N. Yanagisawa/Y. Imagawa/O. Ohyama/M. P. Rutner/A. Kurita · Fire safety of bridges – methodology supporting design and forensic evaluation
Fig. 8. Negative bending moment and shearing force interaction M-Q and temperature distribution over depth of composite
Steel Construction 10 (2017), No. 1 7
reach the critical temperatures in the respective structural
member, as found in section 4.
The authors carried out the heat transfer analysis by
using the SOFiSTiK finite element software . The thermal
properties of the carbon steel and normal concrete are
based on Eurocodes 2 and 3 , . The temperature–
time curves provided by the Eurocode are standard temperature–
time curve (ISO), external fire curve (EX) and
hydrocarbon curve (HC), as cross-plotted in Fig. 10 .
Whereas the standard temperature–time curve (ISO)
is used for the fire analysis of buildings, the external fire
curve (EX) is used for the fire response calculation of
members exposed to fire through windows. The hydrocarbon
curve (HC) is used to represent the combustion of
gasoline resulting in temperatures of up to 1100 °C, which
corresponds well to the forensic reports of bridge failures,
e.g. . Hence, in this analysis, the HC curve was used.
Table 3 shows the duration of fire exposure required to
reach the respective temperatures and initiating respective
failure modes. Column 1 in Table 3 lists the four failure
modes discussed, column 2 shows the critical temperature
in °C and column 3 lists the duration of fire exposure up to
failure in minutes.
Referring to Table 3, the 9-Mile Road Overpass failed
due to shearing failure at the intermediate support. This
result is supported by a photo of the post-fire condition of
the bridge, see Fig. 11.
6 Future topics for discussion
Fire protection mitigation measures have been developed,
especially for buildings, but not for bridges . Most
bridges do not have passive fire protection materials that
can withstand the elevated temperatures exceeding 1100 °C
accompanying a fire pool. Governmental agencies around
the world, such as the US Department of Homeland Security,
are interested in mitigation measures for fire damage
and loss of structural integrity of bridges when subjected to
Fig. 9. Negative bending moment capacity depending on
Fig. 10. Fire curves