Steel Buildings in Europe

Part 6: Fire Engineering 6 - 30 If the unprotected member is not adequate, measures have to be taken to improve its fire resistance by:  Choosing a larger cross-section for the steel member  Selecting a higher grade of steel  Providing the necessary fire protection. 4.3 Structural Analysis Figure 4.5 illustrates the general behaviour of a structural member under the effect of the standard fire and applied actions. As the gas temperature θ g rises, the member temperature θ a,t increases and its load bearing resistance R fi,d,t decreases. The critical temperature θ cr is defined as the temperature at which a member can no longer support the design effects of the applied actions. The effects of actions (also called action effects) on a member are the internal forces or moments induced by the actions. For example the wind blowing on a structure is an action (the wind action) and the internal forces and bending moments induced in a column are the effects. Given a structure subject to various actions (e.g. wind, gravity), a member is subject to the design value of an effect, E d . Under the same actions but also subject to fire, the effects on the member are modified, and denoted as E fi,d . The critical temperature θ cr is therefore defined as the temperature at the time of failure, when the resistance of a member is equal to the effect on it: R fi,d,t = E fi,d . Figure 4.5 Behaviour of a structural member in fire