The influence of thermal gradients in steel columns due to pool fires

Abstract

During this thesis the fire safety engineering approach has been used to investigate the influence of hydrocarbon pool fires on steel columns. Using a fire curve which closely resembles a natural fire curve the temperatures occurring in the steel have been investigated using a Computational Fluid Dynamics (CFD) model. The model consists of the compartment which has been discussed in chapter three. As can be seen in chapter four the model which has been introduced in the CFD software closely mimics the actual compartment, including windows, roof openings and a large overhead door in the wall. After the model had been entered the fire curve must be given as well. The fire curve which has been used is based on a pool fire with a three meter diameter and a height of 2.5cm. Using the mass burning rate and rate of heat release the maximum power emitted by the liquid can be calculated. After having run the CFD calculation which took about four days per scenario the results of the temperatures in the steel had been formulated. Having used a CFD calculation the results of this calculation were to be checked by a reference tool. Arcelor Mittal has created a software package called Ozone. Having entered the same compartment and fire curve as had been done in the CFD simulation the results can be compared to each other. The results and the comparison of the two simulations have been evaluated in chapter 6.4. Focussing on the load bearing capacity of the column chapter seven investigates the maximum stress which the cross section can endure in a fire situation. Please note that this chapter only checks the strength of the column at raised temperature and omits any phenomena of instability. As the temperatures have been calculated by CFD and are thus known we can distinguish two cases. The first case is the temperature profile in the cross section of the column at which the highest temperature appears. Secondly the case in which the highest temperature difference occurs in the cross section. Having formulated a series of excel sheets an upperbound solution for the critical elastic buckling load can be calculated for columns with thermal gradients.