SIST ISO 16204:2012
Durability - Service life design of concrete structures
Durability - Service life design of concrete structures
This International Standard specifies principles and recommends procedures for the verification of the durability
of concrete structures subject to:
— known or foreseeable environmental actions causing material deterioration ultimately leading to failure
of performance;
— material deterioration without aggressiveness from the external environment of the structure, termed selfageing.
NOTE The inclusion of, for example, chlorides in the concrete mix might cause deterioration over time without the
ingress of additional chlorides from the environment.
This International Standard is intended for use by national standardization bodies when establishing or
validating their requirements for durability of concrete structures. It may also be applied:
— for the assessment of remaining service life of existing structures; and
— for the design of service life of new structures provided quantified parameters on levels of reliability and
design parameters are given in a national annex to this International Standard.
Fatigue failure due to cyclic stress is not within the scope of this International Standard.
Durabilité - Conception de la durée de vie des structures en béton
Trajnost - Življenjska doba projektiranja betonskih konstrukcij
Ta mednarodni standard določa načela in priporoča postopke za preverjanje trdnosti betonskih struktur, ki so povezani z naslednjim: – poznana oziroma predvidljiva okoljska dejanja, ki povzročajo poslabšanje materiala, ki končno vodi do propada; – poslabšanje materiala brez zunanjih vplivov na strukturo, staranje. Ta mednarodni standard je namenjen uporabi v okviru državnih organov za standardizacijo, ko vzpostavljajo ali potrjujejo svoje zahteve glede trdnosti betonskih struktur. Prav tako se lahko uporabi: – za oceno preostale tehnične življenjske dobe obstoječih struktur; – za načrtovanje tehnične življenjske dobe novih struktur, pri čemer so zagotovljeni kvantificirani parametri glede ravni zanesljivosti; projektni parametri so navedeni v nacionalni dodatek k temu mednarodnemu standardu. Utrujenost materiala zaradi ciklične obremenitve ni v okviru predmeta tega mednarodnega standarda.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-december-2012
Trajnost - Življenjska doba projektiranja betonskih konstrukcij
Durability - Service life design of concrete structures
Durabilité - Conception de la durée de vie des structures en béton
Ta slovenski standard je istoveten z: ISO 16204:2012
ICS:
13.020.60 Življenjski ciklusi izdelkov Product life-cycles
91.080.40 Betonske konstrukcije Concrete structures
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
INTERNATIONAL ISO
STANDARD 16204
First edition
2012-09-01
Durability — Service life design of
concrete structures
Durabilité — Conception de la durée de vie des structures en béton
Reference number
©
ISO 2012
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
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Published in Switzerland
ii © ISO 2012 – All rights reserved
Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviated terms . 5
4.1 Abbreviated terms . 5
4.2 Main letters . 5
4.3 Subscripts . 6
5 Basis of design . 6
5.1 Requirements . 6
5.2 Principles of limit state design . 7
5.3 Basic variables . 8
5.4 Verification . 8
6 Verification of service life design .10
6.1 Carbonation-induced corrosion - uncracked concrete .10
6.2 Chloride-induced corrosion - uncracked concrete .13
6.3 Influence of cracks upon reinforcement corrosion .14
6.4 Risk of depassivation with respect to pre-stressed steel .15
6.5 Freeze/thaw attack .15
6.6 Chemical attack .17
6.7 Alkali-aggregate reactions .18
7 Execution .19
7.1 General .19
7.2 Execution specification .19
7.3 Formwork .19
7.4 Materials .19
7.5 Inspection .20
7.6 Action in the event of non-conformity .20
8 Maintenance and condition assessment .20
8.1 General .20
8.2 Maintenance .20
8.3 Condition assessment .21
9 Action in the event of non-conformity .21
Annex A (informative) Basis of design .22
Annex B (informative) Verification of service life design .24
Annex C (informative) Execution .28
Annex D (informative) Maintenance and condition assessment .29
Annex E (informative) Guidance on a national annex .30
Bibliography .31
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International
Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16204 was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and pre-stressed
concrete, Subcommittee SC 3, Concrete production and execution of concrete structures.
iv © ISO 2012 – All rights reserved
Introduction
This International Standard is based on the principles given in ISO 2394, General principles on reliability for
1)
structures, ISO 13823, General principles on the design of structures for durability, and fib “Model Code
[1] [2]
for Service Life Design” (MC SLD, today implemented in fib Model Code 2010 ). The two International
Standards were prepared by ISO/TC 98, Bases for design of structures.
The limit-states method, as developed in ISO 2394, has been adopted and used for preparing and harmonizing
national and regional standards for structural design around the world. The objective of ISO 13823 is to provide
a framework for the development of standards to predict the service life of components of a structure and
to ensure that these principles are incorporated in the material-specific standards developed by other ISO
Technical Committees.
The objective of fib MC SLD is to implement the principles of ISO 2394 in service life design of concrete structures.
This International Standard treats design for environmental actions leading to deterioration of concrete and
embedded steel.
The flowchart in Figure 1 illustrates the flow of decisions and the design activities needed in a rational service
life design process with a chosen level of reliability. Two strategies have been adopted; in the first, three levels
of sophistication are distinguished. In total, four options are available.
Strategy 1: Design to resist deterioration
Level 1 Full probabilistic method (option 1)
Level 2 Partial factor method (option 2)
Level 3 Deemed-to-satisfy method (option 3)
Strategy 2: Avoidance-of-deterioration method, (option 4)
Establishing the serviceability criteria
Establishing the general layout, the dimensions and selection of materials
Verification by the Verification by the Verification by the Verification by the
“Full probabilistic” method “Partial factor” method. “Deemed-to- “Avoidance of
Involving: Involving: satisfy” method. deterioration”
* Probabilistic models * Design values Involving: method.
- resistance - characteristic values Exposure classes, Involving:
- loads/exposure - partial factors limit states and Exposure classes, limit
- geometry * Design equations other design states and other design
* Limit states * Limit states provisions provisions
Execution specification
Maintenance plan
Condition assessment plan
Execution of the structure
Inspection of execution
Maintenance Condition assessments during operational service life
Figure 1 — Flowchart for service life design
1) The International Federation for Structural Concrete.
In the case of non-conformity to the performance criteria,
the structure becomes obsolete or subject to full or partial redesign
Within Clause 6 the following deterioration mechanisms are addressed:
— carbonation-induced corrosion;
— chloride-induced corrosion;
— freeze/thaw attack without de-icing agents or sea-water;
— freeze/thaw attack with de-icing agents or sea-water.
For these mechanisms widely accepted mathematical models exist.
The other deterioration mechanisms:
— chemical attack, and
— alkali-aggregate reactions,
are not treated in detail primarily because widely accepted mathematical models do not exist at present.
To make this International Standard complete, the missing models have to be developed and comply with the
general principles of Clause 5.
This International Standard includes four informative annexes giving background information for the application
in service life design and one informative annex giving guidance for the preparation of a possible national annex.
vi © ISO 2012 – All rights reserved
INTERNATIONAL STANDARD ISO 16204:2012(E)
Durability — Service life design of concrete structures
1 Scope
This International Standard specifies principles and recommends procedures for the verification of the durability
of concrete structures subject to:
— known or foreseeable environmental actions causing material deterioration ultimately leading to failure
of performance;
— material deterioration without aggressiveness from the external environment of the structure, termed self-
ageing.
NOTE The inclusion of, for example, chlorides in the concrete mix might cause deterioration over time without the
ingress of additional chlorides from the environment.
This International Standard is intended for use by national standardization bodies when establishing or
validating their requirements for durability of concrete structures. It may also be applied:
— for the assessment of remaining service life of existing structures; and
— for the design of service life of new structures provided quantified parameters on levels of reliability and
design parameters are given in a national annex to this International Standard.
Fatigue failure due to cyclic stress is not within the scope of this International Standard.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced document
(including any amendments) applies.
ISO 2394, General principles on reliability for structures
ISO 13823, General principles on the design of structures for durability
ISO 22965-1, Concrete — Part 1: Methods of specifying and guidance for the specifier
ISO 22965-2, Concrete — Part 2: Specification of constituent materials, production of concrete and
compliance of concrete
ISO 22966, Execution of concrete structures
ISO 6935 (all parts), Steel for the reinforcement of concrete
2)
ISO 16311 (all parts), Maintenance and repair of concrete structures
2) To be published. ISO 16311-1, -2, -3 and -4 are under preparation.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
basic variable
part of a specified set of variables representing physical quantities, which characterize actions and environmental
influences, material properties including soil properties, and geometrical quantities
[ISO 2394:1998, 2.2.18]
3.2
characteristic value
X or R
k k
value of a material or product property having a prescribed probability of not being attained in a hypothetical
unlimited test series
NOTE 1 This value generally corresponds to a specified fractile of the assumed statistical distribution of the particular
property of the material or product.
NOTE 2 A nominal value is used as the characteristic value in some circumstances.
3.3
characteristic value of a geometrical property
a
k
value usually corresponding to the dimensions specified in the design
NOTE Where relevant, values of geometrical quantities may correspond to some prescribed fractiles of the statistical
distribution.
3.4
characteristic value of an action
F
k
principal representative value
NOTE It is chosen:
— on a statistical basis, so that it can be considered to have a specified probability for not being exceeded towards
unfavourable values during a reference period;
— on acquired experience; or
— on physical restraints.
[ISO 2394:1998, 2.3.12]
3.5
design criteria
quantitative formulations that describe for each limit state the conditions to be fulfilled
3.6
design service life
assumed period for which a structure or a part of it is to be used for its intended purpose with anticipated
maintenance, but without major repair being necessary
3.7
design situation
set of physical conditions representing a certain time interval for which the design demonstrates that the
relevant limit states are not exceeded
[ISO 2394:1998, 2.2.1]
2 © ISO 2012 – All rights reserved
3.8
design value of a geometrical property
a
d
generally a nominal value
NOTE 1 Where relevant, values of geometrical quantities may correspond to some prescribed fractile of the statistical
distribution.
NOTE 2 The design value of a geometrical property is generally equal to the characteristic value. However, it may
be treated differently in cases where the limit state under consideration is very sensitive to the value of the geometrical
property. Alternatively, it can be established from a statistical basis, with a value corresponding to a more appropriate
fractile (e.g. rarer value) than applies to the characteristic value.
3.9
design value of an action
F
d
value obtained by multiplying the representative value by the partial factor γ or γ .
f F
[Modified from ISO 2394:1998, 2.3.16]
3.10
design value of material or product property
X or R
d d
value obtained by dividing the characteristic value by a partial factor γ or γ , or, in special circumstances, by
m M
direct determination
NOTE See 5.4.2 (3).
[Modified from ISO 2394:1998, 2.4.3]
3.11
execution specification
documents covering all drawings, technical data and requirements necessary for the execution of a particular project
NOTE The execution specification is not one single document but signifies the total sum of documents required for
the execution of the work as provided by the designer to the constructor and includes the project specification prepared
to supplement and qualify the requirements of this International Standard, as well as referring to the national provisions
relevant in the place of use.
[ISO 22966:2009, 3.8]
3.12
inspection
conformity evaluation by observation and judgement accompanied as appropriate by measurement,
testing or gauging
[ISO 9000:2005, 3.8.2]
3.13
limit state
state beyond which the structure no longer satisfies the relevant design criteria
NOTE Limit states separate desired states (no failure) from undesired states (failure).
[Modified from ISO 2394:1998, 2.2.9]
3.14
maintenance
set of activities that are planned to take place during the service life of a structure in order to fulfil the requirements
for reliability
3.15
project specification
project-specific document describing the requirements applicable for the particular project
[ISO 22966:2009, 3.15]
3.16
reference period
chosen period of time which is used as a basis for assessing values of variable actions, time-dependent
material properties, etc.
[ISO 2394:1998, 2.2.8]
3.17
reliability
ability of a structure or a structural member to fulfil the specified requirements, including the design service life,
for which it has been designed
NOTE 1 Reliability is usually expressed in probabilistic terms.
NOTE 2 Reliability covers safety, serviceability and durability of a structure.
[Modified from ISO 2394:1998, 2.2.7]
3.18
reliability differentiation
measures intended for socio-economic optimization of the resources to be used to build construction works,
taking into account all expected consequences of failures and the cost of the construction works
3.19
repair
activities performed to preserve or to restore the function of a structure that fall outside the definition of maintenance
3.20
representative value of an action
F
rep
value used for the verification of a limit state
NOTE Representative values consist of characteristic values, combination values, frequent values and quasi-
permanent values, but may also consist of other values.
[ISO 2394:1998, 2.3.11]
3.21
resistance
capacity of a member or component, or a cross-section of a member or component of a structure, to withstand
actions that lead to deterioration
3.22
serviceability limit state
state that corresponds to conditions beyond which specified service requirements for a structure or structural
element are no longer met
[ISO 2394:1998, 2.2.11]
3.23
serviceability criterion
design criterion for a serviceability limit state
4 © ISO 2012 – All rights reserved
3.24
ultimate limit state
state associated with collapse or with other similar forms of structural failure
NOTE They generally correspond to the maximum load-carrying resistance of a structure or structural element, but
in some cases to the maximum applicable strain or deformation.
[ISO 2394:1998, 2.2.10]
4 Symbols and abbreviated terms
4.1 Abbreviated terms
SLD service life design
SLS serviceability limit state
ULS ultimate limit state
4.2 Main letters
F action in general
R resistance
S action effect
T temperature
X basic variable
a geometric quantity
p probability
t
time
x
distance
α
ageing factor
Δ
margin
γ
partial factor
γ partial factor for concrete
c
γ partial factor for actions without taking account of model uncertainties
f
γ partial factor for actions, also accounting for model uncertainties and dimensional variations
F
γ partial factors for a material property, taking account only of uncertainties in the material
m
property
γ partial factors for a material property, taking account of uncertainties in the material
M
property itself and in the design model used
γ partial factor associated with the uncertainty of the resistance model, plus geometric
Rd
deviations if these are not modelled explicitly
4.3 Subscripts
app apparent
crit critical
d design value
dep depassivation
ini initiation
k characteristic value
prop propagation
nom nominal value
rep representative value
SL service life
5 Basis of design
5.1 Requirements
5.1.1 Basic requirements
The service life design (SLD) of concrete structures shall be in accordance with the general principles given in
ISO 2394 and ISO 13823.
The supplementary provisions for concrete structures given in this International Standard shall also be applied.
The service life design shall either:
— follow the general principles for probabilistic service life design of concrete structures outlined in ISO 2394
(the full probabilistic method);
— use the partial factor method given in this International Standard;
— use the deemed-to-satisfy method given in this International Standard;
— be based on the avoidance-of-deterioration method given in this International Standard.
The serviceability criteria related to durability shall be specified for each project and agreed with the client.
NOTE Guidance for the choice of serviceability criteria combined with appropriate target values of reliability are
[3] [1] [6]
given in Annex E of ISO 2394:1998 , Annex A of fib MC SLD and in JCSS Probabilistic Model Code .
5.1.2 Reliability management
Reliability management shall be in accordance with the general principles given in ISO 2394.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 4.
As guidance to reliability differentiation, this International Standard refers to the following general classifications:
— consequence classes CC1, CC2 and CC3;
— reliability classes RC1, RC2 and RC3.
6 © ISO 2012 – All rights reserved
The three consequence classes relate to minor, moderate and large consequences of failure or inadequate
serviceability of the structure.
The three reliability classes may be associated with the three consequence classes.
[3]
NOTE 1 The three-level differentiation corresponds to that in ISO 2394:1998 , 4.2
[7]
NOTE 2 ISO 13823:2008 , 8.5 and 8.6 apply a four-level differentiation for consequences of failure.
The required level of reliability may be achieved by measures related to, for example, the robustness
of the design and to measures related to quality assurance adopted in the design, execution as well as
inspection/maintenance during a structure’s service life.
NOTE ISO 22966 defines three execution classes, EXC1, EXC2 and EXC3, for the quality management regime, for
which the required strictness increases from class 1 to class 3.
In addition, for service life design, Annex D classifies four levels of condition assessment during the service life:
CAL0, CAL1, CAL2 and CAL3
5.1.3 Design service life, durability and quality management
The design of service life, durability and quality management shall be in accordance with the general principles
given in ISO 2394.
[3]
NOTE In ISO 2394:1998 these provisions are given in Clause 4.
,
The design service life is the assumed period for which a structure or part of it is to be used for its intended
purpose with anticipated maintenance, but without major repair being necessary.
The design service life is defined by
— a definition of the relevant limit states,
— a number of years, and
— a level of reliability for not passing each relevant limit state during this period.
Durability of a structure exposed to its environment shall be such that it remains fit for use during its design
service life. This requirement may be satisfied in one, or a combination, of the following ways:
— by designing protective and mitigating systems;
— by using materials that, if well maintained, will not degenerate during the design service life;
— by providing such dimensions that deterioration during the design service life is compensated for;
— by choosing a shorter lifetime for structural elements that when necessary are replaced one or more times
during the design life;
— in combination with appropriate inspection at fixed or condition-dependent intervals and appropriate
maintenance activities.
In all cases, the reliability requirements for long- and short-term periods should be met.
5.2 Principles of limit state design
The limit state design shall be in accordance with the general principles given in ISO 2394.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 5.
5.3 Basic variables
5.3.1 Actions and environmental influences
Characteristic values of actions for use in SLD shall be
— based on data derived for the particular project, or
— from general field-experience, or
— from relevant literature.
Other actions, when relevant, shall be defined in the design specification for the particular project.
Actions specific to SLD may be given in a national annex to this International Standard.
5.3.2 Material and product properties
The material and product properties shall be identified in accordance with the general principles given in ISO 2394.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 6.
Characteristic values of materials and product properties for use in SLD shall be
— based on data derived for the particular project, or
— from general field-experience, or
— from relevant literature.
Materials and product properties to be determined will depend on the deterioration model used. If different
models with different basic assumptions are applied for mapping the material properties and in the SLD, a
checking process shall be established to ensure that the selected model and applied data are compatible.
Material property values shall be determined from test procedures performed under specified conditions. A
conversion factor shall be applied, when necessary, to convert the test results of laboratory cast and tested
specimens into values that are assumed to represent the behaviour of the material or product in the structure.
5.3.3 Geometric data
Design values of geometrical data for SLD shall be in accordance with ISO 2394 or based on measurements
on the completed structure or element.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 6.
ISO 22966 specifies permitted geometrical deviations. If the design assumes stricter tolerances, the design
assumptions shall be verified by measurements on the completed structure or element.
5.4 Verification
5.4.1 Verification by the full probabilistic method
The general principles for probabilistic service life design of concrete structures outlined in the ISO 2394
shall be followed.
In particular the following three principles shall be applied:
— probabilistic models shall be applied that are sufficiently validated to give realistic and representative results;
— the parameters of the models applied and their associated uncertainty shall be quantifiable by means of
tests, observations and/or experience;
8 © ISO 2012 – All rights reserved
— reproducible and relevant test methods shall be available to assess the action- and material-parameters.
Uncertainties associated with models and test methods shall be taken into account.
5.4.2 Verification by the partial factor method
SLD may be performed in accordance with the general principles of the partial factor method given in ISO 2394.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 9.
The same models as used for the full probabilistic method, but based on design values, shall be used for the
partial factor method. Simplifications on the safe side are permitted.
The partial factor method separates the treatment of uncertainties and variabilities originating from various
causes. In the verification procedure defined in this International Standard, the design values of the fundamental
basic variables are expressed as follows.
The design values of an action are generally expressed as:
F = γ × F (1)
d f rep
where
F is the representative value of the action;
rep
γ is the partial safety factor for the action.
f
The design values of material or product property is generally expressed as:
R = R / γ (2)
d k m
or, where uncertainty in the resistance model is taken into account, by:
R = R /γ = R /(γ × γ ) (3)
d k M k m Rd
where
R is the characteristic value of resistance;
k
γ is the partial factor for a material property;
m
γ is the partial factor associated with the uncertainty of the resistance model plus geometric
Rd
deviations if these are not modelled explicitly;
γ = γ × γ is the partial factor for a material property also accounting for the model uncertainties and
M m Rd
dimensional variations.
Design values of geometrical quantities to be considered as fundamental basic variables shall, in general, be
directly expressed by their design values a
d.
When using the partial factor method, it shall be verified that the target reliability for not passing the relevant
limit state during the design service life is not exceeded when design values for actions or effects of actions
and resistance are used in the design models.
The partial factors shall take into account:
— the possibility of unfavourable deviations of action values from the representative values;
— the possibility of unfavourable deviations of materials and product properties from the representative values;
— model uncertainties and dimensional variations.
The numerical values for the partial factors shall be determined in one of the following two ways:
— on the basis of statistical evaluation of experimental data and field observations according to 5.4.1;
— on the basis of calibration to a long-term experience of building tradition.
5.4.3 Verification by the deemed-to-satisfy method
The deemed-to-satisfy method is a set of rules for
— dimensioning,
— material and product selection, and
— execution procedures,
that ensures that the target reliability for not passing the relevant limit state during the design service life is not
exceeded when the concrete structure or component is exposed to the design situations.
The specific requirements for design, materials selection and execution for the deemed-to-satisfy method shall
be determined in either of two ways:
— on the basis of statistical evaluation of experimental data and field observations according to
requirements of 5.4.1;
— on the basis of calibration to a long-term experience of building tradition.
The limitations to the validity of the provisions, e.g. the range of cement types covered by the calibration, shall
be clearly stated.
5.4.4 Verification by the avoidance-of-deterioration method
The avoidance-of-deterioration method implies that the deterioration process will not take place due to, for example:
— separation of the environmental action from the structure or component by e.g. cladding or membranes;
— using non-reacting materials, e.g. certain stainless steels or alkali non-reactive aggregates;
— separation of reactants, e.g. keeping the structure or component below a critical degree of moisture;
— suppressing the harmful reaction e.g. by electrochemical methods.
The specific requirements for design, materials selection and execution for the avoidance-of-deterioration
method may, in principle, be determined in the same way as for the deemed-to-satisfy method.
The limitations to the validity of the provisions shall be clearly stated.
6 Verification of service life design
6.1 Carbonation-induced corrosion - uncracked concrete
6.1.1 Full probabilistic method
6.1.1.1 Limit state: Depassivation
The following requirement shall be fulfilled:
p{} = p = p{a − x (t ) < 0} < p (4)
dep. c SL 0
where
10 © ISO 2012 – All rights reserved
p{} is the probability that depassivation occurs;
a is the concrete cover [mm];
x (t ) is the carbonation depth at the time t [mm];
c SL SL
t is the design service life [years];
SL
p is the target failure probability.
The variables a and x (t ) need to be quantified in a full probabilistic approach.
c SL
NOTE The limit state “depassivation” is only relevant for structures with sufficient humidity to support a corrosion process.
6.1.1.2 Design model
The ingress of the carbonation front might be assumed to obey the following equation:
xt() =×Wk × t (5)
c
k is a factor reflecting the basic resistance of the chosen concrete mix (like water/cement ratio, cement type,
additions) under reference conditions and the influence of the basic environmental conditions (like mean relative
humidity and CO concentration) on ingress of carbonation. It also reflects the influence of the execution.
W takes into account the varying meso-climatic conditions for the specific concrete member during the design
service life, such as humidity and temperature.
For the design of a new structure, the factors W and k might be derived from literature data or existing structures
where the concrete composition, execution and exposure conditions have been similar to those expected for
the new structure.
When assessing remaining service life of an existing structure, the product of W and k might be derived directly
from measurements on the structure.
Other models may be used, provided that the basic principles formulated in 5.4.1 are fulfilled
6.1.1.3 Limit states: corrosion-induced cracking and spalling
Exemplified with regard to cracking, the following basic limit state function shall be fulfilled:
p{} = p = p{Δr − Δr (t ) < 0} < p (6)
crack (R) (S) SL 0
where
p{} is the probability that carbonation-induced cracking occurs;
Δr is the maximum corrosion-induced increase of the rebar radius which can be accommodated
(R)
by the concrete without formation of cracks at the concrete surface [µm];
Δr (t ) is the increase of the rebar radius due to reinforcement corrosion [µm] at time t ;
(S) SL SL
t is the design service life [years];
SL
p is the target failure probability.
An alternative design approach is:
p{} = p = p{t − t − t > 0} < p (7)
crack SL ini prop 0
where
p{} is the probability that carbonation-induced cracking occurs;
t is the design service life [years];
SL
t is the initiation period (period till depassivation of the reinforcement occurs) [years];
ini
t is the propagation period (period of active corrosion) [years];
prop
p is the target failure probability.
The variables Δr and Δr (t ) or the variables t and t need to be quantified in a full probabilistic approach.
(R) (S) SL ini prop
Other methods may be used, provided that the basic principles formulated in 5.4.1 are fulfilled.
At the time of publishing this International Standard, no time-dependent model with general international
consensus is available for the propagation phase. The time span from initiation to cracking may be estimated
from existing structures where the concrete composition, execution and exposure conditions have been similar
to those expected for the structure considered.
6.1.2 Partial factor method
6.1.2.1 Limit state: depassivation
The following limit state function needs to be fulfilled:
a − x (t ) ≥ 0 (8)
d c,d SL
where
a is the design value of the concrete cover [mm];
d
x (t ) is the design value of the carbonation depth at time t [mm].
c,d SL SL
The design value of the concrete cover a is calculated as follows:
d
a = a − Δa (9)
d nom
where
a is the nominal value for the concrete cover [mm];
nom
Δa is the safety margin (permitted deviation) of the concrete cover [mm].
The design value of the carbonation depth, at a time t , x (t ) is calculated as follows:
SL c,d SL
x (t ) = x (t ) × γ (10)
c,d SL c,k SL f
where
x (t ) is the characteristic value of the carbonation depth at a time t [mm], e.g. mean value of the
c,k SL SL
carbonation depth;
γ is the partial safety factor of the carbonation depth [-].
f
Other methods may be used, provided that the basic principles formulated in 5.4.2 are fulfilled.
6.1.3 Deemed-to-satisfy method
Within this approach a trading-off of geometrical (concrete cover to reinforcement) material parameters (indirectly
linked to diffusion and binding characteristics) and execution aspects (compaction and curing) is applied.
12 © ISO 2012 – All rights reserved
6.1.4 Avoidance-of-deterioration method
Generally, avoidance is achieved if depassivation cannot take place due to infinite resistance of the concrete to
carbonation or zero environmental load or infinite corrosion resistance of the reinforcement.
6.2 Chloride-induced corrosion - uncracked concrete
6.2.1 Full probabilistic method
6.2.1.1 Limit state: depassivation
The following limit state function shall be fulfilled:
p{} = p = p{C − C(a,t ) < 0} < p (11)
dep. crit SL 0
where
p{} is the probability that depassivation occurs;
C is the critical chloride content [% by mass of binder];
crit
C(a,t ) is the chloride content at depth a and time t [% by mass of binder];
SL
a
is the concrete cover [mm];
t is the design service life [years];
SL
p is the target failure probability.
The variables a, C and C(a,t ) shall be quantified in a full probabilistic approach.
crit SL
NOTE If the binder content of the actual concrete composition is not known, the critical chloride content may be
related to the mass of the concrete.
6.2.1.2 Design model
The ingress of chlorides in a marine environment may be assumed to obey the following equation:
x
Cx(,tC)(=− CC−×)erf (12)
ss i
2(××Dt) t
app
In this modified Fick’s second law of diffusion, the factors are as follows:
C(x,t) is the content of chlorides in the concrete at a depth x (structure surface: x = 0 mm) and at time
t [% by mass of binder];
C is the chloride content at the concrete surface [% by mass of binder];
s
C is the initial chloride content of the concrete [% by mass of binder];
i
x is the depth with a corresponding content of chlorides C(x,t) [mm];
D (t) is the apparent coefficient of chloride diffusion through concrete [mm /year] at time t (see
app
Formula 13);
t is the time [years] of exposure;
erf is the error function.
α
t
Dt() = Dt() (13)
app app 0
t
where
D (t ) is the apparent diffusion coefficient measured at a reference time of t ;
app 0 0
α is the ageing factor giving the decrease over time of the apparent diffusion coefficient.
Depending on the type of binder and the micro-environmental conditions, the ageing factor is
likely to lie between 0,2 and 0,8.
NOTE The “apparent” diffusion coefficient after a period t of chloride exposure, D (t), represents a constant
app
equivalent diffusion coefficient giving a similar chloride profile to the measured one for a structure exposed to the chloride
environment over a period t.
The decrease of the apparent diffusion coefficient is due to several reasons:
— continued reactions of the binder;
— influence of reduced capillary suction of water in the surface zone with time;
— degree of saturation of concrete; and
— effect of penetrated chlorides from sea-water or de-icing salts (leading to ion exchange with subsequent
poreblocking in the surface layer).
For the design of a new structure, the parameters C , C , α and D (t ) may be derived from existing structures
s i app 0
where the concrete composition, execution and exposure conditions have been similar to those relevant for
the new structure.
When assessing remaining service life of an existing structure, the factors, with the possible exception of α,
may be derived directly from measurements on the structure.
For both design of new structures, and for the assessment of remaining service life of existing structures, the
ageing factor, α, shall be obtained from in-field observations from structures where the concrete composition,
execution and exposure conditions have been similar to those for the actual structure. At least observations at
two periods of exposure (with a sufficient interval between the observations) are needed for the calculation of
the ageing factor.
Other models may also be used, provided that the basic principles formulated in 5.4.1 are fulfilled.
6.2.1.3 Limit states: corrosion-induced cracking and spalling
See 6.1.1.3.
6.2.2 Partial factor method
See 6.1.2.
6.2.3 Deemed-to-satisfy method
See 6.1.3.
6.2.4 Avoidance-of-deterioration method
See 6.1.4, but substitute “chloride penetration” for “carbonation”.
6.3 Influence of cracks upon reinforcement corrosion
The minimum structural reliability of a cracked reinforced concrete structure shall be of comparable magnitude
to the minimum reliability of a comparable exposed uncracked structure.
14 © ISO 2012 – All rights reserved
A simp
...
INTERNATIONAL ISO
STANDARD 16204
First edition
2012-09-01
Durability — Service life design of
concrete structures
Durabilité — Conception de la durée de vie des structures en béton
Reference number
©
ISO 2012
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO’s
member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2012 – All rights reserved
Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviated terms . 5
4.1 Abbreviated terms . 5
4.2 Main letters . 5
4.3 Subscripts . 6
5 Basis of design . 6
5.1 Requirements . 6
5.2 Principles of limit state design . 7
5.3 Basic variables . 8
5.4 Verification . 8
6 Verification of service life design .10
6.1 Carbonation-induced corrosion - uncracked concrete .10
6.2 Chloride-induced corrosion - uncracked concrete .13
6.3 Influence of cracks upon reinforcement corrosion .14
6.4 Risk of depassivation with respect to pre-stressed steel .15
6.5 Freeze/thaw attack .15
6.6 Chemical attack .17
6.7 Alkali-aggregate reactions .18
7 Execution .19
7.1 General .19
7.2 Execution specification .19
7.3 Formwork .19
7.4 Materials .19
7.5 Inspection .20
7.6 Action in the event of non-conformity .20
8 Maintenance and condition assessment .20
8.1 General .20
8.2 Maintenance .20
8.3 Condition assessment .21
9 Action in the event of non-conformity .21
Annex A (informative) Basis of design .22
Annex B (informative) Verification of service life design .24
Annex C (informative) Execution .28
Annex D (informative) Maintenance and condition assessment .29
Annex E (informative) Guidance on a national annex .30
Bibliography .31
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International
Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16204 was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and pre-stressed
concrete, Subcommittee SC 3, Concrete production and execution of concrete structures.
iv © ISO 2012 – All rights reserved
Introduction
This International Standard is based on the principles given in ISO 2394, General principles on reliability for
1)
structures, ISO 13823, General principles on the design of structures for durability, and fib “Model Code
[1] [2]
for Service Life Design” (MC SLD, today implemented in fib Model Code 2010 ). The two International
Standards were prepared by ISO/TC 98, Bases for design of structures.
The limit-states method, as developed in ISO 2394, has been adopted and used for preparing and harmonizing
national and regional standards for structural design around the world. The objective of ISO 13823 is to provide
a framework for the development of standards to predict the service life of components of a structure and
to ensure that these principles are incorporated in the material-specific standards developed by other ISO
Technical Committees.
The objective of fib MC SLD is to implement the principles of ISO 2394 in service life design of concrete structures.
This International Standard treats design for environmental actions leading to deterioration of concrete and
embedded steel.
The flowchart in Figure 1 illustrates the flow of decisions and the design activities needed in a rational service
life design process with a chosen level of reliability. Two strategies have been adopted; in the first, three levels
of sophistication are distinguished. In total, four options are available.
Strategy 1: Design to resist deterioration
Level 1 Full probabilistic method (option 1)
Level 2 Partial factor method (option 2)
Level 3 Deemed-to-satisfy method (option 3)
Strategy 2: Avoidance-of-deterioration method, (option 4)
Establishing the serviceability criteria
Establishing the general layout, the dimensions and selection of materials
Verification by the Verification by the Verification by the Verification by the
“Full probabilistic” method “Partial factor” method. “Deemed-to- “Avoidance of
Involving: Involving: satisfy” method. deterioration”
* Probabilistic models * Design values Involving: method.
- resistance - characteristic values Exposure classes, Involving:
- loads/exposure - partial factors limit states and Exposure classes, limit
- geometry * Design equations other design states and other design
* Limit states * Limit states provisions provisions
Execution specification
Maintenance plan
Condition assessment plan
Execution of the structure
Inspection of execution
Maintenance Condition assessments during operational service life
Figure 1 — Flowchart for service life design
1) The International Federation for Structural Concrete.
In the case of non-conformity to the performance criteria,
the structure becomes obsolete or subject to full or partial redesign
Within Clause 6 the following deterioration mechanisms are addressed:
— carbonation-induced corrosion;
— chloride-induced corrosion;
— freeze/thaw attack without de-icing agents or sea-water;
— freeze/thaw attack with de-icing agents or sea-water.
For these mechanisms widely accepted mathematical models exist.
The other deterioration mechanisms:
— chemical attack, and
— alkali-aggregate reactions,
are not treated in detail primarily because widely accepted mathematical models do not exist at present.
To make this International Standard complete, the missing models have to be developed and comply with the
general principles of Clause 5.
This International Standard includes four informative annexes giving background information for the application
in service life design and one informative annex giving guidance for the preparation of a possible national annex.
vi © ISO 2012 – All rights reserved
INTERNATIONAL STANDARD ISO 16204:2012(E)
Durability — Service life design of concrete structures
1 Scope
This International Standard specifies principles and recommends procedures for the verification of the durability
of concrete structures subject to:
— known or foreseeable environmental actions causing material deterioration ultimately leading to failure
of performance;
— material deterioration without aggressiveness from the external environment of the structure, termed self-
ageing.
NOTE The inclusion of, for example, chlorides in the concrete mix might cause deterioration over time without the
ingress of additional chlorides from the environment.
This International Standard is intended for use by national standardization bodies when establishing or
validating their requirements for durability of concrete structures. It may also be applied:
— for the assessment of remaining service life of existing structures; and
— for the design of service life of new structures provided quantified parameters on levels of reliability and
design parameters are given in a national annex to this International Standard.
Fatigue failure due to cyclic stress is not within the scope of this International Standard.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced document
(including any amendments) applies.
ISO 2394, General principles on reliability for structures
ISO 13823, General principles on the design of structures for durability
ISO 22965-1, Concrete — Part 1: Methods of specifying and guidance for the specifier
ISO 22965-2, Concrete — Part 2: Specification of constituent materials, production of concrete and
compliance of concrete
ISO 22966, Execution of concrete structures
ISO 6935 (all parts), Steel for the reinforcement of concrete
2)
ISO 16311 (all parts), Maintenance and repair of concrete structures
2) To be published. ISO 16311-1, -2, -3 and -4 are under preparation.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
basic variable
part of a specified set of variables representing physical quantities, which characterize actions and environmental
influences, material properties including soil properties, and geometrical quantities
[ISO 2394:1998, 2.2.18]
3.2
characteristic value
X or R
k k
value of a material or product property having a prescribed probability of not being attained in a hypothetical
unlimited test series
NOTE 1 This value generally corresponds to a specified fractile of the assumed statistical distribution of the particular
property of the material or product.
NOTE 2 A nominal value is used as the characteristic value in some circumstances.
3.3
characteristic value of a geometrical property
a
k
value usually corresponding to the dimensions specified in the design
NOTE Where relevant, values of geometrical quantities may correspond to some prescribed fractiles of the statistical
distribution.
3.4
characteristic value of an action
F
k
principal representative value
NOTE It is chosen:
— on a statistical basis, so that it can be considered to have a specified probability for not being exceeded towards
unfavourable values during a reference period;
— on acquired experience; or
— on physical restraints.
[ISO 2394:1998, 2.3.12]
3.5
design criteria
quantitative formulations that describe for each limit state the conditions to be fulfilled
3.6
design service life
assumed period for which a structure or a part of it is to be used for its intended purpose with anticipated
maintenance, but without major repair being necessary
3.7
design situation
set of physical conditions representing a certain time interval for which the design demonstrates that the
relevant limit states are not exceeded
[ISO 2394:1998, 2.2.1]
2 © ISO 2012 – All rights reserved
3.8
design value of a geometrical property
a
d
generally a nominal value
NOTE 1 Where relevant, values of geometrical quantities may correspond to some prescribed fractile of the statistical
distribution.
NOTE 2 The design value of a geometrical property is generally equal to the characteristic value. However, it may
be treated differently in cases where the limit state under consideration is very sensitive to the value of the geometrical
property. Alternatively, it can be established from a statistical basis, with a value corresponding to a more appropriate
fractile (e.g. rarer value) than applies to the characteristic value.
3.9
design value of an action
F
d
value obtained by multiplying the representative value by the partial factor γ or γ .
f F
[Modified from ISO 2394:1998, 2.3.16]
3.10
design value of material or product property
X or R
d d
value obtained by dividing the characteristic value by a partial factor γ or γ , or, in special circumstances, by
m M
direct determination
NOTE See 5.4.2 (3).
[Modified from ISO 2394:1998, 2.4.3]
3.11
execution specification
documents covering all drawings, technical data and requirements necessary for the execution of a particular project
NOTE The execution specification is not one single document but signifies the total sum of documents required for
the execution of the work as provided by the designer to the constructor and includes the project specification prepared
to supplement and qualify the requirements of this International Standard, as well as referring to the national provisions
relevant in the place of use.
[ISO 22966:2009, 3.8]
3.12
inspection
conformity evaluation by observation and judgement accompanied as appropriate by measurement,
testing or gauging
[ISO 9000:2005, 3.8.2]
3.13
limit state
state beyond which the structure no longer satisfies the relevant design criteria
NOTE Limit states separate desired states (no failure) from undesired states (failure).
[Modified from ISO 2394:1998, 2.2.9]
3.14
maintenance
set of activities that are planned to take place during the service life of a structure in order to fulfil the requirements
for reliability
3.15
project specification
project-specific document describing the requirements applicable for the particular project
[ISO 22966:2009, 3.15]
3.16
reference period
chosen period of time which is used as a basis for assessing values of variable actions, time-dependent
material properties, etc.
[ISO 2394:1998, 2.2.8]
3.17
reliability
ability of a structure or a structural member to fulfil the specified requirements, including the design service life,
for which it has been designed
NOTE 1 Reliability is usually expressed in probabilistic terms.
NOTE 2 Reliability covers safety, serviceability and durability of a structure.
[Modified from ISO 2394:1998, 2.2.7]
3.18
reliability differentiation
measures intended for socio-economic optimization of the resources to be used to build construction works,
taking into account all expected consequences of failures and the cost of the construction works
3.19
repair
activities performed to preserve or to restore the function of a structure that fall outside the definition of maintenance
3.20
representative value of an action
F
rep
value used for the verification of a limit state
NOTE Representative values consist of characteristic values, combination values, frequent values and quasi-
permanent values, but may also consist of other values.
[ISO 2394:1998, 2.3.11]
3.21
resistance
capacity of a member or component, or a cross-section of a member or component of a structure, to withstand
actions that lead to deterioration
3.22
serviceability limit state
state that corresponds to conditions beyond which specified service requirements for a structure or structural
element are no longer met
[ISO 2394:1998, 2.2.11]
3.23
serviceability criterion
design criterion for a serviceability limit state
4 © ISO 2012 – All rights reserved
3.24
ultimate limit state
state associated with collapse or with other similar forms of structural failure
NOTE They generally correspond to the maximum load-carrying resistance of a structure or structural element, but
in some cases to the maximum applicable strain or deformation.
[ISO 2394:1998, 2.2.10]
4 Symbols and abbreviated terms
4.1 Abbreviated terms
SLD service life design
SLS serviceability limit state
ULS ultimate limit state
4.2 Main letters
F action in general
R resistance
S action effect
T temperature
X basic variable
a geometric quantity
p probability
t
time
x
distance
α
ageing factor
Δ
margin
γ
partial factor
γ partial factor for concrete
c
γ partial factor for actions without taking account of model uncertainties
f
γ partial factor for actions, also accounting for model uncertainties and dimensional variations
F
γ partial factors for a material property, taking account only of uncertainties in the material
m
property
γ partial factors for a material property, taking account of uncertainties in the material
M
property itself and in the design model used
γ partial factor associated with the uncertainty of the resistance model, plus geometric
Rd
deviations if these are not modelled explicitly
4.3 Subscripts
app apparent
crit critical
d design value
dep depassivation
ini initiation
k characteristic value
prop propagation
nom nominal value
rep representative value
SL service life
5 Basis of design
5.1 Requirements
5.1.1 Basic requirements
The service life design (SLD) of concrete structures shall be in accordance with the general principles given in
ISO 2394 and ISO 13823.
The supplementary provisions for concrete structures given in this International Standard shall also be applied.
The service life design shall either:
— follow the general principles for probabilistic service life design of concrete structures outlined in ISO 2394
(the full probabilistic method);
— use the partial factor method given in this International Standard;
— use the deemed-to-satisfy method given in this International Standard;
— be based on the avoidance-of-deterioration method given in this International Standard.
The serviceability criteria related to durability shall be specified for each project and agreed with the client.
NOTE Guidance for the choice of serviceability criteria combined with appropriate target values of reliability are
[3] [1] [6]
given in Annex E of ISO 2394:1998 , Annex A of fib MC SLD and in JCSS Probabilistic Model Code .
5.1.2 Reliability management
Reliability management shall be in accordance with the general principles given in ISO 2394.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 4.
As guidance to reliability differentiation, this International Standard refers to the following general classifications:
— consequence classes CC1, CC2 and CC3;
— reliability classes RC1, RC2 and RC3.
6 © ISO 2012 – All rights reserved
The three consequence classes relate to minor, moderate and large consequences of failure or inadequate
serviceability of the structure.
The three reliability classes may be associated with the three consequence classes.
[3]
NOTE 1 The three-level differentiation corresponds to that in ISO 2394:1998 , 4.2
[7]
NOTE 2 ISO 13823:2008 , 8.5 and 8.6 apply a four-level differentiation for consequences of failure.
The required level of reliability may be achieved by measures related to, for example, the robustness
of the design and to measures related to quality assurance adopted in the design, execution as well as
inspection/maintenance during a structure’s service life.
NOTE ISO 22966 defines three execution classes, EXC1, EXC2 and EXC3, for the quality management regime, for
which the required strictness increases from class 1 to class 3.
In addition, for service life design, Annex D classifies four levels of condition assessment during the service life:
CAL0, CAL1, CAL2 and CAL3
5.1.3 Design service life, durability and quality management
The design of service life, durability and quality management shall be in accordance with the general principles
given in ISO 2394.
[3]
NOTE In ISO 2394:1998 these provisions are given in Clause 4.
,
The design service life is the assumed period for which a structure or part of it is to be used for its intended
purpose with anticipated maintenance, but without major repair being necessary.
The design service life is defined by
— a definition of the relevant limit states,
— a number of years, and
— a level of reliability for not passing each relevant limit state during this period.
Durability of a structure exposed to its environment shall be such that it remains fit for use during its design
service life. This requirement may be satisfied in one, or a combination, of the following ways:
— by designing protective and mitigating systems;
— by using materials that, if well maintained, will not degenerate during the design service life;
— by providing such dimensions that deterioration during the design service life is compensated for;
— by choosing a shorter lifetime for structural elements that when necessary are replaced one or more times
during the design life;
— in combination with appropriate inspection at fixed or condition-dependent intervals and appropriate
maintenance activities.
In all cases, the reliability requirements for long- and short-term periods should be met.
5.2 Principles of limit state design
The limit state design shall be in accordance with the general principles given in ISO 2394.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 5.
5.3 Basic variables
5.3.1 Actions and environmental influences
Characteristic values of actions for use in SLD shall be
— based on data derived for the particular project, or
— from general field-experience, or
— from relevant literature.
Other actions, when relevant, shall be defined in the design specification for the particular project.
Actions specific to SLD may be given in a national annex to this International Standard.
5.3.2 Material and product properties
The material and product properties shall be identified in accordance with the general principles given in ISO 2394.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 6.
Characteristic values of materials and product properties for use in SLD shall be
— based on data derived for the particular project, or
— from general field-experience, or
— from relevant literature.
Materials and product properties to be determined will depend on the deterioration model used. If different
models with different basic assumptions are applied for mapping the material properties and in the SLD, a
checking process shall be established to ensure that the selected model and applied data are compatible.
Material property values shall be determined from test procedures performed under specified conditions. A
conversion factor shall be applied, when necessary, to convert the test results of laboratory cast and tested
specimens into values that are assumed to represent the behaviour of the material or product in the structure.
5.3.3 Geometric data
Design values of geometrical data for SLD shall be in accordance with ISO 2394 or based on measurements
on the completed structure or element.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 6.
ISO 22966 specifies permitted geometrical deviations. If the design assumes stricter tolerances, the design
assumptions shall be verified by measurements on the completed structure or element.
5.4 Verification
5.4.1 Verification by the full probabilistic method
The general principles for probabilistic service life design of concrete structures outlined in the ISO 2394
shall be followed.
In particular the following three principles shall be applied:
— probabilistic models shall be applied that are sufficiently validated to give realistic and representative results;
— the parameters of the models applied and their associated uncertainty shall be quantifiable by means of
tests, observations and/or experience;
8 © ISO 2012 – All rights reserved
— reproducible and relevant test methods shall be available to assess the action- and material-parameters.
Uncertainties associated with models and test methods shall be taken into account.
5.4.2 Verification by the partial factor method
SLD may be performed in accordance with the general principles of the partial factor method given in ISO 2394.
[3]
NOTE In ISO 2394:1998 , these provisions are given in Clause 9.
The same models as used for the full probabilistic method, but based on design values, shall be used for the
partial factor method. Simplifications on the safe side are permitted.
The partial factor method separates the treatment of uncertainties and variabilities originating from various
causes. In the verification procedure defined in this International Standard, the design values of the fundamental
basic variables are expressed as follows.
The design values of an action are generally expressed as:
F = γ × F (1)
d f rep
where
F is the representative value of the action;
rep
γ is the partial safety factor for the action.
f
The design values of material or product property is generally expressed as:
R = R / γ (2)
d k m
or, where uncertainty in the resistance model is taken into account, by:
R = R /γ = R /(γ × γ ) (3)
d k M k m Rd
where
R is the characteristic value of resistance;
k
γ is the partial factor for a material property;
m
γ is the partial factor associated with the uncertainty of the resistance model plus geometric
Rd
deviations if these are not modelled explicitly;
γ = γ × γ is the partial factor for a material property also accounting for the model uncertainties and
M m Rd
dimensional variations.
Design values of geometrical quantities to be considered as fundamental basic variables shall, in general, be
directly expressed by their design values a
d.
When using the partial factor method, it shall be verified that the target reliability for not passing the relevant
limit state during the design service life is not exceeded when design values for actions or effects of actions
and resistance are used in the design models.
The partial factors shall take into account:
— the possibility of unfavourable deviations of action values from the representative values;
— the possibility of unfavourable deviations of materials and product properties from the representative values;
— model uncertainties and dimensional variations.
The numerical values for the partial factors shall be determined in one of the following two ways:
— on the basis of statistical evaluation of experimental data and field observations according to 5.4.1;
— on the basis of calibration to a long-term experience of building tradition.
5.4.3 Verification by the deemed-to-satisfy method
The deemed-to-satisfy method is a set of rules for
— dimensioning,
— material and product selection, and
— execution procedures,
that ensures that the target reliability for not passing the relevant limit state during the design service life is not
exceeded when the concrete structure or component is exposed to the design situations.
The specific requirements for design, materials selection and execution for the deemed-to-satisfy method shall
be determined in either of two ways:
— on the basis of statistical evaluation of experimental data and field observations according to
requirements of 5.4.1;
— on the basis of calibration to a long-term experience of building tradition.
The limitations to the validity of the provisions, e.g. the range of cement types covered by the calibration, shall
be clearly stated.
5.4.4 Verification by the avoidance-of-deterioration method
The avoidance-of-deterioration method implies that the deterioration process will not take place due to, for example:
— separation of the environmental action from the structure or component by e.g. cladding or membranes;
— using non-reacting materials, e.g. certain stainless steels or alkali non-reactive aggregates;
— separation of reactants, e.g. keeping the structure or component below a critical degree of moisture;
— suppressing the harmful reaction e.g. by electrochemical methods.
The specific requirements for design, materials selection and execution for the avoidance-of-deterioration
method may, in principle, be determined in the same way as for the deemed-to-satisfy method.
The limitations to the validity of the provisions shall be clearly stated.
6 Verification of service life design
6.1 Carbonation-induced corrosion - uncracked concrete
6.1.1 Full probabilistic method
6.1.1.1 Limit state: Depassivation
The following requirement shall be fulfilled:
p{} = p = p{a − x (t ) < 0} < p (4)
dep. c SL 0
where
10 © ISO 2012 – All rights reserved
p{} is the probability that depassivation occurs;
a is the concrete cover [mm];
x (t ) is the carbonation depth at the time t [mm];
c SL SL
t is the design service life [years];
SL
p is the target failure probability.
The variables a and x (t ) need to be quantified in a full probabilistic approach.
c SL
NOTE The limit state “depassivation” is only relevant for structures with sufficient humidity to support a corrosion process.
6.1.1.2 Design model
The ingress of the carbonation front might be assumed to obey the following equation:
xt() =×Wk × t (5)
c
k is a factor reflecting the basic resistance of the chosen concrete mix (like water/cement ratio, cement type,
additions) under reference conditions and the influence of the basic environmental conditions (like mean relative
humidity and CO concentration) on ingress of carbonation. It also reflects the influence of the execution.
W takes into account the varying meso-climatic conditions for the specific concrete member during the design
service life, such as humidity and temperature.
For the design of a new structure, the factors W and k might be derived from literature data or existing structures
where the concrete composition, execution and exposure conditions have been similar to those expected for
the new structure.
When assessing remaining service life of an existing structure, the product of W and k might be derived directly
from measurements on the structure.
Other models may be used, provided that the basic principles formulated in 5.4.1 are fulfilled
6.1.1.3 Limit states: corrosion-induced cracking and spalling
Exemplified with regard to cracking, the following basic limit state function shall be fulfilled:
p{} = p = p{Δr − Δr (t ) < 0} < p (6)
crack (R) (S) SL 0
where
p{} is the probability that carbonation-induced cracking occurs;
Δr is the maximum corrosion-induced increase of the rebar radius which can be accommodated
(R)
by the concrete without formation of cracks at the concrete surface [µm];
Δr (t ) is the increase of the rebar radius due to reinforcement corrosion [µm] at time t ;
(S) SL SL
t is the design service life [years];
SL
p is the target failure probability.
An alternative design approach is:
p{} = p = p{t − t − t > 0} < p (7)
crack SL ini prop 0
where
p{} is the probability that carbonation-induced cracking occurs;
t is the design service life [years];
SL
t is the initiation period (period till depassivation of the reinforcement occurs) [years];
ini
t is the propagation period (period of active corrosion) [years];
prop
p is the target failure probability.
The variables Δr and Δr (t ) or the variables t and t need to be quantified in a full probabilistic approach.
(R) (S) SL ini prop
Other methods may be used, provided that the basic principles formulated in 5.4.1 are fulfilled.
At the time of publishing this International Standard, no time-dependent model with general international
consensus is available for the propagation phase. The time span from initiation to cracking may be estimated
from existing structures where the concrete composition, execution and exposure conditions have been similar
to those expected for the structure considered.
6.1.2 Partial factor method
6.1.2.1 Limit state: depassivation
The following limit state function needs to be fulfilled:
a − x (t ) ≥ 0 (8)
d c,d SL
where
a is the design value of the concrete cover [mm];
d
x (t ) is the design value of the carbonation depth at time t [mm].
c,d SL SL
The design value of the concrete cover a is calculated as follows:
d
a = a − Δa (9)
d nom
where
a is the nominal value for the concrete cover [mm];
nom
Δa is the safety margin (permitted deviation) of the concrete cover [mm].
The design value of the carbonation depth, at a time t , x (t ) is calculated as follows:
SL c,d SL
x (t ) = x (t ) × γ (10)
c,d SL c,k SL f
where
x (t ) is the characteristic value of the carbonation depth at a time t [mm], e.g. mean value of the
c,k SL SL
carbonation depth;
γ is the partial safety factor of the carbonation depth [-].
f
Other methods may be used, provided that the basic principles formulated in 5.4.2 are fulfilled.
6.1.3 Deemed-to-satisfy method
Within this approach a trading-off of geometrical (concrete cover to reinforcement) material parameters (indirectly
linked to diffusion and binding characteristics) and execution aspects (compaction and curing) is applied.
12 © ISO 2012 – All rights reserved
6.1.4 Avoidance-of-deterioration method
Generally, avoidance is achieved if depassivation cannot take place due to infinite resistance of the concrete to
carbonation or zero environmental load or infinite corrosion resistance of the reinforcement.
6.2 Chloride-induced corrosion - uncracked concrete
6.2.1 Full probabilistic method
6.2.1.1 Limit state: depassivation
The following limit state function shall be fulfilled:
p{} = p = p{C − C(a,t ) < 0} < p (11)
dep. crit SL 0
where
p{} is the probability that depassivation occurs;
C is the critical chloride content [% by mass of binder];
crit
C(a,t ) is the chloride content at depth a and time t [% by mass of binder];
SL
a
is the concrete cover [mm];
t is the design service life [years];
SL
p is the target failure probability.
The variables a, C and C(a,t ) shall be quantified in a full probabilistic approach.
crit SL
NOTE If the binder content of the actual concrete composition is not known, the critical chloride content may be
related to the mass of the concrete.
6.2.1.2 Design model
The ingress of chlorides in a marine environment may be assumed to obey the following equation:
x
Cx(,tC)(=− CC−×)erf (12)
ss i
2(××Dt) t
app
In this modified Fick’s second law of diffusion, the factors are as follows:
C(x,t) is the content of chlorides in the concrete at a depth x (structure surface: x = 0 mm) and at time
t [% by mass of binder];
C is the chloride content at the concrete surface [% by mass of binder];
s
C is the initial chloride content of the concrete [% by mass of binder];
i
x is the depth with a corresponding content of chlorides C(x,t) [mm];
D (t) is the apparent coefficient of chloride diffusion through concrete [mm /year] at time t (see
app
Formula 13);
t is the time [years] of exposure;
erf is the error function.
α
t
Dt() = Dt() (13)
app app 0
t
where
D (t ) is the apparent diffusion coefficient measured at a reference time of t ;
app 0 0
α is the ageing factor giving the decrease over time of the apparent diffusion coefficient.
Depending on the type of binder and the micro-environmental conditions, the ageing factor is
likely to lie between 0,2 and 0,8.
NOTE The “apparent” diffusion coefficient after a period t of chloride exposure, D (t), represents a constant
app
equivalent diffusion coefficient giving a similar chloride profile to the measured one for a structure exposed to the chloride
environment over a period t.
The decrease of the apparent diffusion coefficient is due to several reasons:
— continued reactions of the binder;
— influence of reduced capillary suction of water in the surface zone with time;
— degree of saturation of concrete; and
— effect of penetrated chlorides from sea-water or de-icing salts (leading to ion exchange with subsequent
poreblocking in the surface layer).
For the design of a new structure, the parameters C , C , α and D (t ) may be derived from existing structures
s i app 0
where the concrete composition, execution and exposure conditions have been similar to those relevant for
the new structure.
When assessing remaining service life of an existing structure, the factors, with the possible exception of α,
may be derived directly from measurements on the structure.
For both design of new structures, and for the assessment of remaining service life of existing structures, the
ageing factor, α, shall be obtained from in-field observations from structures where the concrete composition,
execution and exposure conditions have been similar to those for the actual structure. At least observations at
two periods of exposure (with a sufficient interval between the observations) are needed for the calculation of
the ageing factor.
Other models may also be used, provided that the basic principles formulated in 5.4.1 are fulfilled.
6.2.1.3 Limit states: corrosion-induced cracking and spalling
See 6.1.1.3.
6.2.2 Partial factor method
See 6.1.2.
6.2.3 Deemed-to-satisfy method
See 6.1.3.
6.2.4 Avoidance-of-deterioration method
See 6.1.4, but substitute “chloride penetration” for “carbonation”.
6.3 Influence of cracks upon reinforcement corrosion
The minimum structural reliability of a cracked reinforced concrete structure shall be of comparable magnitude
to the minimum reliability of a comparable exposed uncracked structure.
14 © ISO 2012 – All rights reserved
A simplified approach is used by most operational standards. This implies that corrosion of the reinforcement
is not influenced by crack widths under a certain characteristic value. Depending on the severity of the
environment and sensitivity of the structure, this limiting crack width is normally given as a characteristic value
(5 % upper fractile) in the range of 0,2 mm to 0,4 mm
Similar to the procedure given in 6.1 and 6.2, unwanted events with regard to serviceability/functionality shall be
identified (SLS). In addition, it shall be checked whether ultimate limits are affected by continuously corroding
reinforcement within the cracked zone or not.
In harsh exposure conditions (for example exposure classes XD3/XS3 as defined in ISO 22965-1), if
functionality or structural integrity is affected, and if inspection and possible intervention cannot be performed,
an avoidance-of-deterioration is recommended/needed.
6.4 Risk of depassivation with respect to pre-stressed steel
Relevant application rules given in 6.1, 6.2 and 6.3 to avoid depassivation of pre-stressed steel on a ULS
reliability level shall be applied.
Since corrosion o
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