Framework for service life design

Durability by Intent19 February 2002

Objectives of the project:Develop practical service life design ‘system’

Guidance and toolsAllow comparison of different approaches toachieving a structure that is durable for itsrequired service life

Facilitate the minimisation of whole life costs

Consistent with existing codes & standardsOverall framework intended to be genericConcrete-specific at lower levels

Objectives

Ultimately to produce simple, user-friendlycomputer-based system to lead user throughprocess using:

• Simple flow diagrams and/or decision trees• Prompts/questions at key stages• Focused ‘digest-type’ guidance documents• Links to existing guidance• Tools to assist:

•Service life forecasting•Reducing whole life costing

‘The assumed period for which a structure isto be used for its intended purposes withanticipated maintenance but without majorrepair being necessary’.

prEN 1990: Basis of design

Service life

‘Deemed to satisfy’ durability design

‘Deemed to satisfy’ has served industry well inmajority of cases but:

• Does not define service life or end of service life• Risk of premature deterioration in aggressive

exposure conditions• Fails to acknowledge that structures deteriorate

progressively• Limited account of impact of conceptual and

detailed design, construction quality and method.• Limited flexibility

Drivers for service life design

• Whole life costing

• Improved knowledge of degradative processesand other factors contributing to failure

• Improved ability to specify durable concretes

• Additional protective measures

• Development of predictive models

• Sustainability

Incr

easi

ng s

usta

inab

ility

Overdesign andspecification

Zone of sustainableconstruction

Too littlequality

Increasingquality

Present practice

Plateau of sustainablepractice

Plateau of sustainable construction(from Somerville)

Factors affecting service life

• Design

• Construction method

• Materials

• Workmanship

• Repair and maintenance

• Environment

Approach

The main elements of the service life designframework are:

• Client Brief (project brief)• Determination of environmental loads• Definition of performance requirements under

environmental loads• Conceptual design• Detailed design• Execution• Maintenance and management issues in use

Approach

Other key elements in framework include:• Quality• Communication throughout process• Feedback• Tools

• Service life forecasting• Whole life costing

• BRE Durability review

Definition of requiredperformance under defined

‘loads’

Client BriefDefine function and type of structure

Clients basic needs Determine performance requirements

Safety and serviceabilityImportance of continuing of function

required service life and end of service life Management and maintenance strategy

Likelihood of future changes of use LoadsAssessment of:

Dead and imposed loadingAssess & define exposure environment

Aggressive actionsExposure class

Moisture, rainfall, chemicalstemperature, sunlight

etc

Conceptual design (see separate diagram)Construction method and quality issues

Ease of maintenance, upgrade, replacement, deconstruction and reuseBuildability

Assess level of workmanshipAppropriate materials selection based on known performance of materials and components & materials compatibility

Define structure/element criticality (and replacability) and identify durability critical areasEstablish basic defence strategy

Forecasts of structure and element service lifeConduct initial whole life cost assessments

Review of Durability Brief

Review of Detailed Design

Review of Conceptual Design

Structural designCalculations for limit states

DetailingMaterials specifications and QC

Durability/design life optionsDevelopment of basic defence strategy from conceptual design

Revision of whole life costsBuildability assessment

Detailed design (see separate diagram)

Apply best practiceaddress workmanship issues inspection, quality assurance

Communication

Ensure materials specification is achievedE.g. conduct trial castings for concrete

Reviews of Pre-Execution Planning andExecution

Reviews of Specification & Supply ofMaterials and Products

Execution

Review of handover and commissioning

Reviews of refurbishment & demolition

Schematic diagramshowing the main

components of servicelife design

Conduct (ongoing) durability assessments to confirm properties match expectations

Apply maintenance strategy , inspect & repair

Use

End of life -decisions on refurbishment, re-use, demolition

BR

E D

urab

ility

Rev

iew

Qua

lity

issu

esC

omm

unic

atio

nan

d fe

edba

ck

Serv

ice

life

fore

cast

ing,

who

le li

fe c

ostin

g +

sust

aina

bilit

y to

ols

Client Brief

Assessment of loads

Detailed design

Conceptual design

Execution

Maintenance and management issues

Define performance Requirements under environmental loads

Definition of requiredperformance under defined

‘loads’

Client BriefDefine function and type of structure

Clients basic needs Determine performance requirements

Safety and serviceabilityImportance of continuing of function

required service life and end of service life Management and maintenance strategy

Likelihood of future changes of use LoadsAssessment of:

Dead and imposed loadingAssess & define exposure environment

Aggressive actionsExposure class

Moisture, rainfall, chemicalstemperature, sunlight

etc

Conceptual design (see separate diagram)Construction method and quality issues

Ease of maintenance, upgrade, replacement, deconstruction and reuseBuildability

Assess level of workmanshipAppropriate materials selection based on known performance of materials and components & materials compatibility

Define structure/element criticality (and replacability) and identify durability critical areasEstablish basic defence strategy

Forecasts of structure and element service lifeConduct initial whole life cost assessments

Review of Durability Brief

Review of Detailed Design

Review of Conceptual Design

Structural designCalculations for limit states

DetailingMaterials specifications and QC

Durability/design life optionsDevelopment of basic defence strategy from conceptual design

Revision of whole life costsBuildability assessment

Detailed design (see separate diagram)

Apply best practiceaddress workmanship issues inspection, quality assurance

Communication

Ensure materials specification is achievedE.g. conduct trial castings for concrete

Reviews of Pre-Execution Planning andExecution

Reviews of Specification & Supply ofMaterials and Products

Execution

Review of handover and commissioning

Reviews of refurbishment & demolition

Schematic diagramshowing the main

components of servicelife design

Conduct (ongoing) durability assessments to confirm properties match expectations

Apply maintenance strategy , inspect & repair

Use

End of life -decisions on refurbishment, re-use, demolition

BR

E D

urab

ility

Rev

iew

Qua

lity

issu

esC

omm

unic

atio

nan

d fe

edba

ck

Serv

ice

life

fore

cast

ing,

who

le li

fe c

ostin

g +

sust

aina

bilit

y to

ols

Assessment tools

Durability review

Quality communication

Feedback

Service life designframework

Clients basic needsType of structure

FunctionLocation

Site investigationExposure class

Aggressive agents

Wind direction & strengthRain

Temperature (including degreeand frequency of changes)

Definition ofenvironment

Review of data

Further environmentaldata needed?

Performance requirementsSafety and servicability

Importance of continuity of functionSpecify required design life

Specify what constitutes end ofservice life

‘Sustainability’ requirementsRestrictions to design that may affect

durabilityManagement and maintenance

requirementsLikelihood of changes of use and

upgrading

Statement of requiredperformance under defined

environmental loads

Conceptual design

Clarification ofperformance

requirements needed?

Audit of clientbrief

Identification of intended(and possible future) use

and consequent loads

Schematicdiagram for

client brief andstatement of

requiredperformance

Clients basic needs

Performancerequirements

Definition of environment

Required performance under defined environmental

loads

To conceptual design

Client brief & statementof requiredperformance

Site investigation

Client BriefClient’s basic needs including:

• Type of structure• Function• Location• Appearance

Performance requirements including:• Service life and end of service life• Potential changes of use• Maintenance (planned or reactive)• Balance between initial and running costs• Sustainability issues• Restrictions affecting durability

Definition of exposure environment

General environmental conditionsExposure class and aggressive agentsWind direction & strength,RainTemperatureGround conditions

Specific location/orientation of structure

Potential interaction between structure andenvironment

Statement of required performanceunder defined environmental loads

Starting point for the Service life designprocess developed from:

Client briefPerformance requirementsClients basic needs

AndDefinition of exposure environment

Conceptual design How best to resist environment

• Choice of structural form to minimise deterioration• Identification of vulnerable areas• Basic protection strategy (Design-out, Provide resistance)

• Appropriate approach depends on type of structure:• Durability and design life issues differ• Consistent with formal consensus guidance documents• Concept of service life design at different stages of

development• Economic options are different⇒Sub-divide design system according to type of structure

Conceptual design Also consideration of:

• Buildability• Health & safety• Quality issues (materials, workmanship)• Initial service life forecasting• Initial whole life costing

Yes

Detailed design

Assess basic defence mechanism forstructure/elements (based on guidance) see

figures

Provide resistanceDesign out

Classification of structure/elementcriticality (and replacability) and

identification of durability critical areas

Generate ‘outline’ options and conduct buildabilityand whole life cost assessments

(see Figure ?)

Envi

ronm

enta

lLo

ads

Choice of structural form to minimisedeterioration

Construction method and quality issues

Determine appropriate Maintenance approach(see Figure ?)

Are initial and whole life costs acceptable toclient?

Can performance requirements bemet?

Qua

lity

(wor

kman

ship

,m

ater

ials

avai

labi

lity

etc.

)

No

Yes

No

Choice of structural form to minimisedeterioration

Initial buildability assessment

Buildability assessment - are design & maintenance strategies

feasible?

No

Yes

Client brief and performance requirements

under defined loads

Planned replacement

Forecast service life ofelement in its environment

Predict replacementfrequency

Can performancerequirements be met

using different defencemechanism orcombination?

Yes

No

List optional Design strategies + repair,maintenance strategies

Conduct whole life cost (& sustainability)assessment. Select most cost effective option

Schematicdiagram forconceptual

designAudit of

conceptual design

Service life forecasting,whole life costing +sustainability tools

Feed

back

from

per

form

ance

of e

xist

ing

stru

ctur

es

Client brief &Performance requirements

Buildability

Selection of basic defence

strategy

Maintenance strategy

Whole life costing

Quality issues

Environment

ConceptualDesign

Buildability

Identify and quantify materialsdegradation processes, impact of macro

and microenvironment etc.

Selection of appropriate basic protection strategy

Assess secondary processes and selectappropriate additional protection strategies

Design out

Concrete deterioration

(e.g. ASR, sulfate attack,freeze-thaw, etc).

Controlling early age effects

Avoidance of factors such asthermal cracking, plastic shrinkage

& settlement through controllingpeak temperature, appropriate

materials selection, curingconditions etc.

Design out: Use appropriateconcrete parameters based on

codes and standards andassociated guidance

Is risk of deteriorationunacceptable or is multi-layer

approach required?

Select additional protectionstrategy in accordance with

guidance or considerplanned repair or

replacement

Designmaterials

List and assess options usingwhole life costing tools etc.

Concrete

Select most appropriateoptions based on guidance

Yes

No

EnvironmentalLoads

Performancerequirements

Develop design out strategiesfurther under detailed design

Reinforcement corrosion(see separate diagram)

ProvideresistancePlanned

repair orreplacement

Multi-layer

Singlelayer

Selection of basicdefence strategies

Identification of deterioration

Processes Reinforcement

corrosion

Avoidance of concrete

deterioration

Controlling early age

effects

Whole life costing of

options

Structural design•Design calculations•Selection of initial concrete parameters•Reinforcement arrangements•Detailing

Development of durability options selected inconceptual design stage

Also:•Service life and whole life costing•Buildability•‘Life care plan’

Detailed design

Design calculations

DetailingShapes and profiles

JointsDrainage & water

Outer fabric treatmentProvision for inspection &

maintenance

SpecificationsMaterials and products•Concrete•Reinforcement•Joint materials•Etc.Quality control

Structural designDurability/design life

options

Provide designresistance

Multi-layerprotection

(see separatediagram)

Single layerprotection

(see separatediagram)

Design outapproach

(see diagram)

Planned replacement

Forecast service life ofelement in itsenvironment

Predict replacementfrequency

Develop basic defence strategy selectedin conceptual design for each component

Revise whole life cost andbuildability assessments

NO

Can/must structural aspects ofdesign be revised?

Are costs acceptable to the client?

YES

Is design still feasible?

Does design meet clients needs? YES

YES

Execution stage

NO

NO

Reviews of durability design,specification of materials and

products, pre-construction plan andlife-care plan

NO

YES

Service life forecastingwhole life costing

sustainability tools

Conceptual design

Preparation of life-care plan

Preparation of pre-constructionplan

Durability &design lifeoptions

Development of defence strategy

Detailed design

Detailing

Specifications for concrete

cover, QC etc

Structural design

AcceptabilityBuildabilityService life

costs Life care plan

Execution2 approaches to addressing variability.

• Raise standards to acceptable & repeatable level by:• Encouraging better design• Improved communication• Education & training• Benchmarking• Method statements & certification etc.• Durability Review

• Assume current variability & standards, relying on:• Multi-layer protection• Design out approaches• Durability Review

Maintenance and Use

Ongoing assessmentsAppropriate inspection, maintenance and repair(particularly of key areas)End of life decisions

Ensure that further work such asrefurbishment doesn’t impair durabilityDeconstructionEtc.

Design for service life - materials properties

Tools (models) and guidance on their use,benefits, limitations etc.A number of possible approaches including:

! Knowledge and experience! Performance of similar materials! Accelerated testing! Modelling! Combinations of these

Whole life costing

Where several options are available to meetclients requirements

! Use of whole life costing principles to assessoptions

! Select most cost effective option and that mostappropriate to clients needs

! Use sustainability concepts?

Whole life costing ‘tool’ and guidance onuse, limitations etc.

Summary

The main elements of the service life designframework are:

• Client Brief• Determination of environmental loads• Definition of performance requirements

under environmental loads• Conceptual design• Detailed design• Execution• Maintenance and management issues

Summary

Other key factors include:• Quality• Communication throughout process• Feedback• Tools

• Service life forecasting• Whole life costing• Sustainability

• BRE Durability review

Next Steps

Development of computer-based version

Develop individual elements:Key factors to be addressed.Developing interactions within and betweenelements

Preparation of guidance documentsInitially Information papers

Develop interactions and overall frameworkDigests and design system

Framework for service life design

THE ENDThank you for your attention