BS PD 6688-1-2-2007 Background paper to the UK National Annex to BS EN 1991-1-2《BS EN 1991-1-2的英国国家附录的背景文件》.pdf

1、PD 6688-1-2:2007 Background paper to the UK National Annex to BS EN 1991-1-2 ICS 13.220.50, 91.010.30, 91.080.01 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW PUBLISHED DOCUMENT Incorporating Corrigendum No. 1Publishing and copyright information The BSI copyright notice disp

2、layed in this document indicates when the document was last issued. BSI 2007 ISBN 978 0 580 50604 8 The following BSI references relate to the work on this standard: Committee reference B/525/1 Publication history First published April 2007 Amendments issued since publication Amd. no. Date Text affe

3、cted 17225 Corrigendum No. 1 29 June 2007 ISBN corrected PD 6688-1-2:2007 BSI 2007 i PD 6688-1-2:2007 Contents Foreword ii 1 Scope 1 2 Combination rules for mechanical actions for structural analysis BS EN 1991-1-2:2002, 4.3.1 (2) 1 3 Guidance on BS EN 1991-1-2 informative annexes 3 4 UK replacement

4、s for BS EN 1991-1-2 informative annexes 6 Annexes Annex A (informative) Fire load densities (BS EN 1991-1-2:2002, Annex E) 7 Annex B (informative) Equivalent time of fire exposure (BS EN 1991-1-2:2002, Annex F) 13 Bibliography 16 List of figures Figure 1 Comparison between calculated and measured r

5、esponse for a low fire load 4 Figure 2 Comparison between calculated and measured response for a high fire load 4 List of tables Table 1 Summary of values for given in BS EN 1990:2002, Table NA.A1.1 2 Table 2 Loads to apply in the fire limit state in addition to the permanent actions for leading var

6、iable action 1or 23 Table A.1 Net calorific values H uof combustible materials for calculation of fire loads 9 Table A.2 Fire load densities q f,kfor different occupancies 11 Table A.3 Fire growth rate parameters 12 Table A.4 Design fire growth rates 12 Table A.5 Heat release rate per unit area of f

7、ire for different occupancies 13 Table B.1 Conversion factor k bdepending on the thermal properties of the enclosure 14 Table B.2 Height associated with multiplication risk factors 15 Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 16, an ins

8、ide back cover and a back cover.PD 6688-1-2:2007 ii BSI 2007 Foreword Publishing information This Published Document has been prepared by BSI Subcommittee B/525/1. This Published Document is published by BSI and came into effect on 30 April 2007. It was prepared by Subcommittee B/525/1, Actions (loa

9、dings) and basis of design, under the authority of Technical Committee B/525, Building and civil engineering structures. A list of organizations represented on this committee can be obtained on request to its secretary. Relationship with other publications This Published Document is a background pap

10、er that gives non-contradictory complementary information for use in the UK with BS EN 1991-1-2 and its UK National Annex. Use of this document As a guide, this Published Document takes the form of guidance and recommendations. It should not be quoted as if it were a specification and particular car

11、e should be taken to ensure that claims of compliance are not misleading. Any user claiming compliance with this Published Document is expected to be able to justify any course of action that deviates from its recommendations. Presentational conventions The provisions in this document are presented

12、in roman (i.e. upright) type. Its recommendations are expressed in sentences in which the principal auxiliary verb is “should”. Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element. The word “should” is used to expr

13、ess recommendations of this document. The word “may” is used in the text to express permissibility, e.g. as an alternative to the primary recommendation of the clause. The word “can” is used to express possibility, e.g. a consequence of an action or an event. Notes and commentaries are provided thro

14、ughout the text of this document. Notes give references and additional information that are important but do not form part of the recommendations. Commentaries give background information. Contractual and legal considerations This publication does not purport to include all the necessary provisions

15、of a contract. Users are responsible for its correct application. Compliance with a Published Document cannot confer immunity from legal obligations. BSI 2007 1 PD 6688-1-2:2007 Introduction When there is a need for guidance on a subject that is not covered by the Eurocode, a country can choose to p

16、ublish documents that contain non-contradictory complementary information that supports the Eurocode. This Published Document provides just such information and has been cited as a reference in the UK National Annex to BS EN 1991-1-2. 1 Scope This Published Document is a background paper that gives

17、non-contradictory complementary information for use in the UK with BS EN 1991-1-2 and its UK National Annex. This Published Document gives non-contradictory complementary information on: a) background to the decision made in NA to BS EN 1991-1-2 for combination rules for mechanical actions for struc

18、tural analysis; b) guidance on BS EN 1991-1-2:2002, Annex A and Annex B; and c) replacements for informative annexes BS EN 1991-1-2:2002, Annex C, Annex E and Annex F . 2 actions for structural analysis BS EN 1991-1-2:2002, 4.3.1 (2) NA to BS EN 1991-1-2 recommends that the representative value of t

19、he variable action Q Lshould be taken as the frequent value 1.L Q L , for certain situations as described in 2f). The reason for this is given by the following. a) Based on BS EN 1990:2002, 6.4.3.3 equation 6.11b simplifies to the combination of actions for accidental design situations as: G + A + 1

20、 or 2,L Q L+ 2,i Q i where G is the permanent action; A is the accidental action (which may involve an explicit action or refer to the situation after an accidental event such that A = 0); Q Lis the leading variable action (i.e. that which has the largest effect); Q iare other variable actions which

21、 can be imposed, snow or wind loads; 1is the frequent combination factor; 2is the quasi-permanent combination factor. b) In the case of fire, the accidental action A results in increased temperatures and hence reduced resistances of structural members such that A = 0 after the accidental event. Comb

22、ination rules for mechanical PD 6688-1-2:2007 2 BSI 2007 c) BS EN 1991-1-2:2002, 4.3.1 (2) allows the use of 1or 2in the accidental design situation for fire. d) The values for given in NA to BS EN 1990:2002, Table NA.A1.1 for buildings are summarized in Table 1. e) Based on a comparison with existi

23、ng UK practice, two cases related to the following ultimate limit states from BS EN 1990:2002, 6.4.1 have been identified in g). 1) EQU: Loss of static equilibrium of the structure or any part of it considered as a rigid body, where minor variations in the value or the spatial distribution of action

24、s from a single source are significant, and the strengths of construction materials or ground are generally not governing. 2) STR: Internal failure or excessive deformation of the structure or structural members, including footings, piles, basement walls, etc., where the strength of construction mat

25、erials governs. f) The recommendation would be that 1is used for EQU cases and 2for STR cases. Thus for overturning of otherwise “rigid” perimeter columns during fire at actual or potential site boundaries EQU would be considered with wind included; and for internal structural collapse occasioned by

26、 member weakening during fire STR would be considered based on imposed loads without wind or snow. g) Thus, the loads to apply in the fire limit state in addition to the permanent actions are given in Table 2. Table 1 Summary of values for given in BS EN 1990:2002, Table NA.A1.1 Action 1 2 Imposed l

27、oads in buildings Domestic, residential areas; office areas 0,5 0,3 Congregation areas; shopping areas 0,7 0,6 Storage areas 0,9 0,8 Roofs 0 0 Snow on buildings for sites located at altitude H u 1 000 m above sea level 0,2 0 Wind loads on buildings 0,2 0 BSI 2007 3 PD 6688-1-2:2007 3 Guidance on BS

28、EN 1991-1-2 informative annexes 3.1 Parametric temperaturetime curves (BS EN 1991-1-2:2002, Annex A) 3.1.1 General A major exercise was carried out to validate the parametric expressions against well documented fire test data. It was generally found that the temperaturetime response predicted by the

29、 parametric expressions either closely matched the measured fire curve or over-predicted (safe) response. A comparison between calculated and measured response for a low fire load is shown in Figure 1. A comparison between calculated and measured response for a high fire load is shown in Figure 2. W

30、hile there appears to be a difference in temperature time curves between the calculated and measured response when this is considered in relation to the thermal response of a lightly protected structural member this is not significant. Table 2 Loads to apply in the fire limit state in addition to th

31、e permanent actions for leading variable action 1or 2 Case EQU ( 1chosen) STR ( 2chosen) If imposed (I) loads leading Domestic, residential; office areas 0,5I 0,3I Congregation areas; shopping areas 0,7I 0,6I Storage 0,9I 0,8I Roofs 0 0 If snow (S) loads leading Domestic, residential; office areas 0

32、2S + 0,3I 0,3I Congregation areas; shopping areas 0,2S + 0,6I 0,6I Storage 0,2S + 0,8I 0,8I Roofs 0,2S 0 If wind (W) loads leading Domestic, residential; office areas 0,2W + 0,3I 0,3I Congregation areas; shopping areas 0,2W + 0,6I 0,6I Storage 0,2W + 0,8I 0,8I Roofs 0,2W 0PD 6688-1-2:2007 4 BSI 200

33、7 Figure 1 Comparison between calculated and measured response for a low fire load Fire load, 15 kg/m 3 ; opening factor, 0.06 m 1/2 Key x Time, mins 1 EC1 calculated y Temperature, C 2 Measured Figure 2 Comparison between calculated and measured response for a high fire load Fire load, 40 kg/m 3 ;

34、opening factor, 0.07 m 1/2 Key x Time, mins 1 Atmosphere, measured y Temperature, C 2 Atmosphere, EC1 calculated 3 Steel, measured 4 Steel, EC1 calculated 1 000 800 600 400 200 0 0 y 10 20 30 40 50 1 2 x 1 000 800 600 400 200 0 0 y 15 30 45 60 75 x 1 400 1 200 90 3 4 2 1 BSI 2007 5 PD 6688-1-2:2007

35、3.1.2 Non-contradictory complementary information BS EN 1991-1-2:2002, Annex A may be used with the following complementary information. a) The calculations may also be applied to fire compartments greater than 500 m 2 . b) The application of the parametric fire may be extended to compartment height

36、s greater than 4 m. However, for tall compartments, the outputs may be particularly onerous and it may be more appropriate to consider using computational fluid dynamics or other similar calculation methods. c) The insulation factor b for the compartment boundaries assumes ambient temperature proper

37、ties. Elevated temperature values may be used where appropriate reliable data is available. d) The lower limit of the range of opening factors may be extended from 0,02 m 1/2to 0,01 m 1/2 . This broadening of the scope of application of the parametric fires was based on a major calibration/research

38、exercise 1 leading up to the development of the NA to BS EN 1991-1-2. The following is worth noting. 1) Sensitivity analysis was carried out on the effect of increasing the floor areas. 2) The 0.01 factor was based upon historical data and calibration against previous analytical studies. 3) It was d

39、emonstrated that by increasing the compartment height the temperature time history of the fires would result in lower temperature (less severe heating curve). This is because the fire load is expressed as a function of the floor area. 3.2 Thermal actions for external members Simplified calculation m

40、ethod (BS EN 1991-1-2:2002, Annex B) Annex B may be used with the following complementary information. a) The method may overestimate the temperatures and this will commonly occur at window heights of around 0.6 m or less irrespective of the window width. b) Where temperatures of the fire or flames

41、in a building exceed 1 750 K and 1 850 K respectively, the outputs should be considered as overly conservative. These values may be used as upper limits. c) Calculations may provide a negative flame height, which indicates that the flame tip is no higher than the top of the window.PD 6688-1-2:2007 6

42、 BSI 2007 4 UK replacements for BS EN 1991-1-2 informative annexes 4.1 Localized fires (BS EN 1991-1-2:2002, Annex C) This annex may not be used. Replacement UK guidance is given in PD 7974-1:2003, 8.2.1.1 to 8.2.1.14. 4.2 Fire load densities (BS EN 1991-1-2:2002, Annex E) This annex may not be used

43、 A replacement UK informative annex is given in Annex A. The UK was unable to accept BS EN 1991-1-2:2002, Annex E. In particular, there is a fundamental disagreement on the use of factors (given in BS EN 1991-1-2:2002, Table E.2) that multiply the design fire load density depending upon other fire

44、safety measures that may be incorporated in the building. In addition the UK could not accept the multiplication factors given in BS EN 1991-1-2:2002, Table E.1. BS EN 1991-1-2 attempts to apply a risk-based approach through modifying the fire load density. The UK considered the consequences of fire

45、 should not be addressed in the engineering calculations but should form part of a separate analysis after the fire related outputs have been obtained. However, it was considered the contribution of an active suppression system restricting the fire size that was acceptable which is already acknowled

46、ged within Approved Document B to the Building Regulations 2000 2. At some major sites, such as airports, an on-site dedicated fire brigade may exist. In such circumstances it may be appropriate to adjust the fire load calculations to reflect the speed of response and familiarity of the site layout.

47、 However, these provisions should form part of the overall fire safety strategy and should not be taken in isolation. It is intended that Annex A, which contains information from PD 7974-1, may be used to determine the fire load densities for use in calculating fire scenarios, e.g. parametric temper

48、ature time relationships, or time equivalent assessments for estimating the period of heating in the BS EN 1363-1 furnace test. 4.3 Equivalent time of fire exposure (BS EN 1991-1-2:2002, Annex F) This annex may not be used. A replacement UK informative annex is given in Annex B. BSI 2007 7 PD 6688-1

49、2:2007 Annex A (informative) Fire load densities (BS EN 1991-1-2:2002, Annex E) NOTE This annex is intended to be used as a replacement for BS EN 1991-1-2:2002, Annex E. A.1 General The design value of the fire load q f,d(in MJ/m 2 ) is defined as: (A.1) q f,d= q f,k m 1 where q f,kis the characteristic fire load density per unit floor area (MJ/m 2 ) (see A.2); m is the combustion factor (see A.6); 1is a factor of 0,61 that can be applied to take into account sprinklers if installed for life s