Monday, 27 July 2015

Improved travelling fires for structural design

The collapse of 1WTC, New York City, 10:28am Sept 11, 2001.
Photo by
9/11 Photos CC BY.
Our latest paper on travelling fires for structural design has been published in Structures (journal of IStrutE) with the title Improved formulation of travelling fires and application to concrete and steel structures.

Note: It is open access so you can read and share it without need for a subscription. We have posted in open access also our Matlab code to calculate the fire temperatures in zenodo.

Accidental fire can be disastrous, especially in buildings. The effect of fire on structural stability is critical in regard to safe evacuation and safe access for fire fighters, financial losses, and lost business. This is particularly the case in tall buildings where extended evacuation times are required due to phased evacuation practices. The World Trade Centre Tower fires in 2001 have highlighted the need of a more realistic design tools to represent fires in large compartments. 

Innovative architectural designs of modern buildings already provide a challenge to structural engineers. This is above all the case in structural fire engineering. However, most of the understanding and current design codes are based on the assumption of uniform fires in a compartment. In previous work, we have shown that fires in large, open-plan compartments, typical of modern architecture, travel from one part of it to another with non-uniform temperature distribution. These fires are referred to as travelling fires. And Travelling Fires Methodology (TFM) has been developed to account for the travelling nature of fires.

Illustration of a travelling fire and distribution of gas temperatures.
TFM was born in 2010 and offers a paradigm shift in the structural engineering of modern buildings. The concept has already been applied by engineering firms like Arup, BuroHappold or AECOM in the design of a dozen of iconic buildings in the UK (including the renovation of Battersea Power Station in London). TFM accounts for one of the fastest knowledge transfers from research to industry seen in fire protection engineering. TMF is now being studying in detailed in the USA for possible adoption as well.

The focus of this latest paper is on the improvement of the calculations of traveling fire (iTFM) to account for better fire dynamics, and the analysis of the effect on structural members. The proposed changes represent a simple yet powerful fire model. In particular, our paper shows that:
  • Using data from experiments and real fires, we limit the range of possible fire sizes thus reducing the time required for conduct TFM studies.
  • Analytical expressions are presented for generating time–temperature curves which are independent of grid size (previous versions of TFM) and can be easily calculated with any mathematical tool. 
  • Introduction of flapping term leads to reduced near-field temperatures for smaller fire sizes which cover a range between 800 and 1200 °C, as observed in real building fires. 
  • The location of the peak temperature in the compartment is found to occur at the end of the fire path (i.e. far half of the compartment from the ignition source).

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