Thermal Analysis

Figure 1 shows the schematic diagram for the thermal analysis within structural fire engineering design.

Figure 1 Schematic diagram for heat transfer

Model	Design charts / Test data	Simple formulae	Advanced models
Complexity	Simple	Intermediate	Advanced
Heat Transfer Modes	Conduction		Convection Radiation Conduction
Analysis ability	-Test results -Standard fire conditions	-Empirical solutions -Standard fire conditions	-Accurate solutions -Any fire conditions
Member types	Dependent on available test data	Mainly steel members	Any material & construction methods
Input parameters	-Construction type -Member geometry	-Heat flux or fire curves -Boundary conditions -Member geometry -Material thermal properties
Solutions	-Cross-sectional temperature charts -Tabulated thermal data	Simple cross-sectional temperature profile	One to three-dimensional time & space dependent temperature profile
Design tools	-Fire part of Eurocodes -Test/Research reports	-Fire part of Eurocodes -Design guides	Finite element package
	Design charts/tables	Spreadsheet	Computer models

Heat Transfer

Heat transfer is the science to evaluate the energy transfer that takes place between material bodies as a result of temperature difference. The three modes of heat transfer are conduction, convection and radiation. The thermal analysis on structural fire problems can be divided into two parts:

Test Data

The thermal analysis in structural members can be extremely complex, especially for materials that retain moisture and have a low thermal conductivity. The simplest method of defining the temperature profile through the cross-section is to use test data presented in tables or charts which are published in codes or design guides. These test data are generally based on standard fire conditions.

Design Formulae

Simple design equations are presented in codes and design guides to predict the temperature development of bare steel. The approach considers both radiative and convective heat transfer and, although a spreedsheet is required to solve the equation over the fire duration, it is simple to use. Similar equations exist for protected steel sections, however the thermal properties of the proposed protection material are needed, which can be difficult to obtain.

Computer Models

It is possible to use simple heat transfer models based on one-dimensional heat flow. However, simple computer programs are needed to solve the heat transfer equations. Alternatively, advance finite-element heat transfer models can be used, but this requires the relevant expertise to ensure the models are applied correctly and used within their limitations.