Steel frames under fire

Abstract

Fire resistance is the ability of a structure or a member to fulfill required functions (load-bearing capacity, and/or separating function), for a specified fire exposure and for a specified period of time. To apply fire protection to a structure, it is necessary to understand its behaviour in a real fire situation. Therefore, analytical methods are developed to predict the behaviour of fire, temperature rise in the structure and the response of the structure at elevated temperatures.In order to analyze the steel frames under fire conditions, plastic theory has successfully adopted to the steel frames. Plastic theory can predict the collapse loads of framed structures. The fundamental theorems of plastic analyses are named as the Lower Bound Theorem, Upper Bound Theorem and Uniqueness Theorem. These three theorems are also used successfully under fire conditions. As these theorems are used for the calculation of the critical temperatures and their possible distribution at collapse under fire conditions, also the Rankine Approach can be used for the same purpose as well. Second order analyze which is another method to find the critical temperature considering the axial load effects, has to be taken into account during the analyses, too.The aim of this study is to give information needed for calculating the performance of steel buildings exposed to fires. Simple methods are described for determining the critical temperatures for individual steel members to resist fire exposure, including calculations of elevated temperatures and information on the thermal and mechanical properties of steel at elevated temperatures. Fire behaviour of steel structures is also discussed.