11.0 fire design
Fire design in New Zealand is an evolving discipline and important changes have been incorporated within regulations ( and means of compliance ) over time. In the past, documentation with regard to fire rating tray floors has been limited to considering the floor in isolation to both the building as a whole and to the structural system supporting the floor. However, it is now not sufficient to use this philosophy since a large number of factors which are required to be considered, are at worst ignored or at best overlooked in the process.
Prior to the introduction of the Approved Document, Fire Rating requirements for buildings were generally prescriptive and without consideration of structural modelling or failure models. While the approved document has allowed greater flexibility it also requires a greater understanding, particularly in areas where fire engineering and structural design overlap. It is for this reason that issues contained in C/AS1 “Fire Safety” pertinent to fire rating of tray flooring is included here. If careful consideration is given, then required fire ratings can be minimized, and the attainment of greater economies for the flooring system can be achieved.
Further, it is mandatory for all interactive aspects to be taken into consideration, as stated in clause 7.1 of BS5950:
“The fire resistance of composite slab depends on the minimum thickness of concrete and the average concrete cover to any additional reinforcement in the tensile zone, but also on its overall design including any fire protective treatment and restraint offered by the supporting structure.”
