Good Morning everybody. A discussion of fire scenarios and models for steel framed enclosed multi-storey balconies. . Gordon Cooke International Fire Safety Consultant
Good Morning everybody
International Fire Safety Consultant
( Formerly Visiting Professor, School of Engineering and Mathematical Sciences, City University, London) www.cookeonfire.com
Prepared for the Institution of Structural Engineers ‘Steel in Fire‘ Forum meeting , 24 September 2013, London
a) supported from the external wall of the parent building with diagonal tension members, or
b) supported by an existing cantilevered floor.
In both cases the dead load is normally low as the balcony system can be lightweight.
B3. (1) The building shall be designed and constructed so that, in the event of fire, its stability will be maintained for a reasonable period.
Fire resistance in flats (ADB)According to Table A2 of AD B, which applies in England and Wales, structural elements such as beams and columns within a non-sprinklered block of flats need the following amount of fire resistance (the numbers in the first row of the table below are the height of the top floor (not the top of the building) above ground level measured in metres)
This can provide an alternative approach to fire safety. It may be the only practical way to achieve a satisfactory standard of fire safety in some large and complex buildings and in buildings containing different uses e.g. airport terminals. Fire safety engineering may also be suitable for solving a problem with an aspect of building design which otherwise follows the provisions of this (ADB) document.
This specifies a method for determining the fire resistance, in respect with loadbearing capacity and with no separating function, of:
This European standard is used in conjunction with BS EN 1363-1 i.e. involving exposure to the standard fire resistance test exposure (ISO 834).
Section C Design Tables, states in C2.2 that a bare steel column opposite a window with no through draft should be at least two thirds of the window height away from the plane of the window if the limiting temperature of the steel is not to exceed 550 degC. This is conservative and detailed calculations might show that less gap is needed but these calculations are time consuming and tedious.
In this location it is deemed to be outside the trajectory of the jetting flame. Hence for a window height of 2m the bare column should be 1.33m away. Assumes fire load density does not exceed 50 kg/m2 of floor area. Greater gap may be needed if through-draft present
In some cases elements may be exposed to conditions which are less severe than when the element or structure is exposed to a compartment fire. Examples of this are walls at the perimeter of the building which may be exposed to an external fire or flames coming out of windows…
This exposure condition is only relevant to the evaluation of fire resistance of separating elements. Other evaluation techniques exist for the evaluation of beams and columns …
However the National Annex to the Eurocode, BS EN 1991-1-2: 2002, states that Annex F may not be used, and PD 6688-1-2: 2002 should be used as a replacement.
te= kb wvq(31)
Substituting values gives time equivalent of 82 min. This seems high and, again, the calculation result is not acceptable because time equivalent exceeds limit of application i.e. exceeds 30 min.
Note. The limits of application in PD 7974-3 and PD 6688 -1-2 are different (40 min v 30 min)
Law, Margaret. Prediction of fire resistance, Paper No2 of Fire resistance requirments for buildings – a new approach. Dept of Environment and Fire Offices’ Committee Joint Fire Research Organisation, Symposium No 5, London 1973 HMSO
Cooke GME, ‘Fire Protection,’ chapter of Volume 1 of ‘Specification 85′, Published by The Architectural Press, 1985, pp 69.(available on www.cookeonfire.com website under Publications)