fire design of a steel hall without fire protection - hamk...
TRANSCRIPT
Patrik Takács – BSc student , BME / MSc student, TU Vienna László Horváth – BME Department of Structural Engenieering István Szontagh – Ruukki Hungary Ltd.
Fire design of a steel hall without fire protection
METNET Seminar Aarhus, 12-13. November 2011
Fire Design
Goal of the study
Structure and requirements
Temperatures and effects in fire situation
Comparison of fire design strategies
Results
Conclusions
Content
METNET Seminar Aarhus, 12-13. November 2011
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• Eurocodes for fire design of steel structures - EN 1991-1-1:2002 - EN 1993-1-2:2005 •Hungarian National Fire Regulations (2008)
•Hungarian Chamber of Engineers – series of design aids
Goal of the study Fire Design
METNET Seminar Aarhus, 12-13. November 2011
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•Studies at our Department : fire design for typical steel hall structures
•R15
•R30 ????
•Usually with fire protection (painting) •Additional material (strenghten the members) ??? •Change the steel grade ???
Goal of the study – ideas for R30 Fire Design
METNET Seminar Aarhus, 12-13. November 2011
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Fire Design
Characteristics of the building:
Area: ∼30×50 m
Steel hall with storage function
Portal frames
Hollow-sectioned truss beam
Steel columns: welded non-uniform cross-section
Steel grade: S355
The structure
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METNET Seminar Aarhus, 12-13. November 2011
Fire Design Requirements
Function: Storage
Number of storeys: 1
Specific fire load: < 250 MJ/m2 „E” fire risk class
Fire compartment area: < 1500 m2 IV. fire resistance category
Fire resistance requirements:
frame: 15 min – R15
bracing system: 15 min – R15
Extended application field :
frame: 30 min – R30
bracing system: 30 min – R30
National Fire Code H
5
METNET Seminar Aarhus, 12-13. November 2011
Fire Design Fire models
If engineering methods used, then:
Fire scenario: only the standard ISO 834 fire curve is accepted
4 side fire exposure for all members
Uniform temperature distribution in all members
National Fire Code H
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METNET Seminar Aarhus, 12-13. November 2011
Fire Design Determination of Temperatures in case of Fire
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METNET Seminar Aarhus, 12-13. November 2011
Fire Design
Determination of Material Properties
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Temperatures of the structural elements of the trusses
Modul of elasticity
Temperature [°C]
[1/°
C]
(*
10
-5)
[N/m
m2]
[N/m
m2]
Yield strength
Tem
per
atu
re
[°
C]
Time [min]
°C
[°C]
Coefficient of thermal expansion
ISO 834 curve
RHS 150*100*5
RHS 120*120*6
RHS 80*80*4
RHS 60*60*4
METNET Seminar Aarhus, 12-13. November 2011
where:
▪ Ad: design value of an accidental action ( elevated temperatrure in fire)
▪ variable load: frequent value of the principal variable load
Additional effects of actions from thermal deformation can not be neglected!
The changes of the material properties have to be taken into account:
▪ modulus of elasticity -> modification of the internal force distribution
Fire Design Determination of the effect of actions
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Effect of actions in case of fire - general method: for accidental design situations acc. EN 1990:
METNET Seminar Aarhus, 12-13. November 2011
1i
1,11
,, ik,k,1djk, "+""+""""" QQAPGEj
tdfi i2,
Fire Design Determination of the effect of actions
where:
Ed : effect of actions from the structural analysis for normal temperature design
Fields of application according the National Fire Code in Hungary: :
▪ only with ISO-834 fire curve
▪ can be used for individual member analysis
▪ additional effects of actions from the restrained thermal expansion can be neglected
Effect of actions in case of fire – simplified method with ηfi reduction factor:
h fi =gGAGk +y1.1Qk.1
gGGk +gQ.1Qk.1
Efi,d,t =h fi *Ed
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METNET Seminar Aarhus, 12-13. November 2011
Fire Design Eurocode fire design methods
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ConSteel 6.0 fire module
Individual finite
element model
with ηfi reduction factor
in accidental design situation
Determination of the effects of actions in case of fire
Determination of the critical temperature: on the basis of the degree of utilization: μ0
Verification of the fire resistance expressed
in terms of..
..critical temperature:
Θd ≤ Θcr,d
..load-bearing resistance : Efi,d,t ≤ Rfi,d,t
Only for tension members (truss, bracing)
METNET Seminar Aarhus, 12-13. November 2011
For all members
Fire Design
Individual finite element model
Re-defined material
properties (temperature)
Load: mechanical + temperature
Combinations of actions for accidental design situations
Second order effect of actions
Uniform temperature distribution
Determination of the effect of actions
12 / 20 12 / 20 12
METNET Seminar Aarhus, 12-13. November 2011
Fire Design
ConSteel 6.0 fire module
Load case: fire
Can be defined:
fire curve: ISO-834
duration of fire load: 15 and 30 minutes
fire protection yes/not: unprotected steel „I” and hollow sections
3 or 4 side fire exposure: 4 side, with uniform temperature distribution
Second order effect of actions
Determination of the Effect of Actions
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METNET Seminar Aarhus, 12-13. November 2011
Simplified method with ηfi reduction factor : significant differences in truss members method not suitable for trusses !!!
Earlier studies: method is suitable for framed structures made from rolled or welded profiles, because there the normal forces from thermal expansion are not high (reduction of the modulus of elasticity)
FEM analysis: only slight differences between the individual and ConSteel fire-module results (temperatures and internal forces)
both model and method acceptable
we calculated with FEM models (2D and 3D version; individual and firemodule; normal and elevated temperatures = 12 models)
Fire Design Comparison of the internal force results
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METNET Seminar Aarhus, 12-13. November 2011
Fire Design Truss profiles for R15
15 / 20
Bracing system
2. 3. 4.
5.
6.
7. 8.
1.
3. 2.
1.
4.
1.
RHS 150*100*5
2.
SHS 120*6
3.
SHS 80*4
4.
SHS 60*4
5.
SHS 80*4
6.
RS30
7.
RS24
8.
RS20
15
Truss
METNET Seminar Aarhus, 12-13. November 2011
S 355
Fire Design Truss profiles for R30
16 / 20
Bracing system
2. 3. 4.
5.
6.
7. 8.
1.
3. 2.
1.
4.
1.
RHS 150*100*6
2.
SHS 120*10
3.
SHS 100*6
4.
SHS 60*4
5.
SHS 90*5
6.
RS40
7.
RS30
8.
RS20
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Truss
METNET Seminar Aarhus, 12-13. November 2011
S 460
Simplified method – critical time method for tension members
Member check with load-bearing resistances in fire situation
both method acceptable !
Fire Design Member verification in fire situation
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METNET Seminar Aarhus, 12-13. November 2011
250*12
900*10
250*10
250*12
900*10
250*10
250*12
589*8
250*10
250*12
842*8
250*10
250*12
657*8
250*10
250*12
200*6
250*10
250*12
365*6
250*10
Fire Design Column cross-sections for R15
3. D.
1.
2.
B.
A.
C.
3.
1.
2.
Real column member
C.
B.
A.
D.
Replacing column member
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METNET Seminar Aarhus, 12-13. November 2011
S 355
250*20
900*16
250*16
250*20
900*16
250*16
250*20
589*16
250*16
250*20
842*16
250*16
250*20
657*16
250*16
250*20
200*12
250*16
250*20
365*12
250*16
Fire Design Column cross-sections for R 30
3.
1.
2.
Real column member
C.
B.
A.
D.
Replacing column member
19 /
D.
C.
B.
A. 1.
3.
2.
METNET Seminar Aarhus, 12-13. November 2011
S 460
Paper: related to overall constructional weight (load bearing structure + secondary + …)
only load-bearing: columns +58% truss +39% together +49%
Fire Design Increase of weight
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METNET Seminar Aarhus, 12-13. November 2011
Conclusions
Section factor plays a major role in the temperature development:
→ practical to use stockier and thicker cross-sections
Steel frames may be used for R30 with higher steel grade + some changes in the profiles.
In case of statically indeterminate structures - like a trussed
framework, which supports the bending moment as a
couple of tensile and compressive forces - the additional
effects of actions from thermal deformation are significant
and can not be neglected.
FEM softwares may help effectively at the fire desing also.
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Fire Design
METNET Seminar Aarhus, 12-13. November 2011