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Mechanical Propertiesof Grade 8.8 Bolts
at Elevated Temperatures
MSc projectYiannis Theodorou
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Component approach to joint design
Horizontal Zone
Vertical Shear
Compression
TensionZone
H V
Q
L
MK
M
J
P
N
A
E
C
D
B
GN
F
B
Beam Flange WeldColumn Web CrushingColumn Web BucklingWeb to End Plate Weld
Beam Flange Compression
Bolt Bearing(Plate or Flange)QPNMLKJ
Bolt Shear
End Plate BendingColumn Flange BendingBeam Web TensionColumn Web Tension
Web to End Plate Weld
Checklist item
Flange to End Plate Weld
Column Web Panel Shear
Bolt TensionA
E
GH
F
CD
B
REF
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Strength reduction factors measured by Kirby
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 200 400 600 800 1000Temperature 0C
Stre
ngth
Red
uctio
n Fa
ctor
KirbyBS 5950:Part 8
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Comparison of tensile strength of FR andordinary bolts at elevated temperatures
0
0.2
0.4
0.6
0.8
1
1.2
0 100 200 300 400 500 600 700 800 900Temperature 0C
Red
uctio
n of
Ten
sile
Str
engt
h
BOLTEN110N
BOLTEN110N-FR
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Temperature Dependency of Young’sModulus of FR Bolts
0
0.2
0.4
0.6
0.8
1
1.2
0 100 200 300 400 500 600 700 800 900
Temperature 0C
Red
uctio
n of
You
ng's
Mod
ulus
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Aim of study
�To measure the mechanical properties(strength, stiffness, expansion) of grade8.8 bolts across a range of temperatures
�Project Involved� Designing and building furnace� Devising instrumentation
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Schematic diagram of apparatus
PC for video recording
thermocouples
load cell
specimen
furnace
Hydraulic jack
PC for data recording
Data acquisition system
12 V
load
camera
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Experimental apparatus
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Cross -Section of Furnace
specimentarge ts
isola ted mate ria l ha logehalogen lamp
specimen
Cross -Section of Furnace
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View into furnace
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Underside of lid showing halogen lamp
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Location of cameras
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Thermocouples
A
thermocouple loca tionsA
cross section A-Athermocouple loca tion
specimen
halogen lamp
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Temperature control specimen
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Measuring strain
dd
tensile load
L1
T
1
T
2
at high temperatures
at ambient temperatures 20 C
TT
Lo
LT T
0
a
a
a
b
b
b
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Specimens
Group B
Group Aholes 0.5mm (ta rge ts )
holes 0.5mm (ta rge ts )
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Pilot test
�Little difference between side and bottom�As much as 30C along length
the rmocouple loca tions
the rmocouple loca tions
CA
B
A
D
A
halogen lamp
cross section A-Athermocouple loca tion
E
F
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Thermocouple arrangement
�C hottest�Average value used to present results
A
cross section A-Athermocouple loca tions
A
B C D E
Ahalogen lamp
thermocouple loca tion
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Range of temperatures recorded
Test A B C D E Ave.
550 0C 536 555 563 555 337 549 600 0C 582 605 613 606 582 598 650 0C 633 658 663 656 632 649 700 0C 684 711 715 710 686 701 800 0C 787 807 812 807 786 800
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Variation of stress-strain relationshipat 650 0C
Group A - 650 0C
0
20
40
60
80
100
120
140
160
180
200
0.00 2.00 4.00 6.00 8.00 10.00 12.00strain (%)
stre
ss( N
/mm
2 ) 650 C
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SummaryGroup A
Group A
0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
0 2 4 6 8 10 12 14 16 18 20 22strain (%)
stre
ss (N
/mm
2 )
550 C
600 C
650 C
700 C
800 C
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SummaryGroup B
Group B
0
100
200
300
400
500
600
700
800
900
1000
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0
strain (%)
stre
ss (N
/mm
2 )
( )
400 C 300 C 500 C 550 C 600 C
650 C 700 C 800 C 450 C 20 C
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Comparison – tests, Kirby, BS5950
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 100 200 300 400 500 600 700 800 900 1000Temperature,(0C)
Tens
ile S
tren
gth
Red
uctio
n Fa
ctor
Kirby BS 5950:Part 8 Fire Tests
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Comparison: temp + 15C
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 100 200 300 400 500 600 700 800 900
Temperature,(0C)
Stre
ngth
Red
uctio
n Fa
ctor
KirbyBS 5950:Part 8Fire Tests
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Variation of Young’s Modulus with temperature
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 100 200 300 400 500 600 700 800 900Temperature 0C
Red
uctio
n of
You
ng's
Mod
ulus
Fire Tests
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Comparison of variation of E with EC3
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 100 200 300 400 500 600 700 800 900Temperature 0C
Red
uctio
n of
You
ng's
Mod
ulus
Fire TestsEC3:Part 1.2FR-Bolts
carbon steel
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Conclusions
�Halogen furnace worked well�Cameras reasonably accurate for strain
measured�Temperature variation along bolt length not
ideal�Strength reduction
� BS5950 conservative� Kirby recommendations verified
�Stiffness reduction� EC3 Part 1.2 formula for structural steel applicable
to bolts