Damage Estimation of Steel Frame Buildings under Fire Using Collapse Analysis
Jun-ichi Suzuki1, Naoki Yokemura2 and Daigoro Isobe31

Department of Fire Engineering, Building Research InstituteTachihara 1, Tsukuba-shi, Ibaraki 305-0802, JAPANjsuzuki@kenken.go.jp
2

Graduate School, University of Tsukuba
1-1-1 Tennodai, Tsukuba-shi, Ibaraki 305-8573, JAPANs1220917@u.tsukuba.ac.jp
3

Division of Engineering Mechanics and Energy, University of Tsukuba
1-1-1 Tennodai, Tsukuba-shi, Ibaraki 305-8573, JAPAN
isobe@kz.tsukuba.ac.jp

Development of a fire in a steel frame building affects structural stability of the building withincrease in temperature of structural elements exposed to fire. High temperatures of structural
materials, such as steel or concrete, cause degradations of material strength and stiffness.
These thermo-mechanical properties of structural materials would damage not only on
structures of a building but also non-structural elements, e.g. exterior walls, compartment
walls on/in the building because of large deformation of the structural elements. The behaviorof the building exposed to fire generally results in falling and scattering of building
components on the ground near the building.
The objective of this research project is to propose an evaluation method for the relation
between damage of building’s structures and non-structural elements in a fire. To ensure thefire safety of buildings in fire resistance design, it is essential to clarify the damage by a fire.
This research focuses on the behavior and scattered range of exterior walls on a building
exposed to fire, which represents non-structural elements of a building, because falling of thewalls affects safety of evacuees and firefighters around the building.
A modified ASI-Gauss technique [1], which included a computational algorithm for
degradations of structural materials at high temperatures, was used to conduct fire response
analysis for interactions between steel frame structures and exterior walls of a building in thisresearch. Figure 1 showed the floor plan of 12-storey steel frame building for the fire
response analysis. The specification of the building was listed in Table 1. The dimensionof the building was 48 m high, 24 m wide (4-bay) and 26m long (3-bay). Steel grade of thestructures was SS400 (mild steel). The building’s structure was designed for appropriate
seismic capacity with a typical base-shear coefficient (Cb = 0.167). Autoclaved aerated
concrete panel (AAC) and fastening method of AAC was also modeled as exterior walls in theanalysis. Criteria for detaching a wall from structures were that the rotation angle of the wall
exceeded 1/20 in in-plane or out-of-plane deformation shown in Figure 2 and 3 [2].
Fire responses of the 12-storey steel frame building with exterior walls in various fire cases
shown in Table 2 were analyzed. A fire in the building was simply simulated by neglecting
varieties of fire spread in the building, non-uniform fire heating, thermal conduction form
heated elements to adjacent elements and so on. Increase in temperature of structures in afire compartment was considered as one of the effects of fire exposure. Thermal expansion ofstructural elements, degradations of elasticity and yield strength of materials in Figure 4 were- 436 -also implemented [3].
As a result of fire response analysis, it became obvious that falling of exterior walls wascaused by large deformation of local elements even if damage of the whole building was notsevere. Figure 5 showed the horizontal distance of scattered building elements from the edgeof the building. Empirical model [4] for estimating scattered range of exterior tiles and three
curves based on projectile motion with different horizontal velocities were also drawn.
Building elements located in high altitude have a high possibility of scattering farther fromthe building. The calculated curve of projectile motion with horizontal velocity 4.0 m/s wasable to cover almost all data obtained from the analysis. The empirical model also provided
approximate values for the maximum distances of the analysis and Ronan Point Apartment
Tower Accident [5]. It was found that horizontal velocity of elements was induced by contact
and rebound motions between building components in many cases.

6m 6m 6m 6m

Figure 6 showed typical deformation type of structures in a fire. We estimated the damage ofstructure by 4 types of deformation: Slant angle of beams (1) and deflection at midpoints ofbeams (2), contraction of columns (3) and bending deformation of columns (4). Figure 7
showed the relation between steel temperature and degree of damaged elements Nd/Nt. Here,Nd was the number of deformed elements or detached walls. Nt was the total number ofelements above fire floor. The number of detached walls correlated strongly with Dbs. On theother hand, Dbd did not influence on the damage of walls. In general, the severe damages ofouter columns and beams affect largely to the fall of exterior walls; however, some exceptions
where severe damages of inner structure affect the fall of exterior walls were observed.

YX

Steel elements
Floor elements
Exterior walls
ZY

10m6mX10ma) Floor plan and dimensionb) Arrangement of structural elements and walls
Figure 1 Structural model of steel frame building
Table 1 Specification of steel frame building and components
Floor number, Floor height
Total floor load
Base-shear coefficient
Steel grade
Exterior wall
Dimension
Fastening method
Floor SlabThickness

12 stories, 4m
800 kg/m2
Cb=0.167
Mild Steel(SS400, JIS G 3101)
Autoclaved aerated concrete panel600 mm x 125 mm x 4.0 m
Rocking mechanism with bolts and steel plates
Reinforced concrete
150 mm- 437 -BeamConnector(Steel Angle)

Beam
WallWallRotation Angle
1/20 (rad.)RotationAnglea) Original stateb) Displaced state
Figure 2 Out-of-plane displacementa) Original stateb) Displaced state
Figure 3 In-plane displacement

Table 2 Analyzed cases (Location and area of a fire in a single floor)
Fire floor
1, 2, 4, 6, 8, 10, 12F

Case - 2Ii

Case -2IoCase -2Oi

Case -2Oo

Case -3I
Case-3OCase- 4I
Case -4O*Areas in red show fire rooms in which structural elements increase in temperature.
弾性係数

降伏24

Scattered Range (m)σy (T)/ σy (R.T.), E(T)/E(R.T.)

1.0
0.8
0.6
0.40.2

Elastic modulus
Yield strength

0.001612840100 200 300 400 500 600 700
Steel Temperature
温度 [℃] T (℃)

Figure 4 Residual mechanical properties
at high temperatures[2]20Projectile motion
Horizontal Velocity 4.0 m/s
Horizontal Velocity 3.0 m/s
Horizontal Velocity 2.0 m/s
Empirical model:1/3 of Altitude [4]Estimated farthest rangein Ronan Point accident[5]816243240485664

Altitude of Elements (m)Figure 5 Relation between scattered range
and altitude of building elements[4, 5]- 438 -LΔUΔHδmδe
Beam HColumna) Slant angleb) Deflectionc) Contractiond) Bending deformation
Figure 6 Deformation of structural elements

Slant angle of beams(1)
𝐷𝑏𝑠 = 𝛿𝑒 /𝐿
Deflection at midpoint beams(2)
𝐷𝑏𝑑 = 𝛿𝑚 /𝐿
Contraction of columns(3)
𝐷𝑐𝑐 = ∆𝐻/𝐻
Bending deformation of columns 𝐷𝑐𝑏 = ∆𝑈/𝐻
(4)
Where L and H are length of the beam and height of the column respectively; 𝛿𝑒 isdisplacement of the beam in Figure 5; 𝛿𝑚 is deflection of the beam; ∆𝐻 and ∆𝑈 arecontraction and deflection of the columns respectively.

Nd / Nt (-)

0.08

0.06

Dbsが6％以上の梁の数
Beams
Dbs ≧ 6%
Dbdが6％以上の梁の数
Beams
Dbd ≧ 6%
Columns
Dcc ≧ 12%
Dccが12％以上の柱の数
Columns
Dcb ≧ 2%
Dcbが2％以上の柱の数
Detached
Walls
落下した外壁の数

0.04

0.02

0400 425 450 475 500 525 550 575 600 625 650 675 700 725 750
Temperature of steel elements (℃)

Figure 7 Temperatures of steel elements and degree of damaged elements
References[1] D. Isobe, L. T. T. Thanh and Z. Sasaki: Numerical Simulations on the Collapse Behaviors
of High-Rise Towers, International Journal of Protective Structures, Vol. 3, No. 1, pp.1-19,
2012.
[2] Y. Matsuoka, K. Suita, S. Yamada, Y. Shimada, M. Akazawa and T. Matsumiya:
Evaluation of Seismic Performance of Exterior Cladding in Full-scale 4-story Building
Shaking Table Test, Journal of structural and construction engineering, 74(641),
pp.1353-1361, 2009 (in Japanese)[3] NIST NCSTAR 1：Federal Building and Fire Safety Investigation of the World Trade
Center Disaster：Final Report of the National Construction Safety Team on the Collapse of theWorld trade Center Tower，2005．
[4] M. Suzuki, T. Kumagai, T. Maruichi and S. Suematsu: Experimental Study on Scatteringand Falling behaviors of Exterior Wall’s Tiles, Proceeding of the architectural researchmeetings, Kanto Chapter, Architectural Institute of Japan, pp.337-340, 1979 (in Japanese)[5] Pearson, C. and Delatte, N.: Lessons from the Progressive Collapse of the Ronan Point
Apartment Tower, Forensic Engineering, pp.190-200, 2003

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