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

strength design actions are modified by factors that account for the variation of
strength of steel with temperature, and decrease the nominal strength of an
element.
There are a number of changes that can be made to improve Section 11 of NZS
3404 and these are outlined in this section of the report. Changes to the New
Zealand Steel Code such as definitions and connection guidelines have not been
covered in this report so are not commented on.
7.2 ANALYSIS OF THE EUROCODE:
7.2.1 Design Methods for Performance Requirements:
Eurocode 3 states the performance requirement that an element is to be ‘designed
and constructed in such a way that they maintain their required load bearing
function during the relevant fire exposure’. Deformation criteria must be satisfied
if the performance of the member relies on small deflection, ie. if the protection
applied to the beam will not remain in place if there is too much deformation of the
member.
The method in EC3, (1995) follows the principles of normal plastic design, but
with modified loads for fire design and with reduced values of the modulus of
elasticity and the yield stress of steel to allow for the loss of strength at these
temperatures. This is to design structures to satisfy the strength criteria at elevated
temperatures, while the New Zealand Steel Code predominantly suggests methods
to establish the maximum temperatures reached in a member at elevated
temperatures, and the time that this temperature occurs.
NZS 3404 makes a provision to allow for the design of members with reduced
steel properties for fire design, see Section 3.1.1c. However, there are not detailed
guidelines to assist designers in the use of this provision in the code, and the
calculations made must be confirmed by an analysis method using experimental
data. There are no methods recommended to satisfy this.
130