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Thermal Analysis
  Introduction
  Heat Transfer
    Across Boundary
    Within Members
    Computer Packages
  Test Data
    Background
    Steel & Composite
    Concrete
  Design Formulae  
    Unprotected Steel
    Protected Steel
    Unprotected Composite Slab
    Concrete Members
  References

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:

  • The heat transfer by convection and radiation across the boundary from the fire into structural members;
  • The heat transfer by conduction within structural members.

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.

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