CIB W 80 / RILEM 175 SLM Service Life Methodologies

CIB W080 / RILEM 175 - SLM: Service Life Methodologies Factor Methods: State of the Art 41

7. APPLICATION OF FACTOR METHODS

To date, the use of the ISO factor method for prediction of service life of building materials and components has been very limited. Most of the published cases are described in research papers or reports where examples of the use of the applications are provided. Widespread practical application of the method has been limited due to the lack of knowledge of the method among practitioners (i.e. architects, consultants or building owners and managers) or due to the need for useful values of the various factors used in the method. Some examples of application of factor methods are presented here.

There is also an extensive research and development going on regarding design for durability of buildings, sustainable construction and development of sustainable buildings. Several papers have been published during the last years describing different challenges in this area, and they show the necessity of implementing service life of materials and components into the overall methods. Several examples are Wyatt [1998], Lucchini and Wyatt [1999] and Wyatt and Lucchini [1999]. In the later paper, the authors state in the conclusions that

“Whilst there is a complex but important relationship between the building performance the designer may have pre-defined and the level of reliability achieved one cannot guarantee a building’s life future. One can however, be prudent and accept the place of a service life practice and life care to at least seek a building product life. So adopting the service life approach that reflects materials, components and systems service loss and durability would help to improve cost certainty of building ownership and begin to address the challenges posed in striving for sustainable cities and buildings. For it has become clear that designing for durability has an immensely important contribution to make to both the work of CIB W094 and CIB W080 as well as ISO task group responsible for developing the Design Life of Building’s Standard. It is now believed that service life and its practice will come to form and be seen as the corner stone of building asset management’s life care.”

Strand and Hovde [1999] have carried out at study of how service life data of exterior surface materials (wood and brick) influence the LCA of the materials. The authors wanted to emphasize the need for service life data in LCA, how the data occur and how they might influence results. Building materials and components are used for a longer period of time than most other products. LCA of a building product therefore necessitates gathering of data that will be valid for a longer period of time. The building, components and materials also have different life spans, as illustrated in chapter 3 in this report.

The authors apply the factor method as described in ISO 15686 Part 1 [ISO 2000], but mainly highlight the use of factors E (outdoor environment) and G (maintenance level). LCA is carried out for two climates (industrial and rural inland) and for facades facing north or south.

Different intervals for painting, cleaning and replacement are also used. In the conclusions it is stated that:

“Service life prediction methods (SLP) and life cycle analysis (LCA) deal with some common problems. Most of the data in SLP are also needed in LCA.

Information regarding the variation associated with the ESLC is crucial information in LCA. It is extremely important that the basis of both the stated SL and the performed LCA is clear, like e.g. maintenance type and interval. In this study it looks as if the maintenance is in fact the most important information. - - - - - It is a problem that LCA techniques themselves give rise to large variation e.g. due to for example evaluation methods. LCA and SLP can be used together to optimise the service life and the resulting environmental load from different materials. Further development is needed for both systems.”

Hovde [1999] has presented the need for service life prediction of passive fire protection systems. He refers to the factor method as described in ISO 15686 Part 1 [ISO 2000]. Passive fire protection has got an increasing interest and importance in relation to the introduction of performance based building and fire codes. This makes it important to predict the durability and service life of the fire protection, and this will be a specific area for application of service life prediction methods.

A joint committee between RILEM and CIB (RILEM TC 172-EDM/CIB TG 22 “Environmental design methods in materials and structural engineering”) has been working on development of methods for environmental design of materials and structures. A progress report of the work has been presented by Sarja et al. [1999]. In the presentation of the progress report it is explained that the incorporation of an environmental viewpoint into the design of materials and structures, it is necessary to reconsider the entire context of the design process in order to integrate environmental aspects into a set of other design aspects. Further, this kind of process is called integrated life cycle design, and it is said that the aim of the process consists of assimilating, in a practical manner, the multiple requirements of functionality, economy, performance, resistance, aesthetics and ecology all into the technical specifications and detailed designs of materials and structures.

The joint RILEM/CIB committee is producing a manual that will provide methods and methodologies for structural design in order to meet the requirements of sustainable development over the entire service life of the structures. The scope of the manual includes both bearing and non-bearing structures of buildings, bridges, towers, dams and other structural facilities. The main phases of the life cycle design procedure are said to be:

Analysis of the actual requirements Interpretation of the requirements into technical performance specifications for structures Creation of alternative structural solutions Life cycle assessment and preliminary optimisation of the alternatives Selection of the optimal solution between the alternatives Detailed design of the selected structural system

In the progress report a summary of the integrated life cycle design phases and the specific design methods described in the manual are presented in a table as shown in Table A7.1.

Table A7.1: Integrated life cycle design process and central methods for application. (From [Sarja et al. 1999]).

Design phase Life cycle design methods 1. Investment planning Multiple criteria analysis, optimisation and decision making. Life cycle (financial and natural) economy. 2. Analysis of client’s and user’s needs Modular design methodology. Quality Function Deployment Method (QFD). 3. Functional specifications of the buildings Modular design methodology. Quality Function Deployment Method (QFD). 4. Technical performance specifications Modular design methodology. Quality Function Deployment Method (QFD). 5. Creation and sketching of alternative structural Modular design methodology. solutions 6. Modular life cycle planning and service life Modular design methodology. optimisation of each alternative Modular service life planning. Life cycle (financial and natural) economy calculations. 7. Multiple criteria ranking and selection between Modular design methodology. alternative solutions and products Quality Function Deployment Method (QFD). Multiple criteria analysis, optimisation and decision making 8. Detailed design of the selected solution Design for future changes. Design for durability. Design for health. Design for safety. Design for hygrothermal performance. User’s manual. Design for re-use and recycling

In the description of the design process in the progress report, there is also a presentation of alternative methods that can be applied for durability design. These are:

Durability design with structural detailing rules Design of the environmental conditions of the structures for durability Protection of the materials and structures against deterioration Lifetime safety factor method Reference factor method

The reference factor method is the same as the ISO factor method. In the conclusions of the progress report, it is stated that

“Concerning materials and structures, new basic knowledge will be needed especially regarding environmental impacts, hygrothermal behaviour, durability and service life of materials and structures in varying environments. Structural design methods that are capable of life cycle design, multiple analysis decision-making and optimisation will have to be further developed. Recycling design and technology demand further research in design systems, recycling materials and structural engineering. The knowledge obtained will have to be put into practice through standards and practical guides.”

As presented in chapter 6, Rudbeck [1999] has described alternative service life prediction methods in his Ph.D. thesis. The thesis also comprises a description of integrating durability in future building design, and this gives a demand for application of the service life prediction methods. The author discusses the following two methods for integrated life cycle design which were under development in 1999:

Integral Building Envelope Performance Assessment (IBEPA), developed by the International Energy Agency (IEA) Annex 32. Building Envelope Life Cycle Asset Management (BELCAM), developed by the National Research Council, Canada.

Rudbeck also shows how the durability aspect can be integrated into the design process of two flat roof constructions.

Hed has carried out a study of service life planning for a multi family building, which was built in Gävle, Sweden, in 1999. The results have been presented in different publications [Hed 1998, 1999, 2000]. ISO 15686 Part 1 [ISO 2000] was used as a basis for the study, and the final results are given in [Hed 2000. The service life planning was integrated into the design of the building and followed the building process from the design phase to the beginning of the construction of the building. The report comprises three separate papers, and in one of the papers is given a presentation and discussion of the application of the factor method as presented in ISO 15686 Part 1[ISO 2000]. The author states that:

“A problem is that there are still few tests performed of material and component service life, comprising all the effects required of the building component when it is in operation in the building, i.e. following the service life prediction methodology (ISO 1999). - - - - The accuracy of the estimated service life is of course suffering from this fact, so one has to discuss if it is worth the effort of doing the estimations or not. If the goal is to find a precise value it is clear that the goal is not reached. But if the goal is to improve the general situation in service life planning the answer is yes.

The factor method in ISO/DIS 15686-1 is meant to be a tool to improve the estimation of the service life. It was found in the project that this method did not improve service life estimations. This opinion is summarised in the following. Uncertainty of RSLC and values of Factors. The factorial formula (1) comprises in the right side of a reference value (RSLC) and the adjusting Factors, A to G. If the reference value cannot be determined accurately it is not appropriate to adjust these values with a set of uncertain Factors. Uncertainty of the effect by combination of Factors. The method does not support the thoughts that one needs knowledge of cause and effect to estimate the service life. The estimation will be based on uncontrollable occurrences, which can act independently of each other.”

In Finland, a project has been carried out to develop an information management system concerning service life of building products. The purpose of the system is to serve for designers, contractors and organizations responsible for the care and maintenance of buildings. The subject is dealt with from the point of view of product manufacturers paying

NTNU – Norwegian University of Science and Technology Department of Civil and Transport Engineering March 2004 CIB W080 / RILEM 175 - SLM: Service Life Methodologies Factor Methods: State of the Art 45 attention on the content, formulation and delivery of the service life information offered by the manufacturers.

The project results are presented in a report [Häkkinen et al. 2001] in which a comprehensive information system of service life behaviour of building products is introduced. The idea is that this information is given by the manufacturers and it is needed in building design, building and assembling and within the use, care and maintenance of buildings. However, the report does not deal with the service life prediction principles and methods.

An important part of the project was aimed at developing service life prediction methods for facades and roof coverings. It covered facades made of concrete, masonry, timber and steel plate and roof coverings made of bitumen membrane, steel plate and concrete tiles. The factor method described in ISO 15686 Part 1 [ISO 2000] was used. Application of the factor method to estimate the service life of concrete in facades was presented by Vesikari [2000]. As a new method of producing the factor values a computer simulation was applied. By this simulation the environmental stresses, temperature and moisture content in a structural cross-section and degradation of materials were described. This made it relatively easy to determine out the essential properties and structural factors and their effects on service life.

The study showed that the use of only a single of a factor was not sufficient to cover all the material effects or the environmental effects. Two partial factors were therefore established for material parameters, i.e. A1 (dependent on air porosity) and A2 (dependent on water- cement ratio). Similarly, two partial factors were established for environmental parameters, i.e. E1 (dependent on the direction) and E2 (dependent on the geographical location). These practical factors are multiplied to obtain the total effect due to material and environmental parameters. The application of the factor method was illustrated for a multi-storey dwelling facade in southern Finland having a design life of 50 years. The factor method was found to be a suitable prediction method for practical service life design.

In a Nordic Research Training Course funded by the Nordic Academy for Advanced Study (NorFA) that was carried out during 2001 regarding service life of buildings and building products, some of the participants gained interest in the factor method as a simple tool for service life prediction. The title of the course was "Service life of buildings - from theory to practice", and the research students carried out individual project tasks related to the main topic of the course. The project reports are at a preliminary stage, and the intention is that they will form the basis for papers to be published in journals, conferences, etc. In the reports are discussed the possibilities to apply the factor method for service life prediction of different building products, components, structures and installations, such as surface products, exterior wood products, external renderings, sulphur concrete, a solar collector and a fibre reinforced polyester pedestrian bridge deck. This clearly underlines the fact that there is a need for practical and simple service life prediction tools, and that the factor method may be evaluated for practical use on a wide variety of products in the future.

1. One of the reports at the Research Training Course was presented by Marteinsson [2001] in which results of an extensive condition survey of wooden windows in Iceland were presented. The factor method was applied, as described in ISO 15686 Part 1, to estimate the service life of the window components. Results from the condition assessment and the house owners' answers to a questionnaire are combined, and a Weibull probability distribution is then used to evaluate the estimated service life of the windows. In the conclusions of the study, Marteinsson states that NTNU – Norwegian University of Science and Technology Department of Civil and Transport Engineering March 2004 CIB W080 / RILEM 175 - SLM: Service Life Methodologies Factor Methods: State of the Art 46

"The results show that for some materials at least, the synergy between agents that affect the durability of materials is so great that it is difficult to give each and one of the factors in the standard a value even based on results gained by systematic study of the object in use. The results show furthermore that for materials where the durability gains very much from good care and maintenance, then it is a good way to decide on the probability distribution of the service life from information from the user. - - - - - The realistic span in multiplication factor is thus considerable and the user of the methodology will not be able to choose appropriate values for the factors without extensive knowledge about materials and local building practice. In any case he needs information about the main factors for the component and material considered, (and) what span is normal for the factors. The methodology is far from easy to use correctly and at the risk of results being evaluated as being more precise than is reasonable at the present time. - - - - - Handbook of worked examples would be of great value for the designer, without this freedom for each user to define the factors is too great."

NTNU – Norwegian University of Science and Technology Department of Civil and Transport Engineering March 2004