BEHAVIOUR OF AXIALLY LOADED

STRUCTURAL BOLTING

ASSEMBLIES IN FIRE

Lucy Johnson (1), Eric Palmiere (1), Richard Thackray (1),

Ian Burgess (2), Buick Davison (2)

(1) Department of Materials Science and Engineering

(2) Department of Civil and Structural Engineering

StiFF 09/04/2013

Outline

Importance

Structural Bolts

Experimental

Material Testing

Finite Element Modelling

Bolt Assembly Testing

Summary and Conclusions

Importance

Importance

1. Kirby, B.R., The behaviour of high-strength grade 8.8 bolts in fire. Journal of Constructional Steel Research, 1995. 33(1-2): p. 3-38.

2. Gonzalez, F. and J. Lange, Behaviour of Galvanized High Strength Grade 10.9 Bolts under Fire Conditions. 2009: p. 908-915.

3. Hu, Y., et al. Comparative study of the behaviour of BS 4190 and BS EN ISO 4014 bolts in fire. 2007.

Structural Bolts

M20 x 90 x Bolt =

M20 x 10 Nut =

8.8 SB

SB

Fu,nom = 800 Mpa

Fy,nom = 640 MPa

Fy,nom = 1 GPa

Experimental

Experimental

ε

(min-1)

Turned-down bolt Bolt Assembly

v

(mm/s)*

Temperature (˚C) v

(mm/s)**

Temperature (˚C)

20 550 620 700 20 550 620 700

0.002 6.7x10-4 x x x x 2.1x10-3 x x - x

0.01 3.3x10-4 x x x x 1.0x10-2 x x - x

0.02 6.7x10-3 x x x x 2.1x10-2 x x - x

* Based on a 20 mm gauge length where v=ε.L0

** Based on a 62 mm gauge length where v=ε.L0

Constant strain-rate to failure to measure ultimate strain

Material Testing

308 HV 243 HV

242 HV

Min = 255 HV

Material Testing

Decreasing

strength

Increasing

ductility

Material Testing

Material Testing

Material Testing

Finite Element Modelling

1) Temperature and strain rate

dependant material properties

2) Geometry (based on three

cross-sections)

Thread Tolerance

Material Properties

Assembly Tests

Strain measured at ends of

gauge length = 62 mm (necking

failure only)

Displacement measurement at

an area of high contrast

Assembly Tests

Assembly Tests

Assembly Tests

x

Assembly Tests

x

Assembly Tests

x

Assembly Tests

x

Assembly Tests

Summary and Conclusions

Microstructural variations exist which

affect stress-strain behaviour and

failure mode at ambient temperature

Elevated temperature properties are

not influenced by start microstructure

Optimum heat treatment?