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BRANZ TR8 Concrete floor systems

TR8 software is a model to predict the fire resistance of concrete slabs and floor systems and can be used for the design of reinforced or prestressed concrete floor systems when required to have fire resistance.

TR8 software is based on BRANZ technical recommendation TR8 Method for fire engineering design of structural concrete beams and floor systems, which you should use to gain an understanding of the basis for the software. It is referenced by NZS 3101 Concrete structures standard as an acceptable calculation method for determining the fire resistance of concrete floor systems.

The underlying procedure applies structural engineering principles and material properties at elevated temperature to the calculation of the fire resistance of reinforced or prestressed concrete floor systems.

TR8 applies to floor systems with these characteristics:

  • May be rectangular or tapered in cross-section (for beams) or tee-beams with a minimum width of 100 mm.
  • Made with normal weight concrete (assumed density greater or equal to 2,000 kg per m³), lightweight concrete (assumed to be less than 2,000 kg per m³) and the following for slabs only: alluvial quartz concrete (equivalent to NZS 3101 Type A), dacite aggregate concrete (equivalent to NZS 3101 Type B) or pumice aggregate concrete (equivalent to NZS 3101 Type C).
  • Support conditions are assumed to be either simply supported or continuous over the supports.
  • The section includes either prestressing tendons or deformed reinforcing bars.
  • Designed in accordance with the requirements of NZS 3101 and NZS 4203 (now superseded by AS/NZS 1170).
  • It is assumed that the concrete element has reached its equilibrium moisture content and that the occurrence of concrete spalling during fire will be minimal.
  • The mode of failure for the floor system is assumed to be in flexure. Failure is taken as the time at which the reduced moment capacity of the element becomes less than the moment applied to the element.
  • Factors of safety are already included into the fire resistance period and with respect to the normal design loads. In fire design, it is normal to allow the load factors and design live loads to be reduced.

See experimental comparisons with the model in this journal article: Performance of concrete floors exposed to real fires.