CCIP Hybrid Good Practice Guide

C. H. Goodchild BSc, CEng, MCIOB, MIStructE

J. Glass BA, Dip Arch, DipBRS, PhD, ILTM

A guide to choosing and using combinations of precast and in-situ concrete for better value structural frames

Best Practice Guidance forHybrid Concrete Construction

1

1. Executive summary 2

2. Introduction 3

3. Why use Hybrid Concrete Construction? 5

4. Best Practice Guidance for Hybrid Concrete Construction 9

5. Achieving best practice 16

6. Case studies 28

Ipswich Town Football Club: North Stand 28

Toyota (GB) Headquarters 34

West Car Park, West Quay, Southampton 39

Whitefriars, Canterbury 47

7. Conclusions 51

8. References and further reading 52

Appendix: Background research 53

A.1 Context 53

A.2 Best Practice Guidance for Hybrid Concrete Construction research project 55

A.3 Structural design 61

Best Practice Guidance for Hybrid Concrete Construction

Contents

Published by The Concrete Centre on behalf of industry sponsorsRiverside House, 4 Meadows Business Park, Station Approach, Blackwater, Camberley, Surrey GU17 9ABTel: +44 (0)1276 606800 Fax: +44 (0)1276 606801

TCC/03/09 Published September 2004 ISBN 1-904818-09-9Price Group L © The Concrete Centre

All advice or information from The Concrete Centre is intended for those who will evaluate the significance and limitations of

its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting

from such advice or information is accepted by The Concrete Centre or their subcontractors, suppliers or advisors. Readers

should note that The Concrete Centre publications are subject to revision from time to time and should therefore ensure that

they are in possession of the latest version.

Front cover: Inland Revenue, Nottingham, interior of building.

Photo: Martine Hamilton-Knight/Built Vision. Architect: Michael Hopkins & Partners.

British Precast is the trade federation representing the UK precast and concrete masonry industry. The Structural Precast

Association is a member of British Precast and is supporting this publication. Website: www.britishprecast.org Tel: 0116 253 6161.

CONSTRUCT is an association of member companies dedicated to the task of improving the construction efficiency of in-situ

concrete frames and associated structures. For further details contact the Secretary on 01276 38444.

Acknowledgements

The Advisory GroupJohn Caine Curtins Consulting Engineers

Norman Brown ABC Structures

Clive Budge British Precast Concrete Federation

Mike Downing Downing Associates

Charles McBeath whitbybird

Rob Moura Ascon/Edmund Nuttall

Chris Packer HBG Construction

Mahesh Parmar Anthony Hunt Associates Ltd

Martin Southcott The Concrete Centre

Russ Wolstenholme W S Atkins for DTI

Interviewees and Participants at WorkshopsMatthew Allen Sir Robert McAlpine Design Group

Roger Bailey Tarmac Precast Concrete Ltd

Graham Beardwell Ove Arup & Partners (M&E)

Andy Butler Stanhope plc

Peter Carruthers Sir Robert McAlpine Ltd

Ian Cordingley Upton McGougan Consulting Engineers

Mike Crook HOK Sport

Ian Curry AMEC

John Cutlack Jan Bobrowski & Partners

Brian Cutler Independent Consultant

Phil Doyle Sheppard Robson Architects

Chris Edwards HBG Construction

Adrian Falconer Ove Arup & Partners

Jim Farley Sir Robert McAlpine Ltd

Ian Feast Hammerson plc

Andy Fereday Miller Construction

Jack Gabrielcyzk Taylor Whalley Spyra

Tony Giddings Argent Group

Kevin Gill Gill Associates

Ray Hull Byrne Brothers Ltd

Rob Jones Davis Langdon and Everest

Simon Lake Toyota GB

Suqlain Mahmood Sir Robert McAlpine Design Group

Bob Martin Bison Concrete Products

Gavin Murgatroyd Gardiner & Theobald

Dominic O’Neill Fitzroy Robinson

Robert Reed HBG Construction

Martyn Reeve Sir Robert McAlpine Ltd

Peter Rogers Stanhope plc

David Rose Ipswich Town FC

Peter Stackhouse Lyons Sleeman & Hoare

Thierry Suc Upton McGougan Consulting Engineers

George Tootell CV Buchan

Dennis Vittle The Marble Mosaic Company Ltd

David Walker Trent Concrete Ltd

Russell Woby Hoopers Architectural Services

Researchers on ‘Hybrid ConcreteConstruction for the UK Market’Ghassan Aouad University of Salford

Bousmaha Baiche Oxford Brookes University

Peter Barrett University of Salford

Pal Chana BCA (formerly of Imperial College)

Charles Fowler RPEG, University of Reading

Colin Gray RPEG, University of Reading

Rod Webster CiD

Dedicated to Gerry Shaw.

The Concrete Centre acknowledges and appreciates the support given by many individuals,companies and organisations. These include:

3

Introduction 2

Introduction

Hybrid Concrete Construction (HCC) combines all the benefits of precasting (e.g.

quality, form, finish, colour, speed, accuracy, prestressing) with all the benefits of in-situ

construction (e.g. economy, flexibility, mouldability, thermal mass, continuity, durability,

and robustness). HCC can answer client demands for lower costs and higher quality by

providing simple, buildable and competitive structures that offer consistent performance

and quality.

To date, the use of HCC has been confined mainly to bespoke structures. Some of these

structures achieved cost savings of up to 30% over more conventional structural frames.

Naturally, the concrete industry was eager to identify how this order of saving might

be achieved consistently and more widely. As well as responding to the challenges

laid down by the Latham 2 and Egan3 reports, wider use of hybrid structures would

significantly improve the productivity and therefore competitiveness of the whole UK

concrete frame industry.

With this in mind, the Reinforced Concrete Council was successful in gaining government

support, through the Department of Trade & Industry Partners in Innovation (PII)

scheme, to carry out a research project entitled ‘Best Practice Guidance for Hybrid

2

1 Executive summary

Executive summary

Hybrid Concrete Construction (HCC) is about providing best value in structural frames.

HCC provides simple, buildable and competitive structures that answer client demands

for better value. It meets industry requirements for increased prefabrication, increased

off-site activity, safer and faster construction and consistent performance.

Despite the challenges thrown down by the Latham2 and Egan3 reports and their

successors, the UK has been slow to realise the benefits of HCC. One of the barriers to

HCC’s more widespread use was found to be the lack of comprehensive guidance, a

situation which this publication aims to change.

Based upon work carried out under a PII research project, this publication demonstrates

how to achieve best practice. The guidance explains the benefits that result from:

■ early involvement of specialist contractors

■ using a lead frame contractor

■ using best value philosophy

■ holding planned workshops

■ measuring performance

■ trust

■ close co-operation – with an emphasis on partnering.

The guidance is supported by case studies and shows that although there are intense

periods of co-ordination during the design phase, there are tremendous rewards on site

and in use. Best value is achieved through communication and measured in terms of

buildability, construction speed, aesthetic, quality, environmental and whole-life cost

benefits.

HCC can achieve very significant cost savings and give rise to some very satisfied

clients. This publication is intended to show how this can be achieved.

Figure 1 Gatwick office project

Showing precast floor beams onto

in-situ beams and columns.Photo: J Doyle

5

Why use Hybrid Concrete Construction? 3

3. Why use Hybrid Concrete Construction?

Hybrid concrete technology is used primarily to achieve fast and cost effective construction

by removing labour-intensive operations on-site and replacing them with mechanised

production in precasting yards and factories. Potentially there are many other advantages;

these are discussed below.

Traditionally, cost is the most influential factor in the choice of frame material. Although

the structure of a building represents typically only 10% of construction cost, the

choice of structural frame material can have dramatic effects on the cost of other

elements of construction – such as external cladding, services and internal planning. It

also affects net-to-gross floor area ratios10. It can even determine whether air conditioning

or suspended ceilings are necessary. Selecting the correct structural framing material is

vital to a project’s feasibility and success.

Individually, each structural material has merits, yet there is greater benefit in combining

materials. The advantages of one material compensate for the drawbacks of another.

In-situ reinforced concrete is commonly viewed as the most economic framing option,

4

2 Introduction

Concrete Construction’. The research was completed under the auspices of the

Reinforced Concrete Council’s successor, The Concrete Centre.

This project built on previous research1 that had identified an enthusiasm for HCC.

Combinations of precast and in-situ concrete were found to be broadly cost neutral;

construction times were equal if not better than conventional construction methods

and HCC offered many other potential benefits such as reduced whole-life costs. Yet

its acceptance and more widespread use was hindered by a general lack of experience

or guidance.

This publication aims to change that situation. It is the main output from the best

practice research project, which itself was based on obtaining a fundamental

understanding of customer requirements, design concerns, construction business

processes and supply chain issues. This understanding has been achieved through the

help of many individuals and companies within the construction industry. It forms

the basis of this best practice guidance, which has been written, and therefore should

be viewed in the light of broader based initiatives in improving the construction

procurement process. These initiatives include:

■ Constructing the Team (Latham)2

■ Rethinking Construction (Egan)3

■ Movement for Innovation (M4i)4

■ Value management5

■ Construction Best Practice Programme6

■ Process Protocol7

■ Accelerating change8

■ Learning from the best9

�The belief is that if everybody involved in a project can work to an agreed

set of processes and procedures, then we will not only be more efficient,but

we will be in a much better position to meet the client�s business needs.�

Process Protocol7

Cost

Figure 2Italian floor construction

Hollowcore floor units have been

placed on in-situ beam formwork with

heavy duty falsework.Photo: Gruppo Centro Nord

7

Why use Hybrid Concrete Construction? 3

An increasingly frequent maxim is the ratio 1 : 5 : 20014. This represents the relationship

between capital cost, operating costs and business costs during the life of a building. It

recognises the importance of 'whole life cost' and changes the emphasis from first cost

to whole-life cost. Here, HCC can excel, not only in terms of energy demands, which

relate to the ‘5’, but also in terms of comfort and aesthetic leading to productivity

gains, which relate to the ‘200’.

Project cost is inextricably linked to speed as faster programmes mean earlier investment

income, lower interest charges, reduced construction preliminaries and, consequently,

optimal development cost.

Speed depends on designs that are easy to procure and construct. Encouraging speed of

construction through buildability should be a fundamental objective of design. It may

take more design effort and require contractual flexibility, but it results in more satisfied

clients, designers, contractors and end-users.

HCC essentially takes work away from site and into the factory, thus reducing the duration

of operations critical to the overall programme on site. Precasting is not constrained by

site progress or conditions and can continue independently of on-site operations.

Construction on-site should be quick provided there has been sufficient co-ordination

and attention to detail. Some HCC techniques can reduce or eliminate the need for

follow-on trades such as ceilings and finishes. This enables even faster programme

times, but requires greater co-ordination and care in detail and protection.

Buildability is the extent to which design simplifies construction and eradicates

unnecessary cost, subject to the requirements of the completed building. HCC’s key

strength is buildability. The nature of HCC forces pre-planning and the resolution of

construction issues, for instance, just-in-time deliveries reducing crane hook time

become a natural part of the process.

High quality finishes can be most easily produced in factory conditions in precast units.

In-situ elements and joints are important structurally but may not need to achieve

the same quality of finish and so can be hidden from view. Where finishes to in-situ

elements are required, the quantities can be minimised.

Traditional formwork typically accounts for up to 40% of in-situ frame costs and can be

a slow option. The trend is towards faster construction, better quality, more prefabrication

and reduced site activity. These demands can be met by HCC, where a high percentage

of the work is carried out in a factory and requires less skilled on-site labour than

traditional methods.

Speed

Buildability

Construction

6

3 Why use Hybrid Concrete Construction?

while precast concrete promotes speed and high quality. Combining the two by

adopting hybrid techniques gives even greater speed, quality and overall economy.

The resulting elemental cost of the frame may be higher, but total project costs are very

often lower than more conventional frames due to time and buildability savings on site.

For instance, use of a hybrid concrete frame instead of a composite steel frame on a

shell-and-core office project in central London led to savings of 29% and increased net

lettable floor area from 33,700 m2 to 38,200 m2 – (a 13% increase)11.

Whole-life costs are especially important for owner-occupiers and PFI operators. HCCs

can help reduce energy requirements – they give excellent facility for fabric energy

storage – using the thermal mass of concrete to moderate energy demands in cooling

and heating buildings.

Figure 3Toyota (GB) interior

Showing exposed precast concrete floor units.Photo: Barry Bulley/Trent

1 5 200

CAPITAL COST COST IN USE BUSINESS COSTS

To operate and maintain the building will cost five times the capital costs over the life of the building. However, thecost to the business, including salaries and staff productivity, of occupying the asset is 200 times the capital cost.

In some quarters this has been extended by attributing 0.1 to the cost of design and 1000 to the cost of theoutputs from the building.

Table 1 Long-term costs

of buildings14

HCC reduces the potential for accidents by providing successive working platforms on

a generally less cluttered site. Safety aspects of leading-edge work are similar to, and

should be guided by, recommendations for precast flooring12. Precast spandrel beams

can provide immediate edge protection.

A high proportion of the work is carried out in the precast factory by experienced

personnel. On site, the innovative use of HCC and the fact that buildability is a key

concern helps ensure that each safety plan is drafted on the individual project’s merits.

Concrete produces eminently lettable buildings which are stable, robust, fire resistant

and adaptable, as well as solid, quiet and essentially vibration free. Equally concrete's

thermal properties can be exploited in naturally ventilated low-energy buildings. The

finish and shape of exposed units can be used to help with even distribution of lighting

levels and to reduce noise levels..

Structurally, concrete is very versatile. Long spans can be achieved using large units, or

by pre-stressing or post-tensioning. Precast units can be 'welded' together using modern

very high strength concretes, which allow full tension laps between reinforcing bars to

be achieved in laps of only six diameters13.

HCC has much to offer. It can respond to the often competing needs for economy,

safety, speed, quality, flexibility, durability, service integration, appearance, function,

material availability and preferred construction methods.

HCC requires a high level of commitment from all parties at all stages of the design and

construction process and from all the contributors to that process. For full advantage

to be taken, HCC should be considered at the beginning of the design process because

it becomes progressively more difficult to influence design and reduce costs as design

development proceeds.

The remainder of this publication is devoted to best practice guidance so that the

commitment required might be better directed and the advantages of HCC are fully

exploited and delivered consistently.

9

Best Practice Guidance for Hybrid Concrete Construction 4

4. Best Practice Guidance

The ‘new’ processes necessary to achieve best practice in HCC are shown in Figure 4 as

the ‘Best Practice Guidance for Hybrid Concrete Construction process map’.

This process map has been derived from two larger process models developed during

the research project described in Appendix A.2. The larger models were developed,

refined and honed through a series of thirteen individual interviews with practitioners

and five workshops. One model illustrated the whole process and reflected what the

interviewees considered to be the ‘how it should be’ process within an Egan-compliant

procurement framework. This is presented as Figure 5. Another model (not featured)

described ‘how it is’. Figure 4 highlights the differences between the two larger models

and shows how to make ‘how it is’ into ‘how it should be’.

Figures 4 and 5 are aimed at achieving best value, as defined by the client, through

partnering and collaborative team work. They have been aligned with RIBA Stages of

Work 15; Process Protocol 7, a tool for looking at the procurement process in construction

projects; and with research by Gray16 and Barrett17 into in-situ and HCC processes.

Usefully, these new route maps can be applied to achieve best practice in all concrete

frame construction: they are considered to be equally applicable to in-situ, HCC or

precast concrete frame construction.

The ‘new’ processes shown in Figure 4 are explained in more detail below.

Early involvement of specialist contractorsDuring the early part of the procurement process the project manager should facilitate

the involvement of contractors and specialists much earlier than is traditionally the

case. Specialists should be appointed during conceptual design while structural options

are still being considered. This allows committed specialist knowledge to be brought to

bear at the time when options are being chosen. There may be contractual ramifications

arising from this change, but design becomes a much more participative affair.

For contractors, early appointment allows them to be committed to a project with the

confidence that their input will be rewarded. Design decisions are part-owned by the

eventual constructors, which benefits the whole project. Without early appointment (or

reward) contractors, in a commercial world, will not give more than courteous attention

to helping a project in the initial stages when their ideas and experience might

ultimately benefit another company. For example, one leading specialist company

usually sets a limit of one day of free advice per project.

Early appointment of specialist contractors goes against traditional tendering processes,

but this is the very nub of partnering. The client has the option of tendering or trusting,

8

3 Why use Hybrid Concrete Construction?

Safety

Other benefits

Summary

Best practice

New processes for best practice

11


LFC should be approached and, ideally, appointed after initial conceptual design makes it

clear that an HCC solution may be suitable. Specialists’ knowledge can then be brought

to bear in working up concepts into viable schemes and is also available to help with

detailed design and buildability issues. The model moves away from the traditional

relationship where specialist contractors are detached from the design process.

Best valueThe model is devised around a more ‘Eganesque’ procurement regime, whereby best

value, partnering and project feedback play a much stronger part than is the case in

more traditional forms of procurement. Traditional procurement routes are based

on competitive practices, which often preclude the formulation of teams and the

achievement of a best value outcome. The emphasis in this new model is on achieving

10

4 Best Practice Guidance for Hybrid Concrete Construction

but tendering costs time and it also tends to create adversarial relationships from the

start. Trust encourages teamwork.

Lead frame contractorsIn the model, a lead frame contractor (LFC) is appointed to take overall responsibility

for the structure. This role could be undertaken by a multi-disciplinary firm, a precaster

or an in-situ contractor. The LFC could be large enough to undertake the whole frame

package themselves or act as the single point of responsibility, procuring various

work packages from other specialist suppliers, which might include precasters, in-situ

contractors or even steel fabricators.

LFC is a function recognised in construction management methods of procurement. An

Figure 4Best Practice

Guidance for

Hybrid Concrete

Construction

process map

Gateway (see ProcessProtocol)7

Appointment

Blue textRecommended‘new’ ways ofworking

Black textNormal practice

HPIHybrid ConcreteConstructionPerformanceIndicators (ourversion of KPIs)

Define ‘best value’.

Undertake value andrisk assessment.

Think HCC.

Think HCC.

.

Develop FES (Fabric Energy Storage)strategy.

Agree terms for earlyinvolvement.

Agree terms forearly involvement.Liaise withspecialist suppliers.Provide advice.

Provide advice asrequired.

Propose HPIs.Carry out ‘best value’workshop.Addresssustainability.

Evaluate qualityrequirements of frame.

Agree HCC option.

Agree FES strategy.

Agree HPIs. Participatein ‘best value’workshop.

Agree HPIs. Participatein ‘best value’ workshop.Provide technical andfinancial advice. Finalisestructural concept.

Agree HPIs. Participatein ‘best value’ workshop.Provide advice.

Participate in ‘best value’workshop if required.

Agree information flowsand approvals procedure.Facilitate contractor helpin design.

Visit specialists. Checkfor repetition. Integratestructure and services.

Agree HCC specification.Check for repetition.Integrate with services.

Integrate structure and services.

Liaise with designers toproduce final scheme.

Liaise with designers &specialist suppliers. Startproduction drawings.Provide advice.

Run an ‘open book’.Start productiondrawings.

Agree strategy for on-sitedecision making.

Liaise with LFC (andspecialist suppliers).

Liaise with specialistsuppliers to agree startdates, method statements,H&S plan and productiondrawings.

Generate productiondrawings. Produce methodstatement & H&S plan.

Measure performanceagainst HPIs

Agree programme.

Participate in virtualrun through.

Monitor performanceagainst HPIs.

Measure performanceagainst HPIs

Erect frame.

Erect frame.

Participate in workshop.

Arrange workshop.Feedback and makerecommendations for future projects.

Make recommendationsfor future projects.Participate in projectfeedback workshop.

z`

Participate in workshop.Give feedback.Make recommendations.

DESIGN (1)

Work up chosen option

DESIGN (2)

Production information

CONSTRUCTION(1)

Off-site manufacture

CONSTRUCTION(2)

On-site work

USE (1)

Post-handover

USE (2)

Occupancy

BRIEFING

Demonstrate the need

FEASIBILITY

Is it worth doing?

CONCEPTUALDESIGN (1)

Consider the options


Choose the option

PARTY HBased on traditional procurement

WORK STAGE h

DESCRIPTION h

CLIENT

PROJECT MANAGER

ARCHITECT

ENGINEER

OTHER DESIGNERS(INCLUDING QS)

MAINCONTRACTOR/ CONSTRUCTIONMANAGER

LEAD FRAMECONTRACTOR

SPECIALISTSUPPLIERS

END USER

Facilitate earlyspecialist involvement.

Measure performance against HPIs.

£

£

£

£

v v v vv

vKEY

WORKSHOPS h(see Table 4)

0: REUNION 1: DESIGN ROUND TABLE 2: START UP 3: RISK 4: PRE-CONSTRUCTION 5: POST-COMPLETIONREVIEW

2: START UP

13


Value Indicators and measuring performance Value-based methods require that value be measured (or at least estimated). First cost

should not be the only indicator of value and appropriate performance indicators need

to be selected and used.

Suitable indicators for HCC are presented in Table 2, with those towards the top being

the more important. The top six of these indicators might form the basis of HCC

Performance Indicators (HPIs) for a specific project.

Various forms of construction can be compared for ‘value’ by scoring each option

against indicators chosen and weighted by the client. Integrating score and weighting

gives a measure by which options can be compared, objectively.

Another indicator, safety, is an absolute necessity and must always be addressed.

Work stages The procurement process can be broken down into a series of work stages. There are

several ways of describing these work stages. Table 3 shows how the ‘work stages’

used in this publication align with the better known RIBA Stages of Work15 which

reflect traditional methods of procurement, and with Process Protocol Phases7, which

reflect more contemporary methods of procurement. These work stages were found

to best describe HCC. Indeed, they are particularly relevant to the procurement of

structure and are certainly relevant to the procurement of all forms of concrete frame

construction18.

12


Table 2 Value Indicators:

Hybrid Concrete

Construction

Performance

Indicators (HPIs)18

Note* The RIBA stages G and H

have been placed in this boxfor a reason. In traditionalprocurement, tenders can

interfere with RIBA Plan Stage F– Production Information,

which precludes any benefit tothe design process from the

early involvement of specialists.

Table 3Work stages

DESIGN (1)


DESIGN (2)


CONSTRUCTION(1)


CONSTRUCTION(2)

On-site work

USE (1)

Post-handover

USE (2)

Occupancy

BRIEFING


FEASIBILITY

Is it worth doing?




Choose the option

WORK STAGE h

DESCRIPTION h

RIBA PLAN OFWORK STAGE(TRADITIONAL)

PROCESSPROTOCOL PHASES (NON-TRADITIONAL)

Phase 0:Demon-strating theneed.

Phase 1:Conceptionof need.

Phase 2:Outlinefeasibility.

Phase 3:Substantivefeasibilitystudy &outlinefinancialauthority.

AAppraisal.

B Strategic brief.

C Outline proposals.

Phase 4:Outline conceptual design.

Phase 5:Full conceptual design.

G Tenderdocuments*.

H Tenderaction*.

D Detailed proposals.

E Final proposals.

F Production information.

J Mobilisation.

K Constructionto practicalcompletion.

L After practical completion.

Phase 6:Co-ordinated design,procurement & fullfinancial authority.

Phase 7:Production information.

Phase 8:Construction.

Phase 9:Operation & maintenance.

best value for the client. One of the ramifications of this is that the project manager,

in particular, has more responsibility for ‘continuous improvement’ aspects such as

running Value Engineering workshops, monitoring on-going progress and organising

end-of-project feedback.

The question then becomes “What is best value?” This, of course, has to be decided by

an individual client for an individual project. Traditionally, value equated to cost, but

notions of whole-life costs, maintenance, comfort, aesthetics, worker efficiency, staff

retention, safety, certainty of delivery, the introduction of other Key Performance

Indicators 6 etc. make the modern concept of best value much more rational and

therefore valid. One of the roles of the design and project management teams is to

assess the relative importance of these indicators to particular clients on particular

projects. The problem then becomes one of measurement.

INDICATORS NOTES

Speed Productivity/efficiency on site; time; programme; lead-in time.

Cost First cost; running costs; whole-life costs; business costs; cost of package; value for money.

Spans/lettable area Floor depths/building height; preferred grid; vertical access routes; third-party aspects (spans).

Flexibility in use Low maintenance; good performance.

Fire Fire protection; robust fire protection; fire resistance.

Services integration Air conditioning options; control; sound/thermal insulation; fabric energy storage.

Buildability ‘Being tolerant’; tolerances; planning.

Environmental Sustainability indicators; operational energy; waste.

Finish Certainty of finish; architectural merit; visual surfaces.

Quality Certainty of quality of product.

Site conditions Access; site constraints; logistics.

Structure Dynamic requirements; load carrying ability; overall stability; temporary stability.

Market conditions Risk; capacity; resources; capacity available; certainty.

RolesSpecific feedback on the ‘how it should be’ model (Figure 5) included comments on

roles and responsibilities. Some useful ideas for improving ‘traditional’ communications

between the various professions involved are shown in Table 5.

Project workshopsProject workshops are designed to facilitate better communication, promote best value

and prevent, as far as possible, unforeseen problems from arising 18. The workshops lead

towards a clear feedback loop for continuous improvement, project and project-to-

project learning. The suggested programme of formalised workshops is shown in Table 4.

This recommended programme of workshops was perhaps the most insightful theme to

emerge from research. There was steady feedback on the importance of inclusive and

participative workshops throughout the course of a project. Regular design development

and progress meetings would continue as a matter of course.

15


14


r Produce separate ‘concrete profile’ CAD drawings, extracting and isolating the structural frame from itssurroundings and making it simpler for the engineer and lead frame contractor to consider.

r Hand over drawings and calculations to specialist suppliers to accelerate the ‘taking off’ process and prevent‘reinventing the wheel’.

r Develop a pre-briefing document (including M&E requirements) and with the design team, confirm the business plan, develop the design for it and organise the money for the design.

r Keep an ‘interface register’ between clusters to record anomalies and clashes for easy resolution during design development.

r Consider presenting a ‘concrete concept’ that responds to the client’s priorities rather than purely technicalperformance criteria.

r Signal their willingness to work in the consulting engineer’s office during design development to aid, forexample, the design of connections.

r Carry out an ‘as built’ survey at end of construction for the record.

r Look at costs more holistically with whole-life costing, providing a better service to the client.r Analyse growth in costs to see where lessons lie in patterns of spending for the next project.

r Optimise hook time for cranes on site.r Develop innovative connections.

Table 5 Roles ARCHITECT

CONSULTING ENGINEER

CLIENT / DEVELOPER

MAIN CONTRACTOR / CONSTRUCTION MANAGER

LEAD FRAME CONTRACTOR

QUANTITY SURVEYOR

PRECAST MANUFACTURER

Briefing

Feasibility

Conceptual Design (1) Conceptual Design (2)

Conceptual Design (2)Design (1)

Design (2)

Use (1)

�Reunion�

Design team �round table�

Start-up / best value

Risk workshop

Pre-construction

Post-completion

Usually takes place if the project partners areundertaking repeat business, but notexclusively. Aim is to check lessons fromprevious projects – the client, in particular,may have input here.

Aim is to clarify client aspirations; to establish‘what do we want’. This takes place after thebudget has been agreed.

This workshop takes place on appointment of all the specialists (sometimes ValueEngineering may be used here as the designconcept should be taking shape).

Now that the project is understood, the aimis to generate creative solutions for anyinterface problems that arise, rather thantrying to ‘fix’ them on site.

The purpose is to check that everyone iscontent with the programme on site and to run through the final details with ideallya virtual reality simulation to help thediscussion (this should be developed duringdetailed design).

The project review lessons are drawn outduring the workshop for the next project.(This is vital as it draws everyone backtogether after what may be a lengthy project process).

Client, project manager, design team,quantity surveyor (QS) if appointed. Maincontractor and perhaps a few selectedsuppliers may be invited. Project manager will take the lead.

Client, project manager, design team. Quantitysurveyor, if appointed, will take the lead. Maincontractor and/or specialists may be invited.

Main contractor/construction manager likelyto take the lead. All specialist contractors andsuppliers, project manager, design team andQS may be asked to attend.The client maybe represented by the project manager.

Main contractor/construction manager takesthe lead.All specialist contractors and suppliersshould attend. Project manager, design teamand QS may be invited.The client may berepresented by the project manager.

Main contractor/construction manager takes the lead. All specialist contractors andsuppliers should attend. Project manager,design team and QS will be invited.The client may be represented by the projectmanager.

Client and client advisors will take the lead.All project participants are invited and should attend.

Table 4Recommended

workshops and review

meetings

FUNCTION / DESCRIPTION WHO SHOULD ATTEND?WORK STAGE TITLE

17

Achieving best practice 5

When precast items are used, negotiations usually go through several stages and

everyone benefits if customers and clients have already considered and prepared some

answers to the questions highlighted in Table 6. Beware of imposing non-essential

constraints as these can restrict flexibility of design later on.

Price on value: resist pricing on initial cost only and resist ‘last job’ syndrome. Definitions

of value/value for money are different for different parties, (e.g. some may advocate

lowest initial cost, fastest, lowest whole-life cost, or most satisfactory to the user).

Do these really reflect the client’s requirements? Are design and construction teams

influenced by process issues rather than product?

The structural design of hybrid forms of construction can be seen as a barrier. However,

designers are comfortable with in-situ concrete design and, in general, are comfortable

with precast concrete design. They may be less familiar with composite concrete

design. However, composite concrete elements may be considered as being monolithic

and homogeneous. In the case of proprietary items, design is often covered by

manufacturers’ literature. For bespoke works, temporary load cases, the construction

stage loading and final load cases all need to be considered. Notes on the structural

design of HCC are given in Appendix A.3.

HCC needs a main contractor with commitment to the HCC method as well as

civil/structural expertise. Some of the best examples of HCCs have been alternatives

driven by trade contractors that have been accepted by enlightened construction

managers. In the future, as designs become more sophisticated, the use of HCCs will

become more common, increasing the need for specialist design input.

Contractors should at least be given the opportunity to comment on initial designs.

HCC is a very positive way to create large areas of floor very quickly, but advantages

can be lost if the in-situ reinforced concrete work is complex.

It is important to obtain specialist knowledge as soon as possible. The degree of

importance depends on the degree of innovation/newness and this influences the

choice of procurement route. Generally, generic forms of HCC such as using hollowcore

slabs on in-situ beams can be constructed using traditional forms of contract – but

even these relatively simple forms of HCC still benefit from specialist design input.

Bespoke types of HCC benefit from using non-traditional contractual arrangements

(e.g. construction management, design and build). Using inappropriate forms of contract

can result in adversarial relationships and lack of trust. But trust is the very basis of

teamwork. Bespoke HCC solutions are more likely to be successful on large projects

where investment in design and management time should pay back handsomely.

The Standard Method of Measurement (SMM) is ineffective in assessing overall

process benefits.

16

5 Achieving best practice

5. Achieving best practice

The ‘how it should be’ process model is presented in Figure 5. It is the key to best

practice for HCC.

To achieve best results, best practice needs to be applied throughout the procurement

process. Chapter 4 highlighted the new aspects and this chapter expands on these to

guide users through the whole procurement process, from feasibility to completion and

use. Guidance recommendations are supplemented by anecdotal points.

Communication and two-way understanding is central to achieving best practice. Good

performance requires contractors to understand what clients want but equally, clients

and designers should know what contractors need in order to perform. To help with this,

an outline of the process, from the specialist contractor’s point of view, is presented

throughout this chapter as Tables 6, 7, 9 and 10. An understanding of this process and

the issues involved will help ensure that agreements on timescales, quality, performance,

budgets, costs and rewards are realistic, practical and ultimately produce a highly

satisfactory result.

Think HCC! HCC has to be thought of as one of the options to be studied by the

architect and structural engineer at feasibility stage.

If HCC is not presented early on as an option to address the client’s requirements, then

it is much less likely to be used and the opportunity will have been lost. HCC solutions

can make a project feasible and in design-and-build tenders, it can make the difference

between winning and losing.

Think in terms of partnering – for instance, set up an open book approach for

procurement and remember weeks can be lost in a traditional tendering process.

An open book arrangement is one whereby:

■ actual costs are paid with agreed margins for overheads and profit

■ the difference between the actual cost and target cost is shared in a specified way

between the client and contractor – pain and gain are shared on an agreed basis

■ sharing the risk acts as an incentive mechanism to promote efficient working.

The decision to prefabricate should come early. Where HCC or indeed precast

construction is a possibility, seek advice from a precaster or talk to a LFC. Preferably

make visits to precasters. Precasters should be chosen not only on cost and value but

also on suitability, availability and quality.

Feasibility stage

Conceptual Design (1)

PRE-ENQUIRY ✔ Gain knowledge✔ Think precast at earliest concept stage✔ Evaluate quality requirements✔ Understand what can realistically be achieved✔ Seek specialist advice for initial project concept✔ Be able to discuss outline concepts of project at

initial contact e.g.r Type and user Site geometry and characteristicsr Grid requirementsr Unit sizesr Site accessr Environmental considerationsr Building performance/lifetime effectr Adequacy of supplyr Skill shortagesr Programme requirementsr Overall costr Weight restrictions on units.

✔ Don’t expect initial answers to be definitiveon price or programme, methods, etc.

r Arrange to meet precaster r Teamwork/trust – does it need to go

out to tender? Is partnering feasible?

ENQUIRY ✔ Define responsibilities✔ Who is responsible for what? – Define

responsibilities early and expect to maintain a cost-to-risk balance. Ensure other teammembers take responsibilities commensurate to their earnings and expertise

✔ Balance cost versus risk✔ Clarity✔ Who are the players and how do they relate?✔ Seek advice on specifications, both design and

architectural, e.g. tolerances and finishes✔ Don’t just print off the specification used on

the last job✔ Send specifications to precasters for comment

prior to issue✔ Commercial terms and conditions, standard /

non standard:r Parent company guarantees/performance

bondsr Retentionsr Warrantiesr Liquid and ascertained damagesr ‘Pass the risk down’ syndrome

✔ Financial✔ Payments – when? – on time?✔ Don’t ‘scatter gun’ the enquiry: effort will be

proportional to chance of getting the job – don’t expect too many free ideas

COMMITMENT ✔ Financial✔ Contractual✔ Ability to provide and deliver

Table 6Precast Checklist 1:

From initial enquiry to contract

19


18


PARTY HBased on traditional procurement

WORK STAGE h

DESCRIPTION h

Obtain userfeedback. Developpre-briefingdocument, discussfunding mechanisms.Brief project manager(if used); briefarchitect; brief QS.

CLIENT

Agree business plan.Agree M&E.Define ‘best value’.Liaise with PM oncontracts, etc.Agree costs;agree budgets.

Liaise with PM to facilitate early involvement.Agree terms for earlyinvolvement.Provide comment as required.

Provide comment as required.

Provide comment asrequired.Give final approvals.

Provide comment as required.Give approvals as required.

Provide comment as required. Provide comment as required.Check progress.

Participate in project feedbackworkshop.Agree recommendations for future projects.Receive building from MC/CM.

GATEAgreeneeds/aspirations.

SOFTGATE Decide ‘Is it worth it?’

GATEApprovescheme design.

GATEAgreefinaldesigndrawings.

Agree servicesrequired by client.Establish client needs.

ARCHITECT (latest)

Obtain outlineplanning permission.Think hybrid (HCC)!Refine client needs.Formulate designideas.

Develop scheme design.Develop specification.Generate floor plans etc.Seek advice from specialists;discuss plans with engineer.

Obtain full planningpermission.Evaluate qualityrequirements of frame.Agree scheme design.

Generate ‘concrete frameprofile’ drawings.Visit specialists, agreeHCC specification, checkdesign for optimumrepetition, integratestructure and services.Work up final drawings; refinespecification;liaise with engineer;liaise with other designers.

Liaise with LFC on production drawings.Invite LFC to work in engineer’s office.Obtain Building Regs approval.Check against specification.Produce some detail drawings.

Oversee manufacture.Approve moulds.Approve finishes.

Provide information as required.Oversee construction.Give final approvals?

Make recommendations for futureprojects.Participate in project feedbackworkshop.DELIVER-

ABLEDefineclientneeds/aspirations.

DELIVER-ABLEPresentdesignideas.

DELIVER-ABLEHand overfinaldrawings.

DELIVERABLEPresentscheme design.

GATESign offworks.

0: REUNION Only held if project participantshave worked together previously.

1: DESIGN ROUND TABLEClient and design team meet forthe first time, with others invitedif appropriate.

2: START UPHeld when all participants areappointed.Value engineering may be used.

3: RISK WORKSHOPNow the project is understood,effort is made to iron out anyproblems.

4: PRE-CONSTRUCTIONEveryone convenes prior to start on site to agree procedures etc.

5: POST-COMPLETION REVIEWEveryone participates in this ‘post-mortem’.

Make requirements known.Undertake survey of user needs.END USER Provide comment as required. Provide comment as required. Participate in ‘best value’ workshop

if required.Provide comment as required.

Provide comment as required. Participate in project feedbackworkshop (if required).

SPECIALISTSUPPLIERS(e.g. in-situ contractor,precaster or steel fabricator)

Optional entry point (with LFC).

Engage in a negotiation to obtainletter of intent.Provide advice as required (e.g. costs, programme, structure,environmental aspects andfinishes).

Liaise with LFC, establish an order of cost.Agree HPIs, participate in ‘best value’workshop, provide advice as required(e.g. costs, programme, structure,environmental aspects and finishes).

Run an ‘open book’.Start production drawings.

Develop inventiveconnections.Optimise hook time.Generate productiondrawings.Produce own methodstatement, produce own H&S plan.

Participate in VR frame erection run through.

Erect frame to agreed programme. Participate in project feedbackworkshop.

DELIVER-ABLEFinaliseproductiondrawings.

LEAD FRAMECONTRACTOR(i.e. Multi-disciplinary firm,in-situ contractor or precaster)

Optional entry point.

Agree terms for early involvement.Liaise with potential specialistsuppliers, provide advice asrequired (e.g. potential structuralsolutions, budget costings ofalternative HCC combinations).

Liaise with MC/CM.Agree frame responsibilities.Present the ‘concrete concept’.Agree HPIs, participate in ‘bestvalue’ workshop, provide technicaland financial advice as required,finalise desired structural concept.

Liaise with designers to produce final scheme.Liaise with specialist suppliers,start production drawings, providetechnical and financial advice asrequired.

Send team to work in engineer’s office.Participate in VR erection program.Liaise with specialistsuppliers to agree startdates during erection.Produce own methodstatement, produce ownH&S plan, liaise with MC/CM.

Agree programme to ensure sitedelivery times (e.g. mouldprocurement, precast unit production)with specialist suppliers.Carry out enabling works.

Carry out full ‘as-built’ survey.Erect frame to agreed programme.

Participate in project feedbackworkshop.Negotiate partnering on futureprojects.DELIVER-

ABLEAgreeproductiondrawings.

MAIN CONTRACTOR /CONSTRUCTIONMANAGER

Optional entry point.Provide advice as required.

Define packages / clusters.Advise on site logistics/buildability.Agree terms for early involvement.Provide advice as required.

Establish an ‘interface register’.Agree HCC frame responsibilitieswith LFC.Agree HPIs, participate in ‘bestvalue’ workshop.Provide advice as required.

Start using VR erection program.Liaise with designers to produce final scheme.Generate ‘main’ method statement.Produce H&S plan.Produce construction programme.Agree specialist sub-contracts.

Confirm HPIs.Continue to use VR erection program.Liaise with LFC (and specialist suppliers).Liaise with engineer.Agree method statements.Agree H&S plans.Agree deliveries.

Carry out final VR run-through.Measure performanceagainst HPIs.Carry out enabling works.

Measure performanceagainst HPIs.Measure specialists’performance.Manage construction.

Participate in project feedbackworkshop.Feedback on HPIs to PM/client.Feedback on specialists’ performance.Make recommendations for futureprojects.

SOFT GATEAgreeschedulebased on VR erectionrun-through.

GATEHand overto client.

CHECKINGAUTHORITIES

Advise on planning permission. Provide institutional checks. Advise on planning permission.Provide institutional checks.

Provide Building Regs approval. Provide Institutional checks.Provide Building Regs approval.

Oversee construction.

OTHER DESIGNPROFESSIONALSe.g. M&E Engineer Think HCC!

Agree basic M&E strategy.Advise PM as required.

Develop FES strategy.Develop services strategy.Provide advice as required.

Agree FES strategy.Agree scheme design.

Integrate structure and services.Work up layouts; liaise with engineer; liaise witharchitect.

Refine layouts (if required). Provide information as required. Provide information as required.Oversee construction.Give final approvals?

Make recommendations for futureprojects.Participate in project feedbackworkshop.DELIVER-

ABLEHand overlayouts.

GATESign offworks.

ENGINEER

Think hybrid (HCC)!Agree basic M&E strategy.Advise PM as required.

Assess HCC options.Develop structural concept.Discuss plans with architect;seek advice from specialists;discuss construction programme.

Agree HCC option.Agree scheme design.

Hand over designdrawings/calcs to LFC/specialists.Agree HCC specification,check design for optimumrepetition.Integrate structure and services.Work up GA drawings; carryout design calculations; liaisewith architect; liaise with otherdesigners;discuss ‘main’methodstatement with MC/CM.

Check method statements.Check specialists drawings.Refine GA drawings (if required).Generate RC drawings.

Oversee manufacture.Approve moulds.Approve finishes.

Provide information as required.Oversee construction.Give final approvals?

Make recommendations for futureprojects.Participate in project feedbackworkshop.DELIVERABLE

Produce schemedrawings.

DELIVER-ABLEHand overGAdrawings.

GATESign offworks.

Discuss funding mechanisms.Agree services required by client.

QUANTITYSURVEYOR

(latest)

Liaise with PM on cost plans. Expectto pay for LFC/specialist’s advice.Assess costs; assess budgets; advise PM as required.

Provide whole-life costinformation.Review forms of contract.Provide advice as required.

Help administer contracts.Provide advice as required.Agree scheme design.

Review costs.Review budgets.Report to PM as required.

Review costs.Review budgets.Review contracts.

Review costs.Review contracts.Agree payments with PM.

Analyse growth in contract costs.Participate in project feedbackworkshop.

Discuss funding mechanisms,define team roles, make contractconditions clear, make terms andconditions fair, instigate ‘no blame’culture.Agree services required by client.

PROJECT MANAGER

(latest)

Expect to pay for LFC/ specialist’s advice.Undertake value assessment.Undertake risk assessment.Agree form of contract.

Propose terms for earlyinvolvement.Identify appropriate specialists.Establish design parameters.Manage design development.

Propose HPIs.Carry out ‘best value’ workshop.Address sustainabilityAgree overall programme.Agree scheme design.

Agree design information flows, agreedesign approvals procedure, facilitatecontractor involvement in design,convene final approvals process.Manage design process.Agree ‘main’ contract; appoint MC orCM; liaise with MC/CM.

Agree communication strategy for on-site decision making.Manage design process.Liaise with designers.Liaise with MC/CM.

Manage construction process.Liaise with MC/CM.

Liaise with MC/CM on HPIs andperformance monitoring.Manage construction process.Liaise with MC/CM.Agree payments with QS.

Carry out project feedback workshop.Feedback on HPIs to client.Make recommendations for futureprojects.

BRIEFING

[A]


FEASIBILITY

[B]

Is it worth doing?



CONCEPTUALDESIGN (2)[D & G/ H:TENDERS]

Choose the option

DESIGN (1)

[E]


DESIGN (2)

[F]


CONSTRUCTION (1)

[K]


CONSTRUCTION (2)

[K]

On-site work

USE (1)

[L]

Post-handover

USE (2)

Occupancy

£

£

£ £

£

£ £

£ £

£ £

£ £

£

£

v

★ ★

v

★ ★

★★

★

★

★

v v

v

v

v

vv

This is a generic model basedon what is considered to be

good practice within an Egan-compliant procurement

framework.The modeldescribes a scenario in which a

project manager facilitatesearly involvement of

contractor and specialists. Thewhole model is oriented

towards achieving best value(as defined by the client) via

‘partnering’ and collaborativeteam working.

Figure 5The ‘how it should be’

process map

WORKSHOPS hExact timing will depend on contract

type (partnering or prime contracting).

£

v

★

[A]Approximatecorrelation withRIBA Plan ofWork stages

Red textActivities thatshould takeplace to achievebest practice

Blue textEvidence frominterviews

Black textNormal practice

GATEAn activity that must becompleted forthe project tocontinue

Formal entrance/appointment ofa party

DELIVERABLEA key deliverablethat must beproduced for the project tocontinue

HPIHybrid ConcreteConstructionPerformanceIndicators (ourversion of KPIs)

KEY

21


Potentially, HCC can result in interface problems or clashes which are different from

traditional contracts (e.g. storage, phasing). If identified early on, these risks can be

managed and controlled. HCC is good for single point responsibility, hence the advocacy

of a LFC.

An interface register should be set up and maintained to highlight the possible

risks/interface difficulties that might occur, particularly between packages or clusters,

i.e. frame and cladding, frame and services.

While there is a need for good services integration, HCC timescales do not necessarily

tally with services design timescales. Usually, the M&E services design will need to be

well developed by the time an HCC scheme is finalised, and it should be finalised by the

time an HCC scheme is detailed. Although this is not a problem specific to HCCs, it can

have detrimental effects on HCCs if late changes are required. Managing information

about service voids, especially large ones, is important. For example, is the coring of

holes a strategy or defeat?

Tolerances must be realistic and the precaster and engineer should discuss, establish

and agree the scope and practicality of tolerances for a specific project. Equally, it

is important to address any differences between tolerances for precast and in-situ

elements. This is also a good time to discuss fixings – the precaster should give early

advice.

Teamwork with buy-in from all parties early on creates confidence. There needs to be

a high degree of co-ordination and this leads to ‘ownership’ of the project and team

bonding. All parties become motivated to work closely together.

There may be a need to assure the client that HCC is the right option. The architect, or

more often the engineer, needs to act as a ‘champion’, explaining and promoting the

benefits of HCC. When LFCs come on board, they can confirm budgets and establish

‘can do’ confidence.

20


Quality needs to be defined, planned and managed. It needs commitment and

accountability which are best achieved by a formal Quality Assurance scheme. Various

aspects must be considered including:

■ accuracy or quality of surface finish

■ quality of design or construction

■ performance

■ effect on other elements or processes

■ fitness for purpose.

Factory conditions for precast element production allow high standards of workmanship,

whereas in-situ elements may not achieve the same standards. If necessary these in-situ

elements can usually be hidden from view but if not, agree and issue guidelines on

consistency of finish including a strategy on protection and making good any damage.

Continue to make a case for HCC.

When considering forms of contract, it should be recognised that traditional forms of

contract can make HCC difficult because they preclude the vital early involvement of

specialist contractors. The traditional tender process involves a large amount of often

unproductive work – and usually there is a mass of information to assimilate at once.

Negotiating with the various sub-contractors in a short tender period can be difficult

when there are many issues to be resolved.

Alternative forms of agreement can minimize these difficulties. They can reduce delays

in getting prices and reduce the risk of these delays inhibiting progress. Where first cost

is a prime concern, trust can be enhanced using an open book policy. The lead frame

contractor (LFC) is usually the most likely party to promote this idea. It enables the LFC

to test the market’s capacity and readiness, to compare estimates and talk in detail to

potential suppliers without resorting to formal competitive tendering. The client and

project manager must trust the LFC to undertake this task, so the LFC will have to make

a good case and demonstrate that there will be full transparency during the use of an

open book.

Pre-assembly requires considerable off-site management of off-site activities. There is

increased management of design, integration of design, early service design decisions,

approvals and communications. Design co-ordination means understanding supply

chains, planning and producing design information and approvals on time, for example,

services designs will have a significant impact on structure. The project manager should

map out the processes involved and issue guidelines on, for example, issuing information,

approvals procedures, change control and the methods by which production and

assembly knowledge are fed into the total design process. Project managers should

choose people who can deal with such issues.

ConceptualDesign (2)

23


oral exchange of information and informal, as well as formal, co-ordination between

architect, structural engineer, precaster, LFC, etc. on such issues as finishes, positions for

services, lifting sockets, etc.

The precaster should give early advice to the design team, to prevent problems later

(e.g. on fixings etc). Precasters are at their most efficient when they are able to progress

whole packages, rather than hit-and-miss sections. Units with an architectural quality of

finish need special attention from all.

Details should be discussed and resolved amongst the whole team – designers

(architectural and structural), contractors, precasters and the LFC. For example, lengths

of bearing for hollowcore units on one project were specified from a structural

perspective as being 75 mm minimum, 150 mm was achieved, but 225 mm was

wanted on site to facilitate buildability. The message didn’t get across to the design

team that the constructors wanted wide bearings. Equally, counter-arguments from the

designers (and quantity surveyors) did not get through to the constructors. This issue

should have been aired and decided upon well before construction. Most of the issues

that will need to be resolved with the precaster are highlighted in Table 7.

That said, buildability of HCCs is usually good because almost all the issues will have

been discussed and agreed before the building goes to site. But it must be designed in.

Agree and issue guidelines on:

■ Tolerances.

■ Dimensional constraints.

■ Making things fit together (e.g. cast low, fill or pack).

■ Craneage and transportation.

■ Design of temporary works.

■ Propping (e.g. Is temporary propping a real problem costwise, timewise or just

perception? Props at 1/2 or 1/3 spans may be considered satisfactory as they may

not freeze-up an area. However, staging left in place may well do so).

■ Concreting on site:

r special measures

r non-shrink concretes

r ready-mixed supply or batch small volumes on site

r can in-situ concrete be poured into tight positions (e.g. under the

hollowcore unit?)

r self compacting concrete.

■ Preparing precast units for concrete pours.

■ Detailing rules – as traditional construction? Should loose splice bars lap with bars

within the precast units?

■ Protection of finishes, details and projections.

■ Differential floor cambers on adjacent floor units.

■ How to stop joints leaking and the cost of sealing joints.

■ Alternative details (e.g. would continuity reinforcement get over the need for a nib?).

22


Before the design work begins in earnest there should be a pause to reflect and,

importantly, get client feedback.

If an open-book approach has been agreed, its administration and success will depend

on close working and good communication between the designers, the precasters, QS

and/or LFC. For teams with less experience of such an approach, an experienced member

should lead and ensure complete transparency. Reassurance and regular checking will

be necessary.

Because of the amount of information in circulation, HCC may not necessarily be an

easy process to manage. People need to be clear about their inputs to the process and

team ethos, especially when thinking and working outside ‘traditional’ methods.

The use of 3D modelling techniques, Virtual Reality (VR) simulation programmes, or

animation based on CAD should all be considered. Such tools can be very powerful in

managing/optimising the construction programme for an HCC structure, especially

because the method often involves quite specific sequences of component installation

and in-situ stitching on site, which can benefit from detailed visualisation.

Correct decisions made promptly and without later changes are key to managing the

process. Regular meetings with a ‘one-stop client’ and all other parties involved are

essential because time constraints will put pressure on design. This demands good

Design (1)

Figure 6Inland Revenue Building interior

The competition brief required value for money and a

fast-track construction programme. The design fully

exploited the potential of precast concrete and

prefabrication of other major structural elements to

achieve real buildability. The superstructure was

manufactured almost entirely off site, at the same time as

the in-situ construction of the substructure took place.Photo: Martine Hamilton-Knight/Built Vision

DESIGN

✔ General arrangement drawings

✔ Mould drawings

✔ Unit details

✔ Repeatability

✔ Calculations

✔ Approval periods

✔ Interface with other disciplines notably services

✔ Freeze dates

✔ Approval procedures

MOULD PROCUREMENT

✔ Standard/non standard/ complexity

✔ Internal/external/resourcing

✔ Type – timber/steel

✔ Quality

PRODUCTION

✔ Reinforcement, plates, bars, inserts

✔ Capacity

✔ Finishing

✔ Stripping

✔ Handling

✔ Storage

DELIVERY & ERECTION

✔ Unit size restraints

✔ Site restraints

✔ Management

✔ Falsework and formwork

✔ Health & safety/CDM

IN-SITU WORK

✔ Responsibilities

✔ Finish

✔ Falsework and formwork

✔ Reinforcement

✔ Concrete

✔ Concreting

✔ Curing and protection

✔ Depropping


From design to start on site

25


and reference should be made to the National Structural Concrete Specification (NSCS)20,

which covers tolerances under Construction Accuracy (Table 8).

“To arrive at the optimum cost and buildability, a common understanding on

tolerances for the structure, cladding and finishes should be shared by all parties.

Discussion is needed at the design stage on any tighter tolerances envisaged, since

they will result in higher costs and may not, in any event, be realistic.

Common sense must prevail should any item fail to meet the tolerance specified. It

is important to consider whether the work is still acceptable, having regard to the

operations that follow and the intended use of the structure. Checking must be carried

out as construction proceeds so that any remedial work which is required can be

sensibly planned and executed.”

National Structural Concrete Specification20

The clauses provided in NSCS are intended to simplify tolerances. It should be noted

that the fit-up of abutting elements with different permitted deviations requires careful

consideration.

The factory-based precast concrete industry works to improve upon the component

tolerances specified in BS 8110.

A strategy to overcome potential problems should be put in place. For instance,

guidance for landing precast elements onto in-situ elements, especially in-situ columns,

should be developed. In this case a preferred detail might be to either:

■ cast columns 100 mm low, place a collar around the column, place precast floor

elements and concrete the remaining column with the floor topping or

■ with beam soffits temporarily supported in place with help from the column

formwork, cast the whole column in-situ as one.

24


Connections need to be well designed. They should be simple and adaptable with

realistic tolerances and plenty of repetition. Repeated use of the same details allows

optimisation of construction method.

Establish early on the responsibilities for falsework, remembering that the supply of

relevant information is a duty under Health & Safety Act/CDM regulations.

The National Structural Concrete Specification (NSCS)20 is ideally suited to in-situ, precast

and HCC. Under the NSCS approach, the specialist concrete contractor (SCC) builds what

is shown on the drawings to a specified standard of workmanship. Prescriptive restraints

have been avoided to enable the SCC’s experience to be used to achieve efficient

construction. This specification helps innovation, efficiency and competition. All parties

involved in the construction process benefit – from the client to the subcontractor:

■ Clients receive better, less costly construction.

■ Designers no longer have to devise their own standard specifications, but may

concentrate their efforts on writing the individual project specification.

■ Contractors are able to identify more clearly the risks and requirements of the project

and have more freedom to innovate and develop their own solutions.

Make sure the processes of HCC are clear to all. Programming problems mostly arise from

lack of familiarity with techniques and uncertainty of procurement and are particularly

likely to affect smaller projects, which do not necessarily have the management resources

to understand and control unfamiliar processes.

This is a busy period for the designers in co-ordinating design and technical information.

A high level of communication is required, especially between architect, structural

engineer and services designers as well as with the contractors, because of the large

amount of design checking perceived to be necessary. Interchanges need commitment

underpinned by mutual trust. HCC requires team players prepared to work closely

together and to ensure that others are not let down. Paper based communication will

not be sufficient. Regular round-table meetings with oral exchanges resolve issues faster

than a more conventional approach.

Resolving all the design details at the design stage gets it right on site. 3D, VR or

physical models help enormously. The architect and others in the design team need to

be supportive of the structural engineer to resolve issues such as impact of ‘builders’

work’ on site. Late tweaking of details distracts effort and costs money, these should

have been resolved earlier.

Realistic tolerances must be allowed for; small numbers in specifications are no answer.

Precast units are generally quality assured; nonetheless, realistic tolerances are needed

Design (2)

Table 8Extract from the National Structural

Concrete Specification20

TOLERANCES FOR FORMED ELEMENTS

The linear dimension of formed elements shall be accurate to within the following distances (where L is length, height or width of element in the direction considered).

L Permitted deviation, D mm

Up to and including 600 mm 8 mm

Over 600 mm up to and including 1.5 m 10 mm

Over 1.5 m up to and including 8 m 15 mm

Over 8 m up to and including 15 m 20 mm

Over 15 m up to and including 30 m 30 mm

Over 30 m 30 mm + 1 mm per metre or part

27


At this stage delivery, erection and

construction issues should have been

agreed (see Table 9). Where feasible, a

final VR run through should be carried

out. Confidence can be strengthened

by having warranties for materials/units

stored off site and by inspecting

prototypes of any bespoke precast

units – this gives excellent evidence

on aesthetics and value.

To save crane time, mark each precast

item with a reference identifying

orientation and lifting point positions

(consider bar-coding/e-tagging).

It is vital to protect precast units on

site, particularly architectural units,

otherwise they will not retain their

ex-mould appearance. There needs to

be a strategy for protection so propping

and protection must be carefully

planned. For instance, damp marine

ply may mark architectural units.

The main contractor should be

instructed not to carry out any

‘unauthorised’ remedial works or builders’ works to the precast units. These are

specialist tasks. Procedures for remedial works should be included in the specification.

Construction on site tends to be very quick; this is the reward for the effort in working

up the co-ordinated design. Examples are given in the case studies in chapter 6.

The post-completion workshop allows

all parties to the project to give feedback

to others and to learn from the other

members of the design and construction

team and from users (see Table 10).

The outcome should be measured in

terms of Performance Indicators and,

in particular, the Hybrid Performance

Indicators used to make the value judgements during the conceptual design process.

26


The LFC must be given unambiguous information and instructions by the design team,

especially the architect. Avoid late decisions and design changes because the effects are

magnified further along the process and supply chain. Despite pressures on the design

team, especially the structural engineer, to release information quickly, it is important

to manage and co-ordinate information. Sufficient time should be made available to get

it right. In the interests of good communications, it is advantageous to invite the LFC’s

team to work in the engineer’s offices.

Problems need to be identified and notified early to mitigate additional costs. For

instance, lack of basic setting-out information could lead to delays or piecemeal

production, which is more expensive or could lead to acceleration charges.

Repeatability is key to economy in precast production. It should be appreciated that

minor changes, curves/radii etc. have major impacts on design time and mould re-use.

The aim should be to rationalise numbers of units and moulds. The cost and speed of

manufacture of precast concrete units, particularly the bespoke units, is dependent on

mould use and demouldability. The optimum use of timber moulds is about 30 units

(tolerances are difficult to maintain after about 30 uses); for steel moulds about 90

units is optimum 21. If the precaster can achieve a faster casting cycle time, then the

overall cost and time will decrease. Issues such as demoulding, optimising hook time

for cranes on site, protection strategy for precast units on site also need to be resolved.

Design of the units should be finalised under guidance from the precaster.

Avoid using units where projecting reinforcement is intended to lap with reinforcement

projecting from adjacent precast items – unless tolerances can be guaranteed to avoid

clashes. Use loose splice bars.

Figure 7Paternoster Square office development

The structural scheme consisted of precast vaulted ceiling

units onto in-situ beams and columns. It was chosen to

demonstrate speed and minimum construction depth in

comparison to rival materials.Photo: J. Doyle

DELIVERY

✔ More than just maximising payloads

✔ ‘Just in time’ delivery planning

✔ Correct sequence

✔ Nil damage deliveries

✔ Weight/size restriction

✔ Loading for minimal site handling

✔ Storage on trailers if necessary

ERECTION AND CONCRETING

✔ Competent and trained workforce

✔ Access/hardstanding

✔ Erection sequence – following trades

✔ Craneage – mobile/static

✔ Shared services – cranes/scaffolding etc

✔ Survey of previous works

✔ Erection procedures – H & S/CDM

✔ Falsework and formwork: checks and

responsibilities

✔ Reinforcement, post-tensioning

✔ Welding, bolting, grouting

✔ Concrete deliveries

✔ Curing and protection procedures

✔ Matching finishes

✔ Depropping and release to following trades

STABILITY

PROTECTION

✔ Avoidance of damage

✔ Repair strategy

FEEDBACK

✔ Performance

✔ Price

✔ Experiences for next time


Delivery, erection and construction


Feedback

Construction (1)

Construction (2)

At post-construction stage

29

Case studies 6

It became apparent early in the design process that quality of manufacture and

tolerance control was going to be critical to the achievement of the required erection

programme. The number and complexity of the interfaces between precast and

steelwork and the need for continuous co-ordination between suppliers and the

erection crew led to the conclusion that supply and erection of the entire structure

should form one subcontractor package. As a result an LFC was appointed whose entire

package was negotiated from its inception on an ‘open-book’ basis. This allowed the

earliest possible specialist input into the design process and gave continuity through to

the construction phase.

The structure itself has 14 massive precast concrete shear walls each 3 m wide and over

11 m high. As may be seen from Figures 9 and 10, they form the backbone to the stand,

taking the vertical and lateral loads from the upper tier and roof. Each wall consists of

an upper and lower unit. To maintain accuracy of fit and alignment, these wall units

were match-cast in pairs with steel shoe connectors at mid height. These shoes were

then welded together on site. Particular care had to be taken to place coupler fittings

correctly within the walls to receive steel beams. A high level of accuracy was achieved:

the general level of tolerance was 50% of the limits specified in BS 8110: Part 1:

1997 22. The interfaces between precast and steelwork and the co-ordination required

for successful construction is illustrated by Figures 12 to 16. These show details of the

wall unit W1, part of the cantilever shear wall system, and its fitments.

The upper tier of the stand is a balanced cantilever with the shear walls providing

stability against over-turning forces and wind loads. The lower tier consists of precast

28

6 Case studies

6. Case studies

These case studies show how HCC has been used with great success on a range of

building types and locations.

The studies come from a series of 'knowledge capture' workshops that were convened

in order to identify key events and evaluate what went right and what could have been

improved on particular projects. In addition to producing evidence of the successful use

of HCC, they provided a way of testing the process maps being developed at the time.

They were, in essence, facilitated post-completion workshops, which the participants

found to be enormously valuable.

From the outset, the design and construction of the new 7,500-seater North Stand at

Ipswich Football Club (Figure 8) was dominated by a tight schedule. Work on site could

not start until the end of the 2000/2001 football season but had to be completed as

soon as possible during the next. It was clear to the design team that to achieve this

goal, the following aspects had to be considered:

■ The use of off-site prefabrication.

■ Minimal use of applied finishes.

■ Inherent structural fire resistance of the structure.

■ Ease of erection.

■ Reduced erection time by minimising the number of components.

All these factors indicated that precast concrete would be the most appropriate material

for the project, and this was reflected in the structural design which was essentially

precast augmented by in-situ stitches and toppings and steel beams and a steel roof.

Figure 8North Stand – Ipswich Town Football Club

Photo: C. Goodchild

Above: Figure 9From the North

Photo: Hufton+Crow/View Pictures

Right: Figure 10Typical cross-section of the stand – North

Ipswich Town Football Club: North Stand

Figure 11Shear walls and staircases during construction

Photo: Jan Bobrowski and Partners

3130

6 Case studies Case studies 6

Figure 12General arrangement – Elevation on a lower

wall unit, type W1

Inset right: Figure 13Detail B

Below: Figure 14Wall type W1 – RCC details

33

Case studies 6

North Stand began in May 2001. Superstructure erection began on 16 July and was

completed in 23 weeks by Christmas 2001. The lower tier was used for the first time

on 16 November.

Amongst the best aspects of this project were thought to be:

■ regular meetings with all involved and with a ‘one stop client’

■ early and firm decisions being made; prompt decisions made everything else work

■ unambiguous instructions helped progress the timescale

■ having a LFC on board went hand-in-hand with the hybrid form of construction

■ having an ‘open book’ policy reduced delays on getting prices, and reduced risk of

these delays inhibiting progress – which relied on trust.

Project Team:

Client Ipswich Town FC

Architect HOK Sport

Engineers Jan Bobrowski & Partners

M&E Engineers Hannan Associates

Supervising Architect Hoopers Architectural Services

Quantity Surveyor Gill Associates

Main Contractor Jackson Building Ltd

Lead Frame Contractor ABC Structures

Precast Suppliers Trent Concrete Ltd, Tarmac Topfloor

Steel Suppliers H Young Structures & Westbury Tubular Steel Ltd

References:

Concrete April 2002

Concrete Quarterly Winter 2003

32

6 Case studies

concrete staircase-like units, which span, unconventionally, front to back. They provide

the propping forces necessary to stabilise the shear walls in the transverse direction.

There are 499 units in the upper tier, as opposed to only 289 on the lower tier which

occupies almost the same plan area. Fewer units in the lower tier resulted in a

substantial saving in erection time. On the lower tier, around 800 m of grouting was

undertaken, whereas the more traditional form of construction on the upper tier

required nearly 2300 m. To differentiate their appearance from the upper tier units, the

lower tier units were made from different concrete mixes.

Stitching together the primary and secondary elements into a single entity resulted in

considerably fewer elements and a structure that could be erected as a self-finished

article. The precast units required no additional fire protection or applied finishes.

Longitudinal stability is provided by a combination of moment connections and

diaphragm action from the floors and tiers. The roof structure is essentially a separate

structure spanning 92 m onto Vierendeel towers. Secondary trusses cantilever to the

front and rear of the main truss.

The initial structural design brief was given in January 2001 and demolition of the old

Above left: Figure 15Detail of mild steel shoe for wall type W1

Above right: Figure 16Section 7-7

Right: Figure 17Steel beam connection onto wall type W1 and

its designer. Note: also angle support for

stair landing above

Photo: C. Goodchild

Far right: Figure 18Stair core showing shear wall W1

Photo: C. Goodchild

Right: Figure 19Detail through end of terrace unit

Above: Figure 20Section 4-4

35

Case studies 6

A hybrid of exposed precast and hidden in-situ reinforced concrete was chosen for the

building frame after an intense design period with collaboration between all members

of the design team. It was selected because of its visually striking appearance, ceiling

height, energy efficiency, flexibility and speed. It was also integral with the concept of

using a low energy displacement ventilation system for comfort conditioning within the

offices. The exposed structural soffits of the floors act as reservoirs for storing ‘coolth’, a

feature which contributes to the lowering of heat loads across the daily cycle of occupation.

HCC allowed a high proportion of the frame to be manufactured in quality controlled

factory conditions off-site and led to high speed construction on site. During the design

development process, the design was continually modified to accommodate lighting,

extract ducts, buildability and architectural developments, and yet maintain repetition.

Detailed models were made of the office floor showing the relationship of the precast

units to other key components and interfaces, such as the glass façade, the suspended

lighting units and the central services distribution zone.

Each floor of the wing is constructed from precast concrete coffered floor panels

supported by an in-situ concrete perimeter beam and by an internal ‘shoulder’ beam

system. The shoulder beam system consists of two in-situ concrete downstands hung

from an upstand column head (named ‘drup’ – a ‘drop’ that goes up). The floor panels

were fully integrated with the services with pre-formed slots and holes for ducts and

conduits.

34

6 Case studies

Located in Epsom, Surrey, this exciting and glamorous building entirely meets the

client’s brief for the most advanced and innovative workplace possible. The modern and

flexible office environment has been fully realised by using an exposed hybrid concrete

structure to get best value – in the client’s terms.

The project started as an architectural design competition, which resulted in the

concept of a two storey building orientated around a dramatic entrance rotunda. Four

15 m wide office wings radiate from a glazed ‘street’ where circulation and informal

meeting facilities are concentrated. The building is designed for up to 500 people and

has a gross floor area of 14,200 m2. Daylight potential is maximised in the offices by

the use of large areas of clear glazing offering largely uninterrupted views of a pleasant

landscape.

Toyota (GB)Headquarters

Figure 22Interior of one of the offices at the

Toyota (GB) headquarters

Photo: C. Goodchild

Figure 21A model of Toyota (GB) headquarters

Photo: C. Goodchild

Figure 23Section through office wing

Photo: whitbybird

37

Case studies 6

appearance. Great care was taken in the specification of mould type, tolerance and

finish to control imperfections.

All the units were cast in fibreglass lined moulds. This produced the specified high quality

ex-mould finish required to eliminate the need for decoration, which in turn saved on

the need to bring in further finishing trades and aimed to reduce maintenance costs

during the life of the building. At the first inspection of the precast unit at the works,

the unit was hoisted up to its correct height for a clearer and more accurate inspection.

The ten tonne floor units were delivered to site with three units per lorry. Adopting a

‘just in time’ policy, all units and components were lifted directly into place, to avoid

storage and double handling.

The shape of the overarching structural steel roof is derived from a large diameter torus.

This form maximised repetition of curvature and standardisation within the 150 tonnes

of structural steel components in the 80 m x 45 m partially glazed roof.

Structural design began in December 1997 and the site started in January 1999 with

three months of demolition. Practical completion was achieved in April 2001.

36

6 Case studies

An in-situ concrete structural topping locks all the floor members together in composite

action. Each floor plate uses 34 panels of approximately 6 x 3 m plan dimension within

a 9.0 x 7.5 m column grid. By careful detailing it was possible to limit the number of

panels in each floor plate to seven. The repetition reduced costs, increased efficiency of

production and helped avoid site errors. The maximum weight of panel was restricted to

10.5 tonnes for handling purposes.

Because of the complex shape and presence of service voids within the panels, the

design of floor plates included finite element analysis. The reinforcement also had to

be planned and modelled in three dimensions prior to production.

The building’s columns are generally 8.5 m high structural steel encased in 500 mm

diameter pre-cast concrete with a similar finish to the floor panels. Advantage was

taken of the stiffness of the columns to act as vertical cantilevers for the frame stability

against horizontal loading. This also helped to preserve the clear open space within the

building, as no internal bracing was needed. The column encasement was held back at

floor levels, which enabled perimeter beam reinforcement to pass through the web of

the steel column and thus help ensure a moment connection necessary for the frame

action assumed.

Air is supplied through the floor plenum and extracted through the ceiling soffit, while

the thermal mass of the exposed concrete ceiling helps reduce heat load.

Benchmarking visits were made to various sites to establish the required quality and

fit of the coffers. These visits involved the main contractor, the specialist concrete

contractor and the design team. The project specification was taken from a previous

project and agreed.

The concrete mix for both the pre-cast floor panels and columns was Derbyshire

Limestone aggregate with Antique White cement to create a light, off-white

Below left: Figure 25Structure/services integration

Photo: whitbybird

Below right: Figure 26Steel billets were used to ensure transfer of loads

between precast floor units and in-situ beamsPhoto: whitbybird

Below left: Figure 28PC floor unit being lifted into position.

Note: falsework and formwork, ducts

in units, columnsPhoto: Barry Bulley/Trent

Below right: Figure 29During construction

Photo: whitbybird

Figure 27Perimeter beam construction sequence

The in-situ beam picks up the precast floor panels.

Beam reinforcement passes through the web of

the encased structural steel column to help guarantee

a moment connection.

Figure 24Falsework

Photo: whitbybird

39

Case studies 6

The West Quay shopping centre in Southampton is home to over 150 shops, restaurants,

bars and cafes. It is served by two car parks, the largest of which is the main West Car

Park – now one of the largest multi-storey car parks in the UK. By cost it was just 7%

of the whole West Quay development. However, because of a deferred start, the

multi-storey car park’s completion became critical to the centre’s opening in time for

Christmas 2000.

The structure is 95 m long, 95 m wide and 20 m high – eight-storeys with 15 split

levels. In plan it is divided into four equal quadrants by movement joints. Each quadrant

has varying architectural treatment and layout requirements (Figure 31). There are a

total of seven stair cores plus two double lift cores. Headroom is 2.2 m clear.

Various structural frame options were considered at scheme design stage: structural

steelwork, wholly precast concrete, in-situ concrete and post-tensioned. The selected

scheme was based on composite precast double tee floor units spanning 15.8 m onto

in-situ concrete beam-and-column frames.

The decision to use HCC followed a value engineering exercise. By combining the cost

advantages of in-situ and the speed advantages of precast, the design and build

contractor concluded that the structure could be completed on time and within budget.

Another consideration was the piled foundations: piling had been installed with the

main development. Unfortunately, this piling was to a preliminary scheme and design

changes increasing the thickness of cladding (from 100 mm thick to 165 mm) and

service loads, meant that additional piling was needed. The choice of a relatively

lightweight double tee slab structure helped control overall loads and thereby reduced

the need for further piling to just 14 continuous flight auger piles.

38

6 Case studies

The Toyota (GB) Corporate Headquarters won the Building category in the 2001/2002

Concrete Society Awards. Among the best aspects which helped win the award were:

■ Early decision to prefabricate and have a sustainability/low energy concept.

■ Close teamwork with overall buy-in early on and confidence that project could be

delivered. There was a high degree of co-ordination and ‘ownership’. The team

bonded, established a proximity and were motivated to work closely together.

■ Arrangements for manufacture were very satisfactory. Warranty for materials/units

stored off site was included which established confidence.

■ The quality of the precast units was assured. The frame went well as all details on

paper had been resolved beforehand. The structural engineer’s use of 3D drawings

was vital – it reduced costs and helped to resolve details.

■ Construction efficiency was enhanced by prefabrication.

■ Use of a prototype factory unit to help secure the client’s confidence in precast.

■ The speed of construction of precast and subsequent progress built confidence within

the client organisation.

Two years after moving in the client remains very pleased with the building:

■ “It looks good”. “Wouldn’t change a thing.”

■ Compared to the previous offices they now have a building three times larger, with

double the staff, but the energy costs are 40% less than before.

■ “Very comfortable – even in the heat wave of 2003.”

■ Moving from rented space to being an owner-occupier will pay back in 10-15 years with

far better energy consumption, a more manageable and positive environment. Internal

planning works well with minimum turnover of staff and reduced absenteeism.

HCC was the obvious and logical solution, combining the quality finish and repetition of

precast with the flexibility of in-situ.

Project Team:

Client Toyota GB plc

Project Manager Insignia – Richard Ellis

Architect Sheppard Robson

Structural Engineer whitbybird

M&E Engineers Arup

Quantity Surveyor Davis Langdon & Everest

Main Contractor Takenaka (UK)

Precast Concrete Trent Concrete Ltd

Concrete Frame Duffy Construction Ltd

References:

Sheppard Robson Toyota brochure

whitbybird PowerPoint presentation 16 September 2003

Concrete Quarterly Summer 2001 – 199

IStructE www.istructe.org.uk. David Alsop Commendation 2002

Concrete Society www.concrete.org.uk

Figure 30The first floor balcony in the ‘drum’ overlooks the

reception area and gives access to meeting roomsPhoto: C. Goodchild

West Car Park,West Quay, Southampton

Figure 31East elevation showing

the curved pedestrian entrancePhoto: C. Goodchild

41

Case studies 6

east/west direction. The units have scarf ends for seating onto nibs. The scarfs were

extended to provide 300 mm wide channels for services such as electrical, CCTV and

lighting. This feature also provides the flexibility to the client to increase the service

provision at a future date without compromising headroom (see Figures 34 and 36).

The ramps presented some challenges. The in-situ framing initially considered for each

end of the ramps would have caused significant difficulties with the load paths down to

the foundations. However, by using cranked double tees in the normal bay no additional

framing was required (Figure 39). This arrangement provided the additional benefit of a

more consistent soffit line.

Lateral loads were taken by shear walls and cores. Tie bars cast in the in-situ beams

were bent down over the precast units and cast into the structural screed to ensure

diaphragm action and robustness.

The construction method required that two bays were left open for mobile crane access

so that units could be lifted directly off lorries and straight into position in the other

bays. Once the top level was complete, the infill bays were constructed with the cranes

backing out slowly towards Harbour Parade.

40

6 Case studies

The span of the slabs is almost 16 m.This meant that precast slabs could be either 600 mm

deep double tees or 400 mm deep hollowcore units. Double tees were used as they

were lighter: the dead load is 5.0 kN/m2, including screed, against 6.7 kN/m2 for the

hollowcore. To allow greater headroom some hollowcore units were used in lobby areas.

The double tee beams are 2.4 m wide with 600 mm deep ribs. The beams’ width is the

same as the width of the car parking bays and fits neatly into the 7.2 m grid in the

Figure 32General layout

Below left: Figure 33Double tee slabs

Photo: C. Goodchild

Below right: Figure 34Scarf joints onto in-situ beam

allow for cables and conduitsPhoto: C. Goodchild

Right: Figure 37Prefabricated edge beam cage

Photo: Sir Robert McAlpine Ltd

Far right: Figure 38Edge detail

Above left: Figure 35Section through edge beam

Above right: Figure 36Section through internal beam

43

Case studies 6

42

6 Case studies

Stability during the construction phase was ensured by welding the double tee units

together at 2.4 m centres and to the in-situ beams at 1.2 m centres. Each welded

connection had a tensile capacity of 105 kN and together in effect formed a diaphragm

in the temporary condition.

The shear walls between the half levels proved slow to construct as they could only be

concreted in shallow lifts.

The car park is an integral part of the West Quay development and, therefore, has

special perimeter architectural treatment. This includes precast concrete cladding

systems using reconstituted stone and knapped flint and curved in-situ concrete

features at the entrances and other prominent areas. The interfaces with cladding called

Right: Figure 40The shear wall between two half-levels

Photo: C. Goodchild

Far right: Figure 41Spandrel cladding on east elevation

Photo: C. Goodchild

Figure 39Section through ramp – showing cranked

double tees

Figure 42Fixing detail 59

Above : Figure 43Section through spandrel cladding

Above right: Figure 44Fixing detail 60

Right: Figure 45Co-ordination works! Fixing detail 59 in place

Photo: C. Goodchild

45

Case studies 6

44

6 Case studies

for a significant degree of co-ordination, especially for the curved pedestrianised

entrance (Figure 31).

Best aspects of this project were:

■ The hybrid concrete frame worked well as a system, in terms of the overall result

and lack of interface problems.

■ The potential advantages of using double tees were fully realised and proved to be

a very positive way to create large areas of floor very quickly.

Figure 46East Elevation with buttress cladding

Photo: C. Goodchild

Below left: Figure 47Buttress cladding – detail 54

Below right: Figure 48Buttress cladding – detail 58

Left: Figure 49Buttress cladding section – East elevation

Below: Figure 50Buttress cladding – detail 62

47

Case studies 6

The switch from a purely in-situ to a hybrid concrete structure of precast hollowcore

floor slabs and in-situ beams and columns helped win this major retail scheme for the

design-and-build contractor. Its adoption helped to shave some 15 weeks from the

original construction programme.

The site owner, Land Securities, is working in partnership with Canterbury City Council

to deliver an exciting new £100m retail scheme that will transform 12 acres in the

heart of the city centre. Upon completion in 2006, Whitefriars will be fully pedestrianised

and comprise 38 retail units, one department store, two further major stores and a 520

space multi-storey car park.

Following an architectural competition, public consultation and detailed discussions

carried on through 1996 and 1997, before formal planning permission was granted in

January 1999. Detailed design was undertaken while demolition, enabling works and

extensive archaeological digs were carried out on site. Tenders went out in January

2002. The contract was awarded in April 2002 and work started on 1 July 2002.

The structure was originally designed as a fully in-situ concrete frame with two-way

solid slabs and downstand beams. Over the relatively short tender period the contractor

concentrated efforts on finding alternative solutions to those indicated on the tender

drawings. He was looking for advantages that would deliver a quicker and more

buildable project at a price to win the job. Considerable effort was therefore put into

rationalising the substructure and the shopping and car parking areas (Zone C).

The advantages of a hybrid construction, using precast concrete hollowcore floors units,

quickly became apparent. The number of in-situ concrete beams was almost halved due

to the greater spans achieved by the hollowcore units. Less formwork and propping

was required and the frame construction programme was reduced by one month. Cost,

weight and deeper beams mitigated against a fully precast scheme.

Using hollowcore slabs in the HCC scheme reduced the overall weight of the floor slabs

and the amount of in-situ concrete placement required. This, in turn, reduced the overall

numbers of lorry movements to the site, a sensitive issue in this historic city, especially

during rush hour.

46

6 Case studies

■ Delivery and construction went smoothly. Because there were relatively few types of

floor unit there was flexibility to stop deliveries or bring them forward. The quality of

the double tees was good.

■ There were good relationships, good exchange of information and regular meetings

to resolve issues. Early specialist advice, for example on fixings etc., prevented

problems later.

■ Precast cladding panels were produced under pressure of time. Ideally, the cladding

contractor should have had a whole package of architectural designs with

‘engineering’ input at an early stage, without late tweaking of details. Regular

meetings meant that issues were resolved around the table, and this proved to be

faster than a conventional approach.

The client is very happy with the car park. It is user-friendly and feedback is very good.

A comparable project, built by another method, has not stood the test of time. The

split-level works well for car circulation and number of spaces.

Team member’s comment: “Quite proud of it!”

Project Team:

Client Hammerson plc

Client’s Concept Architect BDP

Design Consultants Chapman Taylor Architects

Engineers Pell Frischmann

Client’s Q S Cyril Sweett & Partners

D&B Contractor Sir Robert McAlpine Ltd

Engineers Sir Robert McAlpine Design Group

Contractor’s Foundation Engineers Ove Arup & Partners

Precast floors Tarmac Precast Concrete Ltd

Precast cladding The Marble Mosaic Company Ltd

References:

Allen, M. Paper to Southern Branch Concrete Society

Precast Concrete in Construction BPCF supplement, Construction News, 2000

Façade Winter 2000/01

Parking Review May 2001

Figure 51Artist’s impression of Whitefriars Street

Photo: Land Securities

Figure 52Gravel Walk elevation – Zone C

Whitefriars,Canterbury

49

Case studies 6

48

6 Case studies

The use of hollow core units had two other major benefits:

■ Construction of the extensive basement was critical to the programme and a form of

top-down construction was necessary to achieve overall time savings. The solution lay

in using the hollowcore floor to prop the secant piled retaining wall at ground floor level

while excavation and construction took place over the whole basement area below.

■ Use of hollowcore also minimised the amount of propping required between ground

floor and basement 4 to 5 m below. Additionally, it reduced the amount of concrete

required as no structural topping was needed to create the necessary diaphragm.

Units were delivered, lifted and landed onto partly-cast supporting in-situ beams. The

ends of all units were delivered with open ends, 500 - 600 mm long. Reinforcement

was introduced through the top of the supporting beam and extended into the open

ends of the slab units. When concreted, this detail provided robustness and integrity

to the diaphragm.

Figure 53Site plan: the basement access and delivery

area extends over the whole site

Overall, this method saved weeks on the construction programme and contributed

significantly to the success of the tender.

In Zone C, the relatively lightweight hollowcore units allowed bays of 8 m x 9.6 m at

retail unit level to be converted to bays of 16 m x 9.6 m to suit car park layouts above

– admittedly this required some fairly substantial in-situ beams to span 16 m, but

nonetheless it saved on column construction and time on unnecessary beams.

In the car park areas, the hollowcore slabs are designed to act compositely with a 75 mm

thick reinforced concrete structural topping. These floors are designed for a very severe

exposure condition in accordance with BS 8110, whilst all internal areas, such as those

for shopping, are left as the bare plank, ready to receive a cementitious finishing screed.

The use of prefabricated stair components reduced the requirements for scaffolding.

Their use also enabled the contractor and subcontractors to access all areas of the

constructed floors immediately after the stair units had been placed.

Car park loading

Shop unitloading

Figure 58Zone C, 1st Floor – the hybrid solution significantly

reduced the number of beams required

Right: Figure 56One bay of hollowcore was temporarily left out of

Whitefriars Square, the ground floor slab between

zones B and D. This gave access for constructing the

basement while working on the critical upper

storeys along Gravel Walk beyond

Photo: C. Goodchild

Far right: Figure 57Completed ground floor soffit

Photo: C. Goodchild

Right: Figure 54The Gravel Walk entrance during construction

Photo: C. Goodchild

Far right: Figure 55Falsework for in-situ beams remains in place while

hollow core units are placedPhoto: C. Goodchild

51

Conclusions 7

7. ConclusionsHybrid Concrete Construction is about providing best value for clients.

It is not necessarily about first cost. But it is about savings from improved buildability

on site and these savings soon overtake any material cost differences. It is also about

inherent benefits – such as thermal mass. Thermal mass leads to energy savings; it also

leads to occupier comfort which, in turn, leads to user efficiency. By using the 'whole-life’

cost approach and recognising the 1 : 5 : 200 relationship between initial cost, maintenance

and lifetime business costs, the advantage of HCC can be seen more clearly.

Value has to be measured in the client’s terms and best value will only be achieved by

changing from ‘traditional’ procurement methods. The processes advocated by this

document align very closely with the ideals of Rethinking Construction 2. Best Practice

for HCC is set out in Chapter 5 where the whole ‘how it should be’ process is mapped

out and described. Many leading companies already use methods similar to this model

– and the model is just as applicable to getting best value out of purely in-situ and

precast construction as it is for combinations of the two. Chapter 4 highlights the ‘new’

processes necessary to achieve the desired results. These include:

■ The early involvement of specialist contractors.

■ The use of a lead frame contractor.

■ Adopting a programme of project workshops.

■ Adopting the principles of best value.

Adopting the principle of best value means that there has to be some way of measuring it.

Value indicators must weigh up the relative importance of cost, speed, quality, robustness and

lettability etc. Issues such as whole-life costs, energy usage and the effects of the structure

and design on overall business costs need to be considered and factored in. As the case

studies demonstrate, the purpose is to provide best value in the client’s terms. For example:

■ The North Stand at Ipswich Town FC was delivered fast, in only 23 weeks.

■ The Toyota (GB) Headquarters delivered award-winning quality.

■ The West Car Park at Southampton’s West Quay is inviting and user-friendly.

■ Adopting the hybrid frame at Whitefriars helped save 15 weeks on the programme.

Positive comments such as “quite proud of it” and “wouldn’t change a thing” come

from satisfied clients and are the result of commitment and team effort. The successful

outcomes on these projects were achieved with enlightened attitudes between parties

and a willingness to adopt innovation and best practice guidance. This is all within an

environment of trust promulgated by clarity of roles and purpose, promoted by an open

book approach to contract procurement. The high levels of buildability called for higher

than usual levels of pre-planning and team players, but as has been proven, HCC delivers.

HCC will be driven further by the need to manufacture off-site and construct safely on

site. HCC brings quality, value and speed but more significantly, consideration of overall

business costs will become the compelling argument for using HCC.

50

6 Case studies

The remaining retail units have steel frames, which were designed as fully composite,

except at perimeter locations where the plain beams support the loads while allowing

for holes through adjacent slabs.

At the time of writing, this project was still on site but amongst the best aspects of this

project are:

■ The in-situ /precast, hybrid solution helped win the job by saving time and money. It

provided a solution that achieved the contractor and client’s cost and programme

requirements.

■ The decision to go ‘top down’ with the basement construction was made feasible by

using hollowcore units and proved to be a turning point in winning the contract.

Again, the HCC solution saved time and money.

■ Together with reducing the number of beams/columns and the decision to go top

down, the HCC scheme saved 15 weeks on the initial programme estimates.

■ There were good working relationships amongst all parties. The precaster was

involved at a reasonably early stage.

Contractor’s comment: “This is a high standard concrete frame – it looks good.”

Project team:

Client Land Securities in partnership with Canterbury City Council

Concept Architect Chapman Taylor

Client’s Engineers Upton McGougan Consulting Engineers

Project Managers MACE

D&B Contractor HBG Construction

Engineers HBG Construction

Contractor’s Architect Lyons + Sleaman + Hoare

Frame Contractor Whelan & Grant

Precast floors Bison Concrete Products

Above left: Figure 5916 m spanning beams at upper car park level

Photo: C. Goodchild

Above right: Figure 60Typical section through beam

53

Appendix

Appendix Background researchThe best practice guidance given in this publication follows on from earlier pieces of

research carried out for the concrete industry within the context of many initiatives and

drivers for change in the wider construction industry.

The Reading Production Engineering Group (RPEG) at the University of Reading investigated

the Barriers to Hybrid Concrete Construction23 by using force field techniques. These are

used to identify and remove impeding forces (or barriers). Impelling forces will then,

naturally, take the adoption of a technique or practice forward into more widespread

adoption and practice.

Hybrid Concrete Construction for the UK market1 aimed to identify the most advantageous

systems, quantify potential benefits and discover how these benefits might be achieved

more widely in practice. The research by Oxford Brookes University School of Architecture,

The University of Salford and Imperial College, London, investigated client and customer

requirements, business processes, perceived barriers to use and structural design.

Following the completion of the research above, the construction industry witnessed

several major advances in the process of construction procurement. Most notably, the

Rethinking Construction2 task force report, led by Sir John Egan and published in 1998,

contained the clear message that the industry would not significantly improve unless

it embarked upon radical change. This would involve a totally new approach to the

delivery of the construction product.

From these ideals the ‘Movement for Innovation’ (M4i) was born. This is now part of

Constructing Excellence. M4i continues to lead radical improvement in construction

in terms of value for money, profitability, reliability and respect for people, through

demonstration and dissemination of best practice and innovation.

Other initiatives were being taken forward at the same time:

■ Value management and principles of value engineering were being applied to

construction projects.

■ Government had sponsored the ‘Construction Best Practice programme’ 6 to

provide support to individuals, companies, organisations and supply chains in the

construction industry seeking to improve the way they do business.

■ Several bodies undertook process research. Under the EPSRC ‘Innovative Manufacturing

Initiative’ (IMI), research into Process Protocol was undertaken during 1995-98

(Figure 61). Researchers used manufacturing principles as a reference point for a

framework of common definitions, documents and procedures that were developed

to help construction project participants work together seamlessly.

Previous concrete industry research

A.1 Context

52

8 References and Further Reading

Government and other initiatives

8. References and further readingReferences

1 GOODCHILD, C H et al. Hybrid Concrete Construction for the UK market: final report on research into using combinations of in-situ and precast concrete in structural frames to achieve better value for UK customers. Crowthorne, BCA, on behalf of theindustry sponsors of the RCC, 2001. 422 pp. Ref. 97.369. ISBN 0 720 1528 X.

2 SIR MICHAEL LATHAM. Constructing the Team: final report of the government/industry review of procurement and contractualarrangements in the UK construction industry. London, DOE, 1994. ix, 130 pp.

3 EGAN. Rethinking Construction, Rethinking the construction client, the national debate. London, DTI, 1998. 40 pp.

4 Movement for Innovation (M4i) now see www.constructingexcellence.org.uk/

5 CONNAUGHTON, J N & GREEN, S D Value management in construction: A client’s guide. London. CIRIA Special Publication129, 1996. 73 pp. ISBN 0 86017 452 2.

6 Construction Best Practice Programme (CBPP) now see www.constructingexcellence.org.uk/

7 KAGIOGLOU, M et al. A generic guide to the design and construction Process Protocol. University of Salford, 1998.ISBN 090 289 617 2.

8 THE STRATEGIC FORUM FOR CONSTRUCTION. Accelerating change. 2002 London, Rethinking Construction (c/o TheConstruction Industry Council). 42 pp. ISBN 1 898671 28 1. See www.strategicforum.org.uk.

9 STEEL CONSTRUCTION INSTITUTE AND BRITISH CEMENT ASSOCIATION, Learning from the best. Ascot, SCI, 2003. Ref.RT952. www.steel-sci.org/Publications.

10 GOODCHILD, C H Cost model study: a report on the comparative costs of concrete and steel framed office buildings.Crowthorne: BCA on behalf of the industry sponsors of the RCC, 1993. 48 pp. Ref. 97.333. ISBN 0 7210 1469 0.

11 GOODCHILD, C H Hybrid Concrete Construction: combining structural materials for speed, quality and economy in buildings.Crowthorne, BCA on behalf of the industry sponsors of the RCC, 1995. Ref. 97.337. 64 pp. ISBN 0 7210 1479 8.

12 PRECAST FLOORING FEDERATION. Code of practice for safe erection of precast concrete flooring and associated components.Leicester, PFF, 2001. 88 pp.

13 Innovation and Research Focus No 51 November 2002, Institution of Civil Engineers, London, ISSN 0960 5185 (see also www.crc-tech.com).

14 EVANS, R, HARYOTT, R, HASTE, N & JONES, A The long-term cost of owning and using buildings, 1998. London, RoyalAcademy of Engineering. See www.raeng.org.uk/news/publications/reports.

15 RIBA. The RIBA Plan of Work Stages 1999. See www.architecture.com/go/Architecture/Using/Contracts_306.html.

16 GRAY, C In situ concrete frames: a strategy for improving the performance and productivity of the in situ concrete frame industrywhich will lower the cost of construction for the industry and its clients. (Improving concrete performance series). Reading,Reading Production Engineering Group, University of Reading, 1995. 24 pp. ISBN 0 7049 0505 1.

17 BARRETT, P Current business processes and desirable process improvements (workpackage 3): a report by the University ofSalford, in Goodchild et al. (2001), Hybrid Concrete Construction for the UK market (Ref. 1 above).

18 GLASS, J A best practice process model for Hybrid Concrete Construction. Article submitted to Construction Management andEconomics Journal.

19 BROWN, N The procurement of structural precast concrete. Paper given at Concrete Society seminar, Cirencester 1997.High Wycombe, ABC Structures, 01494 441144.

20 CONSTRUCT, the Concrete Structures Group. National Structural Concrete Specification for Building Construction. 2nd edition.Crowthorne, BCA, 2000. 72 pp. Ref. 97.378. ISBN 0 7210 1571 9.

21 DAWSON, S. Cast in Concrete. Leicester, Architectural Cladding Association, 2nd Edition, 2003. 96 pp. ISBN 0 9536773 3 8.

22 BRITISH STANDARDS INSTITUTION. Structural use of concrete: Part 1. Code of practice for design and construction.(BS 8110 Part 1). London, BSI, 1997.

23 READING PRODUCTION ENGINEERING GROUP. Barriers to Hybrid Concrete Construction: an unpublished report by RPEG,University of Reading, 1997 in Goodchild et al, Hybrid Concrete Construction for the UK market (Ref 1).

24 GLASS, J Best Practice Guidance on Hybrid Concrete Construction: Work stage 2: Practitioner interviews (confidential researchreport). Oxford Brookes University, 2002.

25 GLASS, J Best practice guidance on Hybrid Concrete Construction: Work stage 3: Knowledge capture workshops (confidentialresearch report). Loughborough University, 2003.

26 ELLIOTT, K S Multi-storey precast concrete framed structures: a design guide, Oxford, Blackwell Science, 1996. 601 pp.ISBN 0 632 03415 7.

27 CEN. pr EN1992-1-1. Eurocode 2: Design of concrete structures – Part 1.1: general rules and rules for buildings, April 2003version. Brussels, CEN.

28 GHALI, A, FAVRE R, & ELBADRY, M Concrete structures, stresses and deformations, 3rd edition, London, E & F N Spon Ltd,2002. 584 pp. ISBN 0 415 24721 7.

29 CEB-FIP Model Code 1990, Thomas Telford Ltd, November 1993, 480 pp. ISBN 0 727 71696 4.

Further reading■ BRUGGELING, A S G, & HUYGHE, G, F Prefabrication with concrete. Rotterdam, A A Balkema. 1991, 380 pp.

ISBN 90 6191 183 4.

■ CIRIA. Snapshot – Standardisation and pre-assembly based on research project RPS32, London, CIRA, 1998. 7 pp.

■ FIP COMMISSION ON PREFABRICATION. Composite floor structures. London, SETO Ltd, 1998. 58 pp. ISBN 1 874266 38 7.

■ FIB, COMMISSION 6 ON PREFABRICATION. Planning and design handbook on precast building structures. 2nd Edition BFTBetonwerk + Fertigteil-Technik, Gutersloh, Germany, 2004. 139 pp.

■ GRAY, C Value for money – helping the UK afford the building it likes. University of Reading. 1996. 60 pp.

■ HARLAND, C M, Supply chain management: Relationships, chains and networks, British Journal of Management, Vol. 7,Special Issue, S63-S80. 1996.

■ HUNTON, D A T Precast concrete in buildings – Past, present and future. Betonwerk + Fertigteil-Technik, 10/90. pp. 70–77.

■ MALE, S et al. The value management benchmark: framework document. London, Thomas Telford. 1998. 64 pp.ISBN 0 7277 2729 X.

The Partners in Innovation project Best Practice Guidance on Hybrid Concrete Construction

was a 15-month study to identify and disseminate best practice on hybrid concrete

structures. This publication forms the main output from that project.

Essentially, the research undertaken by Dr Glass consisted of a series of interviews24 with

a range of industry professionals to produce procurement process maps and discuss

relevant issues. The process maps were created and examined in each successive

interview and iteratively amended so they became increasingly robust. Finally, in a series

of Knowledge Capture Project Workshops25, held on site, they were tested against

events that occurred on actual HCC projects. The ‘how it should be’ process map (Figure

5) is the basis of the best practice given. However, along the way, the many examples

and anecdotes given have been collected, analysed and used to provide further pointers

to achieving best practice in HCC18.

The Accelerating Change8 report published in September 2002 by The Strategic Forum for

Construction set out rigorous targets intended to produce a more modern and dynamic

industry. The report challenged the construction industry to provide maximum value for

clients and end users and to provide a consistently world-class product. It committed

the Forum to produce an integration aid to help the industry to achieve this target.

Learning from the Best9 extracted lessons from Rethinking Construction2 demonstration

projects. It found that considerable improvements have been made by companies that

have adopted new methods of working.

Within this changing business environment, the Reinforced Concrete Council (RCC) set out

to produce Best Practice Guidance for Hybrid Concrete Construction. It was researched

during 2002 and 2003 by Dr Jacqueline Glass of Oxford Brookes University’s School of

Architecture and more recently of the Department of Civil and Building Engineering at

Loughborough University. The research was managed by the RCC (and its successor, The

Concrete Centre) and guided by an industry advisory group made up of representatives

of leading exponents of new approaches to concrete frame procurement.

Figure 61Process Protocol mapCourtesy of University of Salford

AppendixAppendix

5554

A.2 Best Practice Guidance for Hybrid

Concrete Construction research project

Liaison withProcess

Manager

Liaison withother Activity

Zones

Establishthe need

for aproject

Establishthe need

for aproject

DEVELOPMENTMANAGEMENT

RESOURCEMANAGEMENT

PROJECTMANAGEMENT

DESIGNMANAGEMENT

FACILITIESMANAGEMENT

PRODUCTIONMANAGEMENT

HEALTH &SAFETY,

STATUTORY ANDLEGAL

MANAGEMENT

PROCESSMANAGEMENT

Prepareoutline

BusinessCase

ConsiderRisk

Issues

Prepareoutline

Businesscase

DevelopinitialStake-holder

List

DevelopinitialStake-holder

List

Establishinitial

Comm-unicationStrategy

Compileinitial Risk

Register

Establishinitial

Comm-unicationstrategy

PrepareProject

ExecutionPlan

PrepareProcess

ExecutionPlan

Finalisethe

Statementof Need

for aproject

Finalisethe

Statementof Need

for aproject

PrepareProjectBrief

PrepareProjectBrief

Updateoutline

BusinessCase

ConsiderRisk

Issues

Updateoutline

BusinessCase

Assessstake-holder

impact &require-ments

Assessstake-holder

impact &require-ments

ConsiderSite andEnviron-mentalissues

ConsiderSite andEnviron-mentalissues

UpdateComm-

unicationStrategy

Updateinitial Risk

Register

UpdateComm-

unicationStrategy

UpdateProject

ExecutionPlan

UpdateProcess

ExecutionPlan

Under-take

outlineFeasibilitystudiesfor eachoption

Under-take

outlineFeasibilitystudiesfor eachoption

UpdateProjectBrief

UpdateProjectBrief

Updateoutline

BusinessCase

ConsiderRisk

Issues

Updateoutline

BusinessCase

UpdateSite andEnviron-mentalissuesReport


UpdateComm-

unicationStrategy

Updateinitial Risk

Register

UpdateComm-

unicationStrategy

UpdateProject

ExecutionPlan

UpdateProcess

ExecutionPlan

SOFT

GA

TEPH

ASE

rev

iew

SOFT

GA

TEPH

ASE

rev

iew

SOFT

GA

TEPH

ASE

rev

iew

UndertakesubstantiveFeasibilitystudies onthe most‘feasible’options

UndertakesubstantiveFeasibilitystudies onthe most‘feasible’options

UpdateProjectBrief

UpdateProjectBrief

UpdateBusiness

Case

ConsiderRisk

Issues

UpdateBusiness

Case


PrepareinitialCDM

assess-ment


UpdateComm-

unicationStrategy

Updateinitial Risk

Register

UpdateComm-

unicationStrategy

UpdateProject

ExecutionPlan

UpdateProcess

ExecutionPlan

HA

RDG

ATE

PHA

SE r

evie

w

ReviseProjectBrief

ReviseProjectBrief

Revisefull

BusinessCase

ConsiderRisk

Issues

Revisefull

BusinessCase


ReviseCDM

assess-ment


UpdateComm-

unicationStrategy

Prepareinitial

Cost Plan

Revise Risk

Register

UpdateComm-

unicationStrategy

ReviseProject

ExecutionPlan

ReviseProcess

ExecutionPlan

SOFT

GA

TEPH

ASE

rev

iew

UpdateProjectBrief

PrepareOperationPolicy andMainten-ance Plan

UpdateProjectBrief

UpdateBusiness

Case

ConsiderRisk

Issues

UpdateBusiness

Case


UpdateCDM

assess-ment


UpdateComm-

unicationStrategy

UpdateCost Plan

Update Risk

Register

UpdateComm-

unicationStrategy

UpdateProject

ExecutionPlan

HA

RDG

ATE

PHA

SE r

evie

w

ReviseProcess

ExecutionPlan

ReviseProcess

ExecutionPlan

FinaliseBusiness

Case

ConsiderRisk

Issues

UpdateOperation

Policyand

Mainten-ance Plan

FinaliseBusiness

Case


UpdateCDM

assess-ment


UpdateComm-

unicationStrategy

Revise Risk

Register

UpdateComm-

unicationStrategy

ReviseProject

ExecutionPlan

ReviseProcess

ExecutionPlan

HA

RDG

ATE

PHA

SE r

evie

w

FinaliseProjectBrief

UpdateOperation

Policyand

Mainten-ance Plan

FinaliseProjectBrief

FinaliseSite andEnviron-mentalissuesReport

ConsiderRisk

Issues

FinaliseHealth &

SafetyPlan

FinaliseSite andEnviron-mentalissuesReport

FinaliseComm-

unicationStrategy

FinaliseCost Plan

UpdateRisk

Register

PrepareProduc-

tionInform-ation

FinaliseComm-

unicationStrategy

PrepareHand-over Plan

Startenablingworks

PrepareHand-over Plan

UpdateProject

ExecutionPlan

UpdateProcess

ExecutionPlan

SOFT

GA

TEPH

ASE

rev

iew

Updateand

imple-mentHand-

over Plan

FinaliseRisk

Register

Developas-builtinform-ation

Revise &implementOperationPolicy &Mainten-ance plan

Manage& under-

takeconstruc-

tionactivities

ManageHealth &

Safety

Updateand

imple-mentHand-

over Plan

ConsiderRisk

Issues

UpdateProject

ExecutionPlan

UpdateProcess

ExecutionPlan

HA

RDG

ATE

PHA

SE r

evie

w

Under-take PostProjectReview

ConsiderRisk

Issues

Ongoingupdate ofOperationPolicy &

Mainten-ance plan

Under-take PostProjectReview

FinaliseProject

ExecutionPlan

FinaliseProcess

ExecutionPlan

Performongoingreview ofFacilitiesLifecycle

PHASE ZERO PHASE ONE PHASE TWO PHASE THREE PHASE FOUR PHASE FIVE PHASE SIX PHASE SEVEN PHASE EIGHT PHASE NINE

OPERATION & MAINTENANCECONSTRUCTIONPRODUCTION INFORMATIONDETAILED DESIGN, PROCUREMENT

& FULL FINANCIAL AUTHORITYFULL CONCEPTUAL DESIGNOUTLINE CONCEPTUAL DESIGN

SUBSTANTIVE FEASIBILITY STUDY& OUTLINE FINANCIAL AUTHORITY

OUTLINE FEASIBILITYCONCEPTION OF NEEDDEMONSTRATING THE NEED

OUTLINEPLANNINGAPPROVAL

DETAILEDPLANNINGAPPROVAL

PRE-PROJECT PHASES PRE-CONSTRUCTION PHASES CONSTRUCTION POST-CONSTRUCTIONPHASE

FinaliseProcurement

Plan

FinaliseProcurement

Plan

Prepare FeasibilityDesign Brief

Prepare FeasibilityDesign Brief

Prepare initialProcurement Plan

Prepare initialProcurement Plan

UpdateProcurement

Plan

UpdateProcurement

Plan

UpdateProcurement

Plan

UpdateProcurement

Plan

UpdateProcurement

Plan

UpdateProcurement

Plan

Prepare conceptDesign Brief

Prepare conceptDesign Brief

Prepare outlineConcept Design

Prepare outlineConcept Design

Prepare fullConcept Design

Prepare fullConcept Design

Produce Detailed Design

Produce Detailed Design

USE & CREATION OF LEGACY ARCHIVE

FEEDBA

CK TO

OTH

ER PROJEC

TS VIA

LEGA

CY A

RCH

IVE

PROCESSMANAGEMENT/

CHANGEMANAGEMENT

FEED

BAC

K F

ROM

CU

RR

ENT

& P

AST

PRO

JEC

TS

57

Appendix

56

Appendix

Thirteen interviews were conducted with senior practitioners within the field of

concrete frame construction. They were used to develop, test and confirm process

models for HCC, to agree HCC performance indicators (HPIs) and to discuss any other

relevant issues.

The process models described and documented the activities, roles and responsibilities

of various players in the procurement, design and construction of a hybrid concrete

structure. The aim was to ensure that both traditional procurement and partnering type

regimes were reflected and analysed in two models; the first ‘how it is’ and the second

‘how it should be’.

The framework used was based on Process Protocol7.(Figure 61). This framework was

aligned with RIBA Stages of Work15, but above all it was developed to reflect the

specifics of concrete frame construction. The models’ horizontal axes included stages

of work from briefing, feasibility and design through to construction, hand-over and

occupancy. The vertical axes listed the full range of occupations/professions that one

might expect to be involved (i.e. client, architect, quantity surveyor, main contractor,

precaster etc.). Thus, the matrices were populated with tasks, deliverables and ‘gateways’

(i.e. ‘what should be done, by whom and at what stage’) as appropriate.

The second model, the ‘how it should be’ model, is reproduced as Figure 5 and details

activities under a partnering style procurement route. It may be thought of as being

more akin to the Rethinking Construction model with strategic alliances formed early

on in the programme.

The models were validated by the project advisory group before circulation to

interviewees for detailed feedback. After the interviews, the models were amended to

take account of feedback from the various practitioners. There was genuine consensus

that the models, subject to those amendments, were a good representation of practice,

both current and ideal.

r Pleased with it.

r Looks good.

r Environment feelsmuch morepositive.

r The positives faroutweigh thenegatives.

r There were somevery positiveaspects to thisproject.

r Quite proud of it.

r We couldn’t havedelivered thisproject viacontractor designportions /packages.

r Duringconstruction, thesite operatedwithout needing amain contractor.

r Ambience

r Tactile finishes

r Needed leadframe contractorand open booktendering

r Prefabrication led to a qualityexposed finish.

r Quality products.

r Known and provenmaterials.

r Achieved excellentlight grey finish;important forlighting.

r Fully integratedapproach conceptensures full earlyintegration.

r Units made incontrolledenvironment withhigh qualitystandards achieved.

r Integration between packagesub-contractors.

r Enabled services to be integratedefficiently andwith confidence.

r Final account forstructural packagewas within + or – 10% oforiginal budgetincludingconstraints causedby outside forcesunknown attender stage.

r Value for money.

r Open bookapproach.

r Maximum planning time for constructionsequence.

r Early decisions byclient/contractorgave materialssupply to site abetter chance of keeping toprogramme.

r Allowed fasterection ofstructure.

POSITIVE COMMENTS ABOUT THE HCC BUILDINGS FROM WORKSHOPS

Knowledge captureworkshops

Table 12Positive comments about the

HCC buildings from workshops

The objective of the workshops was to reconvene project teams (including client,

architect, project manager, engineer, main and specialist contractors, precast

manufacturer and/or others as appropriate) who were involved with completed HCC

buildings or structures. The aim was to capture the key ‘events’ that characterised the

use of HCC. ‘What went right’ and ‘what could have been improved’ were evaluated

such that generic best practice lessons on process and product were extracted. How is

the building performing? Do maps of the process look right? Have drivers and barriers

been identified?

A series of five workshops was held in

various locations around the country

during early 2003. The workshops were

designed and facilitated to maximise the

extraction of both explicit and implicit

knowledge.

The workshops generally followed the

following format:

■ Walk around site.

■ Introductions and briefing.

■ An ‘event line’, detailing the critical events that affected the HCC was constructed. The

aim was to find out how the team came to the decision to use HCC, how they got the

go ahead and how it progressed on site. The exercise revealed what was the ‘process’,

who was involved and when.

As the workshop timetable was very tight, participants were asked to bring relevant

information – by way of drawings (floor plans, sections, and frame details), elemental

costs, frame/element specifications, diaries, form of contract information or other

documents on procurement etc. relating to the project – to help create the event line.

Process mapping

THE KNOWLEDGE CAPTURE WORKSHOPS

Ipswich Town Football Club North Stand

Toyota GB Headquarters Epsom

West Quay Car Park Southampton

Whitefriars Shopping Centre Canterbury

In addition, a ‘not hybrid’ workshop was held withmembers of the Advisory Group in London.

Table 11The Knowledge capture workshops

The event line was evaluated and its content was examined. The aim was to find out

‘what went right?’ ‘what went wrong?’, and ‘what would the team do differently next

time or advise others to do?’ Each participant highlighted at least one good and one

bad aspect of the project and was asked to explain why he or she had chosen that

aspect and how, in the case of it being a negative, it could be resolved next time. The

exercise revealed where the key learning points were and some best practice lessons.

Following a summing up, the project was reviewed as a whole. Members of the group

commented from their perspectives on the HCC aspects in particular. The aim was to

establish whether HCC satisfied the project objective(s) overall.

Each workshop was written up, checked by participants and analysed. Generic lessons

were incorporated into the process model and best practice guidance. The content of

the workshop reports are confidential to the participants; some anecdotes are featured

in Chapter 5.

During the research and interviews several themes came to light. The following (Table

13) summarises the findings:

59

Appendix

58

Appendix

Emergent themes

Table 13Emergent themes18

Note* The term ‘two-stage

contract’ was used here in thecontext that a job is let in two

stages, with the initial inputfrom contractors/specialists

paid for in its own right duringthe first stage (usually

extending only into conceptualdesign).The second stage may

extend up to construction(which is then let out

separately) or may extendthrough design, productiondrawings and construction.

EMERGENT THEMES

Problem solving

Trust

Communications

Get better value

Early involvement

Lead Frame Contractor (LFC)

Workshops

‘How it should be’

r There is an emphasis on problem solving at the design stage, rather than tendering and squeezing of budgets.The ultimategoal should be that on-site operations should go smoothly because any anomalies will be worked out ‘on paper’.

r There is an inherent degree of trust involved, whereby the specialists come forward early on, giving advice in goodfaith, but this goodwill must be honoured in some way to maintain good working relationships.

r Management of communications is key to success and so the role of project manager becomes closely associated withthe business process and personnel aspects of the project. On the other hand, the role of a lead frame contractor (LFC)is to undertake and deliver the practical matters. In general, roles are very clear cut, provided sufficient early agreementsare reached between all the parties.

r Several interviewees suggested that the Best Practice for Hybrid Concrete Construction (HCC) model should apply toany project, not solely HCC because it offers a much better opportunity to get a better value building. Many peoplehad direct experience of this – some even called the model ‘how it is for us – every day’.

r It was thought vital that the architect, engineer, quantity surveyor and M&E engineer were on board at thefeasibility stage. The interviewees felt this better represented true partnering and it was crucial for theseprofessions not to work in isolation.

r Main contractors and specialists could join earlier than conceptual design stage, depending on the client and/or thecontract. In some cases a two-stage contract* was thought to be a good option as too early an involvement may notalways be ideal.

r Providing this would not lead to too many layers of management, the concept of a LFC was favoured.The LFC must bewell versed in all materials.When working with construction managers, the LFC must expect to work within an integraldelivery team or cluster to deliver a frame & envelope package.

r Perhaps the most insightful theme to arise during the interview process was the steady feedback on the importance of workshops throughout the course of a project, leading towards a clear feedback loop for continuous improvementand project-to-project learning.The suggested programme of workshops is shown in Table 4 and is clearly designed tofacilitate better communication, promote best value and prevent unforeseen problems arising as far as possible.

r Regular design development and progress meetings would continue as a matter of course.

r The ‘How it should be’ model, was seen as a good basis for a less adversarial way of working.This way of working ismore favourable to all types of construction, not only HCC.

The Construction Best Practice Programme (CBPP)6 oversaw the development of Key

Performance Indicators (KPIs). This series of simple indicators provides industry with a

method of measuring performance against benchmarks. The M4i Demonstration

Projects programme brought the indicators to life and many of the 180 projects were

measured publicly against the KPIs. M4i thus developed as a springboard organisation

for companies involved with the demonstration projects to share their progress with

other like-minded organisations throughout the UK. The effect of these developments is

that the industry is now more accustomed to indicators and a culture of measurement.

On this basis, it was agreed that while the original HCC list17 of aesthetics, function,

speed, responsiveness, safety, integration, buildability and confidence, was representative

in an academic sense, it needed to be tested against current market conditions. A list

of likely performance indicators was compiled. Interviewees were invited to view this

list as a stimulus for proposing Hybrid Concrete Construction Performance Indicators

(HPIs) from their own viewpoints.

Interviewees were asked to state the most important HPIs (Table 14) from their own

viewpoints and experience and to rank them. The small sample of interviewees

precluded any valid statistical analysis, so the results are presented below simply on

the basis of frequency of citations by interviewees. Three levels of relative importance

emerged and these are shown in Table 15.

The fact that speed and cost issues appear at the head of this list comes as no surprise,

but what was interesting was the frequency of use of terms such as value, value for

Performance indicators

Notes1. First espoused by Rethinking

Construction 2, now firmlyestablished within the

‘Construction Best PracticeProgramme’6 as a

measurement method forcompanies, sector and the

industry as a whole.

2. Proposed in summer 2002as a means of adding more

qualitative issues to theoriginal KPIs.

3. Movement for Innovation(M4i) 4 Sustainability Working

Group Report, these areenvironmental performance

indicators for sustainableconstruction.

M4i,Watford, Herts.

4. Established during a previousresearch project on HCC,

principally by Peter Barrett,University of Salford17.

r Client satisfaction – product

r Client satisfaction – servicedefects

r Predictability – cost of design

r Predictability – cost of construction

r Predictability – time for design

r Predictability – time forconstruction

r Profitability

r Productivity

r Safety

r Construction cost

r Construction time

r Overall cost

r Overall time

r Build quality: performance,engineering systems,construction

r Functionality: use, access,space

r Impact: form and materials,internal environment, urbanand social integration,character and innovation

r Operational energy (CO2)

r Embodied energy (CO2)

r Operational waterconsumption

r Waste (in construction)

r Construction transport

r Biodiversity

r Aesthetics

r Function

r Speed

r Responsiveness

r Safety

r Integration

r Buildability

r Confidence

r Cost

Table 14Potential HPIs list KEY PERFORMANCE

INDICATORS (KPIs)1

DESIGN QUALITYINDICATORS (DQIs) 2

ENVIRONMENTALPERFORMANCEINDICATORS (EPIs) 3

HCC PERFORMANCE CRITERIA 4

61

Appendix

money and best value in describing the commercial criteria for success. The main caveat

to the exercise is that most interviewees stated that: “the final choice will vary from

project to project”.

The predominance of speed/cost is clear, but the second order of HPIs is perhaps the

more critical for this study. Spans, flexibility in use, fire protection and services

integration are proving to be the real battleground for structural frames. This would

indeed be the case on the basis of feedback from the client/developer sector. This group

of interviewees was keenly aware that, with M&E constituting on average one-third of

their capital expenditure on a project, their choice of structural frame will often be

determined by the frame’s facility to optimise the installation and operation costs for

the M&E. HCC may be at an advantage here by being able to offer, for example, thinner

floor slabs, clear span spaces and thermal mass.

Some sectors such as client/developer groups are driven to choose framing materials on

the basis of criteria such as flexibility and M&E provision. This indicates that the offering

from specialist concrete contractors and others should perhaps be targeted more

appropriately to meet these needs.

60

Appendix

Table 15Prioritised Hybrid

Concrete Construction

Performance

Indicators (HPIs)

INDICATORS NOTES

As part of its work on Hybrid Concrete Construction for the UK market 1. Imperial College

was asked to give guidance on the structural design of HCCs. In the main, the principles

of in-situ and precast concrete hold true. In the case of proprietary items, design is

often covered by manufacturers’ literature. Designers may be less familiar with the

design of bespoke composite concrete and so the notes below were prepared.

In general, composite concrete elements may be considered as being monolithic and

homogeneous. Usually, the precast concrete will be stronger than the in-situ concrete; it

will definitely be older and drier. It will be generally conservative to design the elements

on the basis of the lower strength but the different concrete properties of the concretes

should be acknowledged and reference should be made to BS 8110: Part 1, Clause 5.422.

It may be appreciated that not all the information required for design will be available

to designers at the beginning of the design process. Methods of construction,

timescales, materials etc. should be discussed and agreed with the contractors and

other members of the design team as appropriate as the design develops.

Composite reinforced concrete elements and structure should be checked for the

following stages:

Stage 1: Construction stage (dead load + construction loading) The precast units are checked using traditional calculation methods. The loading

includes self weight, weight of wet concrete and construction loading. For proprietary

items, tables for span and load limits are usually provided in manufacturers’ literature

and these construction load checks or temporary propping requirements are generally

implicit. Otherwise, full design checks will be required at both ULS and SLS. Handling

requirements are also often given in manufacturers’ literature.

Intermediate propping of precast units has the advantage of reducing construction

stage span moments, deflections and shears, but has the disadvantage of introducing

possible time and cost penalties on site and of inducing hogging moments over props

which have to be catered for.

Stage 2: Depropping (dead load + construction loading) Checks are generally not required unless removal of intermediate props is proposed

prior to the in-situ concrete reaching its full design strength. Nevertheless, removal of

props causes redistribution of loads and the capacity of members to carry the revised

loads should be considered. In the unlikely event of this being a worse case than the

final design load case, design checks should be made for the revised loads using a

concrete design strength appropriate to the time of removal of props.

Where depropping is needed before the concrete has achieved full design strength,

checks will be required at both ULS and SLS.

A.3 Structural Design

General

The design process

‘Higher’ importance

Speed

Cost

‘Medium’ importance

Spans / lettable area

Flexibility in use

Fire

Services integration

‘Lesser’ importance

Buildability

Environmental

Finish

Quality

Site conditions

Structure

Market conditions

Safety: An absolute necessity and must always be addressed

r Productivity/efficiency on site; time; programme; lead-in time.

r Cost of package; value for money (NB: eight of the 13 interviewees had speed/cost in their top three choices).

r Floor depths/building height; preferred grid; vertical access routes; third-party aspects (NB: clients prioritised maximising lettable area spans of up to 15 metres).

r Low maintenance; good performance.

r Fire protection; robust fire protection.

r Air conditioning options; control; sound/thermal insulation; fabric energy storage.

r ‘Being tolerant’; tolerances.

r Embodied energy/operational energy; waste; M4i sustainability indicators.

r Certainty of finish; architectural merit; visual surfaces.

r Certainty of quality of product.

r Access; site constraints; logistics.

r Dynamic requirements; load carrying ability; overall stability; temporary stability.

r Risk; capacity; resources; capacity available; certainty.

63

Appendix

Stage 3: Full composite action (dead + live loads)Flexure

Reinforcement is calculated for the total ultimate moment using the full composite

section. For prestressed precast units, an alternative method is to calculate the area

of steel required for Stage1 (with precast section only) and add the area required for

Stage 3 (using increased lever arm for composite action). The difference in using either

method is not great if the superimposed moment for Stage 3 is more than twice the

self weight moment for Stage 1. The flexural capacity of composite beams can be

enhanced because the breadth of the compression flange can be increased up to the

maximum permitted value for monolithic construction (BS 8110: Part 1, Clause 3.4.1.2).

Detailed guidance on this is given by Elliot26.

Shear

Shear checks on beams and slabs are made using traditional methods assuming full

composite action. It is conservative to use the lower concrete compression strength

for the shear calculation. For precast hollowcore floor slabs, shear strength can be

calculated or taken from trade literature. The ultimate limit state of shear is not usually

critical and hence any in-situ topping is usually ignored in the calculations. If required,

additional shear strength provided by the topping may be calculated using background

research information.

Interface shear transfer

Full composite action assumes that the shear transfer across the interface between

in-situ and precast is adequate. Interface shear transfer depends on the surface type

of the precast unit and can be calculated using the principles given in BS 8110: Part 1,

Clause 5.4.7.2.1. It may be necessary to provide links to connect the in-situ concrete to

the precast element and to ensure interface shear transfer.

Anchorage and bearing

See BS 8110. Tolerances will need to be considered.

Differential shrinkage

BS 8110: Part 1, Clause 5.4.6.4.1 recommends that differential shrinkage should be

considered where there is an appreciable difference between the age and quality

(strength) of concrete in the precast and in-situ components. Tensile stresses due to

differential shrinkage may require consideration in design and the engineer should refer

to specialist literature in deciding where these stresses may be significant. Further

guidance on this is given by Elliott26.

62

Appendix

Deflections

The main serviceability issue to be considered for composite construction is the control

of deflections. Deflection checks should be carried out on the composite structure as for

a monolithic structure. This will normally be based on a simple span: depth limit given

in current codes. This assumes that the precast and in-situ units act fully compositely

for longer term loading. Deflections can be carried out using the methods given in

BS 8110: Pts 1 or 2. Where rigorous calculations are required for deflections, the method

given in the CEB-FIP Model Code 199029 can be used. This method is similar in principle

to the current Eurocode 2; Design of concrete structures27. The method can be suitably

adapted to take account of varying concrete strengths within the section or the lower

concrete strength can be assumed throughout the section as illustrated by Ghali and

Favre28. Tests have shown that the floor units effectively contribute to the stiffness of

composite beams. However, design models are not yet available to take this advantage

into account.

Striking the formwork is assumed to be carried out in such a way that composite action

is maintained. It will normally be conservative to assess the age for striking as for

normal in-situ construction by specifying a minimum concrete strength for the in-situ

concrete.

Deflection calculations should take into account the different compressive strengths of

the precast and in-situ parts: however, it will generally be conservative to use the in-situ

concrete strength for the whole section. The designer should also consider the practical

implications of deflection at each stage. For example, if a false ceiling is to be provided,

then Stage 1 and 2 deflections may not be considered as being significant and only

Stage 3 deflections might be subject to limitations. In other cases, deflections developed

in the structure before composite action has been established must be added to the

longer term deflections of the composite action. Deflections can be calculated on the

basis of a simple analysis taking into account loading due to the placing of concrete or

other construction loading acting on the precast elements.

Cracking

It will be conservative to check cracking limits for SLS assuming a concrete strength for

the in-situ concrete. Deemed-to-satisfy detailing rules are generally sufficient to check

for cracking at the SLS. If detailed analysis is required, this should be based on the

actual strain distribution due to Stage 1 and Stage 3 loading. Detailed design guidance

is given in Clause 3.4.7 of BS 8110.

Toppings

Structural toppings are not normally necessary to achieve adequate interaction between

the floor units. However, where used, they do increase ultimate moment capacity.

Toppings should be at least 40 mm thick and lightly reinforced. They should be laid on

clean, damp (not wet) surfaces and to avoid shrinkage, the mix should not be too rich

or too wet.

Supports

Some of the practical points to be considered are:

■ minimum support length allowing for tolerances and spalling. Table 16 gives initial

values, which might be decreased (e.g. if temporary supports are provided)

■ evenness of the contact zone along the support

■ rotation capacity – prevention of spalling

■ tie arrangements

■ degree of restraint of the floor units (e.g. unintentional continuity).

Openings

Hollowcore units can be manufactured with openings up to approximately 400 mm

wide internally and up to about 300 mm on an edge. Holes up to about 150 mm

diameter can be core-drilled on site. Larger holes usually involve trimmer angles or

in-situ trimmer beams.

In composite floor-planks, voids and cut-outs can easily be added, even after placing the

floor planks, due to the small thickness of the plates. If required, additional reinforcement

may be placed in the in-situ part of the slab.

64

Appendix

Reinforced concrete orsteel girders

Brick masonry

100 –150 mm

70–130 mm

75 –150 mm

–

70 mm

100 mm

125 mm

125 mm

SUPPORTINGSTRUCTURE

HOLLOWCORE UNITS120 mm - 400 mm thick

RIBBED SOFFIT UNITSLow – heavy loading

FLOOR PLATES

BEAM-BLOCKFLOORS

Table 16Nominal values for support length to

be used at the initial stage of projects

Best Practice Guidance for Hybrid Concrete Construction

This publication emanates from the DTi PII Research Project‘Best Practice Guidance for Hybrid Concrete Construction’.The research was intended to provide introductoryexperience-based guidance on the use of Hybrid ConcreteConstruction for key players as identified in previous research.

This publication aims to provide such guidance and demonstrateshow to achieve best practice. It is a guide to choosing and usingcombinations of precast and in-situ concrete for better value frames.

Charles Goodchild, main author of this publication, is thePrincipal Structural Engineer within The Concrete Centre.

Dr Jacqueline Glass, principal researcher on this project, isLecturer in Architectural Engineering at Loughborough University.

CI/Sfb

UDC

624.05.016-033.3 (083.132)

TCC/03/09 Published September 2004 ISBN 1-904818-09-9Price Group L © The Concrete Centre

Riverside House, 4 Meadows Business Park,Station Approach, Blackwater, Camberley, Surrey GU17 9AB Tel: +44 (0)1276 606800 Fax: +44 (0)1276 606801www.concretecentre.com

Documents

CCIP Hybrid Good Practice Guide