ISO 13822:2010

Bases for design of structures - Assessment of existing structures

ISO 13822:2010 provides general requirements and procedures for the assessment of existing structures (buildings, bridges, industrial structures, etc.) based on the principles of structural reliability and consequences of failure. It is based on ISO 2394. ISO 13822:2010 is applicable to the assessment of any type of existing structure that was originally designed, analysed and specified based on accepted engineering principles and/or design rules, as well as structures constructed on the basis of good workmanship, historic experience and accepted professional practice. The assessment can be initiated under the following circumstances: an anticipated change in use or extension of design working life; a reliability check (e.g. for earthquakes, increased traffic actions) as required by authorities, insurance companies, owners, etc.; structural deterioration due to time-dependent actions (e.g. corrosion, fatigue); structural damage by accidental actions (see ISO 2394). ISO 13822:2010 is also applicable to heritage structures provided additional considerations shown in Annex I are taken into account. ISO 13822:2010 is applicable to existing structures of any material, although specific adaptation can be required depending on the type of material, such as concrete, steel, timber, masonry, etc. ISO 13822:2010 provides principles regarding actions and environmental influences. Further detailed considerations are necessary for accidental actions such as fire and earthquake. ISO 13822:2010 is intended to serve as a basis for preparing national standards or codes of practice in accordance with current engineering practice and the economic conditions.

Bases du calcul des constructions — Évaluation des constructions existantes

General Information

• Status: Published
• Publication Date: 21-Jul-2010
• ICS: 91.080.01 - Structures of buildings in general
• Technical Committee: ISO/TC 98/SC 2 - Reliability of structures
• Drafting Committee: ISO/TC 98/SC 2 - Reliability of structures
• Current Stage: 9093 - International Standard confirmed
• Start Date: 05-Oct-2021
• Completion Date: 13-Dec-2025

Relations

• Revises: ISO 13822:2001 - Bases for design of structures - Assessment of existing structures
• Effective Date: 26-Sep-2008

Overview

ISO 13822:2010 - Bases for design of structures - Assessment of existing structures - is an international standard that establishes general requirements and procedures for assessing the safety, serviceability and remaining life of existing structures. Built on the principles of structural reliability and linked to ISO 2394, it applies to buildings, bridges, industrial structures and heritage assets of any material (concrete, steel, timber, masonry, etc.). The standard guides engineers through assessment triggers such as change of use, life‑extension, deterioration (corrosion, fatigue), increased actions (traffic, seismic), accidental damage and authority or insurer‑requested reliability checks.

Key topics and technical requirements

• Framework and objectives: Defines the assessment procedure from specification of objectives and scenarios to preliminary and detailed assessment stages.
• Data collection and investigation: Emphasizes inspection, document search, testing (including load testing), monitoring and measurement of material and structural properties.
• Structural analysis and modelling: Covers use of appropriate models, limit states, basic variables and treatment of model uncertainties and conversion factors.
• Deterioration and time‑dependent reliability: Introduces deterioration models and considerations for time‑dependent performance and remaining working life.
• Verification and target reliability: Requires verification against reliability targets and performance requirements; includes plausibility checks and guidance on target reliability levels.
• Assessment outcomes and interventions: Specifies reporting, recommendations for repair, rehabilitation, upgrading, inspection and maintenance plans, and decision/judgement criteria.
• Special considerations: Annex I provides additional guidance for heritage structures; other informative annexes cover testing, updating measurements, upgrading design and reporting formats.

Practical applications and users

ISO 13822:2010 is practical for:

• Structural and civil engineers performing condition assessments, life‑extension studies and rehabilitation design.
• Asset owners and facility managers planning maintenance, upgrading, reuse or change of use.
• Consultants, insurers and authorities requiring reliability checks or compliance demonstrations.
• Heritage conservation specialists applying additional Annex I considerations for historical structures.

Typical uses include: assessing bridge load capacity after traffic increase, verifying building safety after deterioration or partial damage, planning upgrades for extended service life, and preparing inspection/monitoring programs.

Related standards

• ISO 2394 - General principles on reliability for structures (foundation for ISO 13822).
• National design codes and material‑specific standards (ISO 13822 is intended as a basis for national codes and practice).

ISO 13822:2010 keywords: assessment of existing structures, structural reliability, deterioration, inspection, load testing, rehabilitation, upgrading, heritage structures, target reliability level.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 13822
Second edition
2010-08-01
Bases for design of structures —
Assessment of existing structures
Bases du calcul des constructions — Évaluation des constructions
existantes
Reference number
©
ISO 2010
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ii © ISO 2010 – All rights reserved

Contents Page
Foreword .v
Introduction.vi
1 Scope.1
2 Normative references.1
3 Terms and definitions .2
4 General framework of assessment.3
4.1 Objectives .3
4.2 Procedure.4
4.3 Specification of the assessment objectives.5
4.4 Scenario.5
4.5 Preliminary assessment .5
4.6 Detailed assessment.6
4.7 Results of assessment.7
5 Data for assessment .7
5.1 General .7
5.2 Actions and environmental influences .7
5.3 Material properties .8
5.4 Properties of the structure .8
5.5 Dimensions .8
6 Structural analysis .9
6.1 Models .9
6.2 Limit states.9
6.3 Basic variables .9
6.4 Model uncertainties.9
6.5 Conversion factors.9
6.6 Uncertainty about the condition of components .9
6.7 Deterioration models.9
7 Verification .10
7.1 Bases .10
7.2 Reliability assessment.10
7.3 Limit states.10
7.4 Plausibility check .10
7.5 Target reliability level.10
8 Assessment based on satisfactory past performance.10
8.1 Assessment of safety.10
8.2 Assessment of serviceability .11
9 Interventions .11
10 Report .11
10.1 General .11
10.2 Conclusions .11
10.3 Sufficient reliability .11
10.4 Insufficient reliability.12
10.5 Recommendations for interventions.12
10.6 Inspection and maintenance plan.12
10.7 Documented information.12
10.8 Reporting style .12
11 Judgement and decision.12
11.1 Decision .12
Annex A (informative) Hierarchy of terms .13
Annex B (informative) Flowchart for the general assessment of existing structures .14
Annex C (informative) Updating of measured quantities.15
Annex D (informative) Testing for static and dynamic properties of structures .21
Annex E (informative) Assessment of time-dependent reliability.24
Annex F (informative) Target reliability level.28
Annex G (informative) Test report format.30
Annex H (informative) Design of upgrading .33
Annex I (informative) Heritage structures.35
Bibliography .44

iv © ISO 2010 – All rights reserved

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 13822 was prepared by Technical Committee ISO/TC 98, Bases for design of structures, Subcommittee
SC 2, Reliability of structures.
This second edition cancels and replaces the first edition (ISO 13822:2001), which has been technically
revised, including the addition of a new Annex I, the associated change to the Foreword and with some minor
editorial changes.
Introduction
The continued use of existing structures is of great importance because the built environment is a huge
economic and political asset, growing larger every year. The assessment of existing structures is now a major
engineering task. The structural engineer is increasingly called upon to devise ways for extending the life of
structures whilst observing tight cost constraints. The establishment of principles for the assessment of
existing structures is required because it is based on an approach that is substantially different from design of
new structures and requires knowledge beyond the scope of design codes. This document is intended not
only as a statement of principals and procedures for the assessment of existing structures but also as a guide
for use by structural engineers and clients. Engineers can apply specific methods for assessment in order to
save structures and to reduce a client's expenditure. The ultimate goal is to limit construction intervention to a
strict minimum, a goal that is clearly in agreement with the principles of sustainable development.
The basis for the reliability assessment is contained in the performance requirements for safety and
serviceability of ISO 2394. Economic, social and sustainability considerations, however, result in a greater
differentiation in structural reliability for the assessment of existing structures than for the design of new
structures.
vi © ISO 2010 – All rights reserved

INTERNATIONAL STANDARD ISO 13822:2010(E)

Bases for design of structures — Assessment of existing
structures
1 Scope
This International Standard provides general requirements and procedures for the assessment of existing
structures (buildings, bridges, industrial structures, etc.) based on the principles of structural reliability and
consequences of failure. It is based on ISO 2394.
It is applicable to the assessment of any type of existing structure that was originally designed, analysed and
specified based on accepted engineering principles and/or design rules, as well as structures constructed on
the basis of good workmanship, historic experience and accepted professional practice. The assessment can
be initiated under the following circumstances:
⎯ an anticipated change in use or extension of design working life;
⎯ a reliability check (e.g. for earthquakes, increased traffic actions) as required by authorities, insurance
companies, owners, etc.;
⎯ structural deterioration due to time-dependent actions (e.g. corrosion, fatigue);
⎯ structural damage by accidental actions (see ISO 2394).
This International Standard is also applicable to heritage structures provided additional considerations shown
in Annex I are taken into account.
This International Standard is applicable to existing structures of any material, although specific adaptation
can be required depending on the type of material, such as concrete, steel, timber, masonry, etc.
This International Standard provides principles regarding actions and environmental influences. Further
detailed considerations are necessary for accidental actions such as fire and earthquake.
NOTE Fire resistance requires properties different from those for structural safety and integrity. Also fire hazards can
be created by change in use. Special requirements are necessary for seismic hazards taking the dynamic action and
structural response into account.
This International Standard is intended to serve as a basis for preparing national standards or codes of
practice in accordance with current engineering practice and the economic conditions.
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 2394:1998, General principles on reliability for structures
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2394 and the following apply.
NOTE See also Annex A.
3.1
assessment
set of activities performed in order to verify the reliability of an existing structure for future use
3.2
damage
unfavourable change in the condition of a structure that can affect structural performance

3.3
deterioration
process that adversely affects the structural performance, including reliability over time due to
⎯ naturally occurring chemical, physical or biological actions,
⎯ repeated action such as those causing fatigue
⎯ normal or severe environmental influences
⎯ wear due to use, or
⎯ improper operation and maintenance of the structure.
3.4
deterioration model
mathematical model that describes structural performance as a function of time, taking deterioration into
account
3.5
inspection
on-site non-destructive examination to establish the present condition of the structure
3.6
investigation
collection and evaluation of information through inspection, document search, load testing and other testing
3.7
load testing
test of the structure or part thereof by loading to evaluate its behaviour or properties, or to predict its load
bearing capacity
3.8
maintenance
routine intervention to preserve appropriate structural performance
3.9
material properties
mechanical, physical or chemical properties of structural materials
3.10
monitoring
frequent or continuous, normally long-term, observation or measurement of structural conditions or actions
2 © ISO 2010 – All rights reserved

3.11
reference period
chosen period of time which is used as a basis for assessing values of variable actions, time-dependent
material properties, etc.
NOTE The remaining working life or the minimum standard period for safety of an existing structure can be taken as
a reference period (see Annex F).
3.12
rehabilitation
work required to repair, and possibly upgrade, an existing structure
3.13
remaining working life
period for which an existing structure is intended/expected to operate with planned maintenance
3.14
repair, verb
improve the condition of a structure by restoring or replacing existing components that have
been damaged.
3.15
safety plan
plan specifying the performance objectives, the scenarios to be considered for the structure, and all present
and future measures (design, construction, or operation such as monitoring) to ensure the safety of the
structure
3.16
structural performance
qualitative or quantitative representation of the behaviour of a structure (e.g. load bearing capacity, stiffness)
in terms of its safety and serviceability
3.17
target reliability level
level of reliability required to ensure acceptable safety and serviceability
3.18
upgrading
modifications to an existing structure to improve its structural performance
3.19
utilization plan
plan containing the intended use (or uses) of the structure, and listing the operational conditions of the
structure including maintenance requirements, and the corresponding performance requirements
4 General framework of assessment
4.1 Objectives
The objective of the assessment of an existing structure in terms of its required future structural performance
shall be specified in consultation with the client (the owner, the authority, insurance companies, etc.) based on
the following performance levels:
a) safety performance level, which provides appropriate safety for the users of the structure;
b) continued function performance level, which provides continued function for special structures such as
hospitals, communication buildings or key bridges in the event of an earthquake, impact, or other
foreseen hazard;
c) special performance requirements of the client related to property protection (economic loss) or
serviceability. The level of this performance is generally based on life cycle cost and special functional
requirements.
4.2 Procedure
The procedure depends on the assessment objectives (see 4.1), and on specific circumstances (e.g. the
availability of the design documents, the observation of damage, the use of the structure). A site visit is
recommended prior to initiating the procedure.
The assessment is carried out taking into account the actual conditions of the structures (see the flowchart in
Annex B) and is composed in general of steps a) to f):
a) specification of the assessment objectives;
b) scenarios;
c) preliminary assessment:
1) study of documents and other evidence,
2) preliminary inspection,
3) preliminary checks,
4) decisions on immediate actions,
5) recommendation for detailed assessment;
d) detailed assessment:
1) detailed documentary search and review,
2) detailed inspection and material testing,
3) determination of actions,
4) determination of properties of the structures,
5) structural analysis,
6) verification;
e) results of assessment:
1) report,
2) conceptual design of construction interventions,
3) control of risk;
f) repetition of the sequence if necessary.
The procedure outlined above may be applied to both the assessment of one specific structure and the
assessment of a group of structures.
4 © ISO 2010 – All rights reserved

4.3 Specification of the assessment objectives
At the outset, the objective of the assessment of the structure shall be clearly specified in terms of its future
performance in an agreement between the client, the authorities when relevant and the assessing engineer
(see 4.1). The required future performance shall be specified in the utilization plan and safety plan.
4.4 Scenario
Scenarios related to a change in structural conditions or actions should be specified in the safety plan in order
to identify possible critical situations for the structure. Each scenario is characterized by a predominant
process or action and, where appropriate, by one or more accompanying processes or actions. The
identification of scenarios represents the basis for the assessment and design of interventions to be taken to
ensure structural safety and serviceability.
4.5 Preliminary assessment
4.5.1 Study of documents and other evidence
Design and inspection documents contain important information that is necessary for a thorough assessment
of an existing structure. It shall be verified that the documents are correct and, in that context, they are
updated to include information of any previous intervention to the structure. Other evidence, such as the
occurrence of significant environmental or seismic actions, large actions, changes in soil conditions, corrosion,
and misuse of the structure, shall be recorded and documented.
4.5.2 Preliminary inspection
The aim of a preliminary inspection is to identify the structural system and possible damage of the structure by
visual observation with simple tools. The information collected is related to aspects such as surface
characteristics, visible deformations, cracks, spalling, corrosion, etc. The results of the preliminary inspection
are expressed in terms of a qualitative grading of structural conditions (e.g. none, minor, moderate, severe,
destructive, unknown) for possible damage.
4.5.3 Preliminary checks
The purpose of the preliminary checks is to identify the critical deficiencies related to the future safety and
serviceability of the structure with a view to focussing resources on these aspects in subsequent assessment.
Based on these results, it is then judged whether or not a further investigation is necessary.
4.5.4 Decisions on immediate actions
When the preliminary inspections and/or checks clearly indicate that the structure is in a potentially dangerous
condition, it is necessary to report to the client that interventions should be taken immediately to reduce the
danger with respect to public safety. If there is uncertainty, the critical deficiencies should be assessed
immediately and actions taken, if necessary.
4.5.5 Recommendations for detailed assessment
The preliminary checks may clearly show the specific deficiencies of the structure, or that the structure is
reliable for its intended use over the remaining working life, in which case a detailed assessment is not
required. Where there is uncertainty in the actions, action effects or properties of the structure, a detailed
assessment should be recommended in accordance with 4.6.
4.6 Detailed assessment
4.6.1 Detailed documentary search and review
The following documents, if available, should be reviewed:
⎯ drawings, specifications, structural calculations, construction records, inspection and maintenance
records, details of modifications;
⎯ regulations and by-laws, codes of practice and standards that were used for constructing the structure;
⎯ topography, subsoil conditions, groundwater level at the site.
4.6.2 Detailed inspection and material testing
The details and dimensions of the structure as well as characteristic values of material properties can be
obtained from design documents, provided that the documents exist and that there is no reason for doubt. In
case of any doubts, details and dimensions of components and properties of materials assumed for the
analysis shall be determined from a detailed inspection and material testing. The planning of such an
inspection is based on information that is already available. The detailed quantitative inspection results in a
set of updated values or distributions for certain relevant parameters that affect the properties of the structure
(see Annex C).
4.6.3 Determination of action
Actions and in particular environmental actions on structures shall be determined by analysis in accordance
with ISO 2394, taking into account provisions laid down in the safety plan and utilisation plan.
4.6.4 Determination of properties of the structures
Testing of the structure is used to measure its properties and/or to predict a load bearing capacity when other
approaches such as detailed structural analysis or inspection alone do not provide clear indication or have
failed to demonstrate adequate structural reliability (see Annex D).
4.6.5 Structural analysis
Structural analysis in accordance with ISO 2394 shall be carried out to determine the effects of the actions on
the structure. The capacity of structural components to resist action effects shall also be determined. The
deterioration of an existing structure shall be taken into consideration. When deterioration of an existing
structure is observed, the reliability assessment of the structure becomes a time-dependent deterioration
problem as described in ISO 2394, and an appropriate analysis method shall be used. In the case of
deteriorated structures, it is essential to understand the causes for the observed damage or malfunction.
Some examples of appropriate analysis methods to assess time-dependent reliability can be found in Annex E.
NOTE For deterioration, it is often more practical to use service-life predictors (such as S-N curves for fatigue or
time-to spalling models for corrosion of reinforcement) based on test data.
4.6.6 Verification
The verification of an existing structure should normally be carried out to ensure a target reliability level that
represents the required level of structural performance (see 4.1 and Annex F). Current codes or codes
equivalent to ISO 2394 that have produced sufficient reliability over a long period of application may be used.
Former codes that were valid at the time of construction of an existing structure should be used as informative
documents. Alternatively, verification may be based on satisfactory past performance (see Clause 8).
6 © ISO 2010 – All rights reserved

4.7 Results of assessment
4.7.1 Report
The results of assessment shall be documented in a report (see Annex G for example).
4.7.2 Conceptual design of construction interventions
If the structural safety or serviceability is shown to be inadequate, the results of the assessment should be
used to recommend construction interventions for repair, rehabilitation or upgrading of the structure to perform
in accordance with the objective of the assessment for its remaining working life (see Annex H).
4.7.3 Control of risk
An alternative approach to construction interventions, which may be appropriate in some circumstances, is to
control or modify the risk. Various measures to control the risk environment include imposing load restrictions,
altering aspects of the use of the structure, and implementing some form of in-service monitoring and control
regime.
5 Data for assessment
5.1 General
Data for assessment should be related to the material properties, structural properties, dimensions, and other
conditions as actually established for the existing structure, and to previous and/or future actions to the
structure.
NOTE Current codes are normally design codes and therefore they may not be appropriate for use directly for
assessment of existing structures. However they should be considered for the assessment. As discussed in Clause 7 and
Annex F, reduced service life and target reliability level may be considered for an existing structure. Furthermore, refined
analyses, testing and a consideration of the actual behaviour of a structure may help in this respect.
5.2 Actions and environmental influences
5.2.1 Actions
Actions shall be determined in accordance with current codes. Changes of actions caused by the change in
use or modification of an existing structure shall be taken into consideration.
5.2.2 Environmental influences
Environmental influences of a physical, chemical or biological nature that may have an effect on the material
properties of an existing structure shall be taken into account. Changes in environmental influences as a result
of change in use or modification of an existing structure shall be taken into consideration.
5.2.3 Original drawings and design specifications
The actions and environmental influences for which the structure was originally designed may be determined
from drawings and design specifications when there is no uncertainty about their validity.
5.2.4 Inspection
Environmental influences should be determined by inspection in cases of uncertainty. In such cases, some
types of actions may also be determined by inspection.
5.2.5 Site-specific data
It can be advantageous to consider the specific characteristics of a structure or its surrounding or to observe
actions when determining actions and environmental influences. It is important to adjust for long-term and
extreme effects that cannot be measured directly when collecting information on actions and environmental
influences.
5.3 Material properties
5.3.1 Actual material properties
Material properties used in the assessment shall be the estimated actual material properties of the existing
structure, not material properties specified in the original design of the structure or in a code or standard. The
material properties shall be assessed by considering deterioration and possible influences of actions (e.g. fire)
during the history of the structure.
5.3.2 Original drawings and design specifications
Material properties may be determined from drawings and design specifications when there is no uncertainty
about their validity.
5.3.3 Material testing
In cases of uncertainty, material properties should be determined by testing, including non-destructive or
destructive material testing. The testing should be planned to produce data which is of direct concern to the
required safety and serviceability of the structure as shown by structural analysis. The use of the structure and
the environmental influences on the structure shall be taken into account.
5.3.4 Sampling and testing procedure
Sampling and testing methods should be in accordance with the relevant International Standards. Sampling
locations and methods that can jeopardize structural reliability shall be avoided. Repair and/or reinforcement
shall be carried out immediately after sampling.
5.3.5 Analysis of test results
When samples are tested, the material properties of the structure shall be determined, statistically if possible,
from the test results.
5.4 Properties of the structure
5.4.1 Testing for static and dynamic properties of structure
If the properties of the structure are not sufficiently understood or if it is not feasible to establish the required
dimensions and material properties by measurement, testing of the structure can be required to define
structural properties. Dynamic testing shall be carried out if the dynamic properties of an existing structure are
required and are not available from other sources (see Annex D).
5.4.2 Geotechnical investigation
Geotechnical and subsoil influences on structural behaviour shall be investigated.
5.5 Dimensions
5.5.1 Actual dimensions
In determining dimensions of components in an existing structure, the actual dimensions should be used.
8 © ISO 2010 – All rights reserved

5.5.2 Determination of dimensions
Dimensions may be determined from drawings and design specifications when there is no uncertainty about
their validity. In cases of uncertainty, dimensions should be determined by inspection and measurement.
6 Structural analysis
6.1 Models
Structural performance shall be analysed using models that reliably represent the actions on the structure, the
behaviour of the structure, and the resistance of its components. The analytical model should reflect the actual
condition of the existing structure.
6.2 Limit states
The structure shall be analysed for the ultimate limit states and serviceability limit states, using the basic
variables and taking account of relevant deterioration processes.
6.3 Basic variables
The following basic variables for use in structural analysis shall be determined by updating information about
the actual condition of the structure:
a) actions;
b) material properties and geotechnical conditions;
c) dimensions of the structural components and subsoil geometry;
d) model uncertainties.
6.4 Model uncertainties
The uncertainty associated with the validity and accuracy of the models should be considered during
assessment, either by adopting appropriate partial factors in deterministic verifications or by introducing
additional random variables representing model uncertainties in reliability analyses.
6.5 Conversion factors
Conversion factors reflecting the influence of shape and size effect of specimens, temperature, moisture,
duration-of-load effects, etc., shall be taken into account.
6.6 Uncertainty about the condition of components
When an existing structure is analysed, the level of knowledge about the condition of components shall be
taken into account. This may be achieved by adjusting the assumed variability in either the load carrying
capacity of the components or the dimensions of their cross sections, depending on the type of structure.
6.7 Deterioration models
When deterioration of an existing structure is observed, the deterioration mechanisms shall be identified and a
deterioration model predicting the future performance of the structure shall be determined on the basis of
theoretical or experimental investigation, inspection, and experience.
7 Verification
7.1 Bases
The assessment of an existing structure shall be based on the verification of structural safety and
serviceability.
7.2 Reliability assessment
The reliability assessment shall be made taking into account the remaining working life of an existing structure,
the reference period, and changes in the environment of a structure associated with an anticipated change in
use.
Economic, social and sustainability considerations result in a greater differentiation in structural reliability for
assessment of existing structures than for the design of new structures.
7.3 Limit states
Verifications shall be based on the limit state concept. Attention should be paid to both the ultimate and
serviceability limit states. Verification may be carried out using partial safety factor or structural reliability
methods with consideration of structural system and ductility of components.
Partial safety factors given in current codes may be modified to take into account the inspection and test
results (concerning, for example, quality of workmanship, conditions of maintenance and strength variation of
materials).
7.4 Plausibility check
The conclusion from the assessment shall withstand a plausibility check. In particular, discrepancies between
the results of structural analysis (e.g. insufficient safety) and the real structural condition (e.g. no sign of
distress or failure, satisfactory structural performance) shall be explained.
NOTE Many engineering models are conservative and cannot always be used directly to explain an actual situation.
See also Clause 8.
7.5 Target reliability level
The target reliability level used for verification can be taken as the level of reliability implied by acceptance
criteria defined in proven and accepted design codes. The acceptance criteria shall be stated together with
clearly defined limit state functions and specific models of the basic variables.
The target reliability level can also be established taking into account the required performance level for the
structure (see 4.1), the reference period and possible failure consequences. Lower target reliability levels for
existing structures may be used if they can be justified on the basis of socio-economic criteria (see Annex F).
8 Assessment based on satisfactory past performance
8.1 Assessment of safety
Structures designed and constructed based on earlier codes, or designed and constructed in accordance with
good construction practice when no codes applied, may be considered safe to resist actions other than
accidental actions (including earthquakes) provided that
⎯ careful inspection does not reveal any evidence of significant damage, distress or deterioration;
⎯ the structural system is reviewed, including investigation of critical details and checking them for stress
transfer;
10 © ISO 2010 – All rights reserved

⎯ the structure has demonstrated satisfactory performance for a sufficiently long period of time for extreme
actions due to use and for the occurrence of environmental effects;
⎯ predicted deterioration taking into account the present condition and planned maintenance ensures
sufficient durability; and
⎯ there have been no changes for a sufficiently long period of time that can significantly increase the
actions on the structure or affect its durability, and no such changes are anticipated.
NOTE If quantitative detailed information is available, satisfactory past performance against accidental actions
(including earthquakes) can be taken into account.
8.2 Assessment of serviceability
Structures designed and constructed based on earlier codes, or designed and constructed in accordance with
good construction practice when no codes applied, may be considered serviceable for future use provided that
⎯ careful inspection does not reveal any evidence of significant damage, distress, deterioration or
displacement;
⎯ the structure has demonstrated satisfactory performance for a sufficiently long period of time for damage,
distress, deterioration, displacement or vibration to occur;
⎯ there will be no changes to the structure or in its use that can significantly alter the actions including
environmental actions on the structure or part thereof; and
⎯ predicted deterioration taking into account the present condition and planned maintenance ensures
sufficient durability.
9 Interventions
Responding to the requirements defined in the utilization plan, assessment of existing structures can result in
several possible interventions including repair, rehabilitation, performance monitoring and maintenance of
critical components, upgrading (see Annex H), and demolition. The cost and risk associated with each of the
interventions should be estimated.
10 Report
10.1 General
Assessment of an existing structure is typically carried out in a manner involving a number of phases of work.
Some form of report is usually required at the end of each phase of the work. Certain aspects of the final
report, which should be issued upon the completion of the assessment, are given in 10.2 to 10.8.
10.2 Conclusions
Clear conclusions with regard to the objective of the assessment in terms of performance requirement
(see 4.3) and the scenarios (see 4.4) should be stated after careful assessment of structural reliability and
cost of interventions as well as public safety, structure preservation and life cycle cost.
10.3 Sufficient reliability
If the existing structure is verified to have sufficient reliability, no further action is required.
10.4 Insufficient reliability
If an assessment concludes that the reliability of a structure is insufficient, appropriate interventions should be
proposed.
10.5 Recommendations for interventions
Recommendations for possible construction and/or operational interventions that are available to the client as
a logical follow-up to the conclusions should be presented. While the engineer should indicate a preferred
solution, it should be noted that it is the client who makes the final decision on interventions. Temporary
intervention for unsafe conditions can also be required immediately.
10.6 Inspection and maintenance plan
In all cases, an inspection and maintenance plan during the remaining working life should be specified
depending on the results of assessment and the utilisation plan and submitted to the client. The date or
conditions for the next assessment should be recommended.
10.7 Documented information
All the information obtained in the assessment should be documented in a report for the client, including the
objective of the assessment, name of engineer (or firm), description of the structure, methods and results of
the assessment, as well as recommendations for relevant further steps, if necessary (see Annex G).
10.8 Reporting style
The report shall be concise and clear. A recommended report format is indicated in Annex G.
11 Judgement and decision
11.1 Decision
The final decision on interventions, based on engineering judgement and the recommendations in the report
and considering all the information available, is made by the client in collaboration or in consultation with the
relevant authority.
NOTE If the client does not respond in reasonable time in matters of public safety, the engineer might have the legal
duty to inform the relevant authority.
11.2 Change in use
An important change in use of the structure made after the assessment invalidates the recommendations
proposed in the report.
12 © ISO 2010 – All rights reserved

Annex A
(informative)
Hierarchy of terms
Annex B
(informative)
Flowchart for the general assessm
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