieved in themiddle third of the span, but additionalstiffening is generally required.

A cellular beam may also be formed bywelding together two sections. For compositebeam design, where the concrete slab acts incompression, the top flange may besignificantly smaller than the bottom flange.

A combination of different universal beam(UB) and universal column (UC) sectionscan reduce the weight of a beam by up to30%, while providing the same compositestiffness as a solid beam of the same depth.The production process for cellular beamsalso allows the sections to be pre-camberedto overcome deflection problems.

Tapered beamsIn the case of fabricated steel sections, thestructural engineer has the greatest freedom inthe selection of section size. These beams mayhave straight tapers, or alternatively be semi-tapered (uniform depth in the middle part ofthe span). A straight taper is simpler tofabricate and, in many cases, is the mosteconomic shape. Typical tapered girdersreduce to approximately half depth at thesupports with a maximum taper angle ofabout 60. A vertical stiffener may be requiredat mid-span for deeper sections. A practicalrange of span/depth ratios is 15 to 25.

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Glossary, page 31; Figure 2, page 7Figure 12 page 18



Glossary on page 32

See also

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Structural issuesOpenings should not be locatedcloser than two times the beamdepth D from the support, or 10%of the span, whichever is greater

Openings should not be less thanthe beam depth D apart

Unstiffened openings should notgenerally be deeper than 0�6 D, norlonger than 1�5 D, and the shearresistance and instability of the webshould be checked

For cellular beams, circularopenings can be created withdiameters of 0�6 to 0�8 times thefinal beam depth, and at spacings of1�1 to 1�5 times the openingdiameter


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Table 3: Summary of typical gross opening sizes for efficiently designed long spancomposite beams incorporating services zones. ©The Steel Construction Institute.

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Services detailed design 1Issues to address during

Services design issues

Detailed design is a critical stage in determining how the services will pass through cellular orwebbed beams. Detailed design must not only address functional requirements, co-ordination, andmethods of fixing and fire protection, but also provide solutions that can be installed productively. Thismeans a design that does not require an excess number of deviations from the drawings, and therebyadditional fittings. Services designers should also consider the maintainability of their design solution.

Figure 11: The detailed design issues for a variable air volume-type air conditioning systetight radius bends in ductwork, for example forced by the need to thread the ductworkcreate air pressure and noise problems. Original diagram ©The Steel Construction Instit

General design information neededFigures 10 and 11 shown on this and thefollowing page represent a simplified diagramof a large, air conditioned open-plan office.

BSRIA AG1/2002 Design Checks for HVAC,lists the design information required forservices instalaltions. With respect to theinterface of services with structural beams, thedesigner should check the following:� Determine the acceptable noise levels inthe occupied space� Check whether the ceiling is to be sealed� Check the return air path, for examplewhether via air handling light fittings, dedicatedgrilles or ceiling gaps� For fan coils, check the position of drainagepipes used for condensate run-off� Determine the relationships between thelocation of cellular beams and the location ofinternal partitions� Agree grille positions in principle inanticipation of future cellular layout� Determine the type and quality of acoustictreatment required for ductwork� Determine the fire protection system forthe ducted and piped services� Identify the fire protection system for thestructure, and the consequential reduction inaperture size for treated cellular beams.

Plant sizing issuesA pre-requisite for successful interfaceengineering between the structure andbuilding services is that the services engineersupplies the structural engineer with basicdimensional characteristics of the key items ofplant to be located in the ceiling void.

Details of associated horizontal distributionthat may need to pass through the beams, suchas ductwork, pipework and cabling, should �

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Glossary, page 31Fire protection issues, page 22Table 4, page 21Table 1, page 11



Glossary on page 31

Key m&e watchpoints


See also


Structural issues

Understand the true dimensionalrequirements for space-criticalitems such as ductwork, fan coils,vav boxes, and plenum boxes thatwill be located in the ceiling void

Provide the services engineer withthe details of the fire protectionsystem for the beamsEnsure the space requirements forall horizontal services are clearlyexpressed in early design teamdiscussions

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Ensure that the design caters forthe position of drainage pipesused for condensate run-off

Obtain details of the fireprotection system for thestructural elements

Determine the reduction in beamopening as a consequence of thechoice of structural fireprotection system, and determinethe centre point of each openingfrom the bottom of the slab

Determine the precisedimensional details for acoustictreatment to ductwork destinedto pass through a beam opening

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em interfaced with a cellular beam. Note that VAV systems are categorised as high pressure systems. Anyk through the cellular beam and then to bend to a terminal unit located close to the beam, will inevitablytute.

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Detailed design issues (continued)

Services detailed design 2Issues to address during

� also be provided. This information should berevisited once suppliers have been selected.

Ductwork sizing and selection issuesDuctwork layouts should be carefullyconsidered to be as short as possible in orderto account for physical constraints such as liftshafts, structural columns and beams, and tominimise tight bends. Ductwork layoutsshould be designed to reduce the need forbuilders’ work, and to be as self-balancing aspossible to reduce damper pressure drops.

Designers need to consider breakout noiseand cross-talk, and take appropriatemeasures. Ideally, the layout should makebest use of any attentuation inherent in thedesign concept.

Ductwork requirementsDuctwork insulation needs to be consideredas early as possible. There are severalpenalties that can be suffered if inadequateattention is paid to insulation, such as:� The inability of the insulated service to fitin the beam aperture� The inability of separate servicesnominated to run together in a single beamaperture, forcing one or more of thoseservices to deviate to another beam apertureor, worse, forced to run beneath a beam thathas not been selected for that purpose.

The services design engineer also needs toknow the details of the structural fireprotection system specified by the structuralengineer. Different forms of structural fireprotection (such as boards and blankets) maysignificantly reduce the final size of the beamaperture. The overall diameter of insulatedand fire protected services must be knownbefore they designed to run through a beam.

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Figure 12: The detailed design issues for a fan-coil based air conditioning system interfaced thread the ductwork through the girder and then to bend to a terminal unit located Construction Institute.


Figure 22, page 28Figure 16, page 25Figure 20, page 27Structural fire protection, page 20



Glossary on page 31

Key m&e watchpoints

See also


Structural issuesDesign ductwork layouts toreduce the need for builders’work, and ensure they are as self-balancing as possible to reducedamper pressure drops

Obtain precise dimensional detailsfrom ductwork and pipeworksuppliers once they are knownand revisit the space allocation

Obtain full details of the structuralfire protection system. Differentforms of structural fire protectionmay significantly reduce the finalsize of the beam aperture

The width of air risers (and hencewidth available for main floorbranches) will determine theservices height needed in theceiling void, and the overallbuilding height

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with a stub girder. Any tight radius bends in ductwork, for example forced by the need to close to the beam, will inevitably create air pressure and noise problems. Original diagram ©The Steel


Structural fire protectionIssues to address for

Structural design issues

Once the beams have been designed, any apertures cut for services distribution and the beamsinstalled, the structural engineer’s job is largely done. However, a good interface with servicespenetrations still depends on other factors such as the nature and quality of the beam fire protection.These factors, plus accurate dimensioning information, must be communicated and clearly shown on thedetailed drawings to enable the high number of trade contractors to follow the co-ordination plan.

The choice of castellated or lattice web beamsmay aid the horizontal distribution of servicesto the extent that it can equate to a significantsaving in floor to ceiling heights. For a multi-storey building, this may equate to an extrafloor of lettable area. It is crucial that allinterface issues are made explicit on all designand installation drawings. Nowhere is thismore important than in the choice ofstructural fire protection.

Cement or gypsum-based materialsThe types of fire protection systems availablecan be classified into three main productgroups: sprays, boards and intumescentcoatings. A summary of the main factorsaffecting product selection in each of thesethree groups is given in Table 4.

Cement or gypsum-based materialscontaining mineral fibre, expanded vermiculite,expanded perlite and/or other lightweightaggregates or fillers, are generally the leastexpensive forms of fire protection. Mineralfibre-based materials are delivered dry to thespray head, where they are mixed with waterand compressed air. Vermiculite or perlitesprays are usually premixed with water beforebeing pumped to the spray head.

These fibre-based materials can provide upto 240 minutes fire resistance and are usuallydefined as being non-combustible inaccordance with BS 476-4. While mostmaterials are applied in situ, some may beapplied to the steelwork before erection.

As long as the fire protection is applied tothe steelwork before the services are installed,it should be possible to pass the pipes andducts through the holes in the beam webwithout needing to take any special measures.However, as the range of thicknesses forcement or gypsum-based materials is between

10 mm and 75 mm, an allowance must bemade for the material thickness whenselecting the required hole size.

Boards and blanketsBlankets, semi-rigid and rigid boards are usedas dry forms of fire protection installed in situas either profile or boxed protection. Basematerials include ceramic fibres, calciumsilicate, rock fibre, gypsum and vermiculite.Most are only suitable for interior use or limitedexternal exposure during construction.

Potential problems with loose fibres may beminimised by an outer sheathing of aluminiumfoil or similar, and by the use of taped joints.

Up to 240 minutes fire resistance can beprovided, although longer fire resistanceperiods often require the use of multiplelayers of boards. In that case the joints in thelayers are staggered.

The difficulty of using board with regard toservice integration is that the board must be cutto allow the services to pass through the beam,while maintaining proper protection of thesteelwork. This is not a practical option forcellular beams or beams with multiple holes.

Intumescent coatingsIntumescent coating systems are classified aseither thin film, which account for the vastmajority of systems used in generalconstruction, or thick film, sometimes referredto as mastics. The materials are reactive,swelling to many times their original thicknesswhen exposed to fire, with the resultant charinsulating the underlying steel substrate.

Thin film intumescent coating systems areapplied either by airless spray, brush or roller.

Further guidance on the off-site applicationof intumescent coatings is given in the SCIpublication, Structural fire design: Off-site

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Figure 16, page 25



Glossary on page 32

See also

All interface issues should be madeexplicit on all design and installationdrawings

As the range of thicknesses for fireprotection materials is between 1�0mm and 75 mm, allowance must bemade for material thickness whenselecting the required hole size

Cutting board-type fire protectionto allow services to pass throughbeams is not a practical option forcellular beams or beams withmultiple holes

If intumescent coatings are usedwith cellular beams, specialistadvice should be sought regardingappropriate thickness

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Table 4: Characteristics of fire protection systems. ©SCI.

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applied thin film intumescent coatings.General guidance on the selection and use

of intumescent coatings can be found inBS 8202-2 . Guidance on the measurement ofcoating thickness can be found in an ASFPdocument, On-site Measurement of IntumescentCoating Systems. If intumescent coatings areused with cellular beams, specialist adviceshould be sought on the appropriate thickness.

Intumescent coatings offer advantages overthe previous types of fire protection system.Compared with cementitious coatings, thecoating thickness is relatively thin (0�3 mm to6�5 mm for thin film) and should not havemuch effect on the selection of hole size.

Whether the coating is applied in-situ oroff-site, the operation is not impaired in anyway by the need to pass services through thebeams. The presence of the coating will alsonot affect the installation of services. However,care must be taken to avoid damaging thecoating during services installation.


Key m&e watchpoints��

Obtain full details of the structuralfire protection system. Differentforms of structural fire protectionmay significantly reduce the finalsize of the beam aperture

Ensure that services contractorsare aware that intumescentcoatings can be damaged bycareless installation

Obtain specific thickness details ofintumescent fire protectioncoatings if they are specified foruse on cellular beams

Obtain precise dimensions of theway fire boards will be fitted tothe beams to ensure space forservices runs are notcompromised

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Services and fire protectionIssues to address for

2

Fire protection issues

The interface engineering of services with beams must take into account fire protection.Fibreboard-based fire protection for beams can reduce apertures by 40 mm all round, and this will reduceusable area by a similar figure if the services passing through the beam are to be thermally insulated. It isvital that these dimensions are known at the design stage, along with the specific locations of fire dampers.The Association for Specialist Fire Protection is working towards defining a set of agreed methodologies.

Good interface engineering should includethe fire protection scheme for the beams, aswell as the dimensional characteristics ofthermal insulation for those services intendedto interface with or pass through the beams.

If the dimensional characteristics of bothforms of covering – along with spacing needs– are not considered early in the design co-ordination process, installers may find serviceswill not fit through beam apertures, forcingpipework and ductwork to deviate laterallyand/or horizontally. This can massivelyincrease installation time and materials costs.

Furthermore, if these issues are factored intothe design co-ordination process by thestructural engineer, services designer andspecialist contractors, it may reveal that a seriesof dimensionally identical holes in a cellularbeam is not an optimal arrangement.

A more efficient services distribution mayaccrue from a series of circular, flat oval orsquare apertures co-ordinated to match theservices distribution. The added cost in designtime is likely to be recouped from a betterco-ordinated, faster installed, and betterperforming services installation.

However, while pipework and ductwork canshare a penetration, fire dampers should not,as it is important to allow the fire damperroom for expansion. Other services runningin the same aperture as the fire damper mayhinder this expansion.

Integrating fire dampersAs there is no industry-agreed interface detail,for fire dampers with structural beams, firedampers are regularly subject to improvisationby installing contractors (figure 13). The sameis true for dampers installed on a ductworkspigot, where the duct is effectively part of thepreceding fire zone.

Figures 14 shows an off-set fire damperinstallation appropriate for use adjacent to afire separation, which could be modifed foruse near to a structural beam. The basicapproach is in accordance with BS 476 Part 20,BS EN 1366-2 and BS ISO 10294-1.

It is rare for fire dampers to be required inlarge open-plan office areas where structuralbeams are most likely to interface with buildingservices. It is also general practice not to createfire compartments in ceiling voids, for examplewhere a void is used as a return air plenum.

While fire partitions will be the norm in coreareas, the universal columns in these areas tendto be larger and connected by smaller transversebeams, enabling the services to run beneathrather than through those beams. The firepartitions will not necessarily be on the line ofthe structural beam, and any fire dampers arelikely to be installed in or near the firepartitioning as shown in figure 14.

The Fire Damper Working Group of theAssociation for Specialist Fire Protection (ASFP)is working towards nationally applicable, testedand assessed fire damper installation methods.The subject is very complex and contentious,and as yet there is no industry-accepted methodof locating fire dampers in structural beams.

In the event that a fire damper is required tobe fitted direct to a structural beam, engineersshould recognise that every component usedto attach a fire damper to a beam – the faceplate, expansion frame and fixing bolts – mustbe fire-rated equal to, or greater than, the firedamper and the fire protection applied by thespecialist contractor.

Irrespective of the method chosen tomount the fire damper, the method must bepresented to the local fire officer for commentsand approval. Fixings into structural steelworkmust be agreed with the structural engineer.

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Figure 18, page 26Figure 9, page 12



Glossary on page 31

Key m&e watchpoints

See also

The m&e interface engineeringshould include details of the fireprotection scheme for the beams,and the dimensional characteristicsof that fire protection

Services engineers should checkthat services will fit through fireprotected beam apertures withoutthe need for deviations

Services engineers should establishwhether the steelwork fireprotection is to be contracted outto a specialist fire protectioncontractor, and determine theprecise dimensional details of thesteelwork fire protection

All fire damper installation methodsmust be presented by the ductworkdesigners to the local fire officerfor comment and approval

All fixings onto the structuralsteelwork must be agreed with thestructural engineer

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Figure 14: A fire/smoke damper set-off from a fire partition (potentially a structuralbeam). Reference: BSRIA Detail Drawings.

Fixings and hangers for fire-rated ductworkto have the same fire rating as duct

Fire separationconstruction

Penetration seal as specified by the manufacturerof fire-rated ductwork

Non-combustiblefire stoppingmaterial

Retaining anglesfixed to duct with5 mm diametersteel fasteners atmaximum 400 mm centres

Ductwork hangerposition close enough to damperto prevent twistingduring installationand operation

Access panel fitted to appropriateside of damper

Steel angle orchannel undercentre line ofdamper

Expansion clearance3 mm per 300 mmwidth and height ofduct to cater forexpansion

Sheet steel2-hour fire-rated ductwork

Drop rods fittedto soffit, maximumstress 10 N/mm2

Figure 13: A fire damper suspended from a beam. Poor co-ordination forced the cutting of the beam fire protection systemfor Unistrut fixings – a typical improvisation by a services installer.

©BS

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Key installation issues

2

Services installation 1Properly co-ordinated drawings are critical to ensuring a quality installation. Get it right, and theclient will inherit cost-effective, well-installed, well performing and easily accessible services. Get it wrong,and the materials and labour overspend will adversely affect the speed, quality and profitability of theproject. The sums involved will not be small: on city office projects contractors can overspend by £250 000for additional fittings to cope with unforseen services deviations, plus a similar sum for lost productivity.

By the time designers’ drawings get to thecontractors, the emphasis tends to be on thevolume of services that need to be fitted intothe ceiling void in a given time, rather thanthe location of vent, point, drain points, andpotential points of leakage.

At the installation stage, good interfaceengineering should also concentrate oninstalling the services in a manner that willconsume the least amount of operative hourson site, and create the least problems forsubsequent operation and maintenance.

Unfortunately, the advice of the installing orspecialist contractors is rarely sought at thestage when the designers are concentrating onsystem functional requirements, such as airmovement and temperature. However, asuccessfully engineered interface is one that:� facilitates the installation� can be installed productively� does not require too many fittings to dealwith deviations.

Services running parallel to beamsIt is important that the services design teamunderstands the effects of running services inparallel to the beams. If the co-ordinationprocess is carried out in two dimensionsonly, then it is possible that neither the plannor the elevation drawings will reveal a co-ordination clash between pipework runningparallel to a beam, and the circular ductworkrunning at 90o to the beam, and chosenspecifically to take advantage of the circularpassageways in a cellular beam.

The cost to the client in terms of delayswhile pipework is reconfigured by theinstalling contractor could be better spent atthe scheme design stage by nominatingrectanglar holes in the beam, and then usingmore space-efficient flat oval ductwork.

Issues to address during

Figure 15 shows a cellular beam in line witha lattice beam. Designers can be mislead intobelieving that the centres of the apertures inboth beams may be assumed to be identicalfor each hole in the cellular beam, whereasthe centre points of adjacent triangles in thelattice beam can be offset by up to 200 mm.The tolerances will be tighter once fireprotection is applied.

Depth restrictionsThe height available for services distributionis defined by the distance between the ceilingand the lowest of the beam apertures. In figure22, between 40 and 60 mm of depth from theunderside of the slab to the bottom face of thebeam is effectively lost as a distribution zone.

This may be a crucial issue for distributionservices that must be laid to a fall, and need to

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Figure 18, page 26Figure 9, page 12Figure 22, page 28Table 4, page 21



Glossary on page 31

Key m&e watchpoints

See also

Design should enable services tobe installed in a manner that willconsume the least amount ofoperative hours on site, andcreate the least problems forsubsequent operation andmaintenance

Check that the chosen beam fireprotection system will not reducethe free area of the beam aperturebelow that required for services

Check the details of theinstallation method for the beamfire protection system to ensuredesign clearances for services willbe maintained

Pay particular attention to therelationship between the actuallocation of beam apertures andservices (such as fan coilcondensate pipework) that needto be laid to a fall

Obtain the actual measurement ofthe distance between the soffitand the top edge of the lowestaperture in the beam. This willdetermine the true void areaavailable for services distribution

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Left, figure 15: A cellular beam in line with a lattice web beam.Designers can be misled into believing that the centres of theapertures in both beams will always be in line – they will not, adifference that may be greater once fire insulation is applied (seeFigure 16). ©BSRIA.

start as high as they can in the ceilingplenum.

Figure 16 also shows a lattice beamenclosed by a fibreboard-based fireprotection system of about 40 mm thickness.The board is fixed to the steelwork usingadhesive, or spot-welded pins to which thefoil-faced board is then attached.

With this kind of fire protection, the freearea of beam that can accommodate servicesis vastly reduced – a factor that must be takeninto account by the services designer at thedetailed design stage.

Above, figure 16: A lattice beam enclosed by a fibreboard-based fire protectionsystem. Note that the free area of the beam is now considerably reduced. ©BSRIA.

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Structural issues

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Services installation 2Issues to address during

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Although the highly serviced installationshown in figure 17 appears at first glance tobe well co-ordinated, closer inspection willreveal a high number of deviations bothhorizontally and vertically.

Some of these deviations could have beenavoided had the beams been strategicallyequipped with different sizes and shapes ofopenings, such as flat oval or rectangular,more closely related to the location ofservices.

Here, the services designers have made thebest use of what was made available, but abetter co-ordinated installation could haveresulted had the structural design providedholes in the beam in the shape, size, numberand location required by the servicesengineer. That they haven’t is probablyevidence of a sequential (rather thanintegrated) design process between thestructural and services engineers.

Figure 18 shows a problem created by afocus on services running through beams atthe expense of those services running parallelto them. While the design team were correctto place the gravity pipework as high in thevoid as possible, more attention could havebeen paid to co-ordination to ensure that thefan-coil flow and return pipework did nothave to deviate, creating the need for morefittings and the potential for higher flowresistance. It is not unusual for the co-ordination ofservices to be done in two dimensions. If thisis considered in plan view, the consequenceswill not be immediately obvious. In this case,had the design team been more strategic withthe beam openings, flat oval ductwork couldhave been used instead of circular ductwork,enabling the pipework to maintain a clearrun.

Figure 19 shows an example of how poorlyco-ordinated services with cellular beams canlead to deviations and the creation ofpotential problems.

Here, the pipework contractor has beenforced to run flow and return pipeworkbeneath the beam. Having created a low

point in the circuit, the contractor had to fitdrain cocks. Not only could these valvesinterfere with the suspended ceiling, theycould also clash with light fittings that mayneed a clear depth of 150 – 200 mm.

Figure 20 shows pipework attached to afan-coil unit. The white polymer pipeworkcarries the condensate from the fan coil, andneeds to be laid to a fall.

The requirements of this one item can

Figure 17: While this installation shows the integration of serviceswith structure, deviations laterally and horizontally hint at asquential rather than a truly integrated design process. ©BSRIA.

Figure 18: Poor services-to-beam interface engineering. Not onlyhas the pipework been forced to deviate beneath the ductwork,but this is necessitated the labour-intensive fitting of joints anddrain cocks. ©BSRIA.

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Figure 11, page 16Figure 12, page 18



Glossary on page 31

Key m&e watchpoints

See also

Ensure that the spacerequirements for all horizontalservices are clearly expressed inearly design team discussions

Refer to manufacturer’sdimensional information andconstantly revisit the spacerequirements

Ensure that fan-coil flow andreturn pipework does not have todeviate, creating the need formore fittings and the potential forhigher flow resistance.

Be aware that apparently minorservices systems, such ascondensate pipework, can drivethe entire co-ordination processand deserve equal attention in thedesign process

Be aware that deviations inpipework can force the fitting ofdrainage cocks and valves thatcould subsequently compromiseother services and the suspendedceiling

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Figure 19: More poor services-to-beam interface engineering. The fitting of draincocks and valves such as these could not only interfere with other services such aslight fittings, they could be low enough to foul the suspended ceiling. ©BSRIA.

drive the entire co-ordination process, but ascan be seen, the close proximity of the fancoil to the beam – plus the inability to lineup all the fan coil pipework with theopenings in the beam – has forced thecondensate pipework to deviate immediately.Forcing the condensate pipework to deviateso soon after leaving the fan coil unit maymean that the fall will be far shallower than isrequired to drain the condensate effectively.

Figure 20: Poor interface engineering between a cellular beamand a fan-coil unit. The condensate pipework has been forced todeviate immediately after leaving the fan coil unit. More attentionat the design stage could have avoided this problem. ©BSRIA.

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Figure 21 shows the result of an installer’sattempt to co-ordinate services with thebeams shown in figure 15. In the foreground,flow and return pipework has had to deviateto pass through the cellular beam, and thendeviate a second time to find a way throughthe lattice beam in the background andthence to a fan coil unit.

Deviations such as this require additionalcut lengths of pipe and fittings, plus time tomark up, measure and cut the pipe, and extratime for installation. Once finished, each jointis then a potential leakage point.

Figure 22 shows evidence that once serviceshave been run at one level, space may nolonger be available for other services. Here,between 40 to 60 mm of depth has been lostby fixing cabling to the soffit, and thendropping it down so it can run through abeam aperture. Such practice can steal spacefrom other services of greater priority.

As services deviate from the slab topenetrate the beam, additional fixing isrequired, which absorbs the installer’s time.Alternatively, if the services are suspendedfrom the soffit to achieve an uninterrupted,horizontal run through the beams, then thespace above will be lost for distributing anyother services. Designers and contractors needto collaborate to decide on the most space-effective and cost-effective approach.

Figure 23 shows a fan-coil unit with its rigidventilation ductwork fed through theopenings in a webbed beam. The relationshipbetween the fan coil unit and the structuralbeam has created the need for a substantialamount of deviation pieces in the ductwork.

In this case, flexible or semi-rigid ductworkwould have been a faster and more cost-effective installation, rather than the multiplemeasuring, marking, cutting and fittingactivities required to make this solution work.

Such deviation in ductwork creates thepotential for turbulence, noise, pressure dropsand leakage. The advantages anddisadvantages (such as less efficient airflow) offlexible ductwork need to be identified bythe designer during the design process.

Services installation 3Issues to address during

Figure 24 shows an alternative to figure 22.Here the use of flexible ductwork made useof the cellular openings without the need forcomplicated and expensive on-site fabrication.However, although flexible ductwork can beeasily threaded through cellular beams, a highnumber of duct bends can restrict airflow andcreate noise problems.

The headline message from these examplesand those on preceding pages is that thechoice of structural system used on the projecthas a fundamental effect on floor to ceiling

Figure 21: A contractor’s attempt to co-ordinate services through acellular beam and a lattice-web beam. Note the number of deviationsnecessary for the services to pass through the beams. ©BSRIA.

Figure 22: Between 40 to 60 mm of depth can be lost from theunderside of the slab to the bottom face of a ceiling, adverselyaffecting the ability to run cabling horizontally. ©BSRIA.

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Glossary on page 31

Key m&e watchpoints

See also

Note that pipework and ductworkdeviations require additional cutlengths of pipe and fittings whichcreate potential leakage points.

Discuss with the client theinstallation and performancebenefits (and disadvantages) ofusing flexible ductwork asopposed to rigid ductwork

Inform the client that savings fromintegrating services withstructural beams will only beachieved if contractors andinstallers are not required toimprovise the interfaces on site

heights and external envelope area. From aservices fit-out perspective, the choice ofstructural system has a fundamental effect onthe building services design.

In turn, the services design engineer needsto have a better appreciation of the effect thata design will have on the time taken to installthe services by the contractors, and of theknock-on effects in terms of operation andmaintenance of the building. This needs to becommunicated to the client in the early stagesof design.

Figure 23: The use of rigid ventilation ductwork fed through beams can result in ahigh number of deviation pieces, all of which are labour-intensive to fabricate and fit,and as a consequence be a source of air leaks during building operation. ©BSRIA.

Figure 24: An uncontrolled number of bends in flexible ductworkwill cause loss of self-balancing between diffusers, and added noisethrough the diffuser that gets more air. ©BSRIA.

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Key m&e watchpoints, page 71


Mechanical engineering standards Structural standards

Standards

Further reading

Designers and contractors should always follow the guidance laid down in prevailing standards.

BS 5950: Structural use of steelwork in building, Part 1: Code ofpractice for design. Rolled and welded sections BSI, 2001, ISBN 0580 33239 X

BS 5950: Structural use of steelwork in building, Part 8: Code ofpractice for fire resistant design BSI, 1990, ISBN 0 580 18344 0

BS 6399: Loading for buildings Part 1: Code of practice for dead andimposed loads BSI, 1996, ISBN 0 580 26239 1

BS 476: Fire tests on building materials and structures, Part 4: Non-combustibility test for materials BSI, 1970, ISBN 0 580 05694 5

BS 8202: Coatings for fire protection of building elements, Part 2:Code of practice for the use of intumescent coating systems tometallic substrates for providing fire resistance, BSI, 1992, ISBN 0580 21037 5

McKenna P D & Lawson R M, Design of steel framed buildingsfor service integration, SCI-P-166, The Steel ConstructionInstitute (SCI), 1997, ISBN 1 85942 047 8

McKenna P D & Lawson R M, Service integration in Slimdek, SCI-P-273, SCI, 2000, ISBN 1 85942 110 5

Lawson R M, Design for openings in the webs of composite beams,SCI-P-068, SCI/CIRIA, 1989, ISBN 0 86017 283 X

Ward J K, Design of composite and non-composite cellular beams,SCI-P-100, The Steel Construction Institute, 1990, ISBN 1870004 51 5

Lawson R M & McConnel R, Design of stub girders, SCI-P-118,SCI, 1993, ISBN 1 870004 80 9

Neal S & Johnson R, Design of composite trusses, SCI-P-083,The Steel Construction Institute, 1992, ISBN 1 870004 79 5

Fire protection for structural steel in buildings 3rd ed., Associationfor Specialist Fire Protection, 2002, ISBN 1 870409 20 5

The use of intumescent coatings for the fire protection of beamswith circular web openings, AD 269, New Steel Construction, Vol.11 No. 6, Nov/Dec 2003, SCI/BCSA, ISBN 0968 - 0098

Yandzio E, Dowling J J & Newman G M (editors), Structural firedesign: Off-site applied thin film intumescent coatings, The SteelConstruction Institute, 1996, ISBN 1 85942 038 9

EN 12237: 2003 Ventilation for buildings - ductwork - strengthand leakage of circular sheet. ISBN 0 5804 15880

BS 476 Part 20, 1999, Fire tests on building materials andstructures. Method for determination of the fire resistance ofelements of construction (general principles),1987 ISBN 0580158 977

BS EN 1366-2: 1999, Fire dampers, ISBN 0580 324 281

BS ISO 10294-1: 1996 Fire-resistance tests. Fire dampers for airdistribution systems – test method. ISBN 0580 27523 X

BS EN 1366-2: 1999 Fire resistance tests for service installations– fire dampers ISBN 0580 32428 1

BS ISO 10294-1: 1996 Fire resistance tests. Fire dampers for airdistribution systems. Test method 6 ISBN 0580 27523 X

Pennycook K, (ed) Rules of thumb (UK 4th edition) BSRIA BG14/2003, BSRIA 2003 ISBN 0 86022 626 3

Hejab M & Parsloe C, Space allowances for building servicesdistribution systems – detail design stage, BSRIA TN/92, ISBN 086022 350 7

Ductwork turns full circle Lindab (www.lindab.com/Sweden/products/pdf/vent/broschyr/ductwork.pdf)

AG 7/98 BSRIA 1998 Library of system control strategies ISBN086022 497 X

TGH3 On-site measurement of intumescent coating systems.Association of Specialist Fire Protection, ISBN 1870 40912 4

Lawrence Race G, Design checks for HVAC, AG 1/2002, BSRIA2002, ISBN 0 86022 589 5

CIBSE Guide B3, Ductwork, Principles of design, CIBSE 2002,ISBN 1 903287 20 0

de Saulles T, The illustrated guide to mechanical building services,BSRIA AG 15/2002, BSRIA 2002, ISBN 0 86022 606 9

de Saulles T, The illustrated guide to electrical building services,BSRIA AG 14/2001, BSRIA 2001, ISBN 0 86022 586 0


Glossary

Building services terms

Building management system A microprocessor-based system that is connected to devices in theceiling void, such as fan coils, VAV boxes, terminal units, lighting, firealarms and similar devices to enable remote monitoring and control.

Chilled beams/ceiling panel A simple cooling device incorporating a chilled-water pipe and mountedin a ceiling void. It requires a ceiling void depth of about 300 mm.A chilled ceiling comprises a serpentine arrangement of pipework,fitted to a slim, perforated ceiling panel. It needs a shallow ceiling voidof between 60 – 70 mm.

Condensation pipework Pipework required to drain condensation from devices such as fan coilsunit (qv). Condensation pipework needs to be laid to a fall across the

ceiling void to enable the condensate to be drained.

Constant volume system A simple system used to provide a fixed volume of tempered air inmulti-zone buildings often associated with partially centralised air/watersystems, such as fan coils (qv).

Fan coil unit A device in the ceiling void which comprises a fan, heating coil, coolingcoil and air filter, housed in a metal casing. The fan-coil unit is suppliedwith air from the main air supply ductwork. This air passes into aplenum chamber with multiple outlets for connection to one or moreterminal devices (qv), plus connections for valves and controls

Fire damper A device connecting two zones or sections of ductwork and designed toclose under a fire or high heat condition, and rated to maintain itsintegrity for a pre-determined time, at or below a certain temperature.

Pressure drop A term describing variations in air or water differential pressure causedby obstructions or constrictions to flow. Pressure drops can be causedby bends or in-line elements such as fire dampers (qv).

Terminal device The final device at the end of a mechanical ventilation or airconditioning system. Its primary role is to supply and direct air intothe occupied zone at the desired temperature and location.Terminal devices may be connected to a separate diffuser located in asuspended ceiling or in a raised floor.

Variable air volume (VAV) An air-conditioning system consisting of centralised plant connectedto supply air ductwork distributed in the ceiling void, which carriesair at a given temperature to terminal devices (qv) called VAV boxes.These boxes regulate the amount of air entering the occupied space

Variable refrigerant flow An air-conditioning system requiring a ducted air supply, (insulated)(VRF) pipework for refrigerant gases, and micro processor-based electronics

to control the devices. The VRF units are normally housed in terminaldevices (qv) called ceiling cassettes.


Glossary

Structural terms

Bending moment The total bending effect at any section of a beam due to the self-weight andapplied loading.

Castellated beam A steel beam with regularly spaced hexagonal openings in the web, formed bycutting and re-welding a hot-rolled section.

Cellular beam A steel beam with many regularly spaced circular holes in its web, formed by aproprietary fabrication process.

Composite beam A steel beam supporting a concrete slab with a shear connection (usuallystuds) between the beam and slab, such that they act compositely together.

Intumescent coating A coating applied to steel beams or columns that expands to many times itsinitial thickness when heated, thus providing an insulating layer to the steel.

Non-composite beam A steel beam that acts alone and is not assisted by the concrete slab incarrying the load.

Primary beam A structural member designed to transfer loads from the secondary beams tothe columns.

Secondary beam A structural member supporting the floor slab, spanning between columns orprimary beams.

Shear resistance The ability of a section to resist the shear forces acting on it.

Stub girder Vierendeel girder consisting of a universal column section as a bottom chord,a concrete slab as a top chord and steel stubs as verticals.

Tapered beam A beam in which the depth of the web varies along its length.

Truss girder A triangulated frame built up wholly from members in tension andcompression used as a beam.

Universal beam (UB) A hot-rolled steel I section consisting of a web and two flanges of uniformthickness.

Universal column (UC) A hot-rolled steel H section consisting of a web and two flanges of uniformthickness.

Vierendeel girder After Professor Vierendeel. An open-web girder without diagonal members,but with rigid joints between the top and bottom chords and the verticals.

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