Bushfire-related building losses cause adverse economic impacts to countries prone to bushfires. Building materials and components play a vital role in reducing these impacts. However, due to high costs of experimental studies and lack of numerical studies, the heat transfer behavior of building’s external components in bushfire-prone areas has not been adequately investigated. Often large-scale heat transfer models are developed using Computational Fluid Dynamics (CFD) tools, and the availability of CFD models for heat transfer in building components improves the understanding of the behavior of systems and systems of systems. Therefore, this paper uses a numerical modeling approach to investigate the bushfire/wildfire resistance of external Light gauge Steel Framed (LSF) wall systems. Both full-scale and small-scale heat transfer models were developed for the LSF wall systems. Experimental results of six internal and external LSF wall systems with varying plasterboard thickness and cladding material were used to validate the developed models. The study was then extended to investigate the bushfire resistance of seven external wall systems under two different bushfire flame zone conditions. The results illustrate the significant effects of fire curves, LSF wall components and configuration on the heat transfer across the walls. They have shown 1) the favorable performance of steel cladding and Autoclaved Aerated Concrete (AAC) panels when used on the external side of wall systems and 2) the adequacy of thin-walled steel studs’ load-bearing capacity during bushfire exposures. This study has shown that most of the investigated external LSF walls could be reused with cost-effective retrofitting such as replacing the Fire Side (FS) steel cladding after bushfire exposures. Overall, this study has advanced the understanding of the behavior of external light steel framed walls under bushfire flame zone conditions.
75 mm AAC (external) and 16 mm gypsum plasterboard (internal)
Glass fibre (24 kg/m3)
600
Tab.1
Fig.1
Fig.2
Model ID
Model dimensions (width × height) (mm)
Top and bottom boundary
Cavity sides boundary
B1
600 × 3000
ADIABATIC
MIRROR
B2
600 × 1000
ADIABATIC
MIRROR
B3
200 × 1000
ADIABATIC
MIRROR
B4
600 × 200
ADIABATIC
MIRROR
B5
1200 × 200
ADIABATIC
MIRROR
B6
600 × 200
ADIABATIC
Steel studs
Tab.2
Fig.3
Fig.4
Description
Mesh size
15 mm
10 mm
5 mm
Cell count
2028
7200
172800
No of message passing interface processes
3
3
3
CPU time (min)
75
238
3847
Tab.3
Fig.5
Fig.6
Fig.7
Fig.8
Fig.9
Fig.10
Fig.11
Fig.12
Test ID
Failure time (min)
Failure criterion
Test
Model
Internal walls
T1
94
79
insulation failure (average temperature)
T2
56
59
insulation failure (average temperature)
T3
106
108
insulation failure (average temperature)
T4
197
> 240
insulation failure (maximum temperature)
External walls
T5
23
22
insulation failure (average temperature)
T6
> 210
> 210
–
Tab.4
Fig.13
Test ID
Wall configuration
Details
Maximum ambient surface temperature
Fire Curve 1
Fire Curve 2
PS1
In PS1 to PS5, walls, a 0.42 mm steel cladding was fixed to the FS plasterboard/ fibre cement board using a 40 mm batten
85
63
PS2
101
71
PS3
57
45
PS4
45
42
PS5
218
150
PS6
same as T6
35
31
PS7
same as T6 with no cavity insulation
49
39
Tab.5
Fig.14
Fig.15
Fig.16
Fig.17
Fig.18
Fig.19
Fig.20
Fig.21
Fig.22
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