© ISO 2012 Buildings and constructed assets — Service life planning — Part 2 Service life prediction procedures Bâtiments et biens immobiliers construits — Conception prenant en compte la durée de vie[.]
Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6707-1, ISO 15686-1 and the following apply.
3.1.1 accelerated short-term exposure short-term exposure (3.1.19) in which the agent intensity (3.1.5) is raised above the levels expected in service
3.1.2 ageing degradation due to long-term influence of agents (3.1.4) related to use
3.1.4 agent whatever acts on a building or its parts to adversely affect its performance
EXAMPLE Person, water, load, heat.
3.1.5 agent intensity measure of the extent to or level at which an agent (3.1.4) is present
In ISO 15686, "agent intensity" figuratively encompasses various measurable quantities, including UV radiation, rain intensity, relative humidity, SO2 concentration, freeze-thaw cycles, and mechanical pressure.
3.1.6 component product manufactured as a distinct unit to serve a specific function or functions
3.1.7 degradation process whereby an action on an item causes a deterioration of one or more properties
NOTE Properties affected can be, for example, physical, mechanical or electrical
3.1.8 degradation indicator deficiency which shows when a performance characteristic (3.1.14) fails to conform to a requirement
EXAMPLE When gloss is a performance characteristic, gloss loss is the corresponding degradation indicator When mass (or thickness) is a performance characteristic, mass loss is the corresponding degradation indicator.
3.1.9 dose-response function function that relates the dose(s) of a degradation (3.1.7) agent (3.1.4) to a degradation indicator (3.1.8)
3.1.10 inspection of buildings performance evaluation or assessment of residual service life of building parts in existing buildings
3.1.11 in-use condition any circumstance that can impact the performance of a building or other constructed asset, or a part thereof under normal use
3.1.12 long-term exposure ageing exposure (3.1.3) under in-use conditions (3.1.11) and with a duration of the same order as the service life anticipated
3.1.13 mechanism process causing change over time in the composition or microstructure of a component or material that can cause degradation
3.1.14 performance characteristic physical quantity that is a measure of a critical property
A performance characteristic, such as reflectance, can align with a critical property Conversely, when strength is the critical property, attributes like thickness or mass may serve as performance characteristics in specific situations.
3.1.15 performance requirement performance criterion minimum acceptable level of a critical property
3.1.16 predicted service life service life predicted from recorded performance over time
EXAMPLE As found in service life models or ageing tests.
3.1.17 predicted service life distribution probability distribution function of the predicted service life (3.1.16)
The SLPgeneric methodology enables the prediction of the service life distribution of a building or its components, tailored to specific performance requirements and suitable for various environments.
3.1.19 short-term exposure ageing exposure (3.1.3) with a duration considerably shorter than the service life anticipated
A predictive service life test refers to a specialized short-term exposure program combined with a performance evaluation procedure, aimed at assessing the longevity and reliability of materials or products.
In an established set of critical properties for a building or its components, the critical property that first fails to meet the required performance standards when exposed to a specific service environment is of utmost importance.
The time acceleration factor is a numerical function utilized to convert the outcomes of aging tests on components, which are conducted through accelerated short-term exposure, into an estimated service life or a predicted distribution of service life.
Abbreviated terms
ESLC estimated service life of a component
PSLDC predicted service life distribution of a component
PSLC predicted service life of a component
RSLC reference service life of a component
Brief description of service life prediction (SLP)
The proposed methodology is designed to be versatile, enabling service life prediction (SLP) for various building components based on specific performance requirements It is applicable to a range of in-service environments, ensuring accurate assessments for diverse conditions.
In practice, a Service Level Profile (SLP) typically focuses on a limited number of standard service environments or a specific reference environment, along with an analysis of how variations in degradation agents affect intensity sensitivity.
The term “prediction” of an SLP study refers to one of four ways, or any combination of these, to assess the service life, as follows:
— speeding-up of the time dimension (at accelerated short-term exposures);
— interpolation/extrapolation using data of similar components;
— interpolation/extrapolation using data from similar service environments;
— extrapolation in the time dimension (at short-term in-use exposures).
The systematic methodology for the SLP of building components involves identifying necessary information, selecting or developing test procedures, conducting tests, interpreting data, and reporting results Key steps in the SLP process are illustrated in Figure 1, highlighting an iterative research approach that enhances predictions as knowledge expands Not all steps are mandatory; for example, pre-testing can often be omitted or shortened if prior knowledge exists While the service life of a component is typically not represented as a single value (PSLC), it is instead characterized by a predicted service life distribution (PSLDC), defined by parameters such as expectation value and standard deviation In cases of expensive testing, the focus may solely be on determining the PSLC.
The selection of the single-value reference service life of a component (RSLC) is influenced by the desired safety margin For replaceable, non-structural components, the expected value (mean) of the distribution, known as the PSLC, is typically used as the RSLC However, maintenance schedules and interactions with other components may necessitate a more cautious approach In contrast, for non-replaceable and structural components requiring a safety margin, a significantly more conservative RSLC is essential, often guided by relevant standards or codes.
Connection to ISO 15686-1 and ISO 15686-8
This section of ISO 15686, specifically ISO 15686-1 and ISO 15686-8, outlines a tool for accurately determining the reference service life of a component (RSLC) or directly forecasting its service life The RSLC is essential for assessing the estimated service life of a component (ESLC) for a specific design object using the factor method detailed in ISO 15686-8 The RSLC is derived from the predicted service life data collection (PSLDC) established in this part of ISO 15686 The conditions under which the PSLDC is established serve as the reference condition, which is then compared to the actual conditions of the design object to estimate the necessary factors for the factor method.
User needs, building context, type and range of agents, performance requirements, materials characterization
Identification of degradation agents, mechanisms and effects, choice of performance characteristics and evaluation techniques, feedback from other studies
Checking mechanisms and loads, and verifying choice of characteristics and techniques by short-term exposure
In-use-condition (not accelerated) exposure
Process performance-over-time or dose-response functions to establish prediction models Service life prediction
Dose-environmental classes Response classe s (degradation indicator )
Figure 1 — Systematic methodology for SLP of building components
To determine the RSLC for a specific design object, the SLP conducted under varying conditions is analyzed, and the PSLDC that deviates the least from the specific condition is selected Additionally, an SLP performed under diverse conditions allows for the estimation of factors in the factor method, particularly addressing the differences between the specific and reference outdoor environments This estimation can be achieved through interpolation and extrapolation techniques.
Range of SLP and problem description
Initially, the problem to be solved shall be defined and the range of the study established, including identification or specification of essential data.
NOTE These issues can vary from case to case depending on the aim and ambition of the SLP and on the level of existing knowledge of the component.
The article discusses two extreme ranges of study regarding component testing The first, a specific study, focuses on a particular application within a defined service environment and performance requirements, aiming to establish the Performance Sensitivity Level Determination Criteria (PSLDC) and assess its sensitivity to moderate variations In contrast, the general study encompasses a broader application of the component, addressing a wider range of service environments and loosely defined performance requirements, with the goal of establishing performance-over-time functions for selected performance characteristics across various applications.
5.1.2.1 Specification of the service life environment
When predicting the service life of products or components, it is essential to identify specific or generic in-use conditions for the study This includes detailing the component's intended use and its design implications, as well as describing the environment where the building will be located, which encompasses both static and dynamic mechanical stresses Additionally, the analysis should address occupancy effects, such as water vapor, heat, or abrasion, and consider the operational principles of the building, like high or low thermal inertia, when relevant.
5.1.2.2 Quantification of the set of performance requirements
The set of performance characteristics shall be identified and the corresponding requirements quantified in accordance with critical properties specified.
NOTE This can take the form, for example, of a failure mode and effect analysis (FMEA) See 5.6.
The set of performance requirements shall conform to the information obtained in accordance with 5.1.2.1.
5.1.3.1 Specification of ranges of service life environments
All types of environments where the component is intended to be used, or being within the range of the study, shall be described, including static and dynamic mechanical stress.
The various types of environments may be grouped into a discrete number of classes, each class being representative for certain ranges of agent intensities.
It is essential to consider how different usages and positions of the component can significantly influence in-use conditions and the potential synergistic effects of degradation agents Refer to section 5.2.3 for more details.
The degradation of materials is significantly influenced by the micro-environment, which includes the environmental conditions near a component's surface, such as pollutant concentration and driving rain, as well as the internal conditions within the component, like mechanical stress.
5.1.3.2 Quantification of the set of performance requirements
To begin, it is essential to identify a set of performance characteristics based on the specified critical properties Subsequently, to narrow the performance range for the service life analysis, the minimum acceptable performance requirements for the component must be defined.
NOTE The set of performance requirements can include specifications on, for example, strength, optical transmission, acoustical insulation and aesthetic qualities.
The performance requirements shall be in accordance with 5.1.3.1.
The component to be evaluated shall be characterized thoroughly in terms of structure, physical properties and chemical composition.
A critical review is essential for assessing the adherence of an SLP study to the methodological and reporting standards outlined in ISO 15686 It is important to plan and confirm the approach, including the execution and responsible parties, during the study's definition phase.
A critical review of an SLP shall be conducted where the results are to be disclosed to the public.
For other applications, for example for company-internal product development, critical review may be omitted.The process of critical reviewing is described in Clause 6.
Preparation
Once the study's scope is established, it is essential to identify and propose degradation agents, potential degradation mechanisms, and methods for accelerating or inducing degradation within aging exposure programs.
5.2.2 Identification of degradation agents and their intensities
The type and intensity distribution of the expected degradation agents, based on the knowledge as compiled in accordance with 5.1.2.1 or 5.1.3.1, shall be identified.
Quantifying the intensity of biological agents and those from occupancy can be challenging; however, professional judgment typically allows for the establishment of upper limits within the normal range.
One or several reference environments shall be considered, the number depending on the range of the study
A list of relevant degradation agents is presented in Table 1.
Agents are categorized based on their origin, with external agents typically stemming from the atmosphere or ground, while internal agents are linked to occupancy, design, and installations Notably, ISO 6241 does not explicitly mention that external agents can arise from design-related issues, such as incompatible neighboring components Additionally, the impact of atmospheric agents on internal degradation must be acknowledged.
Table 1 — Degradation agents affecting the service life of building components a
Forces and imposed or restrained deformations Kinetic energy
Vibrations and noises Electromagnetic agents Radiation
Electricity Magnetism Thermal agents Extreme levels or fast alterations of temperature
Chemical agents Water and solvents
Oxidizing agents Reducing agents Acids
Bases Salts Chemically neutral Biological agents Vegetable and microbial
Animal a Condensed from ISO 6241:1984, Table 4.
5.2.3 Agents related to occupancy and significance of installation and maintenance practices
While occupancy-related agents are typically excluded from aging exposure programs, their potential impact on the service life of building components necessitates evaluation when considered critical This assessment can be conducted through building inspections, in-use exposure, or a combination of both methods, as outlined in sections 5.4.3.3 and 5.4.3.5.
NOTE However, abuse is usually considered beyond the scope of these test methods.
Normally, installation and possible maintenance undertaken for samples of the ageing exposure programme should follow practices recommended by the manufacturer or good practice if such are not given.
Evaluation of effects imposed by variations in installation and maintenance procedures may be included as part of the study.
It is of crucial importance not to exaggerate any maintenance procedure, which may lead to erroneous PSLC compared to real use.
5.2.4 Identification of possible degradation mechanisms
Identifying all potential mechanisms through which the recognized degradation agents are known or thought to alter the properties of the component is essential for the preparation process.
Mechanisms can be identified at different levels, depending on the available knowledge of the component's chemistry When the chemistry is well-documented, specific mechanisms can be linked to chemical reactions like hydrolysis and photo-oxidation Conversely, if the chemical properties are less understood, mechanisms may be described more generally, including thermal decomposition, volatilization, diffusion, corrosion, fatigue, wear, shrinking/swelling, and rotting.
5.2.5 Identification of possible effects of degradation
Possible effects of degradation on performance characteristics of the component shall be identified on the basis of data obtained in accordance with 5.2.2 and 5.2.4.
5.2.6 Choice of performance characteristics and performance evaluation techniques
The essential properties related to the performance requirements outlined in sections 5.1.2.2 or 5.1.3.2 should be understood in relation to the performance characteristics that exhibit degradation as specified in section 5.2.5.
To ensure compliance with ISO 15686, suitable measurement and inspection techniques must be selected for each performance characteristic Quantitative data is essential for conducting a Service Life Prediction (SLP), and initial values for the chosen performance characteristics should be established prior to the commencement of the aging exposure program.
Information from other studies, concluded or running, should always be sought.
Useful information can be derived from a combination of general knowledge about similar components, measurement techniques, and exposure program design, as well as detailed data on the performance-over-time functions of closely related cases In favorable conditions, this approach can significantly decrease the required test volume and range, as well as shorten the testing period.
The information obtained in accordance with 5.2.2 to 5.2.7 will help in establishing procedures for inducing the identified mechanisms of degradation using the degradation agents identified.
When utilizing accelerated short-term exposure, it is crucial to prevent extreme intensity levels of degradation agents from causing degradation mechanisms that would not typically occur during normal service conditions.
NOTE The postulations that are made in this step lay the groundwork for selecting or designing preliminary exposure programmes.
Pre-testing
Pre-testing, as outlined in section 5.2.8, is essential for evaluating the selected performance characteristics of a component This evaluation should occur both before and after exposure to degradation agents that the component may encounter during service, including all significant suspected agents When conducted properly, this process yields valuable results.
— establish the primary degradation agents and their order of importance,
— support or rule out the previously identified mechanisms by which property changes occur,
— establish the agent intensity levels necessary to induce property changes and demonstrate how rapid changes in the selected performance characteristics can be induced by exposure to extreme intensities,
Understanding the primary degradation agents that lead to property changes is essential This knowledge can help identify additional or alternative property changes that may be significant and beneficial as performance characteristics.
5.3.2 Intensities of degradation agents employed in pre-tests
Intensities shall be levelled in relation to the quantitative in-use distributions or ranges identified in accordance with 5.2.2.
Weather and climatological data for the most extreme climates where the component will be utilized can guide the selection of agent intensities in pre-tests.
Ageing exposure programmes
The full exposure program will be meticulously crafted to deliver essential data aligned with the study's scope and objectives, taking into account the information and data gathered through the aforementioned procedures.
Ageing exposure, as defined in section 3.1.3, encompasses a wide range of scenarios where samples are subjected to degradation agents, as outlined in Table 1 This includes instances where mechanical loads are applied, resulting in exposure to mechanical agents.
5.4.2 Design and performance of exposure programmes
Due to the stochastic nature of component properties and environmental characteristics, which are represented by statistical distributions, it is essential for the exposure program to include a variety of specimens or test objects This approach allows for a comprehensive statistical analysis of the test data, enhancing the reliability of the results.
When dealing with experimental building and in-use exposure, as outlined in sections 5.4.3.4 and 5.4.3.5, it can be challenging to follow certain procedures, especially when tests are expensive In these situations, it is advisable to estimate distribution widths or ranges using alternative sources of information whenever possible.
For all exposure programmes, the conditions shall be recorded continuously or at sufficiently short intervals, for the following reasons (partially depending on the type of exposure programme):
— to enable establishment of performance-over-time or dose-response functions, see A.2.4.2 and A.2.4.3;
— to provide a relationship between different exposure periods and sites, and especially to compare results with data from the field, and exposure programmes with uncontrolled conditions; see 5.4.3.2;
— to check that the actual environmental conditions are representative of the environmental reference conditions (for exposure programmes with uncontrolled conditions);
— to verify that the intended degradation agent intensities are achieved (for exposure programmes with controlled conditions).
NOTE 1 The sources of recording can vary from official environmental databases to detailed measurements of degradation agent intensities at or in the vicinity of the test samples.
In the realm of environmental characterization, significant advancements are being made, particularly in the development of standardized measurement techniques and enhanced dispersion models These improvements are integrated into Geographic Information Systems (GIS) software, which aids in the effective mapping of environmental data across various scales, from meso/local to micro levels.
The exposure program will either involve the real-time use of a complete system to gather performance feedback on its components over time or focus on the exposure of specific components It is essential that the program is structured to consider all significant factors.
Even for a specific study, the exposure should preferably take place in more than one type of service environment.
The different ways of generating data from long-term exposures are described in the following four categories:
— exposure in experimental buildings, see 5.4.3.4;
Standardized ways of performing atmospheric field exposures have been in operation for some time, see A.2.3.1.1.
It is essential to note that
The results of field exposure are closely tied to the specific site of exposure To effectively transform this data for application to a different geographic location, it is essential to understand performance over time, dose-response relationships, and the environmental characteristics of both locations.
— care should be taken when drawing conclusions from one exposure period to another, especially if the time of exposure is short,
Exposing component samples to the environment can be considered an accelerated exposure method, such as using exposure racks set at a 45° angle and oriented towards the sun The level of acceleration varies depending on the type of component being tested.
Monitoring environmental conditions during field exposure is essential to assess degradations and performance losses compared to laboratory results for accurate re-scaling Utilizing weather station data located near the field exposure site can enhance this evaluation.
The service life of building components can be assessed through thorough inspections of various buildings It is essential to include a sufficient number of buildings in the study, utilizing statistical sampling methods to ensure accurate results.
Durability evaluations of building components may be carried out by exposing the component in dedicated experimental test buildings.
Similar difficulties may apply as outlined under field exposure, see 5.4.3.2.
In-use exposure is an intentional use of a component in a full-scale building or structure under normal use, in order to evaluate the service life of the component.
Short-term exposure programs should be designed to be less intense than pre-tests to minimize the risk of degradation from mechanisms not typically experienced in service It is essential to measure the key properties that indicate degradation both before and after the aging process Additionally, the potential for synergistic effects among degradation agents must be considered.
It is essential to verify that the degradation mechanisms and corresponding reaction rates observed during accelerated short-term exposures align closely with those experienced in actual service conditions.
5.4.4.2 Short-term in-use exposures
Short-term exposures often involve accelerated aging, although this is not always the case When early-stage property changes indicating degradation can be identified—typically through advanced surface analysis techniques—an exposure setup that mimics in-use conditions, similar to those used for long-term exposures, can be implemented.
The performance evaluation during exposure will focus on selected characteristics using specific measurement and inspection techniques This assessment will occur at narrow intervals aligned with the study's objectives Additionally, the exposure program is designed to identify key degradation mechanisms quickly, ensuring that any changes over time are monitored effectively.
The exposure must be conducted in a manner that, except for brief in-use instances, ensures that at least one performance characteristic—specifically the one related to the terminal critical property—declines to a level that meets or falls below the required performance standard for a statistically significant number of samples by the end of the exposure period.
5.4.5.2 Comparison of types of degradation
The types and range of degradation obtained from accelerated short-term exposures shall be checked against those from in-use conditions.
If the categorization of these degradations demonstrates a good agreement, a time acceleration factor shall be evaluated to calculate the service life using the results of short-term exposure tests.
Analysis and interpretation
Degradation models based on the PSLDC (or PSLC) are developed through a systematic analysis of performance evaluations from various ageing exposure programs, which may include long-term and short-term exposures Initially, performance-over-time or dose-response functions are established from the evaluation data If the existing exposure conditions do not encompass all scenarios for component assessment, additional functions can be synthesized or extrapolated to create a performance function for hypothetical conditions Ultimately, the PSLDC (or PSLC) is derived from these functions by incorporating the required performance metrics of the tested component, defined through specific performance characteristics or degradation indicators The PSLDC is specifically determined by the performance-over-time or dose-response function of the critical property identified as the terminal critical property, with dose variables analyzed in terms of time and intensity to explicitly define service life.
Extra caution should be taken with all extrapolations (see A.2.4.1); support from mechanism-based models is strongly recommended.
In addition to interpolation/extrapolation in exposure conditions, interpolation/extrapolation in time and material properties (for similar components) may be utilized.
The study focuses on the PSLDC (or PSLC) under defined conditions, examining its sensitivity to moderate changes in the service environment and performance requirements, which are generally represented as partial derivatives.
A complementary approach: the failure mode and effect analysis (FMEA)
Failure mode and effect analysis (FMEA) is a systematic approach for identifying potential degradation issues of building components within specific environments This method allows for the prediction of a product's behavior based on its structural characteristics.
It is based on a two-level systemic view of the product:
The article provides a structural overview of the product, detailing each sub-component as outlined in section 5.1.4 It explains how these components are physically interconnected and describes the environment in which the product will be utilized.
NOTE 1 A list of degradation agents such as provided by ISO 6241:1984 can be used to describe the environment.
— a functional view, obtained though functional analysis, where the different functions of each sub-component are defined in accordance with the end user’s needs.
The procedure follows an iterative approach to identify potential failure modes of each sub-component, along with their causes and effects Each identified effect may lead to additional failures, prompting the determination of a second set of failure modes, and this process continues until all failure scenarios are fully outlined The outcome of the failure modes and effects analysis is typically presented as a comprehensive list of failure scenarios, often summarized in a table format.
FMEA primarily relies on the performance and properties of sub-component materials rather than the final product This makes it especially valuable for evaluating innovative products with uncertain in-use behavior.
5.6.3 Use of FMEA results in service life prediction procedures
Information obtained through FMEA might be useful at different stages of the service life prediction procedure.Possible uses of FMEA in SLP procedure are for help in
NOTE Structural and functional analysis as mentioned above bring a comprehensive answer to 5.1.4.
General description of critical review
The critical review process shall ensure that
— the methods used to perform the SLP are consistent with this part of ISO 15686,
— the methods used to perform the SLP are scientifically and technically valid,
— any external data used are appropriate and reasonable,
— the interpretations reflect the limitations identified and the goal of the study, and
— the reporting is transparent and consistent, and suitable to inform the intended audience (e.g the public or the client experts).
Needs and requirements for critical review
Utilizing SLP results for building planning presents unique challenges, as it impacts stakeholders outside the SLP study, necessitating a thorough critical review In certain cases, conflicting recommendations may arise from external entities, such as certification and technical approval organizations These mandatory measures can heighten the requirements but should not undermine the critical review process outlined in ISO 15686.
Process of critical review
Defining the scope of a critical review is essential, as it outlines the purpose of the review, the topics to be addressed, the depth of analysis required, and the stakeholders involved in the process.
A critical review of the study should be conducted by an independent expert, preferably external, who possesses the necessary scientific and technical expertise in accordance with ISO 15686 The review statement can be prepared by the individual conducting the SLP study and subsequently reviewed by the expert, or it can be entirely authored by the expert It is essential to include the review statement, the expert's comments, and any responses to the recommendations in the final report.
The study's results will be shared with all relevant stakeholders, ensuring transparency in the findings, analyses, data, methods, assumptions, and limitations Detailed presentation of this information will enable readers to evaluate its quality effectively Additionally, the report will facilitate the use of results and interpretations in alignment with the study's objectives.
The report shall include measured, calculated or estimated statistical distributions.
NOTE 1 Distributions can, for example, be expressed in terms of distribution functions, standard deviations or levels of confidence.
As short-term exposures typically involve a significant degree of uncertainty, the results shall be considered with care.
A report on an SLP shall, wherever applicable, include the following information. a) General aspects:
1) details of the commissioning client of the SLP;
2) details of the commissioned specialist of the SLP;
3) date and identification number of the report;
4) statement that the study has been conducted in accordance with all the requirements of this part of ISO 15686. b) Goal and range definition c) Component description:
1) main or other identification marks of the components;
2) designation of the components in accordance with recommendations or prescriptions expressed in official standards or regulations;
4) properties of the components such as performance data and model descriptions;
5) name and address of manufacturer or supplier of the components;
6) date of supply of the components.
When actual tests have been performed, include the following. d) Exposure programme description, including exposure at pre-tests:
1) general exposure situation, i.e at outdoor exposure data as latitude, longitude, altitude, distance from coast, special factors like high wind, climate type, etc.;
2) design of the exposure programme, including possible maintenance undertaken for samples, and any accidental deviations thereof;
3) environmental data (including any neighbouring dissimilar components), degradation agent intensities and cycling data;
4) exposure period. e) Performance evaluation description, including evaluation at pre-tests:
1) methods of measurements or inspections;
2) component data, results of measurements or inspections. f) Interpretation of data:
1) account for external data sources utilized;
4) limitations of the interpretation, related to methodology as well as to data;
When sharing the results of the SLP with a third party, a comprehensive third-party report must be created This report should include all relevant information, excluding any details deemed confidential by the commissioning client and the commissioned specialist It serves as a reference document and should be accessible to any third party receiving the communication.
NOTE 2 ISO 15686-4 provides more detailed guidance on methods of presenting and formatting data on SLP.
Guidance on process of SLP
A.1.1 Brief description of SLP (see 4.1)
Figure A.1 illustrates the potential variable patterns of performance over time for specific characteristics of a component within a given service environment These performance characteristics represent measurable, physical quantities associated with the critical properties identified for the tested component.
The Performance Specification Life Cycle (PSLC) is defined as the moment when the performance-over-time function intersects with the performance requirement, particularly when only one critical property is identified In cases where multiple critical properties are recognized, leading to several performance-over-time functions and requirements, the PSLC is determined by the earliest predicted intersection.
1 critical property 1: terminating critical property
Figure A.1 — Hypothetical performance-over-time functions
In reality, performance over time reflects a statistical distribution of declining performance characteristics Most quantities in a System Life Performance (SLP) process are statistically distributed and should be analyzed using suitable statistical methods This applies to component properties, degradation agent intensities, and, ultimately, service lives.
Instead of focusing solely on performance characteristics, it is possible to track degradation indicators over time using dose-response functions These functions establish a relationship between the doses of key degradation agents and one or more degradation indicators.
A.2.1.1 Identification of degradation agents (see 5.2.2)
The most relevant agents within ageing exposure programmes on building components usually originate from the atmosphere, such as the following:
— freeze–thaw and wind (mechanical);
— temperature: elevated, depressed and pulsed (thermal);
— precipitation: solid, liquid, vapour (chemical);
— air contaminants: gases, aerosols, particulates (chemical).
Quantitative data on atmospheric agents can be sourced from published weather, climatological, and air pollution reports The corrosivity of the environment is assessed based on its impact on various standard materials, particularly metals, across extensive regions This assessment typically adheres to a set of International Standards, including ISO 9223, ISO 9224, ISO 9225, and ISO 9226, which outline the classification of atmospheric corrosivity.
Dose-response functions (see A.2.4.3) relating the dose of agents, mainly of a chemical nature, to the degradation of materials, are available from this work for certain classes of materials.
The IEC 60721 series classifies the intensities of agents that impact the performance of electrical components, and these standards can also be relevant for environmental agents influencing building components.
A.2.1.2 Combined agents and combination of agents
Some agents are influenced by multiple co-existing factors, such as freeze-thaw stress, which results from cycling temperatures and the presence of water While water acts as a chemical agent, temperature serves as a thermal agent that significantly affects the rate of many chemical reactions Additionally, various agents can produce notable synergistic effects, exemplified by the interaction of sulfur dioxide with nitric oxides and the combination of UV radiation with oxygen in photo-oxidation Therefore, the effects of combined agents and their interactions must be regarded as crucial parameters throughout all stages of a systematic life process (SLP).
A.2.1.3 Chemical and physical incompatibility between dissimilar components
Incompatibility between components is a design-related issue that typically arises under specific conditions Each component can be analyzed individually, with incompatibility between a component and its neighboring counterpart resembling the effects of environmental agents, such as atmospheric influences According to ISO 6241:1984, 6.4.1, both neighboring components and atmospheric agents are considered part of a component's environment Examples of incompatibility include corrosion from contact between dissimilar metals in the presence of moisture and stress resulting from differing thermal expansion coefficients of rigidly connected dissimilar components under extreme temperatures.
A.2.1.4 Identification of possible degradation mechanisms (see 5.2.4)
While limitations on available knowledge will always be present, it is crucial to identify various potential degradation mechanisms This approach minimizes errors and enhances the foundation for demonstrating that mechanisms induced during exposure programs, especially in accelerated short-term exposures, accurately reflect those occurring in actual service conditions.
The choice of performance characteristics and evaluation techniques is crucial, as various inspection methods exist with differing levels of sophistication While standardized techniques are often recommended, they tend to be overly simplistic and rely on subjective judgments from practitioners, which undermines the reliability of comparisons across studies This highlights the necessity for further development and standardization of more advanced inspection techniques to enhance their effectiveness and reliability.
A.2.2.1 Biological and incompatibility agents (see 5.3)
Biological and incompatibility agents typically have limited significance unless they interact with extreme values of other agents For instance, fungi and bacteria thrive in warm, moist environments, while chemical incompatibility is primarily a concern when liquid water is present between components Additionally, physical incompatibility becomes relevant only during significant temperature fluctuations Therefore, the impact of biological and incompatibility agents can often be assessed through preliminary tests designed to evaluate the effects of the main agents involved.