design of steel structures under the aspect of fire protection measures tu braunschweig ibmb...
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![Page 1: Design of steel structures under the aspect of fire protection measures TU BRAUNSCHWEIG iBMB Dr.-Ing. E. Richter Institute for Building Materials, Concrete](https://reader030.vdocument.in/reader030/viewer/2022032802/56649dea5503460f94ae5278/html5/thumbnails/1.jpg)
Design of steel structures
under the aspect
of fire protection measures
TU BRAUNSCHWEIGiBMBiBMB
Dr.-Ing. E. RichterInstitute for Building Materials, Concrete Structures and Fire Protection
Technical University of Braunschweig
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iBMBiBMBContents
Introduction Fire exposure
Standard fire, natural fire
Properties of steel in fire Protective materials Steel temperature
Protected and unprotected steelwork
Simple calculation model Critical temperature, Eurocode 3 Part 1-2
Conclusions
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iBMBiBMBIntroduction
General objectives of fire design Load-carrying capacity:
• members in a structural assembly should resist the applied loads in a fire
Insulation:• limitation of temperature of 140 K (average) or
180 K (peak) on the unexposed side of a wall or floor
Integrity• limitation of breaks or cracks to avoid passage
of smoke or flame to the unexposed side of a wall or floor
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iBMBiBMBStandard temperature/time curve
0 30 60 90 120 150 180 time [min]
1200
1000
800
600
400
200
0
tem
pera
ture
[°C
]
ISO 834: - = 345 lg (8t + 1)
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iBMBiBMBNatural fire - Design curves Fully developed compartment fire
Fire load density
Opening factor
= 0.12 m1/2
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iBMBiBMBSteel temperature development
Unprotected steelwork
a,t = · hnet,d · tAm/Vca·a
Am/V section factor [1/m] Am exposed surface area per unit length [m2]V volume per unit length [m3]ca specific heat of steel [J/kgK]a density of steel [kg/m3]hnet,d design value of the heat flux per unit area [W/m2]t time intervall [ 5s ]
·
·
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iBMBiBMBSection factor Am/V
Open section exposed to fire on all sides
Am perimeter
V cross-section area=
Tube exposed to fire on all sides
Open section exposed to fire on three sides
Am/V for unprotected steel members
Am 1
V t=
Am surface exposed to fire
V cross-section area=
Flat bar exposed to fire on all sides
Am 2·(b + t)
V b·t=
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iBMBiBMBSteel temperature
0
200
400
600
800
1000
1200
0 10 20 30 40 50 60 70 80 90
time [min]
tem
pera
ture
[°C
] ISO 834
Am/V small
Am/V large
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iBMBiBMBUnprotected steel column
Damage after fire exposure
Buckling length: lfi 0.5 L Buckling length lfi 0.7 L
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iBMBiBMBStructural steel
Thermal elongation
0
4
8
12
16
0 200 400 600 800 1000
temperature [°C]
elo
ng
atio
n
l/l
[*10
-3]
Example (beam):l = 5 m, a = 600 °C: l 1.4*10-5*(600 - 20)*500 = 4.1 cm
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iBMBiBMBUnprotected steel construction
External steel frame
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iBMBiBMBFire protective materials
Traditional materials ( heavy) concrete (normal, lightweight) brickwork
Modern materials ( light) sprays: Perlite-cement, Vermiculite, glass- or
mineral fibre-cement sprays fire boards: fibro-silicate, gypsum, vermiculite mineral fibre or other mat materials intumescent coatings
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iBMBiBMBSteel temperature development Protected steelwork
a,t = · t - (e/10 -1) · g,t
with = dp · Ap/V
p · Ap/V (g,t - a,t)dp · ca · a ( 1+ /3)
Ap/V section factor for steel members with fire protection material [1/m]Ap area of fire protection material per unit length [m2] V volume of per unit length [m3]ca specific heat of steel, from [J/kgK]cp specific heat of the protection material [J/kgK]dp thickness of the fire protection material [m]t time interval [ 30s ]a,t steel temperature at time tg,t ambient gas temperature at time tg,t increase of the ambient gas temperature during tp thermal conductivity of the fire protection material [W/mK]a density of steel [kg/m3]p density of the fire protection material [kg/m3]
cp · p
ca · a
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iBMBiBMBSection factor Ap/V
Ap/V for protected steel members
Contour encase-ment of uniform thickness
Hollow en-casement of uniformthickness
Contour encase-ment of uniformthickness, exposedto fire on three sides
steel perimetersteel cross-section area
2·(b+h) steel cross-section area
steel perimeter - bsteel cross-section area
Ap
V=
Ap
V=
Ap
V=
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iBMBiBMBSteel temperature
0
200
400
600
800
1000
1200
0 10 20 30 40 50 60 70 80 90
time [min]
tem
pera
ture
[°C
] ISO 834
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iBMBiBMBStructural steel
Stress-strain relationship
700°C
600°C
strain [-]
fy
20/100°C
400°C
500°C
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.005 0.01 0.015 0.02
Structural steelf = 235 N / mm ²y
200°C300°C
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iBMBiBMBCritical steel temperature
crit a = f (utilisation factor 0)
a,cr = 39.19 ln[1/(0.967403,833) - 1] + 482
critical temperature [°C]
utili
satio
n fa
ctor
0
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iBMBiBMBSteel temperature
0
200
400
600
800
1000
1200
0 10 20 30 40 50 60 70 80 90
time [min]
tem
pera
ture
[°C
]
a,cr
ISO 834
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iBMBiBMBProtected steel construction
Box protection with fire boards
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iBMBiBMBProtected steel beam
Intumescent coating
Before fire exposure After fire exposure (35 min ISO-curve)
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iBMBiBMBIntumescent coating
Fire resistance
thickness
fire
resi
stan
ce
A/V = 200
A/V = 291
variation
A/V
d = thickness of intumescent coating
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iBMBiBMBProtected steel construction
Composite steel and concrete structure
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iBMBiBMBComposite cross-sections
Columns
Beams
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iBMBiBMBProtected steelwork
Water cooled structure
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iBMBiBMBProtected steelwork
Main columns with water tank