Coupled Fire Dynamics and Thermal Response of Complex Building Structures.
Coupled Fire Dynamics and Thermal Response of Complex
Prasad, K. R.; Baum, H. R.
Combustion Institute, Symposium (International) on
Combustion, 30th. Proceedings. Volume 30. Part 2.
July 25-30, 2004, Chicago, IL, Combustion Institute,
Pittsburgh, PA, Chen, J. H.; Colket, M. D.; Barlow, R.
S.; Yetter, R. A., Editor(s)(s), 2255-2262 pp, 2005.
combustion; structures; fire dynamics; thermal response;
heat transfer; simulation; structural integrity; vapor
phases; energy release; laod bearing materials;
radiative heat transfer; structural elements; World
Trade Center; thermochemical properties; heat flux;
temperature; soot; heating
Simulation of the effects of severe fires on the
structural integrity of buildings requires a close
coupling between the gas phase energy release and
transport phenomena, and the stress analysis in the
load-bearing materials. The connection between the two
is established primarily through the interaction of the
radiative heat transfer between the solid and gas phases
with the conduction of heat through the structural
elements. This process is made difficult in large,
geometrically complex buildings by the wide disparity in
length and time scales that must be accounted for in the
simulations. A procedure for overcoming these
difficulties used in the analysis of the collapse of the
World Trade Center towers is presented. The large scale
temperature and other thermophysical properties in the
gas phase are predicted using the NIST Fire Dynamics
Simulator. Heat transfer to subgrid scale structural
elements is calculated using a simple radiative
transport model that assumes the compartment is locally
divided into a hot, soot laden upper layer and a cool
relatively clear lower layer. The properties of the two
layers are extracted from temporal averages of the
results obtained from the Fire Dynamics Simulator.
Explicit formulae for the heat flux are obtained as
a function of temperature, hot layer depth, soot
concentration, and orientation of each structural
element. These formulae are used to generate realistic
thermal boundary conditions for a coupled transient
threedimensional finite element code. This code is used
to generate solutions for the heating of complex