ISO TR 12471-2004 Computational structural fire design - Review of calculation models fire tests for determining input material data and needs for further devel.pdf

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1、 Reference number ISO/TR 12471:2004(E) ISO 2004TECHNICAL REPORT ISO/TR 12471 First edition 2004-11-15 Computational structural fire design Review of calculation models, fire tests for determining input material data and needs for further development Conception de calcul des feux de structures tat de

2、s travaux des modles de calcul et dessais au feu pour la dtermination des donnes de base requises et des besoins du dveloppement ultrieur ISO/TR 12471:2004(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed b

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7、o.org Web www.iso.org Published in Switzerland ii ISO 2004 All rights reservedISO/TR 12471:2004(E) ISO 2004 All rights reserved iiiContents Page Foreword iv Introduction v 1 Scope 1 2 Internationally applied methods for structural fire engineering design . 1 2.1 Models for thermal exposure. 2 2.2 Mo

8、dels for structural behaviour 6 3 Characteristics of a reliability-based structural fire engineering design56 . 7 3.1 Structural fire engineering design based on FORM approximation 7 3.2 Structural fire engineering design based on practical design format. 10 4 Predictive model capabilities: uncertai

9、nties of design components 5613 5 Main components of structural fire engineering design. 17 5.1 Design fire exposure. 17 5.2 Thermal material properties and transient temperature state 25 5.3 Mechanical material properties and structural behaviour 29 6 Need for further development of calculation mod

10、els and related computer programs for structural fire design: Examples . 40 6.1 Complete process of structural fire design . 40 6.2 Main components of structural fire design 41 6.2.1 Fire exposure. 41 6.2.2 Thermal and mechanical behaviour 41 7 Need for fire tests to determine input material data fo

11、r structural fire design. 42 7.1 Properties related to fire load density and fire exposure . 42 7.2 Thermal material properties. 43 7.3 Mechanical material properties . 44 Bibliography . 46 ISO/TR 12471:2004(E) iv ISO 2004 All rights reservedForeword ISO (the International Organization for Standardi

12、zation) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to b

13、e represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standa

14、rds are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an Inter

15、national Standard requires approval by at least 75 % of the member bodies casting a vote. In exceptional circumstances, when a technical committee has collected data of a different kind from that which is normally published as an International Standard (“state of the art”, for example), it may decid

16、e by a simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely informative in nature and does not have to be reviewed until the data it provides are considered to be no longer valid or useful. Attention is drawn to the possibility that some of

17、the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO/TR 12471 was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 2, Fire containment. ISO/TR 12471:2004(E) ISO 2004 All rights r

18、eserved vIntroduction Considerable advances have been made in recent years in understanding the behaviour of fires in their development and impact upon buildings. Coupled with developments in computational techniques, it is now possible to predict how structures will behave at the fire limit state (

19、i.e. under fire conditions). As a result of the high level of international fire research in recent decades, more and more components and systems are becoming amenable to analytical and computer modelling. Considerable progress has been made concerning such phenomena and procedures as: reaction of m

20、aterials to fire; fire growth in a compartment; fully developed compartment fire; fire spread between buildings; fire behaviour of load-bearing and separating building structures; smoke filling in enclosures and smoke movement in escape routes and multi-storey buildings; interaction of sprinklers an

21、d fire, including sprinkler and fire venting interaction; process of escape; and systems approach to the overall fire safety of a building, in its most general form comprising fire development models interacting with human response models. This progress in fire research has led to consequent changes

22、 in the field of codes, specifications, and recommendations for fire engineering. Some characteristic trends in these changes are: a) improved connection to real fire scenarios; b) increase in extent of design, based on functional requirements and performance criteria; c) development of new test met

23、hods, that are, as far as possible, material-independent and related to well- defined phenomena and properties; d) increase in application of reliability-based analytical design; e) extended use of integrated assessments; and f) introduction of goal-oriented systems of analysis of total, active and

24、passive fire protection for a building. The most manifest verification of these developing trends probably relates to the fire engineering design of load-bearing and separating structures. An analytical determination of the fire resistance of structural elements is being approved by authorities in m

25、ore and more countries as an alternative to the internationally predominant design that is based on the results of the standard fire resistance test and connected classification. The further step to permit a general practical application of an analytical design, based on a natural compartment fire c

26、oncept, was taken by Swedish authorities as early as 1967. Since then, a few other countries have been officially open to the possibility of structural fire design. A significant contribution was made by the Fire Commission of the Conseil International du Btiment, CIB W14, in the form of a state-of-

27、the-art report, in 1983. The report presented a conceptual approach towards a ISO/TR 12471:2004(E) vi ISO 2004 All rights reservedprobability-based design guide on structural fire safety 1 , supplemented in 1986 by a model code/design guide 2 . These design guides are important aids in drafting corr

28、esponding national regulations and recommendations. For European countries, the Eurocodes (see references 3 to 10 in the Bibliography) issued as European Prestandards and supplemented with national application documents, certainly will contribute to increased practical use of analytical structural f

29、ire design methods. A problem arises between material-related codes and the general code. The material-related codes focus very strongly on the fire design, based on thermal exposure according to the standard fire resistance test. However, the general code, specifying the basis of design and mechani

30、cal and thermal actions on fire-exposed structures, also gives some guidance, in the form of informative annexes, regarding the alternate structural fire design, based on a parametric fire exposure determined by fire models or specified temperature-time curves. An analytical fire engineering design

31、can now be performed in most cases for steel structures. Validated material models for the mechanical behaviour of concrete under transient high-temperature conditions 11 to 13and thermal models for a calculation of the charring rate in wood exposed to fire 14 to 16 , developed in recent decades, ha

32、ve significantly enlarged the area of practical application of an analytical structural fire design. To support this application, design diagrams and tables have been computed and published, giving directly, on the one hand, the temperature state of the fire-exposed structure, and on the other, a fu

33、rther transfer to the corresponding load-bearing capacity of the structure, for instance see references 17 to 47 in the Bibliography. The following clauses begin with a summary of internationally applied methods for a structural fire engineering design. With this survey as general background, the ch

34、aracteristics of a reliability-based approach are described. In order to review the need for further development of calculation models and for fire tests to get the input data required for the design, the design alternative, based on a simulated fire exposure, has been chosen for presentation. For o

35、ther design alternatives, applied in practice, the need for calculation models and related input data is less comprehensive than for the more general approach being dealt with. The presentation is followed by a discussion about uncertainty in the design process. Following this background presentatio

36、n of the reliability-based design process and its inherent uncertainties, the remaining document is devoted to related deterministic models, comprising the fire exposure and the thermal and mechanical behaviour of the structure. These models are supplemented with a survey of the material input data

37、required for the structural fire engineering design. Finally, conclusions are drawn regarding the need for further development of calculation models and tests to determine the input material data required for the structural fire design. TECHNICAL REPORT ISO/TR 12471:2004(E) ISO 2004 All rights reser

38、ved 1Computational structural fire design Review of calculation models, fire tests for determining input material data and needs for further development 1 Scope This Technical Report gives a review of the advances that have been made in measuring and understanding how structural materials respond to

39、 fire in terms of changes in their elevated temperature, and physical and mechanical characteristics, and to identify areas where further work is necessary to generate the data required. Analytical methods for heat transfer are combined with mechanical models to calculate structural behaviour from s

40、ingle elements up to complete frames under real fire and ISO Standard furnace heating conditions. This Technical Report reviews advances in computational analysis and indicates how these can be used with probabilistic analysis to provide a risk-based approach to structural fire engineering design. 2

41、 Internationally applied methods for structural fire engineering design The methods available at present for a structural fire engineering design can systematically be characterized with reference to the matrix according to Table 1 1 2 37 . The matrix is based on two types of models for the thermal

42、exposure of the structure (H1 and H2) and three types of models for the mechanical behaviour of the structure (S1, S2 and S3). Table 1 Matrix of thermal exposure and structural behaviour models, characterizing available methods for structural fire engineering design Model for structure S1 S2 S3 Elem

43、ent Substructure Complete structure Model for thermal exposure H1 Nominal temperature-time curves Test or calculation (deterministic) Calculation exceptionally testing (deterministic) H2 Real fire Calculation (probabilistic) Calculation (probalistic) Calculation (probabilistic) in special cases and

44、for research ISO/TR 12471:2004(E) 2 ISO 2004 All rights reserved2.1 Models for thermal exposure Model H1 describes the thermal exposure according to the standard fire resistance test of structural elements as specified in the ISO 834 48and in corresponding national standards, or according to some ot

45、her nominal temperature-time curve 3 . A fire design, based on this thermal exposure, represents the internationally prevalent situation for load-bearing and separating structural elements. In the standard fire resistance test, the specimen is exposed in a furnace to a temperature rise that is contr

46、olled so as to vary with time within specified limits according to the standard temperature-time curve ( ) o1 0 345 log 8 1 t TT t = + (1) where t is the time, in minutes; T tis the furnace temperature at time t, in C; T ois the furnace temperature at time t = 0, in C. For calculations, it is normal

47、ly more favourable to use the following expression for the standard temperature- time curve () 0,2 1,7 19 o 1025 1 0,324e 0,204e 0,472e ttt t TT = (2) that describes Equation (1) to a fairly high degree of accuracy, as shown in reference 49 in the Bibliography. In Equation (2), then t is time, in ho

48、urs. Other nominal temperature-time curves are the hydrocarbon curve () 0,167 2,5 o 1080 1 0,325e 0,675e tt t TT = (3) representing thermal exposure on structural members due to hydrocarbon type fires, and the external fire curve () 0,32 3,8 o 660 1 0,687e 0,313e tt t TT = (4) representing thermal e

49、xposure on the outside of external walls and on other external members as beams and columns 3 . See Figure 1. In the test, the time to reach the decisive limit state with respect to the load-bearing and/or separating function of the structural element defines its fire resistance, normally expressed in minutes. As an alternative, the fire resistance can be determined by calculation. Internationally, the standard fire resistance test is considered to be one o