Draft
compiled 2 April-08
ISO 13822:2006(E)
Draft compiled after de discussion of the of TC98/SC2/WG6 meeting in Padova on April 1-2 2008
New text proposed for sections I.3.9, I.4 and I.5 also included (in blue)
Annex I
(informative)
[(should be altered into normative?) Informative or normative? It is proposed to keep informative.
The normative / informative character is still to be decided]
Heritage structures
I.1 Introduction
The purpose of the Heritage Structure Annex is to provide additional considerations
to the application of the ISO 13822 Standard to heritage and historic structures. This
annex must be read in conjunction with all of the sections of this standard.
This annex is based on the premise that structure has cultural value in itself.
Heritage structures should be preserved for their own sake and not merely as
supports for the rest of the historic material. It follows that the integrity of the existing
structure should be respected in any interventions.
Discussion of these issues is provided in documents listed in the bibliography.
[The second paragraph is still to be improved]
I.2 Fundamentals
I.2.1 Assessment of heritage structures
The assessment of a heritage structure will include two aspects: that concerning its
structural performance, familiar to engineers, and that concerning its value as a
cultural resource. These two aspects must both be taken into account in any
decision involving possible structural interventions and should therefore be carried
out in tandem.
I.2.2 Heritage value
The heritage value of an historic structure resides in the authenticity and integrity of
its character-defining elements. Contemporary interventions must not compromise
this authenticity and integrity. To retain authenticity, the structure is to be preserved,
as far as possible, with its original materials and structural concept.
NOTE 1- The structure itself often represents an important aspect of the culture of its
period: the construction knowledge, technology, and skills of a given time, and as
such, represent a legacy to future generations. There are numerous examples of
exceptional heritage structures while other heritage structures are typical structural
designs of their time, but nonetheless are critical to the cultural resource in their
supporting role to other character-defining elements, such as architectural material
or paintings.
NOTE- 2 Judgments about heritage value and authenticity may differ from culture to
culture, and thus, there are no fixed criteria. In some geographical areas, keeping
alive traditional construction practice is privileged over the conservation of original
materials.
I.2.3 Limitation of structural intervention
An over cautious approach to structural assessment should be avoided because it
can lead to unnecessary intervention on the structure and result in loss or major
alteration of heritage character defining elements, and ultimately in the loss of
authenticity and historic significance of the cultural resource. Furthermore, excessive
scope of intervention can add unnecessary cost and compromise the viability of a
conservation project, and eventually jeopardize the existence of a cultural resource.
Note: In the case of historic resources the commemorative integrity of an historic
site can be threatened by unjustified structural interventions.
I.3 Terms and definitions
For the purpose of this annex the following terms and definitions have been added,
supplementing those in the core document, to reflect activities related to heritage
structures.
I.3.1 heritage structure
Existing structure, or structural component of a heritage resource, that has been
recognized by the appropriate authorities for its heritage value.
NOTE- Heritage structures may include all kinds of buildings, bridges and civil
engineering works
I.3.2 character-defining elements
Historic materials, forms, locations, spatial configurations, morphology, concept and
details, structural design, uses and cultural associations that contribute to the
heritage value of a structure, and which must be retained in order to preserve its
heritage value
Note 1: Intangible aspects, such as ancient construction knowledge, technologies,
and skills may be identified as character-defining elements.
Note 2: Significant subsequent historic changes and alterations, imperfections and
damage may be identified as character-defining elements, and must be respected
provided that they do not compromise the safety requirements.
I.3.3 heritage value
Aesthetic, historic, scientific, cultural, social or spiritual importance or significance for
past, present, and future generations; heritage value is embodied in its characterdefining elements
I.3.4 cultural resource
Structure, building, landscape, archaeological site or other engineering works that
has been formally recognized for its heritage value
I.3.5 conservation
All actions or processes that are aimed at safeguarding the character-defining
elements of a cultural resource so as to retain its heritage value and extend its
physical life. Conservation includes repair, and upgrading.
Note 1: Several words are used over the world to describe the action and process
of safeguarding and extending the life of a cultural resource: conservation,
preservation, and restoration. Conservation has been used by UNESCO and World
Heritage.
Note 2: conservation is a particular case of rehabilitation as defined in the core
document, in which the respect for cultural value is considered as a constraint.
I.3.6 emergency stabilization
Action or process implemented urgently to temporarily secure a structure which has
insufficient reliability until conservation/preservation can begin.
I.3.7 minimal intervention
Intervention that balances safety requirements with the protection of characterdefining elements.
I.3.8 incremental approach
A step-by-step procedure in which the behaviour of the structure is monitored at
each stage and the data acquired then used to provide the basis for further action.
[Text in next sections I.3.9, I.4 and I.5 proposed by L. Fontaine and D.Yeomans
Discussion pending.]
I.3.9 heritage recording and documentation
Heritage recording is different from heritage documentation in that the former is a record
made in the present while the latter is the assembly of pre-existing documents. [Lyne is to
provide the Getty definition.]
I.4 General framework of assessment
I.4.1 Objectives
The main objective of a structural assessment is to ascertain the current and future structural
capacity with sufficient reliability to minimize the impact of potential structural interventions
on the character defining elements.
The required structural performance shall consistent with objectives listed in section 4.1 of
the core text:
a)
b)
safety performance level for the users,
performance level related to the protection of the cultural resources.
I .4.2 Procedure
For heritage structures the procedure listed in 4.2 of the core document is appropriate
provided that the particularities listed in section I.4.3 to I.4.7 are taken into consideration.
Structural assessment for heritage structure should be typically carried out in collaboration
with a multi-disciplinary team that includes specialists such as engineers (structural,
geotechnical, etc.), architect, landscape architect, heritage recorder, archaeologist,
historian, cultural resource manager, interpreter, material scientist, conservator,
geophysicist, etc. While the structural engineer should deliver a specific structural
evaluation report, the ramifications of this report should be discussed within the multidisciplinary team and decision typically reached in a consensus process.
I. 4.3 Specification of assessment objectives
In heritage structures the principal objective of the assessment must be the determination of
the current, and future structural performance, any limitations of that performance and
therefore any limitations on allowable actions. The typically uncertain nature of heritage
structures means that a precise specification of investigative procedures and analysis is often
impossible at the outset and that the agreement between the client and engineer must allow
for revisions and extensions as required.
I 4.4 Scenarios
Scenarios for interventions must respect the heritage values. The heritage values will
normally place severe restrictions on possible scenarios and therefore more than one
scenario will need to be assessed.
I 4.5 Preliminary assessment
I 4.5.1 Historical record
It is essential that an historical report be produced for heritage structures. This should
identify the nature of the original construction, all subsequent alterations and any significant
events that have caused structural damage. Typically cultural resource specialists (such as
historians or archaeologists) should be employed to produce this report. The engineer must
assist them in the identification and interpretation of structurally meaningful records. Where
no such specialist is employed the engineer will need to include historical information in his
assessment report and will therefore be responsible for the identification and interpretation
of historical records.
Note: Historical records were not produced for structural purposes. Although they typically
provided useful information, they could also be misleading and contain information difficult
to interpret. Their reliability must be ascertained carefully.
,
I.4.5.2 Preliminary inspection
Where insufficient documentation exists describing the structure the engineer needs to
identify those areas where some opening up of the structure is required. This might also be to
determine its condition. The engineer must consult the relevant heritage professionals to
obtain approval prior to such opening up.
I 4.5.3 Monitoring
Monitoring is often necessary for heritage structures, and must be carried out when there are
conditions or actions affecting the structural behaviour over time and whose effects or
magnitude are not fully understood. Monitoring may be initiated as part of the ongoing
maintenance or as an early step in the preliminary assessment. Recommendations for further
monitoring should be provided where its initial design has not provided sufficient data for a
detailed understanding of the condition and its effects.
I 4.5.3 Preliminary checks
In addition to the safety and serviceability of the structure the preliminary check needs also
to identify critical deficiencies related to the conservation of character defining features.
I 4.5.4 Immediate actions
Where character defining features are in immediate danger this should be reported to the
client and to any heritage resource manager. Any interim interventions necessary to ensure
the stability of the structure must not cause damage to the heritage character.
I 4.5.5 Recommendations for detailed assessment
Recommendations for detailed assessment need to be made when there is evidence that
character-defining elements may be at risk in the long term.
I 4.6 Detailed assessment
I 4.6.1 Detailed documentary search and review.
In addition to the activities listed in the core document, a history of the use of a heritage
structure affecting its past environmental conditions should be documented. This may need
to draw upon such sources as oral history, historic photographs, as well as maintenance or
other records.
I 4.6.2 Heritage recording
Heritage recording must be carried out by specialists (commonly surveyors, archaeologists
or architectural technologists). This will normally be carried out before or during the
preliminary assessment.
Records should be made in such a way that they can be used as the basis for reporting
structural condition observations, structural modelling and for conceptual design drawings
of construction interventions.
Note: Numerous recording methodologies exist to document heritage structure: survey,
photogrammetry, rectified photography, photo mosaic, hand record, laser scanning, shape
capture, etc.
I 4.6.3 Detailed inspection
A detailed visual and tactile inspection should be carried out. Representative samples of
hidden elements should be inspected. Openings should be carried out in stages, increasing
the number only as analysis shows further openings to be necessary. The potential gain in
information obtained of either dismantling or opening to access hidden features must
outweigh the loss of heritage value.
Dismantling and rebuilding to ascertain the capacity of hidden elements may be carried out
if:
i)
it is recognized by the cultural heritage management authorities part of the
traditional method for repair and maintenance, or
ii)
if it is otherwise absolutely necessary to ensure safety and serviceability.
I 4.6.4 Sampling
As above, samples taken for materials testing should be kept to a minimum and generally
restricted to those parts of the structure that have least heritage value.
I.4.6.5 Preferred testing methods
Non-destructive testing (NDT) and minor destructive testing (MDT) should be used. Historic
structural assemblies are typically complex and non-homogeneous. NDT tests should be
carried out by qualified specialists to ensure proper calibration of instrumentation and
interpretation of the results. In some cases, destructive tests may be necessary to calibrate
NDT
Note: NDT aims to determine physical, mechanical and chemical characteristic of
materials, in-situ stresses, mechanical properties of assemblies, and the presence of
discontinuities. Recent developments in software and instrumentation have increased
significantly the effectiveness of NDT.
I.4.6.6 Destructive testing
Destructive tests, causing significant damage, should only be used when absolutely necessary
either to obtain information that cannot be acquired by other means, or to calibrate NDTs,
preferably in inconspicuous areas and without affecting character-defining elements.
However, as described above, the potential gain in information obtained must outweigh the
loss of heritage value, i.e. the losses resulting from the tests should be less than those that
would be caused by the more severe interventions necessitated by poorer understanding of
the structure.
I 4.6.7 Monitoring
The results of the structural monitoring at this stage can be used to validate the structural
analysis model. Further monitoring should be specified:
i)
where the monitoring results are inconclusive in predicting structural performance,
ii)
where intervention has been delayed or
iii)
where present concerns do not yet justify intervention.
I 4.6.8 Determination of actions
Special provisions within various national codes can be made for enhanced or reduced
values for the actions on heritage structures balancing safety and heritage values.
I.4.6.9 Determination of structural properties
Testing to determine the properties and/or load bearing capacity of the structure shall be
planned in consultation with the heritage management professionals. The need for the test
and any possible adverse effects on the historic fabric shall be clearly identified.
I 4.6.10 Structural analysis
Structural analysis should take into effect the uncertainties resulting from:
i)
limited access
ii)
greater age factors
iii)
more complex load paths
iv)
limited knowledge of archaic structural systems
v)
and therefore it may be necessary to consider more than one structural model. When the
models fail to demonstrate sufficient reliability of the structure it may be necessary to carry
out additional testing of materials and structural properties or monitoring, incorporating the
results in a revised structural analysis.
Note: The information gained through this incremental procedure can be used to gradually
improve the understanding and modelling of the structure.
I 4.6.11 Verification
[Note: provide key messages relative for verification relative to heritage structure.]
I 4.7 Results of assessment
I 4.7.1 Report
In addition to the report format presented in Annex G the following points should be added:
i)
historical report
ii)
heritage records
iii)
monitoring methodology and results
iv)
heritage considerations
v)
limitations of assessment
vi)
and others?
I 4.7.2 Conceptual design of interventions
Further to section 4.7.2 of the core document recommendations that safeguard the character
defining elements of the structure should be provided. In some cases an incremental
approach, i.e. a strategy combining minimal intervention with subsequent monitoring, may be
the optimum solution.
I 4.7.3 Control of risk
In addition to the requirements of the core document, an assessment of the level of risk to
both the structural performance and to the heritage value should be undertaken whenever
there is a contemplated change of use. For heritage structures, because of the uncertainties
listed in I 4.6.10, monitoring after completion of the work should be used to verify the longterm performance of the intervention.
I.5 Data for assessment
I.5.1 General
Sufficient data must be obtained investigation and documentation must be carried out to
reduce the level of uncertainty in order to achieve minimal intervention.
As specified in clause 5 of the CD, investigation, must encompass materials, actions,
environment, existing documents, and other relevant aspects. Particular attention must be
given to investigation of records on the historical performance of the structure.
I 5.2 Actions??????
Special provisions within various national codes can be made for enhanced or reduced
values for the actions on heritage structures balancing safety and heritage values.
I.5.3 Monitoring data
I.5.3.1 monitoring of structural performance
Because crack and deformation may be of seasonal nature, monitoring should ascertain the
extent of progressive movement.
I.5.3.2 Monitoring of environmental conditions
Monitoring of structural movements must be accompanied by monitoring of the
environmental conditions that might be causing those movements.
I 5.4 Determination of dimensions and properties
The dimensions and materials properties of heritage structures must always be measured.
No reliance should be placed upon early drawings and specifications.
I 5.5 Site specific data
Historical records need to be consulted to determine any significant changes that may have
affected site conditions.
I 5.6 Foundations
The assessment of the foundation of heritage structures is complex and requires the services
of a specialist geotechnical engineer. For example these foundations may be subject to
extremely long and complex consolidation processes. Information on previous interventions
should be obtained. When excavating for foundation investigations prior approval and often
archaeological supervision are required.
I 5.7 Site drainage
Site drainage patterns and water table levels may have changed with time and fundamentally
affected the performance of the foundations. Where this is suspected historical data must be
sought.
I.6 Structural analysis
I.6 STRUCTURAL ANALYSIS
[Need to mention limit states, seviciability, and considering limit states on account of
possible damage to artistic contents. Normal serviceability is not applicable, but
some situations need to be considered (artistic paintings…) deformations in case of
paintings or artistic material]
I.6.1 Purpose of structural analysis
In addition to the purposes identified in 4.6.5 of the core document Structural
analysis of heritage structures may also be required to explain the effect of past
actions on the structure and the effect of previous alterations. This requires the
analysis of past states of the structure and may require qualitative as well as
quantitative methods of analysis.
I.6.2 Models
Models of heritage structures should ideally satisfy the requirements of sections
4.6.5 and 6.1 of the core document regarding the accurate representation of actions,
geometry and material properties, while also taking into account the alterations and
deterioration, including those caused by both natural phenomena and human
interventions.
Models shall be calibrated and validated using the evidence available on the
performance and condition of the building. Historical information, as well as
inspection and monitoring shall be used to validate the predictions of analytical
models.
Note: NDT or MDT as described in I.5.5 may be useful for model validation. For
instance, flat jack tests may be used to verify stress levels predicted by models.
I.6.3 Deterioration models
When deterioration of heritage structures analyzed, complex time dependent
deterioration processes such as long-term related damage and other complex
combination of various actions must be taken into consideration.
I.6.4 Model uncertainties
A significant amount of uncertainty may remain, in spite of the validation effort, due
to various factors such as heterogeneity of materials, construction details, extent of
deterioration, or limitation on the information gathered by direct inspection.
The adoption of partial factors, or the possibility of probabilistic model factors
discussed in section 6.4 of the core document may not be realistically applicable to
heritage structures.
In such cases, additional evidence obtained from complementary activities
(comparative analysis, analysis of historical information) may, through engineering
judgment, reduce the uncertainty.
Engineering judgment may take into consideration the comparative approach and
historical approach.
I.6.5 Comparative approach.
Comparison with a number of similar constructions whose behavior is already
understood can be used to obtain insight on the performance and capacity of a
structure. The reliability of the analysis will increase with the number of structures
observed and the similitude between these and the case into examination. Similitude
should encompass both structure and actions.
Note: Comparison with structures that have already experienced severe effects is
particularly useful in assessing seismic performance.
I.6.6 Historical approach
The history of the structure is often a valuable source of information on its
performance. For this purpose, historical investigation must seek for information on
the significant events experienced (including earthquakes and other extraordinary
natural or anthropogenic actions). Effort must be carried out to understand and
characterize, both the historical causes (or actions) and the building’s responses.
Information on historic repairs or strengthening which might have altered its
performance is also needed.
The use of quantitative methods which simulate historical events should be
considered as a means of model calibration.
I.7 VERIFICATION
Mention the need to verify both ultimate and serviciability limit states
I.7.1 Reliability assessment
Heritage structures do not have a defined working life and therefore the approach
recommended by section 7.2 of the core document is inappropriate. Conservation
should therefore be regarded as a continuous or incremental activity.
I.7.2 Plausibility check
The plausibility check must be carried out as part the activities leading to the
validation of the models as mentioned in section I.6.2 of this annex. Explanation of
discrepancies shall lead to improvement of the models.
I.7.3 Target reliability level
The target reliability level chosen for verification shall balance safety considerations
with the protection of heritage value.
In some cases, the protection of heritage value may require the acceptance of a
reliability level lower than that implicit in accepted design codes. In these cases,
parallel measures should be adopted to limit the consequences of a failure on people
or non-movable artistic contents. For example, appropriate or restricted uses may
limit the number of people at risk.
NOTE: Sections 7.5 of the core document and Annex F are also
heritage structures as they recognize the fundamental differences
design of new buildings and the assessment of existing structures.
Annex F specifically identifies the need to consider the heritage
establishing the target reliability level.
applicable to
between the
Furthermore,
values when
I.8 Assessment based on satisfactory past performance
Past performance based assessment is acceptable in structures with historic
damage and alterations if inspection and / or monitoring shows no continuing
distress.
Consider both ultimate + serviceability limit states.
To be further developed and discussed.
I.9 Interventions
[Basic guidance for interventions is presented herein.
Refer back to the structure of the core document
Text in blue still to be developed and discussed].
I.9.1 Root causes
Intervention should address the root cause of the observed symptoms and be based
on a full understanding of those causes.
I.9.2 Demonstrated to be indispensable
Interventions should not be undertaken without demonstrating that they are
indispensable
I.9.3 Minimal intervention
Intervention should be kept to the minimum level that meets structural requirements
in order to ensure the least harm to heritage values.
I.9.4 Compatible materials
Material used for interventions should be compatible with the original material in
terms of mechanical, chemical and other characteristics, and should maintain these
characteristics in the long term. They should not have harmful effects, such as
causing corrosion or decay.
I.9.5 Incremental (step by step) approach
When more time is required to define optimum conservation strategy, intervention
should adopt an incremental or step-by-step approach beginning with a minimum
level of intervention, with the possible adoption of subsequent supplementary or
corrective measures.
I.9.6 Removable measures
Where possible, any measures adopted should be ‘reversible’ so that they can be
removed and replaced with more suitable measures if new knowledge is acquired.
Where they are not reversible, interventions should not compromise later
interventions.
I.9.7 Proven technologies
Intervention should use technologies that possess a proven performance record over
a long period of time.
I.9.8 Structural concept and construction methods
Each intervention should, as far as possible, respect the original structural concept
and heritage value of the structure and of the historical evidence that it provides.
I.9.9 Integrated plan
Intervention should be the result of an integrated plan to meet architectural,
structural, and functional requirements.
I.9.10 Distinctive historic features
The removal or alteration of any historic material or distinctive architectural features
should be avoided wherever possible.
I.9.11 Repair rather than replacement
Repair is always preferable to replacement.
I.9.12 Dismantling
Dismantling and reassembly should only be undertaken when required by the nature
of the material and structure and/or when conservation by other means is more
damaging.
I.9.13 Controllable methods
Measures that are impossible to control during execution should not be allowed. Any
proposals for intervention should be accompanied by a programme of monitoring
and control, to be carried out, as far as possible, while the work is in progress.
I.9.14 Documentation
All interventions including control and monitoring activities should be documented
and retained as part of the history of the structure.
References
Document