Title:
Concurrent fire dynamic models and thermomechanical analysis of steel and concrete structures
Concurrent fire dynamic models and thermomechanical analysis of steel and concrete structures
Author(s)
Choi, Joonho
Advisor(s)
Haj-Ali, Rami M.
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Abstract
The objective of this study is to formulate a general 3D material-structural
analysis framework for the thermomechanical behavior of steel-concrete structures in a
fire environment. The proposed analysis framework consists of three modeling parts: fire
dynamics simulation, heat transfer analysis, and a thermomechanical stress analysis of
the structure. The first modeling part consists of applying the NIST (National Institute of
Standards and Technology) fire dynamics simulator (FDS) where coupled Computational
Fluid Dynamics (CFD) with thermodynamics are combined to model the fire progression
within the steel-concrete structure. The goal is to generate the spatial-temporal (ST)
solution variables (temperature, heat flux) on the surfaces of the structure. The FDS-ST
solutions are generated in a discrete numerical form. Continuous FDS-ST
approximations are then developed to represent the temperature or heat-flux at any given
time or point within the structure. An extensive numerical study is carried out to examine
the best ST approximation functions that strike a balance between accuracy and
simplicity. The second modeling part consists of a finite-element (FE) transient heat
analysis of the structure using the continuous FDS-ST surface variables as prescribed
thermal boundary conditions. The third modeling part is a thermomechanical FE
structural analysis using both nonlinear material and geometry. The temperature history
from the second modeling part is used at all nodal points. The ABAQUS FE code is used
with newly developed external user subroutines for the second and third simulation parts.
The main objective is to describe the nonlinear temperature-dependency of the specific
heat of concrete materials, especially high-strength concretes, that drastically affects their
transient thermal solution. New algorithms are also developed to apply the continuous
FDS-ST surface nodal boundary conditions in the transient heat FE analysis. The
proposed modeling framework is applied to predict the temperature and deflection of the well-documented Cardington fire tests and to predict the time-to-collapse of the recent
Oakland bridge fire caused by a fuel-truck accident.
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Date Issued
2008-10-21
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Text
Resource Subtype
Dissertation