Risks of Residential Buildings

Transcription

1 Workshop 17 - Housing Renewal and Maintenance Risks of Residential Buildings Karel Kubečka Paper presented at the ENHR conference "Housing in an expanding Europe: theory, policy, participation and " Ljubljana, lovenia 2-5 July 2006

2 Risks of Residential Buildings Ing. Karel KUBEČKA, Ph.D. University of Technology, VŠB-TU Ostrava, Faculty of Civil Engineering, Department of tructures, Ludvíka Podéště 1875, Ostrava-Poruba, Czech Republic 1. Abstract. Each human activity is connected with a certain risk level. uch risk is viewed as a probability of injury, damage or failure depending on the type of the human activity. Typical risks of structures are mostly risks of the technical nature. The risk level, or the probability of a damage to or failure of building structures, in the building industry is eliminated by respective standards and regulations. This means that the observance of the existing standards and regulations eliminate most probable risks down to the level that is both socially and economically acceptable. In case of dimensioning of loadcarrying structures in constructions, the observance of the standards and regulations eliminates such risks completely. The definition of qualitative and quantitative risk. The discussion of the scenario role and other problems in the risk analysis. 2. Introduction. Each human activity is connected with a certain risk level. In activities that are generally referred to as the building industry, different risks exist. uch risks result from social conditions in the region or demography of people living there. For instance, if a market research is carried out incorrectly in terms of a purchasing power of residents, the final economic study is misleading, and a shopping centre might be built up in a place where the purchasing power of the people is low. In that case, the investment might be a failure. Typical risks of structures are mostly risks of the technical nature. uch risk is viewed as a probability of injury, damage or failure depending on the type of the human activity. The risk level, or the probability of a damage to or failure of building structures, in the building industry is eliminated by respective standards and regulations. This means that the observance of the existing standards and regulations eliminate most probable risks down to the level that is both socially and economically acceptable. In case of dimensioning of loadcarrying structures in constructions, the observance of the standards and regulations eliminates such risks completely. Risks of constructions ocial and demographic risks Technical risks of buildings and operation units In spite of this, failures and defects of structures may occur. From the point of view of economy, the number of such defects and failures is not negligible. Therefore, experts have been trying to develop methods that will reveal reasons for such defects and failures that occur even if all standards and regulations are fulfilled for the construction concerned. The objective is to minimise building risks down to the economically acceptable level or to eliminate such risks completely. The idea to minimise risks and eliminate the building defects and failures is not new at all. It became however topical after 1980 when a new generation of materials was introduced and started supporting prefabrication in the Czech building industry. This is, in particular, the case of materials thanks to which the building works are not season-dependant anymore. In connection with that idea, a new concept has been

3 developed Pathology of constructions [3]. This concept is addressed by the branch of science that deals with systematic failures, defects and accidents of constructions. It is essential to monitor such phenomena regularly, sort them out, generalise and analyse, the final objective being to define conditions that will minimise the risk levels. 3. Definition of Terms. In order to analyse a problem correctly, it is necessary to define properly terms that are used most frequently: Defect is a defective condition of a specific feature in a unit, in comparison with the required condition. Failure is a phenomenon when a product stops fulfilling the function required by technical conditions. In that case, the failure is demonstration of a defect. Quality of a product is a summary of features describing the ability of the product to fulfill the specific function. ervice life is the ability of the product to fulfil for a certain period of time the specific function required by technical conditions. 4. Defects and Failures of Constructions. Classification of Defects and Failures. DEFECT OF CONTRUCTIN minor serious By stages: pre-project project prep. use and maintenance after designed service life D E F E C T F A I L U R E sudden gradual By types residential civil industrial transport utility complete partial Defects of constructions or parts of constructions that manifest themselves as risk-involving failures can be classified in order to facilitate application of knowledge about the defects and failures. Classification by time characteristics of the failure: sudden failure gradual failure Classification by types of constructions: residential constructions (house buildings) civil constructions (buildings civil amenities) industrial constructions (industrial buildings for production and administration) transport constructions (transport related structures such as roads, railways, and airports including tunnels and bridges) line constructions (distribution of utilities, supporting and protection walls, piping collectors) Classification by the extent of the defect (being the reason for the failure): minor (non-serious) defects that do not reduce considerably applicability of the product for a specific purpose, including aesthetic defects serious defects that might result in breakdown or limited/reduced applicability of a productcritical defects may, on the basis of theoretical assumptions and/or current knowledge and experience, result in dangerous consequences for those who use such product and/or those who are present close to such product

4 5. Using of Knowledge about Defects and Failures for Minimising of Risks for Constructions. The practice has shown that the extent and gravity of the failures is the basis for the decision-making on the method and level used for the sharing of information. Currently, the information is disseminated at the level of experts in specialised seminars, conferences, and journals. In case of accidents, assessment is often provided by communication agencies including mass media governed by the public law. Business policies of individual companies play also an important role. Consequently, some negative phenomena are not published at all in order to protect company s reputation. In past, the more serious was the failure (or accident), the better was the feedback to the production or project organisation. Construction pre-project project use and maintenance FAILURE OF THE CONTRUCTION A N A L Y I normal function CORRECTION 6. Technical Risks of Constructions. Risks can be divided on the basis of different aspects relating to the construction and building activities. Individual topics are given in subsequent chapters pursuant to the time schedule of the building process. Construction Risks (technical risks) pre-project use and maintenance project risks after end of service life

5 7. Definition of Technical Risk The risk is generally defined as a product of an expected damage C and probability Pf of occurrence of such damage. This means the risk is the probability that the damage will occur. R = C P f (1) If several partial factors influence the risk level (as the case is in most applications in practice), the resulting risk is generally expressed as the sum of the individual risk levels. n ( C i P f;i ) R = (2) i= 1 Technical risks of the construction are risks connected with the, building, and use of the construction. The technical risks relate to the creation, existence, and removal, if any, of the building (as well as of technical facilities necessary for operation of the building). The technical risks of the construction are not risks relating to violation of occupational safety and protection that may result in work injuries during the performance of the construction for technology reasons, or social problems connected the building (such as a too big building with many cheap flats), or economic risks of the construction. The general division of the risks is given by the chronology of the construction and service life of the building. The risks can be classified as risks connected with: the period of pre-project of the construction the period of project of the construction the period of of the construction the period of the performance of the construction the period of use and service life of the construction the period after end of the designed service life of the construction The risks can be also classified in terms of the origin and different views relating to specific stages of the building process - from the pre-project to the demolition of the construction after its service life is over: Risks relating to violation of standards o Violation of technology procedures o Violation of technology and subsequent defect of materials Risks relating to poor knowledge of site conditions and absence of source documents (for instance, insufficient geological survey) Risks relating to failure of a human factor o in the survey o in the pre-project and/or project o during the construction o during the service life in relation with the maintenance of the construction Risks relating to unexpected facts that are not covered by human knowledge Risks relating to wilful violation of anticipated facts Denotations of symbols C expected loss [ ] P f probability failure [%] References [1] Závěrečná zpráva za rok CIDEA, VŠB-TU Ostrava, Fakulta stavební, prosinec 2005 (Final Report for 2005 CIDEA, Faculty of Technology VŠB-TU Ostrava, Faculty of Civil Engineering, December 2005) [2] Teplý B.: cénáře a analýza rizik, tavební fakulta VUT v Brně (Risk cenarios and Risk Analyses) [3] JEŽÍK A.: TaZU Brno, Vady a poruchy staveb a zvyšování jakosti ve stavebnictví, časopis Pozemní stavby 5/1986. (Failures and Defects of Constructions. Improving Quality in Building Industry) [4] KUBEČKA K., KREJA M., JONOV D.: Rizika modelování nosných konstrukcí střech. Mezinárodní konference Modelování v mechanice, VŠB-TU Ostrava, Fakulta stavební, Katedra stavební mechaniky února 2006, IBN , strana 41. cénáře a analýza rizik, tavební fakulta VUT v Brně (Risks in Modelling of Roof Carrying tructures) [5] KUBEČKA K: Aktuální problém - zatížení sněhem. Časopis třechy, fasády, izolace II/2006, IN: , strana (Topical Issues now Loads) [6] KUBEČKA K: kutečné zatížení střešních konstrukcí sněhovou pokrývkou. Časopis třechy, fasády, izolace III/2006, IN: , strana (Real Loading of Roof tructures with now)

6 [7] KUBEČKA K: Zatížení střech sněhem podle ČN EN ( ). Časopis třechy, fasády, izolace III/2006, IN: , strana (Loading of Roofs with now pursuant to ČN EN ( ) This outcome has been achieved with the financial support of the Ministry of Education, Youth and port, project No.1M , within activities of the CIDEA research centre.