ThermoThermo--mechanical analysis of steel columns...
Transcript of ThermoThermo--mechanical analysis of steel columns...
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April 18April 18--19 2013, Prague19 2013, Prague
WG1 - E. Nigro
WG2 - G. Cefarelli
D. Sannino
A. Ferraro Di.St. – Department of Structures for
Engineering and Architecture
University of Naples Federico II
ITALY
ThermoThermo--mechanical analysis of steel columns mechanical analysis of steel columns
using different finite element types and using different finite element types and
constitutive laws constitutive laws
Benchmark study: Progetto C.A.S.E. per L’AquilaBenchmark study: Progetto C.A.S.E. per L’Aquila
The “C.A.S.E. Project for L’Aquila” was developed in L’Aquila (province of
Abruzzo, Italy) after the seismic event of 06/04/2009, in order to face up the
housing emergency. The project was characterized by the fabrication of several
seismic insulated buildings.
Isolationdevice
Hereafter the performance evaluation of the structure in lack of passive
protection systems is analyzed
steel column
Concrete slab
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AnalysisAnalysis and Benchmark and Benchmark goalsgoals
� Detailed analysis
Because the column is characterized by
graet values of local slenderness, detailed
analyses are developed in order to
evaluate accurately thermal field and
stress distribution in the capital of the
column, as well as eventual local buckling
phenomena in the stem of the column.
ABAQUS
Non linear analysis including large displacements effects
Brick49075 elements15185 nodes
� BenchmarkThe benchmark is developed in order to
evaluate the influence of the finite element
used in the analysis as well as the influence
of simplified constitutive law for steel at high
temperature
STRAND7 / STRAUS7
Model Type of finite element
Abaqus 10 nodes tetrahedral elements
Straus7 brick 4 nodes tetrahedral elements
Straus7 plate 4 nodes quadrilateral elements
Straus7 beam2 nodes monodimensional
elements
Plate6873 elements6641 nodes
Beam31
elements
T<=400°C
T=500°C
T=600°C
T=700°C
T=800°CT=900°C
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ε
ComparisonComparison betweenbetween thermothermo--mechanicalmechanical propertiespropertiesSteel thermal properties in accordance with EC3-1-2
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(∆l/l)=14⋅10-6( θa-20)
(∆∆∆∆l/l)x103
Steel Temperature (°C)
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0 200 400 600 800 1000 1200
[J/kgK]
ca=650 J/kgK
Steel Temperature (°C)
ca (J/kgK)
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0 200 400 600 800 1000 1200
λa=27,3W/mK
Steel Temperature (°C)
λλλλa (W/mK)
STRAND7
Simplified (elastic-plastic) constitutive law for steel at high temperatures
Steel constitutive law in accordance with EC3-1-2
ABAQUS
Differences: no parabolic branch, no softening
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0 300 600 900 1200 1500 1800 2100 2400 2700 3000
Axi
al L
oad
[kN
]
Time [s]
Mechanical analysis
Mechanical analysis results are different in term of
behaviour, however they are quite similar in
terms of collapse time
0.0
200.0
400.0
600.0
800.0
1000.0
1200.0
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1600.0
0 750 1500 2250 3000 3750 4500 5250 6000
Tem
per
atu
re [
°K]
Time [s]
Different constitutive laws for steel at high temperature
positive
Fire Curve ISO834
Applied Axial Load
Thermal Analysis
Thermal analysis results are
obviously identical. This is fundamental
to permit the comparison based
on different constitutive law
ABAQUS ABAQUS –– STRAND7: STRAND7: differentdifferent constitutiveconstitutive lawslaws
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Stre
ss
[N/m
m2 ]
Time [s]
Von Mises StressYielding stressProportionality limit
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0 300 600 900 1200 1500 1800 2100 2400 2700 3000
Str
ess
[N/m
m2 ]
Time [s]
Von Mises StressYielding stressProportionality limit
Different constitutive laws for steel at high temperature
positive
Fire curve ISO834
Applied Axial Load
The differences of results are due to different constitutive laws.The two models show different behaviour after the achievement of proportional limit
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200.0
400.0
600.0
800.0
1000.0
1200.0
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Tem
per
atu
re [
°K]
Time [s]
0
200
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600
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1000
1200
1400
1600
1800
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0 300 600 900 1200 1500 1800 2100 2400 2700 3000
Axi
al L
oad
[kN
]
Time [s]
ABAQUS ABAQUS –– STRAUS7: different constitutive lawsSTRAUS7: different constitutive laws
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Different constitutive laws for steel at high temperature
positive
Localized Fire (Hasemi)
Applied Axial Load
The differences of results are due to different constitutive laws.The two models show different behaviour after the achievement of proportional limit
ABAQUS ABAQUS –– STRAND7: different constitutive lawsSTRAND7: different constitutive laws
Different plastic strain
InfluenceInfluence of of DifferentDifferent Finite Finite ElementElement : Strand7: Strand7
Brick Plate
Time [s]
The plate model shows greater deformation due to local stress concentration
Simplified constitutive law
for steel at high temperature
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
Fire curve Hasemi
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InfluenceInfluence of of DifferentDifferent Finite Finite ElementElement : Strand7: Strand7
Beam Brick
The greater displacement shown by the beam model can be justified considering that in this
model there aren’t local plastic strain.
Simplified constitutive law
for steel at high temperature
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
Time [s]
Fire curve Hasemi
• Influence of a simplified constitutive law for steel in case of fire
Good evaluation of structural collapseDifferent stress distribution in the memberDifferent evaluation of strain field and residual displacements
• Modeling using 1-dimensional (BEAM) elementIgnore local buckling phenomenon (column)Ignore local crisis phenomenonIgnore local stress concentration (capital)
Thermal analysis consistent with 3D modelExcessive stress concentrations
ConclusionsConclusions
• Modeling using 2-dimensional (PLATE) element
Correct thermal analysisEvaluation of stress concentrations and local buckling phenomenon
• Modeling using 3-dimensional (BRICK) element
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ThanksThanks forfor youryour attentionattention