connection modelling in firefire.fsv.cvut.cz/cost_c26_prague/07-03-30_31/1-03 burgess.pdf ·...
TRANSCRIPT
Connection Modelling in Fire
Ian Burgess
Definition of joint and connection
Joint
Connections
EC3-1.8 Stiffness classification of joints
M
φ
Semi-rigid
Pinned S >0,5EIb/Lb
Rigid
S >kbEIb/LbKb=8 (braced frames)Kb=25 (other frames)
Other classifications
Strength:
• “Full-strength”: Bending strength > Strength of member.
• “Partial-strength”
• “Pinned”: Bending strength < 0.25 Strength of member.
Ductility:
• “Ductile/Class 1”: Sufficient rotation capacity to develop plastic mechanism.
• “Semi-ductile”
• “Brittle/Class 3”: Can only be used in elastic design.
Component Modelling at Ambient Temperature
Beam web
Principal component zones of end-plate
M
Column web
Beam flange, web
Column web
Compression
Beam web
Column web Column
flange End plate
Tension bolts
Tension
EC3-1.8 extended end-plate joint model
M
Beam web tension
Column web tension
Column flange bending End plate
bending
Bolttension
Beam flangeColumn web
compressionColumn
web shear
Equivalent spring model
ce
M
z2
ke,2
ke,1
z1
,
, , , , ,
11 1 1 1 1et i
cwt i cfb i bt i epb i bwt i
k =
k k k k k+ + + +
Simplified spring model
ce
keq
zeq
M
Moment-rotation behaviour in fire
Semi-rigid behaviour of connections in fire: original work
Late 80s – early 90s
• Design opportunity? Interest particularly based on using connection residual stiffness and strength to enhance the fire resistance of “simple” steel beams.
• Analytical studies to assess the likely advantages/problems.
Semi-rigid behaviour of connections in fire: cruciform tests
Mid – 1990s
• Cruciform tests to create small database of M-φcurves. Semi-empirical models to rationalise results.
• 2 successive experimental projects at BRE Garston (Lennon) in “portable” furnace.
1. First series (Leston-Jones) tested a limited range of small non-composite flush-endplate connections.
2. Second series (Al-Jabri ) tested flush and extended endplate connections in composite and non-composite arrangements, including some Cardington connections.
Garston cruciform tests: test arrangement
Column head restrained in position
Load Load
Beam restrained horizontally
Specimen located within furnace
Test Furnace
Specimen
Garston cruciform tests: “portable” furnace
Garston cruciform tests: End-plate Type 2
50
50
150
1010 90
60
375
254x254x89UC(50)
356x171x51UB(50)
6mm FW all round
All holes 22mm dia. forM20 Grade 8.8 bolts
190
High-temperature M-φ-θ characteristics of endplate joints
Rotation (mrad)
Flush End-plate
20 40 60 80 100
20°C 200°C 400°C
500°C
600°C
700°C
35 40 Moment (kNm)
25 20
15 10 5
0 0
20
40
60
80
100
20 40 60 80 100 Rotation (mrad)
Curves at 100°C intervals
Moment (kNm)
20°C/100°C
Flexible End-plate
30
Cardington beam-column joint after fire test
Buckling due to high axial force on heating
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
Tension Compression Shear
M
Column web in shear
Beam web in shear
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
Tension Compression Shear
Column web in shear
M
F
Beam web in shear
Component Behaviour at High Temperatures
Spyrou Component testing 1998-2001: Objectives
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 flush endplate moment-rotation predictions against previous cruciform furnace tests.
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.
Spyrou furnace and control apparatus
Control panel
View portsfor cameras
Loading actuator
Failure modes for tension T-stubs
Failure Mode 2 Failure Mode 3Failure Mode 1
Spyrou compression zone test arrangement
ActuatorReaction Frame
Specimen
Furnace
Roberts’ model for ultimate strength of stocky webs
Uniform stress σyw
ββ c
Pu1 2 3 4
Simplified model of compression zone
tfb
γ/10
β
γ
w
γe
β c
300
w1
γ/10
Leff=e+(γ/5)
1.Yield of column web
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)
β Δw′
Le=β+c/4
c/2Mpfc
1
3. Yield of column flange (final plastic hinges)
Qian shear panel tests
Restrained high-temperature joint testing
Qian & Tan restrained tests
Qian & Tan restrained specimen
UB305X102X25kg/m
14521652
700
1500
16521452100 100
800
ENDPL
UC254X254X107kg/m
ENDPL
100 100
D29D29
D29
D29
D29
D29
D29 D29
Qian & Tan restrained tests
Qian & Tan restrained tests
Qian & Tan restrained tests
1. Modified Rotational Models
Component Modelling in Fire
Simoes da Silva (2001) component approach
• Find ambient-temperature force-displacement response at ambient temperature according to EC3-1-8 component method principles.
• Apply high-temperature material reduction factors for stiffness and strength to produce high-temperature equivalents.
Simoes da Silva modelling of Sheffield tests
Modified rotational models: Qian & Tan
?
VNb
Nc
Nc
cwt cfb epb bt
bwscws cwc bfc
F
?
FRd
K
F
?
FRd
Elastic-plastic component Rigid-plastic component
cwt cfb epb bt
cwt cfb epb bt
cwt cfb epb btMV
M
Component Modelling in Fire
2. General Connection Elements
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.
K1
K2
Kc
The “Component” method with axial force
FcKc
F2
F1K1
K2
Ft
M
• 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.
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
F
Component-Based Connection Element (Block)
kC kTekTc
kS
u
w
φ
lT,1
lT,3
lT,2
lC,1
lC,2
21
kC kTekTc
kS
u
w
φ
lT,1
lT,3
lT,2
lC,1
lC,2
21 21Compression Spring- Column Web
Tension Spring –
T-Stub in End-Plate
Shear Spring- Bolts
Comparison of joint element with tests by Leston-Jones
0
100
200
300
400
500
600
700
800
900
0 10 20 30 40 50 60 70 80Connection rotation [mrad]
Stee
l temp
eratu
re [°
C]
BFEP 5 - 5 kNmBFEP 15 -15 kNmBolt rows individuallyBolt rows as a group
Component-based connection element: beam shear panel
kC kTekTc
kS
u
wφ
lT,1
lT,3
lT,2
lC,1
lC,2
21
kC kTekTc
kS
u
wφ
lT,1
lT,3
lT,2
lC,1
lC,2
21 21
Implementation of joint element in software
I
J
K
L
The end …
… nearly …
Next emphasis
Floor beam Shear tab plate
Column tree
Robustness in tying (tension) of typical connection details in fire.
Example: WTC5 system
Failure of tab plates in WTC 5 column trees
Combined catenary tension and shear
Current work on robustness
… Thank you