216-SAM : Strategies for the assessment of historic masonry structures with NDT

Technical Committee 216-SAM

General Information

Deputy Chair: Dr. Christiane MAIERHOFER
Activity starting in: 2005
Activity ending in: 2014
Cluster E

Subject matter

The assessment of the structural safety of historic masonry structures, the record of damages, material parameters and enhanced moisture is usually carried out by the designer performing manual optical inspections, laboratory tests on cored samples, drilling tests and mechanical tests on site and load carrying tests. But the internal structures of wall, columns, arches etc are often inhomogeneous and differ significantly at various positions as, the elements being frequently built as multiple leaf masonry.

Without any volume inspection damages can increase and might suddenly cause complex consequences (e. g. spalling, large cracks, collapse), before they can be detected at the surface.

During the last decade, several methods have been developed and improved for monitoring and on-site diagnosis based on non-destructive (NDT) and minor destructive (MDT) approaches (like radar, ultrasonics, sonics, flat-jack, strain gauges rooted on optical fibres etc). The developed technologies collect very precisely data on the present situation of the building structures as well as of possible modifications, if regular inspection and/or monitoring is performed .

Diagnosis based on these data sets allows to get the following information:

Morphological characteristics
- Determination of the thickness of masonry structures
- Localisation of plaster delaminations
- Investigation of multi-leaf masonry, determination of the thickness of the leafs
- Localisation of metal parts, inclusions, voids and other inhomogeneities
- Localisation of internal interfaces/change of materials
- Localisation of hidden crack patterns

Mechanical characteristics of masonry
- Investigation of the state of stress, compressive strength, elastic properties, correlation between mechanical parameters and NDT parameters (e.g. modulus of elasticity from flat-jacks and velocity from sonic tests)

Control of the repair intervention
- Control of the effectiveness of grout injection

- Localisation of moisture, determination of moisture content, causes of damage

Although at present it is possible to solve many problems of historic masonry through application of NDT or MDT procedures, public awareness about these possibilities is very limited.

At time, only in very few cases these methodologies are applied on-site and contribute to the sustainable long-term maintenance of immoveable Cultural Heritage. This is due to the fact that these services are still too expensive and time consuming. Most of the NDT, MDT and monitoring techniques are not tested and calibrated for all materials applied in historic constructions. Further on, the achieved results, the methods themselves and the possibilities for data processing and analysis are still not user friendly and not acceptable for the end-users. Another important topic is the lack of information about these possibilities. Therefore, at time there are only very few and only national located standards and recommendations, which describe the application of NDT and MDT methods in civil engineering.
The availability of information in Europe as well as worldwide must be improved considerably.

The approach of the new Rilem TC will be the concentration of in-depth knowledge gained about this topic by research institutions, service providers and users. Their experiences will be combined, assessed and will be applied to solve specific testing problems of historic masonry structures and materials. This requires multidisciplinary work between engineers, scientists, building researchers, users historians and owners of Cultural Heritage buildings, which at time is only performed sporadic. E. g., this mode of operations has been proven in the frame of the European funded research project Onsiteformasonry, where a high level of assessment has been gained from common on-site measurement campaigns.

Different levels of investigation should generally be taken into account:
- theoretical studies, like the development of numerical models, describing the behaviour of masonry structures
- experimental laboratory research (calibration and validation of testing procedures, determination of material properties)
- archive study, building survey, recording of damages, evaluation of building conditions, monitoring
- on-site investigations at pilot sites
- parallel investigations with different approaches to find synergy effects

The range of application starts with simple masonry structures like single walls or pillars and can be exceeded up to larger building complexes. The latter requires the integration of technologies for building diagnostics and monitoring in the safeguarding and management process of Cultural Heritage buildings.

Terms of reference

The main objectives of the RILEM TC are

1) State-of-the-art-report
Main problems in the structural and material assessment which can be solved with NDT, MDT and monitoring
methods at time will be summarised. Also the state-of-the-art of the methodologies will be given. Results of running and finalised research projects will be considered.

2) Comparison, combination and calibration of NDT, MDT and monitoring methods related to specific problems
Related to well described testing problems, which will also be simulated by masonry test specimens,
measurement and calibration procedures will be developed and described. Quantitative data will be given for accuracy, limits and added value obtained from the combination of methods.

3) Recommendations for the on-site application of combined NDT, MDT and monitoring techniques
These recommendations will be developed for informing and teaching of end-users. The selection, the application as well as the presentation and interpretation of results will be described.

4) Seminars and training courses
For the spread of knowledge, the procedures for the efficient selection of the adequate testing methods and
their combination as well as the correct on-site application will be described and demonstrated in seminars. Training courses at selected test specimen and on-site will be offered for service providers and operators.

These objectives will be reached by collaborative work of international working groups being involved in the development of NDT, MDT and monitoring techniques, in the application of these techniques, in the structural and material assessment of historic masonry structures, in building research as well as in building management.
This work will be planned during regular meetings and will be scheduled for about 5 years.
The members will be recruited from running and secluded European research projects, from former RILEM TCs (TC MDT, …) and from individual connections. Members from research institutes, universities, industry, service providers and Cultural Heritage administration and management will contribute for facing all aspects of application.
Related to the objectives, the work will imply bibliographical research as well as a large amount of communication for the set-up of the state-of-the-art. Specific actions are planned considering round-robin tests at reference test specimen, three to four technical meetings for discussing the results and efficient data recording, analysis and interpretation procedures and a workshop with external contribution. Special equipment will not be required.

Detailed working programme

Task 1: Definition of testing problems and application of NDT, MDT and monitoring techniques
a) Generation of a state-of-the-art-report about the application of NDT, MDT and monitoring techniques for the assessment of masonry structures and material. A bibliographic survey will be obtained and running and finished research projects will be evaluated. The state- of-the-art report will be generated in the first year an will be updated during the duration of the TC. In this work also the results achieved by the previous RILEMTC177MDT will be taken into account as a starting point.
b) Definition of typical testing problems of masonry structures, which could be solved (have a high potential to be solved) with NDT, MDT and monitoring techniques. Selection of those testing problems, which will be handled in the TC. These testing problems will be fixed during the first year of the TC.
c) Specification of calibration and validation procedures, which will be performed in the frame of round robin tests at selected reference test specimen and, if possible, on-site. This work will be performed in the first half of the second year.
d) Specification of useful and efficient combination and procedures for the application of NDT, MDT and monitoring techniques to obtain a maximum of information about the investigated material/structure. This specifications will be set in the second half of the second year.

Task 2: Calibration and validation of NDT, MDT and monitoring techniques
a) Selection of test specimen, design and construction of new ones with help from industry. These specimen will be the basis for the round robin tests and can also be represented by selected elements (e. g. a column) from a real building. These specimens will be selected (and constructed if required) during the second year.
b) Performance of round robin tests related to the specification of calibration and validation processes in Task 1. Several test specimen at different locations will be investigated with complementary NDT and MDT methods related to the validation of these methods, e. g. accuracy, reproducibility, limits etc. These tests will be performed during the third and fourth year.
c) Common data analysis and interpretation and a comparison of results obtained form the round robin tests will be performed during technical meetings (three to four technical meeting will be planned, additional to regular TC meeting). These meeting will occur parallel to the measurement during the third and fourth year.
d) The results of the round robin tests as well as further knowledge and experiences of the partners will be summarised in a calibration and validation report. This report will be finished during the fifth year.

Task 3: Recommendations
The recommendation about the application strategies of single and combined NDT, MDT and monitoring techniques will be developed based on the results of Task 1 and Task 2. These recommendation should describe in detail, how the selection, planning and performing of on-site assessment has to be performed. Limits and accuracies related to different testing problems will be specified.
In the future, these recommendations should be integrated into a building management system, providing regular building maintenance and assessment together with NDT, MDT and monitoring. Especially buildings and constructions of major importance should be under steady surveillance.

Task 4: Spread of knowledge
a) In the third year of the TC, a workshop will be arranged which will address to the needs of users and owners of buildings. Possibilities of NDT, MDT and monitoring applications will be presented and the demands of users and owners will be discussed.
b) Short seminars (1 to 2 days) at universities and further educational institutions are planned to inform on technical achievements, and advantages and limits on the assessment of masonry structures and materials. The
c) For teaching service providers and users, Training Courses will be offered at various sites. The different technologies will be demonstrated and the course participants will be trained on the application of selected techniques at test specimens.

Technical environment

This TC intends to continue and emphasise the TC Masonry Durability and On-site Testing recently closed and chaired by Luigia Binda. Additionally, it supplement the new TC INR: Interpretation of NDT results and assessment of RC structures chaired by Denis Breysse, by the application of similar, modified and complementary NDT, MDT and monitoring techniques to masonry, and especially inhomogeneous historic masonry. These mentioned TCs are inside the same cluster E.: Special Construction Materials and Components (Convener: Luigia Binda).
The idea of implementing a new TC on the strategies of the investigation of masonry structures and materials was born during the work in the recently finished European Research and Development Project ONSITEFORMASONY (On-site investigation techniques for the structural evaluation of historic masonry buildings, in which several strategies have been developed and tested including up to ten complex case studies at historic building sites. Also guidelines about 10 different NDT and MDT methods (e. g. radar, ultrasonics, impact-echo, microseismics, geoelectric, sonic pulse velocity ….) have been generated as well as recommendations about single steps on how to proceed on-site. These deliverables will be a direct input into the new TC and will be further discussed and developed until these can be published as a RILEM Recommendation.

Expected achievements

The following results are anticipated:
- State-of-the-art report dedicated on testing problems of masonry structures and materials, which can be solved with modern single or combined NDT, MDT and monitoring methods;
- Validation reports as results of round robin tests concerning the combined application of NDT, MDT and monitoring techniques
- RILEM Guideline recommendations for strategies on how NDT, MDT and monitoring techniques will be selected and applied for maintenance and assessment of masonry and especially historic masonry structures
- Workshop for spread of knowledge but also for receiving contributions from users and owners of masonry structures
- Dissemination of knowledge, via seminars (1-2 days) and training courses.

Group of users

Experts in NDT, MDT, monitoring practice and structural assessment, testing laboratories, managers of Cultural Heritage, construction companies, owner and user of Cultural Heritage buildings, engineers, service providers.

Specific use of the results

The quality of life in any urban environment is strongly affected by the safety and the functionality of its infrastructure. The knowledge about the state of deterioration of any building or structure not only supports the management of the Cultural Heritage but also reduces the effect of reconstruction on the environment to a minimum.
Cultural Heritage Buildings which are open for public can only be used with restrictions during repairing interventions. Efficient monitoring and diagnosis strategies enables advanced planning of efficient intervention and repair and thus reduces costs and trouble.