FIRE DESIGN OF STEEL MEMBERS - Civil and Natural Resources ...

can be obtained from either a single experimental test or from regression data from
a series of tests.
For all members with four sided exposure conditions, the limiting temperature is
recommended by NZS 3404 to be taken as the average temperature of all results
taken by thermocouples taken during the test. For columns with three sided
exposure conditions, the limiting temperature is taken as the average temperature
of the thermocouples located on the face furthest from the wall, or alternatively the
temperatures from members with four sided exposure can be used for more
conservative results.
NZS 3404:1997 states:
The variation of steel temperature with the time measured in a standard fire
test may be used without modification provided:
a) The fire protection system is the same as the prototype;
b) The fire exposure condition is the same as the prototype;
c) The fire protection material thickness is equal to or greater than that of
the prototype;
d) The section factor is equal to or less than that of the prototype; and
e) Where the prototype has been submitted to a standard fire test in an
unloaded condition, stickability has been separately demonstrated.
When the results of a series of tests are to be used, the variation of temperature
with time can be interpolated provided the tests meet the limitations provided in a)
– e) above.
NZS 3404 also has an option to use a regression analysis to form a relationship
between temperature and time by using the following formula:
t = k
di
di
T
+ k1 hi
+ k
2
+ k3T
+ k4hiT
+ k5
+ k 3.11
SF
SF
SF
o 6
where:
t = time from start of the test (min)
k o – k 6 = regression coefficients
d i = thickness of fire protection material (mm)
T = steel temperature (°C), T>250 °C
SF =section factor of steel member, exposed surface area to mass ratio (m 2 /t)
45