H O L M E S F I R E N E W Z E A L A N D A U S T R A L I A C A L I F O R N I A W W W . H O L M E S F I R E . C O M

C O M M E R C I A L R E TA I L I N D U S T R I A L H E R I TA G E A S S E M B LY H O T E L S A N D R E S O RT S R E S I D E N T I A L H E A L T H C A R E E D U C AT I O N M I X E D U S E S TA D I A I N F R A S T R U C T U R E C O R R E C T I O N S C A R PA R K S P R O F I L E A N D C A PA B I L I T Y

holmesfire

FIRE RESISTANCE OF CONCRETE STRUCTURESConcrete is non-combustible and has low thermal conductivity – and it is for this reason that it is used so prevalently for fire rated construction. For reinforced concrete structures, the cover concrete keeps the reinforcing steel and the concrete core cool so that the load resistance can be maintained, this is the driver behind the thickness of a concrete fire rated floor or wall. Concrete structural elements are typically designed for fire by using tabulated information in prescriptive codes. These prescriptions can not only be restrictive, they are generally based on idealised tests and do not represent real life conditions.

Holmes Fire employs a range of analysis methods, including advanced non-linear finite element analysis, to analyse and predict the structural behaviour of concrete structures in real fires. These complex calculation techniques can account for the real life considerations that the standard fire tests do not consider. This enables our Fire Engineers to:

• determine the inherent fire resistance of structural elements, such a slabs, which are less than the minimum dimensions required by code; • determine the performance of concrete elements under high challenge fires (e.g.: hydrocarbon fire in tunnel structures);• analyse unprotected steel connections in precast concrete elements to determine if adequate fire resistance is achieved; and• determine the residual strength of concrete structures after being exposed to a fire.

Project case studies

In Australia, the concrete code (AS 3600-2009) requires a minimum 200 mm thickness for flat slabs to satisfy the requirements for structural fire stability. Using finite element analysis, Holmes Fire is able to justify the use of thinner slabs by demonstrating that the fire rating requirements are satisfied. This provides a reduction in the slab thickness of at least 15%, resulting in significant cost savings due to the reduced volume of concrete and formwork.

Holmes Fire can also utilise 3D finite element analysis to assess unprotected steel connections embedded within precast concrete floor systems. This bespoke analysis provides significant cost savings to the project as it negates the requirement for expensive and unnecessary passive fire protection to the exposed steel. This analysis also negates the need to undertake full scale fire tests which are generally be prohibitively expensive.