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April19April19--20 2013, Prague20 2013, Prague
WG1 - E. Nigro
WG3 - I. Del Prete
WG3 - G. Cefarelli
D. Sannino
A. Ferraro
Di.St. – Department of Structures for
Engineering and Architecture
University of Naples “Federico II”
ITALY
The influence of joint modeling on fire The influence of joint modeling on fire behaviourbehaviour
of steel frame structureof steel frame structure
SummarySummary
� Analyses of steel frame structure in case of fire, carried out through 1D Finite Element Model, are sufficient to simulate the global behaviour, but it does not allow to take into account the joint behaviour.
� 3D Finite Element Model, that includes the joint model, is capable to simulate the global structural behaviour taking into account the influence of the joint on stiffness and resistance.
� The comparisons between the analyses results of steel frame structure exposed to fire, carried out through 1D and 3D Finite Element Model, including or less joints model, are shown in order to evaluate the influence of joint behaviour on the analysis results.
3D Finite Element Model
(STRAUS7)
3D FEM including bolted joint modeling(STRAUS7)
1D Finite Element Model(SAFIR2011)
A
A
A-AIPE300 (S235)
B B
B-B350x350x8
(S235)
pin-pin joints on beam
pin-pin joints on beam
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ComparisonComparison betweenbetween thermothermo--mechanicalmechanical propertiespropertiesSteel thermal properties in accordance with EC3-1-2
0
2
4
6
8
10
12
14
16
18
20
0 200 400 600 800 1000 1200
(∆l/l)=14⋅10-6( θa-20)
(∆∆∆∆l/l)x103
Steel Temperature (°C)
0
200
400
600
800
1000
1200
0 200 400 600 800 1000 1200
[J/kgK]
ca=650 J/kgK
Steel Temperature (°C)
ca (J/kgK)
0
10
20
30
40
50
60
0 200 400 600 800 1000 1200
λa=27,3W/mK
Steel Temperature (°C)
λλλλa (W/mK)
STRAUS7
Simplified (elasto-plastic) constitutive law for steel at high temperatures
T<=400°C
T=500°C
T=600°C
T=700°C
T=800°CT=900°C
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.00 0.05 0.10 0.15 0.20
ε
Steel constitutive law in accordance with EC3-1-2
SAFIR
Thermal Thermal analysesanalyses resultsresults� Comparison between beam’s 2D FEM in SAFIR2011 and STRAUS7
ISO834
T=20°C
SAFIR20112D model
STRAUS72D model 0
200
400
600
800
1000
1200
0 20 40 60 80 100 120
Beam's bottom flange temperature ( °C)
ISO834
SAFIR 2011
STRAUS7
Time (min)0
200
400
600
800
1000
1200
0 20 40 60 80 100 120
Beam's web temperature ( °C)
Time (min)
ISO834
SAFIR 2011
STRAUS7
0
200
400
600
800
1000
1200
0 20 40 60 80 100 120
Beam's top flange temperature ( °C)
Time (min)
ISO834
SAFIR 2011
STRAUS7
ISO834
T=20°C
SAFIR20112D model
STRAUS73D model 0
200
400
600
800
1000
1200
0 20 40 60 80 100 120
Time (min)
ISO834
Beam's bottom flange temperature ( °C)
Time (min)
ISO834
Temperature in steel beam(SAFIR 2011)
Temperature in steel beam(STRAUS7)
� Comparison between 2D FEM in SAFIR2011 and 3D FEM in STRAUS7
0
200
400
600
800
1000
1200
0 20 40 60 80 100 120
Time (min)
ISO834
Beam's web temperature ( °C)
Time (min)
ISO834
Temperature in steel beam(SAFIR 2011)
Temperature in steel beam(STRAUS7)
0
200
400
600
800
1000
1200
0 20 40 60 80 100 120
Time (min)
ISO834
Beam's top flange temperature ( °C)
Time (min)
ISO834
Temperature in steel beam(SAFIR 2011)
Temperature in steel beam(STRAUS7)
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Thermal Thermal analysesanalyses resultsresults� Comparison between beam’s 2D FEM in SAFIR2011 and STRAUS7
ISO834
T=20°C
SAFIR20112D model
STRAUS72D model 0
200
400
600
800
1000
1200
0 20 40 60 80 100 120
Beam's bottom flange temperature ( °C)
ISO834
SAFIR 2011
STRAUS7
Time (min)0
200
400
600
800
1000
1200
0 20 40 60 80 100 120
Beam's web temperature ( °C)
Time (min)
ISO834
SAFIR 2011
STRAUS7
0
200
400
600
800
1000
1200
0 20 40 60 80 100 120
Beam's top flange temperature ( °C)
Time (min)
ISO834
SAFIR 2011
STRAUS7
ISO834
SAFIR20112D model
STRAUS73D model
� Comparison between 2D FEM in SAFIR2011 and 3D FEM in STRAUS7
0
200
400
600
800
1 000
1 200
0 20 40 60 80 100 120
Temperature ( °C)
Time (min)
ISO834
Temperature in steel column(SAFIR 2007)
Temperature in steel column(STRAUS7)
ThermoThermo--mechanicalmechanical analysesanalyses resultsresults
Comparison between 1D FEM in SAFIR2011 and 3D FEM in STRAUS7 in terms of axial stress in beam and column
0
100
200
300
0 5 10 15Time (min)
Axial Stress (N/mm2)
Proportionality limityielding stress
stress in beam's bottom flange (SAFIR 2011)
stress in beam's bottom flange (STRAUS7)
-400
-300
-200
-100
0
100
200
300
400
0 5 10 15 20
Axial stress (N/mm2)
Time (min)
stress in column's top flange (SAFIR 2011)
stress in column's top flange (STRAUS7)
Proportionality limityielding stress
� When beam achieves proportionality limit, numerical results are quite different, due to the assumption of simplified steel constitutive law at high temperature in STRAUS7.
� The different beam’s behaviour in 3D FEM influences column’s behaviour, too, which is yet more stiffeness, due to the less temperature achieved in hot column
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ThermoThermo--mechanicalmechanical analysesanalyses resultsresults
Comparison between 1D FEM in SAFIR2011 and 3D FEM in STRAUS7 in terms of beam and column’s displacement
-800
-700
-600
-500
-400
-300
-200
-100
00 5 10 15 20
Time (min)
Displacement (mm)
SAFIR 2011
STRAUS7
-20
-10
0
10
20
30
40
50
60
70
0 5 10 15 20
Time (min)
Displacement (mm)
SAFIR 2011
STRAUS7
-800
-700
-600
-500
-400
-300
-200
-100
00 5 10 15 20
Time (min)
Displacement (mm)
SAFIR 2011
STRAUS7
STRAUS7 with bolted joint model
ThermoThermo--mechanicalmechanical analysesanalyses resultsresultsComparison between 1D FEM in SAFIR2011 and 3D FEM in STRAUS7, including joint model
-800
-700
-600
-500
-400
-300
-200
-100
00 5 10 15 20
Time (min)
Displacement (mm)
SAFIR 2011rigid beam-column
joint
STRAUS7 with bolted joint model
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
0 5 10 15 20
Time (min)
SAFIR 2011rigid beam-column
joint
Displacement (mm)
STRAUS7 with bolted joint model
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ThermoThermo--mechanicalmechanical analysesanalyses resultsresultsComparison between 1D FEM in SAFIR2011 and 3D FEM in STRAUS7, including joint model
Simplified check of joint(EC3-1-2)
-800
-700
-600
-500
-400
-300
-200
-100
00 5 10 15 20
Time (min)
Displacement (mm)
SAFIR 2011
STRAUS7
STRAUS7 with bolted joint model
-800
-700
-600
-500
-400
-300
-200
-100
00 5 10 15 20
Time (min)
Displacement (mm)
SAFIR 2011rigid beam-column
joint
STRAUS7 with bolted joint model
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
0 5 10 15 20
Time (min)
SAFIR 2011rigid beam-column
joint
Displacement (mm)
STRAUS7 with bolted joint model
ConclusionsConclusions
� The comparison in terms of thermal analyses results of beam’s 2D and 3D FEM
shows the complete agreement between the SAFIR 2011 and STRAUS7 model
� The comparison in terms of thermal analyses results of column’s 2D and 3D
FEM shows quite differences, due to longitudinal column’s heat transfer, that it
can’t be take into account in 2D FEM.
� In terms of thermo-mechanical results, when structural elements achieve
proportionality limit, numerical results become quite different, due to the
assumption of simplified steel constitutive law at high temperature
implemented in STRAUS7
� 3D FEM, including joint model, exhibits behaviour quite similar to SAFIR 1D FEM,
with beam-column rigid joint
� Nevertheless, 1D and 3D FEM show the same failure time
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ThanksThanks forfor youryour attentionattention