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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

2

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