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John Street Apartments

The project involved a mixed-use 12 storey residential and retail building of steel construction, with four levels of basement carparking. Holmes Fire provided Fire Engineering for the entire building including:

  • Substituting the active stair pressurisation system serving the residential levels with a passive solution to enhance the life safety provisions of occupants as well as the fire brigades, whilst reducing design, installation and maintenance costs;
  • Allowance for extended residential travel distances and long public corridors avoiding the need for smoke separations in the public corridors;
  • Analysis of extended travel distances within the carparks to limit the number of exits required and provide more car spaces;
  • Justifying the discharge of fire-isolated stairs into covered areas that do not meet requirements of the BCA Deemed-to-Satisfy Provisions;
  • Allowing the fire brigade hydrant booster assembly to be located away from the main entry and adjacent to a substation; and
  • Omission of redundant protection to the steel members throughout the basement carparking levels,to provide cost savings and expedite the construction.

As part of the justification of the omission of protection to steel members within the carpark, a comprehensive case study was conducted to determine a realistic fire event within the carpark, reviewing international literature and experimental data on the subject. From this a realistic high challenge design fire for the space was developed, and applied as part of a detailed numerical modelling effort to predict the structural behaviour of the steel members and concrete floor slabs under load during a fire scenario. This was complicated by the large number of different member types and long member spans.

The structural fire analysis, which involved the use of 3D structural modelling, demonstrated that the stability of the carpark steel structure is able to maintain its integrity when exposed to realistic car fires, considering completely unprotected secondary beams and reduced protection to the primary beams. Sensitivity studies were conducted to provide robustness in design, and to determine the extent of protection which could be removed. Overall cost savings to the project were significant notwithstanding the added robustness inherent in the proposed design.