Post on 03-Jul-2018
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Component Studies for Steelwork Connections in Fire
Component Studies for Steelwork Connections in Fire
Spyros Spyrou, Buick Davison,Ian Burgess, Roger Plank
University of Sheffield, UK
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Semi-rigid behaviour of connections
At ambient temperature
• Interest based on using connection stiffness and strength to enhance the performance of structural frames.
• Initial approaches based on cantilever and cruciform tests, to create database of M-φcurves. Some semi-empirical models to rationalise results.
• Large range of joint types, arrangements, dimensions implied that database for general design purposes would be very large.
• Finite element models of joints need to be complex in order to produce accurate results.
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The “Component” method
• Feasible approach based on modelling the zones of fundamental behaviour (“components”) within a connection then constructing a model of the connection.
FcKc
F2
F1K1
K2
Ft
M
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Component zones in end-plate joint
Column web in tension
Column web in compression
Beam flange incompression
Beam web in tension and compression
Column flange andend plate in bending
Bolts in tension
Column web in shear
M
Beam web in shear
ShearTension Compression
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Modelling connection behaviour in fire
• Late 1980sSCI sponsored 11 tests at Warrington on different cruciform connection arrangements. One load level applied to each. Concluded that reduced plastic capacity of joint would reduce the midspan bending moments.
• 1990Simple beam fire resistance enhancement design method published in SCI-P-086.
• 1996Included in widely-distributed British Steel design examples.
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Cardington beam-column joint after fire test
Buckling due to high axial force on heating
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Component zones in end-plate joint with axial thrust
Reduced tension
Highercompression in web
Beam flange in highercompression
Beam web mainly incompression
Reduced force on column flange
Lower tension
Column web in shear
M
F
Beam web in shear
ShearTension Compression
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The “Component” method with axial force
• In fire axial compression acts together with moment due to restraint to thermal expansion. Component model would deal with this automatically, though M-φcurves change due to thrust.
FcKc
F2
F1K1
K2
Ft
M
FcKc
F2
F1K1
K2
Ft
M
F
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Objectives of this project
Tension Zone
• Do experiments on T-stubs at high temperatures.
• Develop simplified/semi-empirical model of tension component behaviour for end-plate joints.
• Check both against finite element modelling.
Compression Zone
• Examine experimentally the effect of elevated temperatures on column web buckling.
• Develop simplified/semi-empirical model of column web compression component behaviour for end-plate joints.
• Check both against finite element modelling.
Generally
• Check moment-rotation predictions against previous cruciform furnace tests.
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Furnace and control apparatus
Loadingdevice and
Control panel
View portsfor cameras
Loading actuator
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Furnace test setup
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T-stub Type B/C tension component specimen
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High-temperature T-stub through viewport
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Failure modes for tension T-stubs
Failure Mode 1 Failure Mode 2 Failure Mode 3
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Forces on a T-stub assembly
kn m
Le Q
δep
F
w wv
x
QSimplified Model
• Uses this arrangement with normal elasto-plastic structural mechanics to track the failure modes.
At High Temperatures
• Uses EC3 strength & stiffness reduction factors for steel sections/plate. Kirby strength reduction for bolts. EC3 stiffness reduction factors verified by separate tests.
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Failure mode 1
0
50
100
150
200
250
300
350
400
450
500
0 1 2 3 4 5 6 7 8Displacement (mm)
Force (kN)
505°C
700°C
740°CA
C D
First plastic hinge
Yield & fracture of bolts
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Failure mode 2
00
50
100
200
250
300
350
400
450
4 8 12 16 20 24 28 32 36
D
0
50
100
150
200
250
300
350
400
450
500
Displacement (mm)
Force (kN)
505°C
540°C
705°C
650°C
415°C
A
C
B
First plastic hinge
Second plastic
Yield & fracture of bolts
hi
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Failure mode 3
Force (kN)
350Ambient
410°C
505°C
510°C
610°CC
D
AC
D300
250
200
150
100
50
0-1 0 1 7 82 3 4 5 6
Displacement (mm)
1919
Von-Mises stresses from ANSYS modelling of T-stubs
High temperatureAmbient temperature
2020
Comparison between simple model and finite element analysis
Force kN Force (kN)300 300
660C
ANSYS
0
50
100
150
200
250
0 2 4 6 8 10 12 14Displacement (mm)
ANSYS
410C
Simple250
Simple200
150
100
50
00 1 2 3 4 5
Displacement (mm)
2121
Compression zone: column web
M M
2222
Compression zone test arrangement
ActuatorReaction Frame
Specimen
Furnace
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Column specimen inside the furnace
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Formation of plastic hinges in column flange
Second hinge
Second hinge
First hinge
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Simplified model of compression zone
Roberts’ model for ultimate strength of stocky webs
Uniform stress σyw
ββ c
Pu1 2 3 4
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Principles of simple compression zone model
2 3
β
γ'
w
γ'e'
βc
650tfb
w1
Lt
Yielding
2. Yield of column flange (first plastic hinges)
γ/10
β
γ
w
γe
βc
300
tfb
w1
γ/10
Leff=e+(γ/5)
1.Yield of column web
β ∆w′
Le=β+c/4
c/2Mpfc
1
3. Yield of column flange (final plastic hinges)
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Ultimate strength of compression zoneUltimate strength is seen from tests to be higher than the load at which the final hinges are created
For Plate Girders
• Markovic tested 11 semi-emprical ultimate strength formulae.
• Drdacky formula is the only one which applies to relatively stocky (h/t~75) webs. Compares with h/t~20 to 30 for rolled H-sections.
+=Ρ
wcwc
fbwcwcwcu d
ctt
Et 5.19.055.0 2 σ
• New Formula developed from Drdacky, because original gave unsafe predictions compared with FE analyses with varying contact area.
+
+=Ρ
cdc
tt
Etwcwc
fbwcwcwcu β
βσ2
26.165.02
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Comparison between tests and various web capacity formulae at high temperatures
100
150
Forc
e(
350
TestsEC3
UC152x152x30
DrdackyModified Drdacky
300
kN) 250
200
50
0400 500 600
Temperature (ºC)00 100 200 300 700 800
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Comparison of modified Drdacky formulawith tests
0
100
200
300
200 400 600 800Temperature (°C)
Force (kN)
0 200 400 600 800Temperature (°C)
Force (kN)
UC152x152x30 100
200
300
400
UC203x203x46
200 400 600 800Temperature (°C)
Force (kN)
200
400
600
800
UC203x203x71
0 200 400 600 800Temperature (°C)
Force (kN)
UC203x203x86400
800
1200
0
3030
3D finite element analysis: web buckling
Out-of-plane deflection contours
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Typical test and analysis results for compression zone
3D ANSYS
0
20
40
60
80
100
120
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17Displacement (mm)
Force (kN)
Test
2D ANSYS
UC203x203x46 at 670°C
Simplified model
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Component model of beam-column joint
Kt
Kc
P
M
3333
High-temperature M-φ curves: test and component model
100
200
300
400
500
600
700
800
0 10 20 30 40 50 60 70 80 90
FB11 (4 kNm)
FB13 (13 kNm)
Beam Flange Temperature (°C)
FB14 (17 kNm)
FB12 (8 kNm)
100Rotation (Millirads)
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Observations
• Connection behaviour is important during fires. For safety the connections must stay connected, even when beams are highly distorted.
• The traditional approach in ambient-temperature design is to use M-φ data for beam-column joints.
• Extended in fire to M-φ-θ to include degradation of steel properties with temperature.
• With restraint this database would become M-φ-N-δ-θ.Clearly unfeasible.
• For flush/extended end-plate joints the project has produced workable simplified models for the tension zone and the column web component of the compression zone.
• Next step: beam flange compression zone.
• Later: shear panels in column & beam webs.