Durability and maintenance - Appunti - Voto 30

Durability and maintenance

First lesson (11 March 2020)

Durability and maintainability for building’s components and systems, both for design and for the production stage; besides it will contribute to develop ability for building’s maintenance management. The chief disciplinary and methodological items are:

• Service life planning
• Service life and reliability evaluation for building’s components
• Durability control and certification of building’s products
• Building’s maintenance

Service life planning

Quality as a function of performance over time.

Durability

Durability is a requirement. It is the capacity to keep the performance levels and the required functional characteristics during time, under the influence of foreseen actions. In order to evaluate it, we have to introduce two parameters:

• Service life: Period of time after installation during which a building or its parts meets or exceeds the performance requirements upper or equal to the accepted limits.
• Reliability: It is the probability that the system or the component works with no failures at a determined level, for a fixed time t and in fixed environmental conditions, that is the probability of the building (component, technological subsystem) to keep its own quality unchanged during time in defined service conditions. It is a statistical value.

Reference standards

International:

ISO 156868 “Buildings and Constructed Assets. Service Life Planning” divided into nine parts:

• General principles
• Service life prediction procedures
• Performance audits and reviews
• Description of the data required in estimating service life
• Maintenance and life cycle costing
• Guidelines for considering environmental impacts
• Performance evaluation for feedback of service life data from practice
• Reference service life and service life estimation
• Guide on the inclusion of requirements of service life assessment and service life declaration in product standards.

National (Italian):

UNI 11156 “The evaluation of building components’ durability”

• Terminology and definition of evaluation parameters
• The method for the evaluation of reliability propensity
• The method for the evaluation of service life

Building quality

Building quality is the set of properties and characteristics of the building, or of its parts, which satisfy clear or implicit requirements through performances. It consists of:

• Space functional quality - Related with the distribution of spaces.
• Environmental - Related with the quality of the spaces: acoustic performance, indoor quality, etc.
• Technological - Quality measure of the level of components, an entire wall, or roof.
• Technical - Related to the characteristics of the materials used.

Technological quality

Technological quality is related to four aspects:

• Characteristic quality, initial performances
• Operative, related with the attitude to obtain specific level of maintenance.
• Useful - Related to durability: reliability + service life
• Maintenance

Technological quality aspects

Technological quality aspects include controllability, aptitude to cleaning, reparability, aptitude to substitution; parameters: availability, mean time of reparation. Technological quality aspects reference technological requirements.

Q = characteristic technological quality for a class of technical elements performance quality at time 0, out of system and context Durability: reliability, service life

Q = useful technological quality product aptitude to maintain initial characteristic technological performance levels

Q = maintenance technological quality reparability, aptitude to substitution; product aptitude to obtain specific levels of maintenance parameters: availability, mean time of reparation economy of product

Q = operative technological quality economy of necessary machinery product aptitude to obtain specific levels of economy of necessary workmanship economy and operability in the construction phase economy of necessary controls economy of production

Reliability: probability to not have failure, so we have to introduce the probability of failure:

Prof. Bruno Daniotti – Building Durability and Maintenance

F· i = 1 – iF· i = Failure rate, probability that a failure will happen between the time t=0 and t=i included, of a sample of N homogeneous elements and working in the same conditions are given by.n i is the number of the sample components which have suffered a failure until the moment t=i included.

If I know this distribution, it is easy to go for maintenance planning. It depends on the available data. If I don’t know this distribution, I can use another method: Component’s Reliability Propensity, based on the analysis of four aspects of reliability:

• Functional
• Executive
• Inherent
• Critical

So: reliability on one side, service life on the other one.

Service life evaluation

1. Methodology for buildings components experimental reference service life measurement. Based on the measurement in the laboratory of degradation of performances during time. Materials and components are exposed to aging, then we have to measure the degradation of performances.
2. Methods to evaluate estimated service life in design conditions:

• Factor method
• Engineering methods
• Statistical methods

The factor method

Simplified method for the evaluation of Estimated Service Life. It consists of a multiplication of seven different factors.

ESL = RSL * A * B * C * D * E * F * G

• RSL: Reference Service Life
• A: Quality of components
• B: Design level, quality in the design stage
• C: Work execution level, quality during the construction stage
• D: Indoor environment, internal condition in the building
• E: Outdoor environment, external temperature, pollution, rain and so on
• F: In-use conditions, related to operational condition, so the use by the people, impact risk
• G: Maintenance level, can be used to measure the quality of maintenance

Statistical methods

In this method degradation is generally regarded as a stochastic process, for each property during each time period, a probability of deterioration is defined (models like the Markov chain model are usually used). The decay of performance is represented with a statistical distribution. This method is available for very specific materials like concrete. It can be used with the mark of chain in order to predict decay in time. Very complex.

Engineering methods

Compromise between the simplicity of the factor method and the complexity of the statistical method. They may have probabilistic inputs, but these inputs must be linked by simple, determinate equations. Compromise solution, methods which are as easy to use as the factor method and describe actual degradation processes like probabilistic methods do.

Two methods:

• Enhanced Factor Method
• Performance Limits’ Method based on the modeling of technological performance decay. It is related to the prediction of the components’ performance decay during time. We are going to use the first one: Enhanced Factor Method In which we use the calculation method of factor method, but each factor is represented by statistical distribution, that has three values: Minimum, Maximum, Most probable

The Construction Products Directive/Regulation

This is essential, it provides the base requirements. The products must be suitable for construction works which (as a whole and in their separate parts) are fit for their intended use, account being taken of economy, and in this connection satisfy the following essential requirements where the works are subject to regulations containing such requirements. Such requirements must, subject to normal maintenance, be satisfied for an economically reasonable working life.

1. Mechanical resistance and stability
2. Safety in case of fire
3. Hygiene, health, and the environment
4. Safety in use
5. Protection against noise
6. Energy economy and heat retention
7. Sustainable use of natural resources, introduced in 2013

The working life

The Working Life: The Construction Products Directive A specific service life. The Working Life of the product is seen as the time period during which the performance characteristics of the product itself are keeping at a such level to permit at the works, rightly designed and executed, to satisfy six Essential Requirements of the Directory. The Working Life depends on the spontaneous durability of the products which are undertaken to the agents, and it depends on the ordinary maintenance, excepted the extraordinary repairing operations.

• The Working Life depends on the spontaneous durability of the products which are undertaken to the agents, and it depends on the ordinary maintenance, excepted the extraordinary repairing operations. This is the base for certification of components. It is measured through laboratory test, ex: thermal shock.

Foreseen working life Assumed working life of construction products

Building process management (second lesson)

Law reference: UNI 10723 “Processo edilizio - Classificazione e definizione delle fasi processuali degli interventi edilizi di nuova costruzione”. Construction process. Classification and definitions of the process steps for new constructions.

Building process

It can be defined as a structured sequence of stages, which lead from the relief of buildings’ customers-users needs to their satisfaction through design, production, construction, and management of the building. The starting point is the needs, the goal is to satisfy these needs through three different stages:

I. Decision process

All the process stages coming before the building construction and fixing the aims, the pre-design development, the design development, and the planning.

• Pre-design stages Are defined the aim and the goals of the building. Typology of building, design life of the building (how many years the building has to last), economic pre-design (budget).
• Design Stage Technological design, with the definition of performances of the building components. Definition of service life and reliability of building components. Management design: we have the first maintenance plan. Management planning: we have the scheduling of all maintenance activity during the life cycle.

II. Executive process

All the operative stages driving to the building execution on the basis of what design and planning steps have fixed: production, prefabrication, construction.

III. Management process

All the operative stages, from the beginning of the building life, until the end of its functional and economic life cycle, aim to ensure its functioning. In the framework of the management process the main stages are:

• Maintenance Collecting the repair or replacement operations of the building parts to secure the right functioning during time, on the basis of management planning. It is based on management planning, defined in the decision process.
• Management Considering the activities to be developed to maintain the building in optimized serviceability conditions, apart from its performance decay, on the basis of management planning operative instructions concerning the:
• Checking, inspection, during it we have to check the degradation level of components, we have to evaluate the symptoms of degradation. These are important information for avoiding the failure, for example, the failure of structural parts where we have to do regular checking in order to prevent the structural collapse.
• Cleaning of its parts.
• Plant usage: Considering the operations to develop for the right working of the building technical plants and equipment on the basis of the management planning.

In the decision process we have:

• Management Design, working up the operation project of technical equipment and the building maintenance plan, considering what has been prepared in the space-functional, technological and executive design.
• Management Planning, developing on the basis of optimization criteria, the time sequences of the technical equipment use operations and maintenance operations, fixed in the management design stage. We have the scheduling: we have to define when to do maintenance.

It can be executed with the following criteria, on the basis of durability and reliability data of the components and of the critical failures:

• Emergency maintenance: not programmed maintenance carried on after an unforeseeable failure, usually owing to a project or executive pathology It cannot be predicted.
• Maintenance after failure: programmed maintenance executed after a not critical foreseeable failure. Ex: painting, in case of failure we can do maintenance.
• Preventive predictive of threshold maintenance: programmed maintenance executed at steady age or at steady time spaces (ex. painting), fixed upon the knowledge of durability data (ex: man. Equipment parts) for critical failures (Es: waterproofing of the roof).
• Preventive maintenance under condition: programmed maintenance executed after the achievement of a limit condition, estimated with inspections based on diagnostic cards, with frequency, which is due to the reliability, for critical failures (ex: structural parts).
• Opportunity maintenance: maintenance executed in advance compared with the maintenance planning because of a profitable moment, on the occasion of the maintenance operations about some building parts. Save money by practice maintenance. Ex: external surface of facade.

Building quality

The set of properties and characteristics of the building (or of its parts) which satisfy clear or implicit requirements through performances. It usually consists of:

• Space functional quality It’s the set of space/functional characteristics of building space elements.
• Environmental quality The set of environmental performances of building space elements: Thermal requirements, Acoustical requirements, Air purity requirements, Light requirements.
• Technological quality The set of technological performances of building’s subsystems and components. It is related to the performance of building components, ex: enclosure of the building must have sufficient thermal resistance in order to insulate the indoor environment from outdoor, to avoid the rain entering.
• Technical quality The set of characteristics of building’s elements and articulated as for technical requirements. Related to the characteristic of materials used in the building, like concrete, wood. Ex: mechanical resistance of concrete.

In Italy, we use a functional classification system: UNI 8290 “Technological system. Classification and terminology” This standard does not take into account the processes, but only the parts of the building. The subdivision presents three levels:

1. Classes of Technological Units
2. Technological Units
3. Classes of Technical Elements

Building technological system

The set of technological units or components considering their technological requirements and their specific technological performances.

Building Component/Technical Element: A more or less complex building product able to carry out entire or partial functions of one or more technological units and it is a peculiar component of a technological subsystem (ex: windows, continuous or discontinuous roofing, vertical wall load-bearing or self-supporting, etc.).

Our final goal: Building quality

When we speak about requirement, if we consider a wall, there’s a:

• Technological requirement: the Thermal Insulation Related to environmental performance of the building (thermal comfort) It is guaranteed through the performance level: thermal transmittance (U) Durabilità dei materiali e manutenzione Layer’s thermal resistance.

Environmental and technological quality of the building

1. LEVEL (ex: thermal insulation) Building products technological and functional complexity Building- The simple element is a building product with entirely fixed sizes (ex. Block, tile, etc.) The parameters are related to:
2. Design- Semi-manufactured product: building product fixed in two directions, which has to be adapted as sizes It is guaranteed by: at construction stage (ex: panels, coil, membrane) Technological quality of the components
3. LEVEL Performance, useful, executive and maintenance quality lime, cement, sand, plaster, etc.) Our final goal: Building quality Components It is guaranteed by: design Related to environmental performance of the building (thermal comfort) Environmental and technological quality of the building

1. LEVEL Technical quality of the elements (products) It is guaranteed by: The parameters are related to: Prof. Bruno DANIOTTI – Useful technological quality design 1 - 9 Technological quality of the components
2. LEVEL Performance, useful, executive and maintenance quality Components It is guaranteed by: design Technical quality of the elements (products) Technological quality aspects
3. LEVEL Technological quality aspects reference technological requirements Prof. Bruno DANIOTTI – Useful technological quality