World Journal of Engineering and Technology, 2014, 2, 20-26
Published Online September 2014 in SciRes. http://www.scirp.org/journal/wjet
http://dx.doi.org/10.4236/wjet.2014.23B004
How to cite this paper: An, A.Y., Ryu, E.M. and Ki m, H.S. (2014) Investigations on Structural Safety of Office Room Based on
Fire Simulation and Transient Heat Transfer Analysis. World Journal of Engineering and Technology, 2, 20-26.
http://dx.doi.org/10.4236/wjet.2014.23B004
Investigations on Structural Safety of Office
Room Based on Fire Simulation and
Transient Heat Transfer Analysis
Ah Young An, Eun Mi Ryu, Hee Sun Kim
Department of Architectural Engineering, Ewha Woman’s University, S eoul, Korea
Received May 2014
Abstract
This study aims at investigating heat propagations inside the structural members due to fire using
fire simulation and transient heat transfer analysis. Toward that goal, fire simulation and tran-
sient heat transfer analysis for a 5-story build ing a re carried out sequentially using Fire Dyn am ics
Simulator (FDS) and ABAQUS 6.10-3, respectively. As results from fire simulation, temporal tem-
perature information is obtained depending on various locations of the building, which is used as
boundary condition for the structural elements generated in transient heat transfer analysis. Pre-
dictions from the transient heat transfer analysis show that the structural members are exposed
spatially non-uniform temperatures which can cause significant eccentric deformation and ace-
leration of structural damages .
Keywords
Fire Simulation, Heat Transfer, Structural Safety, Fir e
1. Introduction
Even though concrete is well known as thermal resistant material, concrete structures exposed to severe fire ac-
cident show significant degradation of structural capacities and lead to building collapse. Since performing ex-
periments for safety evaluation of fire damaged structures requires huge cost and time, there is a need for quan-
titative modeling approaches that can evaluate structural safety based on accurate predictions of fire and heat
propagations.
Fire simulation tools such as CFAST, JASMINE, SOFIE, FiRECAM and FDS, have developed by research
laborato ries and academic in stitutions in man y counties. Am ong them, this stud y uses Fire D ynamics Simulator
(FDS) developed at the Building and Fire Research Laboratory (BFRL) at the National Institutes of Standards
and Technology (NIST) [1] [2] . T he program calculates the temperature, density, pressure, velocity, and chemi-
cal composition within each numerical grid cell at each discrete time step. It computes the temperature, heat flux,
and mass loss rate of the enclosed solid surfaces. The FDS code is formulated based on Computational Fluid
Dynamics (CFD) of fire-driven fluid flow. The FD S numerical solution can be carried o ut using either a Direct
Numerical Si mulation (D NS) met hod or Large Ed dy Si mulatio n (LES). T he latter is no t sever ely limited in grid

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size and time step as the DNS method. In addition to the classical conservation equations considered in FDS, in-
cluding mass species momentum and energy, thermodynamics-based state equation of a perfect gas is adopted
along with chemical combustion reaction for a library of different fuel sources. FDS has a visual post-processing
image simulation program named “smokeview”. In FDS, the Heat Release Rate (HRR) per unit area of a fire
source can be prescribed and numerically characterized directly avoiding calculating the heat release using
chemical combustion reaction. Therefore, it is important to find accurate HRR curve or fire load according to
various types and amount of fire sources. Madrzykowski [3], Kar lsson and Quintiere [4], Au [5], and Cho w [6]
reported experimental or numerical studies about HRR curves in various fire environments. Especially, Madr-
zykowski [3] performed fire experiment on office roo m with different work station configurations and measured
HRR and radiation during fire. In the study, peak HRR of work station ranged from 2.8 MW to 6.9 MW and
growth ra te changed from “slow-medium” to “fast-ultra fast” phase.
Since the fire simulatio n focuses on predicting fire propagations based CFD of fire-d riven fl uid flow and has
limitation on predicting temperature distribution inside the structural members, transient heat analysis needs to
be performed in order to evaluate safety of fire damaged structures. Choi [7], Choi, Kim, Haj-Ali [8], and C hoi,
Haj-Ali, Kim [9] proposed sequentially coupled analytical methods for predicting temperature distributions and
structural behaviors of structural members considering temperature dependent thermal and mechanical proper-
ties of concrete. In their studies, the proposed methods were applied to simulate reinforced concrete beams,
steel-concrete building, and bridge under fire for the model validation and showed good agreements. Harmathy
[10] [11] provided properties of building materials such as concrete, steel, etc., at elevated te mperatures and re-
ported that the properties of different concrete are within upper and lower bounds depending on aggregates, ad-
mixtures, and mix proportions. In addition, Choi [9] performed parametric analyses, in order to examine effect
of the wide ranges of material properties on thermal and structural behaviors of fire damaged concrete struc-
tures .
This paper aims at evaluating safety of structural members of office rooms based on fire simulation and tran-
sient heat transfer analysis. Towards that goal, fire simulating approaches by investigating effect of various in-
fluencing parameters on fire propagations. Then, the spatial-temporal te mperature infor mation ob tained fro m the
fire simulation is used as boundary condition of structural members for transient heat transfer analysis. Finally,
safety of the structural members is evaluated based on temperature distributions predicted from transient heat
transfer analysis considering temperature dependent thermal and mechanical properties of concrete.
2. Modeling Approach
2.1. Fire Simulation Approach
In this study, fire simulation is performed on a 5-story building located in Seoul, South Korea. The structural
system of the buildin g is fram ed struct ur e made of normal strength concretes reinforced by deformed steel bars.
Since fire simulation requires relatively long computational time, only two out of five stories are modeled with
an assumption that fire is initiated from a room located on a fourth floor shown in Figure 1. With the assump-
tion, only fo urth and fifth flo or are modeled because heats tend to be propagated toward the upper floor. Based
on architectural and structural plans, elements for walls, slabs, and ceilings are generated. For walls and ceilings,
concrete and insulation material properties are included in the model and slabs are consid ered as reinforced con-
crete with 150 mm of thickness. Doors and windows are assumed as open and 2.17 m/s of northwestern winds
are prescribed.
In order to investigate effect of parameters on fire and heat propagation, variables for fire simulations are
chosen as period of fire, size of inflammable materials and fire gro wth phase. Fire simulations are performed for
30 and 60 min to examine effect of fire period to heat propagation. In addition, sizes of inflammable materials
are 15 m2, 42 m2, and 210 m2, determined by size of typical work stations, one room, and five rooms, respec-
tively. However, area of hallway is not included in the size of inflammable materials because possible fire
source is not stacked in hall way by law. From the fire si mulation, te mporal-temperatures are ob tained at differ-
ent locations of the rooms and hallway of fourth and fifth floor. Finally, fire loads are prescribed in a form of
heat release rate (HRR) curve, and the time to reach steady phase of HRR curve determines whether the fire is
slow, medium or fast growth phase. Figure 2 shows two p ossible HRR curve s for office building, based on the
literature revie ws [4]. In addition, maximum value of the HRR curve is prescribed as 876.1 9 kW/ m2, according
to Madrzykowski’s study [3].

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Figure 1 . Floor plan (Marked area: location of fire initiation).
Figure 2. Heat release rate (HR R) cu rve.
2.2. Transient Heat Transfer Analysis
Transient heat transfer analysis is performed to predict temperature distributions between and inside the struc-
tural members. In the study, commercial finite element (FE) analysis software, ABAQUS 6.10-3 is used to gen-
erate FE elements of the fire initiated compartment which size is 8.4 m × 7.2 m in area and 2.4 m in height. The
FE model includes structural members, such as four columns, eight girders, two beams, and a slab. According to
struct ura l p lans, c ro ss sectio n of the co lumn s i s 500 mm × 500 mm. In addition, cross sections of the gird e rs and
the beams are 650 mm × 350 mm and 550 mm × 350 mm, respectively. The thickness of the slab is 150 mm.
The initial te mperat ure is pr escribed as 20˚C, and the temporal-spatial temperatures obtained fro m the fire simu-
lation are prescribed using in-house written code in Fortran language to the surfaces of the structural members
exposed to the fire. Prescription of the temporal-spatial temperature information is important, because it is ob-
served from fire simulation that temperatures are not non-unifo rm even within o ne span d epending on the loca-
tions. Therefore, the prescribed temperature varies along x, y, and z axis depending on the distance from the lo-
cation of fire source. As results, time to reach 500˚C at location of reinforcing steel bars is examined at different
structural members .
3. Results
3.1. Fire Simulation
Figure 3 illustrates time-temperature curve obtained at location of fire source depending on medium and fast
fire growth phases. As shown, there is no s igni fica nt difference of time-temperature curves due to fire growth
phase. Especially, time-temperature curves in range of 0 - 800 sec show almost identical, even though times to
reach maximum HRR value are about 350 sec and 700 sec for fast and medium growth phase, respectively. In
the early stage of fire, temperature around fire source increases drastically within less than 200 sec until it
reaches 900˚C - 1000˚C. After reaching 900˚C - 1000˚C, time-temperature curve becomes steady state with only
slight increase. Therefore, it can be also seen that the increase of temperature depending on time period of fire
accident is not critical after 200 sec, with a condition that the fire simulation doesn’t include decay phase of
HRR or fire suppression.
Figure 4 illustrates time-temperature curves predicted from different locat ions sho wn in Figure 5. As s ho wn,

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Figure 3. Time-temperature curve depending on fire growth phase.
Figure 4. Time-temperature curve at different locat ion.
Figure 5. The location of sensor.
temperature difference within the fire initiated room is about 200˚C. Maximum temperature of hallway varies
from 200˚C - 400˚C, and the higher temperature occurs in the west side of the hallway (E) compared to right
side of the hallway (C). Because the fire simulation is modeled with northwestern winds with a speed of 2.17
m/s referring to the local weather report, temperatures are transferred towards the west. In addition, maximum
temperatures obtained at different locations depending on sizes of inflammable materials are illustrated in Fig -
ure 6. When the model includes inflammable materials located in the rooms nearby fire sources, maximum
temperature at hallway (D) increases more than about 700˚C, compared to the case that the inflammable mate-
rials is located only at the corner of the room. However, it is interesting to note that maximum temperatures of
fire initiated room are not sensitive to size of inflammable materials relative to maximum temperatures of hall-
way. Figure 7 a l so shows ti me-temperature curves predicted at differe nt heig hts of the model. Since temperature
tends to move upward due to convection, temperature at 2 m above the fire source is about 200˚C higher than

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the temperatures right above the fire source. However, it seems that temperatures are not transferred to the upper
floor until 30 min after fire initiation due to in sulation ef fect of the concrete slab.
3.2. Transient Heat Transfer Analysis
Figure 8 shows temperature distributions predicted from transient heat tra nsfer analysis prediction along with
Figure 6. Maximum temperature depending on area of
fire sour ce.
Figure 7. Time-temperature curve obtained at differen t heigh t above the fire source.
Figure 8. Predictions from transient heat transfer analysis with
times to reach 500˚C.

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25
times for the temperat ure inside the cover thickness to reach at 500˚C. It is important to check if the inner te m-
perature reaches at 500˚C, because structural members lose structural capacity if the temperature exceeds 500˚C
according to Choi’s study [12]. In addition, compressive strength of normal strength concrete degrades about
50% at 500˚C [10] [11]. From the fire si mulation, the te mper atures predicted from M-60-210 model are used in
the transient heat transfer analysis, because the case is the most realistic and critical. As seen from Figure 8,
temperatures inside the cover thickness for the most of structural members reach 500˚C at 2500 - 3600 sec after
fire initiation. Since the prescribed temperature on the s ur fa c e s o f t he st ructural members varies according to the
results pred icted fro m fire simulation, times to reach 500 ˚C varies d epend ing o n the lo cati ons a nd the struct ural
members. Among the structural members, upper section of the column closed to fire source reaches 500˚C at
around 2500 sec, which denotes that the column nearby the fire source is the most critical in terms of str uc tura l
safety. Girders are the next critical members, because three surfaces are exposed to high temperatures. However,
temperatures inside the slab do not reach 500˚C duri ng 1 ho ur o f fi re , s ince the te mperatures are relatively low in
the bottom and the hallway. The predictions denote that partial surfaces of the str uc tural members are subjected
to non-uniform temperatures which can lead significant eccentric deformation and acceleration of structural
damages.
4. Conclusion
This study incl udes fire simul atio n and tran sient heat tr a nsfe r anal ysis to investiga te heat p rop agations insid e the
structural members due to fire. In the fire simulation, parametric studies for the effect of fire growth phase and
size of inflammable materials on ti me-temperature curves are included. Also, temperatures are examined at dif-
ferent locations and heights of the fire initiated room and hallway. As results, it is shown that temperature in-
creases drastically in the beginning of fire, then maintains its maximum temperature for the rest of fire. Medium
and fast growth phases do not cause differences on time-temperature curves. However, temperature increases
with the size of inflammable materials, and the more significant result is examined in the hallway. In the tran-
sient heat transfer analysis, temporal-spatial temperature i nformation obtained from the fire simulation is used a s
boundary conditions of the structural members and time to reach 500˚C inside the cover thickness is examined
to investigate struc tural safety fro m the predicted heat p ropagations. The results from the tr ansient heat tra nsfer
analysis show that location of cover thickness for most structural members reaches 500˚C within one hour of fire,
except for a floor slab. Among the me mbers, upper part of the column located nearb y fire source reaches 500˚C,
followed by lower part of the girder attached to the column. The predicted results show that not only the struc-
tural members reach 500˚C at different time level, also they are exposed to spatially non-uniform temperatures
due to convection, which can cause significant eccentric deformation and acceleration of structural damages.
Acknowledgements
This research was supported by Basic Science Research Program through the National Research Foundation of
Korea (N R F ) funded by the Mini stry of Science, ICT & Future Planning ((No . NRF -2013R1A2A2A04014772).
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