ABSTRACT
There are three main steps in the fire resistance analysis of steel structures. The first step is determining the fire temperature resulting from a given fire exposure scenario. This can be carried out using the methodologies described in Chapter 3. The second step is to establish the temperature history in the steel structure, resulting from fire temperature. The second step forms the basis for undertaking the structural analysis which is the third step of fire resistance calculation. The accuracy of calculations in the second stage is critical for obtaining realistic fire resistance predictions. In fact in many cases an estimate of fire resistance can be obtained based on predicted steel temperatures alone through the use of critical temperature failure criterion. Establishing temperature history in the steel structure typically involves heat transfer
analysis. For this simple or advanced calculation models described in later sections can be used. The detailed steps for heat transfer calculations are contained in variousmanuals and
guides. Eurocode provides different approaches for evaluating temperatures in steel section. The complexity of these methods, discussed later in the chapter, varies with the type of analysis and is related to the accuracy of temperatures. AISC steel design Manual (AISC 2005) does not contain the equations for such calculations. However, ASCE manual (ASCE 1992) details the procedure for temperature calculations under various exposure (2, 3 or 4 sided) types and boundary conditions. One of themost important input for the heat analysis is the high temperature thermal
properties of steel and insulation materials. The high temperature properties of steel as per North American and Eurocode practices are listed in Annex I. In addition, the room temperature thermal properties of common fire protection material are provided in Annex I. For simple calculation methods room temperature thermal properties may be sufficient to estimate the temperatures in steel structures.
