Experimental Investigation of

the Behaviour of Fin Plate

Connections in Fire

Hongxia Yu

Ian Burgess

Buick Davison

Roger Plank

Background

Objective1. Tying capacity 2. Rotational capacity

�Steel beams go into catenary action at very high temperatures;

�The connections are subjected to significant tying force;

�Capacities of the connections to resist the tying forces are essential to prevent progressive collapse

A series of tests are arranged to investigate the robustness of steel connections at elevated temperatures.

Test Setup

Furnace

Reaction

frame

Load Jack

Test Measurement

Camera 1

Camera 2

Strain

gauges

�The loads are measured by

strain gauges fixed to the bars

�At normal temperature, load

force is directly measured.

�At high temperatures, force

equilibrium is used to

calculate the load.

�Camera 1 is put in front of the furnace to measure the connection deformation

�Camera 2 is fixed facing the central pin connecting the three loading bars to

measure the angles between the three bars.

View of the Test SetupSetup of the

reaction frame

and the furnace

Setup of the

test specimen

View of the

specimen from Camera 1

View of loading bars from

Camera 2

Tested Fin Plate Connection

6505504502055

6505504502035

Temperaturesα

2163

2382

217

203

1

kNkN

Actual ultimate tensile load

Specified minimum ultimate tensile

load

Sampleidentity

40

60

60

40

200

40

50 50

100

10

UC254×89

S355

UB305×40

S275

α

Grade 8.8

M20

Bolt Property

Steel Property

0

100

200

300

400

500

600

0 0.3 0.6 0.9 1.2 1.5

StrainS

tress (

Mp

a)

0

0.3

0.6

0.9

1.2

1.5

0 100 200 300 400 500 600 700

Temperature

Red

ucti

on

facto

r

Test ResultReduction of the maximum Resistances

steel strength reduction

factor (EC3: Part 1.2)

Bolt strength reduction

factor (Y. Hu)

35 load

angle

55 load

angle Grade 10.9

bolts

Bolt strength reduction

factor (Brian Kirby)

Force-rotation Relationships

0

50

100

150

200

0 5 10 15 20

Rotation (Degree)

Fo

rce (

kN

)

0

20

40

60

80

100

0 2 4 6 8 10 12

Rotation (Degree)

Fo

rce (

kN

)

0

10

20

30

40

50

0 2 4 6 8 10 12

Rotation (Degree)

Fo

rce (

kN

)

0

5

10

15

20

25

0 3 6 9 12

Rotation (Degree)

To

tal

Fo

rce (

kN

)

20°C 450°C

550°C 650°C

Deformed Shape and Failure Mode

Failure modes at ambient temperature

Load

angle 55

Load angle 35

Deformed Shape and Failure Mode

Deformation after Test 550oC and

load angle 55

The steel beams and columns were deformed so little that they were

repeatedly used for three temperatures of 450oC, 550oC and 650oC in

each set of tests.

Behaviour of Grade 10.9 Bolts

One Test was performed using Grade 10.9 Bolts at 550°C and 35 load angle

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14 16 18 20

Rotation (Degree)

Fo

rce

(kN

)

Grade 10.9 Bolts

Grade 8.8 Bolts

Double Shear Tests of Bolts

0

50

100

150

200

250

300

350

0 2 4 6 8 10

Displacement (mm)

Fo

rce

(k

N)

2mm

Calibration of the Bolt Forces

44.13o

65125

185

145.95kN

For Test at 20oC and loaded at 55o

( ) 62.10113.44sin95.145 =×o

( ) 76.10413.44cos95.145 =×o

73.4545.0 =×V

V:

T:

M:

166375.0

73.45

3

76.104

3

62.10122

=

++

=F

Assume plastic state, maximum shear

force per bolt isAt the peak load, the maximum

force and the load angle are:

F=145.95kN α=44.13o

kN

kN

kN

kN.m

For Test at 20oC and loaded at 35o

At the peak load, the maximum

force and the load angle are:

F=185.11kN α=25.26o

The maximum shear force

per bolt is 155.5kN

Compare to Design Codes/Guidelines

Test 1: 20oC, 55o

Fv=166kN

Test 2: 20oC, 35o

Fv=155.5kN

Green BookBearing resistance of beam web: 55.2kNShear resistance is not critical if D>=2×tw

EC3: Part 1.8Bearing resistance of beam web: 83.6kNShear resistance of single bolt: 107.4kN

Beam web bearing

failure!

Design strength satisfy!

Design strength reduction follow steel!

Design strength

reduction follow

Bolt!

Bolt shear

failure!

Unexpected low

resistances at elevated

temperatures!

FEM Simulation of Bolts in Shear

0

200

400

600

800

1000

0 0.03 0.06 0.09 0.12

Strain

Str

es

s (

Mp

a)

Fracture strain

-50

0

50

100

150

200

0 1 2 3 4 5 6

Displacement (mm)

Fo

rce

(k

N)

Infinity

0.07

0.1

0.2

0.25

Plastic fracture strain of 0.25

gives approximately the same resistance and ductility

as the test result.

Conclusions

� Fin plate connections failed by bolt shear fracture.

� The maximum resistances are no less than the design

guide recommendations.

� Rotational ductility of this connection type is limited.

� Fin plate connections failed by bolt shear fracture.

� Reduction of the maximum resistances follows that of the bolts.

� Fin plate connections lose resistances very fast at elevated temperatures as bolt strengths reduce fast.

At normal Temperature

At elevated Temperature