Mechanical Propertiesof Grade 8.8 Bolts

at Elevated Temperatures

MSc projectYiannis Theodorou

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

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

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

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

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

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

Experimental apparatus

Cross -Section of Furnace

specimentarge ts

isola ted mate ria l ha logehalogen lamp

specimen

Cross -Section of Furnace

View into furnace

Underside of lid showing halogen lamp

Location of cameras

Thermocouples

A

thermocouple loca tionsA

cross section A-Athermocouple loca tion

specimen

halogen lamp

Temperature control specimen

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

Specimens

Group B

Group Aholes 0.5mm (ta rge ts )

holes 0.5mm (ta rge ts )

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

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

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

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

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

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

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

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

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

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

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