N. Yanagisawa/Y. Imagawa/O. Ohyama/M. P. Rutner/A. Kurita · Fire safety of bridges – methodology supporting design and forensic evaluation
a severe fire . In order to avoid serious damage to a
bridge due to fire attack, we are proposing that fire protection
panels (FPP) be added to protect viaducts or bridges
at locations where there is a high probability of fire exposure
following an accident , .
FFPs cover a steel frame structure that is connected
to the bottom flanges of the I-girders, providing an additional
vertical space of 600 mm, as shown in Fig. 12. Please
note that the air volume within the additional 600 mm
depth provides fire insulation additional to the FFP.
The weight of the FFP mitigation construction is about
Fire safety in bridge design is not as developed as fire safety
in building design, even though a bridge failure can cause
significant economic damage and impact on an area. This
research introduces a methodology capable of identifying
the governing failure mode of a bridge structure exposed
to severe fire loading and defining the regions of the bridge
facing the greatest fire exposure risk. Hence, this proposed
methodology is also able to support forensic work identifying
the failure mode of a bridge that has failed due to a
The proposed methodology is a multi-step procedure.
Firstly, the critical structural members or cross-sections of
the bridge structure are identified. Failure of these critical
structural members or cross-sections would trigger a specific
failure mode, e.g. shear or bending failure mode. The
stress resultant due to dead load acting on the critical
structural member or cross-section identified is then calculated.
Further, the load-carrying capacity of the critical
member or cross-section identified is calculated and the
8 Steel Construction 10 (2017), No. 1
decay of this capacity taking into account the temperature
dependent reduction in strength is determined. The
critical temperature at which the capacity becomes equal
to the stress resultant due to dead load is found by interpolation.
In a final step, the duration of fire exposure of the
respective critical member or cross-section taken to reach
that critical temperature becomes the parameter that enables
the criticality of members and cross-sections of the
bridge to be identified and ranked. It is emphasized that
the fire signature, pool fire location and size affect the
identification of critical structural members and cross-sections
and should be known beforehand. In this study,
which investigated the collapse of the 9-Mile Road Overpass,
the fire loading was assumed to be uniformly distributed
along the whole bridge span, which was confirmed
by photographs taken during the fire incident and by reports.
In an effort to mitigate fire damage, the fire protection
panel (FFP) is introduced, which is part of a sacrificial
structure shielding the bridge superstructure from exposure
to fire from underneath.
 Ham, D. B.; Lockwood, S.: National Needs Assessment for
Ensuring Transportation Infrastructure Security. American
Association of State Highway & Transportation Officials
(AASHTO), Washington, D.C., 2002.
 Kodur, V. K.; Gu, L.; Garlock, M. E.: Review and Assessment
of Fire Hazard in Bridges. Transportation Research Record
2172, TRB, Washington, D.C., 2010.
 Roberts, J. E.; Kulicki, J. M.; Beranek, D. A.: Recommendations
for Bridge and Tunnel Security. Report FHWA-IF-03-036
(FHWA)/AASHTO Blue Ribbon Panel, 2003.
 National Fire Protection Association (NFPA): NFPA 502 –
Standard for Road Tunnels, Bridges, and Other Limited Access
Highways, 2011 ed., Quincy, MA.
Table 3. Time of fire exposure up to failure
Collapse temperature [°C] Time to failure [min]
1) Tensile normal force of suspender 830 20.4
2) Shearing force at intermediate support 820 9.5
3) Positive bending moment at centre of main girder 720 16.2
4) Negative bending moment at intermediate support 800 17.7
Fig. 11. After the fire accident of the 9-Mile Road Overpass
Fig. 12. Structural detailing of fire protection panel (FFP)
connected to I-girder bridge