BSI PD 6688-1-2:2007
$102.76
Background paper to the UK National Annex to BS EN 1991-1-2
| Published By | Publication Date | Number of Pages |
| BSI | 2007 | 22 |
This Published Document is a background paper that gives 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:
- background to the decision made in NA to BS EN 1991-1-2 for combination rules for mechanical actions for structural analysis;
- guidance on BS EN 1991-1-2:2002, Annex A and Annex B; and
- replacements for informative annexes BS EN 1991-1-2:2002, Annex C, Annex E and Annex F.
PDF Catalog
| PDF Pages | PDF Title |
|---|---|
| 3 | Contents 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 replacements 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 response 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 y 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 variable action y1 or y2 3 |
| 4 | Foreword |
| 5 | Introduction 1 Scope a) background to the decision made in NA to BS EN 1991-1-2 for combination rules for mechanical actions for structural 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 Combination rules for mechanical actions for structural analysis [BS EN 1991-1-2:2002, 4.3.1 (2)] 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: 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. |
| 6 | c) BS EN 1991-1-2:2002, 4.3.1 (2) allows the use of y1 or y2 in the accidental design situation for fire. d) The values for y given in NA to BS EN 1990:2002, Table NA.A1.1 for buildings are summarized in Table 1.ÒÒ Table 1 Summary of values for ÒÒÒ> given in BS EN 1990:2002, Table NA.A1.1 e) Based on a comparison with existing UK practice, two cases related to the following ultimate limit states from BS EN 1990:2002, 6.4.1 have been identified in g). 2) STR: Internal failure or excessive deformation of the structure or structural members, including footings, piles, basement walls, etc., where the strength of construction materials governs. f) The recommendation would be that y1 is used for EQU cases and y2 for STR cases. Thus for overturning of otherwise “rigid” per… g) Thus, the loads to apply in the fire limit state in addition to the permanent actions are given in Table 2. |
| 7 | Table 2 Loads to apply in the fire limit state in addition to the permanent actions for leading variable action >1 or >2 3 Guidance on BS EN 1991-1-2 informative annexes 3.1 Parametric temperature-time curves (BS EN 1991-1-2:2002, Annex A) 3.1.1 General |
| 8 | Figure 1 Comparison between calculated and measured response for a low fire load Figure 2 Comparison between calculated and measured response for a high fire load |
| 9 | 3.1.2 Non-contradictory complementary information a) The calculations may also be applied to fire compartments greater than 500 m2. b) The application of the parametric fire may be extended to compartment heights greater than 4 m. However, for tall compartment… c) The insulation factor b for the compartment boundaries assumes ambient temperature properties. 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 m1/2 to 0,01 m1/2. This broadening of the scope of … 2) The 0.01 factor was based upon historical data and calibration against previous analytical studies. 3) It was demonstrated 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 method (BS EN 1991-1-2:2002, Annex B) 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 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. |
| 10 | 4 UK replacements for BS EN 1991-1-2 informative annexes 4.1 Localized fires (BS EN 1991-1-2:2002, Annex C) 4.2 Fire load densities (BS EN 1991-1-2:2002, Annex E) 4.3 Equivalent time of fire exposure (BS EN 1991-1-2:2002, Annex F) |
| 11 | Annex A (informative) Fire load densities (BS EN 1991-1-2:2002, Annex E) A.1 General A.2 Determination of fire load densities A.2.1 General a) from a fire load classification of occupancies is given in A.3. b) for an individual project by performing a fire load survey is given in A.4. A.2.2 Definitions |
| 12 | A.2.3 Protected fire loads A.2.4 Net calorific values |
| 13 | Table A.1 Net calorific values Hu of combustible materials for calculation of fire loads a) |
| 14 | A.3 Fire load classification of occupancies |
| 15 | Table A.2 Fire load densities qf,k for different occupancies a) A.4 Individual assessments of fire load densities A.5 Combustion behaviour |
| 16 | A.6 Rate of fire growth Table A.3 Fire growth rate parameters µ a) Table A.4 Design fire growth rates a) |
| 17 | A.7 Rate of heat release Table A.5 Heat release rate per unit area of fire for different occupanciesa) Annex B (informative) Equivalent time of fire exposure (BS EN 1991-1-2:2002, Annex F) |
| 18 | a) be taken as 0,09 when qd is given in MJ/m2; or b) be related to the thermal property of the enclosure according to Table B.1. Table B.1 Conversion factor kb depending on the thermal properties of the enclosure |
| 19 | a) awareness of fire and the ability of the occupants to reach a place of safety; and b) influence of the size and height of the building or structure on the consequences of failure to life safety and neighbouring property. Table B.2 Height associated with multiplication risk factors |
| 20 | Bibliography [1] DOE/DETR/ODPM/DCLG PII Contract 39/3/489cc1703 Development of the UK and European design codes – Natural fires and the response of structural steel. [2] UNITED KINGDOM. The Building Regulations 2000 Approved Document B: Fire Safety. London: The Stationery Office, 2000. [3] SOCIETY OF FIRE PROTECTION ENGINEERS. SFPE Handbook of Fire Protection Engineering, 3rd edition, Maryland (USA): SFPE, 2002. |
Related products
-
BSI PD 7974-3:2019
Application of fire safety engineering principles to the design of buildings – Structural response to…
