Behaviour of Restrained Columns in Fire

Y C WangManchester Centre for Civil and

Construction Engineering

Small Furnace

Medium Furnace

Large Furnace

Reaction Frame to

Large Furnace

Objectives

• Bending moment variations in restrained columns in fire

• Effective lengths of restrained columns in fire

Test Programme• 18 restrained steel columns: 9 using fin

plate connections, 9 using extended end plate connections, 3 axial load level, 3 bending moment level

• 16 restrained concrete filled columns: 8 using fin plate connections, 8 using extended end plate connections, two tube sizes, two load levels, balanced and unbalanced beam loads

Restrained Column Arrangement

Column: 203x203x46UC

Beam: 254x146x43UBJacks

Reaction frame

Figure 2: Schematic arrangement

Restrained Column Arrangement

Column: 203x203x46UC

Beam: 254x146x43UBJacks

Reaction frame

Figure 2: Schematic arrangement

Column Head Support

Column segmentoutside furnace

JackLoadcell

Reactionframe

Head plate

Roller bar

Loosely fittedbolts inslotted holes

Restrained Column Arrangement

Column: 203x203x46UC

Beam: 254x146x43UBJacks

Reaction frame

Figure 2: Schematic arrangement

Beam End Support

Reactionframe

Restraint beam

Rollerbars

Performance of Sliding Joints -Loading Phase

Figure 3: Comparison between measured column axial load and total applied load at ambient temperature

0

200

400

600

800

1000

1200

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80

Nominal time

Load

(kN

)

Test SCRII8

Test SCRII5

Total applied load

Measured column axial load

Performance of Sliding Joints -Fire Exposure Phase

Figure 4: Comparison between calculated column axial load and total applied load

0

100

200

300

400

500

600

700

800

900

1000

0 100 200 300 400 500 600 700

Average temperature in column (oC)

Load

(kN

)

Test SCRII8

Test SCRII5

Total applied load

Calculated column axial load from strain gauges on reaction frame

Restrained Column Arrangement

Column: 203x203x46UC

Beam: 254x146x43UBJacks

Reaction frame

Figure 2: Schematic arrangement

Bending Moments in Restrained Steel Columns

Figure 5: Change of bending moments at column head

-40

-30

-20

-10

0

10

20

0 100 200 300 400 500 600 700

Average temperature in column (oC)

Ben

ding

mom

ent (

kN.m

)

Lower beam load = upper beam load

Lower beam load = 0.5*upper beam load

Bending Moment Distribution at Fire Limit State

Initial bendingmoment diagram

Bending momentdiagram in fire

Test Failure Temperatures

400

450

500

550

600

650

700

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Ratio of beam loads

Failu

re te

mpe

ratu

re (o C

)

Test SCRI1

Fin plate connections (series SCRI)

Extended end plate connections (series SCRII)

Load ratio=0.3

Load ratio=0.7

Load ratio=0.5

Effective Lengths of Restrained Steel Columns in Fire

L

x

Le

03.06.00

:,mindet,,,

00

00

22

2

02

2

0

2345

=++⇒=∂∂

=⇒=∂∂

=⇒=+++++=

=

=

=

CBLAL

bygivenlengtheffectiveisLederbetoECBA

D

FFExDxCxBxAx

eeLx

x

e

x

x

x

eχδ

χδ

δδ

Effective Length Ratios

Test numberTest

series 1 2 3 4 5 6 7 8 9

SCRI 0.8 0.775 0.775 0.825 0.664 0.74 0.809 0.78 0.809

SCRII 0.76 0.768 0.751 0.83 0.777 0.761 0.786 0.786 0.766

Comparison between Test Results and BS 5950 Part 8

400

450

500

550

600

650

700

400 450 500 550 600 650 700

Test limiting temperature (oC)

Cal

cula

ted

limiti

ng te

mpe

ratu

re (o C

)

Le=1,with BMLe=1,without BMLe=0.7,with BMLe=0.7,without BMLe=0.84,without BM

Comparison between Test Results and Eurocode Part 1.2

Fi 21 C i b t t t d E d 3 f il l d

200

300

400

500

600

700

800

900

200 300 400 500 600 700 800 900

Test load (kN)

Euro

code

failu

re lo

ads

(kN

) Le=1.0, without BMLe=0.7, without BM

Effective Length of Restrained Concrete Filled Columns

Fin Plate Connections1600

220

SCR31

870

SCR32

890

SCR33

920

SCR34

900 430

SCR35

1600

200

SCR36

920

SCR37

1560

210

SCR38

Extended End Plate Connections

1630

SCR44

1630

SCR41

940

SCR42

900

SCR43

900

Bending Moments in Restrained Concrete Filled Columns

-100

-80

-60

-40

-20

0

20

40

0 10 20 30 40 50 60

Fire test time (minutes)

Col

umn

bend

ing

mom

ent a

t top

(kN

.m)

SCR53SCR43

SCR41SCR52

Comparison of Results: Fin Plate Connections

0

500

1000

1500

2000

2500

3000

3500

0 500 1000 1500 2000 2500 3000 3500

Test failure time (sec)

Cal

cula

ted

failu

re ti

me

(sec

)

Le=1, with eccentricityLe=1, without eccentricityLe=0.7, with eccentricityLe=0.7, without eccentricity

Le=0.7L

Le=L

SCR38SCR31

SCR36

SCR32

SCR37

SCR33

SCR35

SCR34Arrow indicating conditions to be used in Fire Resistant calculations

Comparison of Results: Extended End Plate Connections

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Test failure time (seconds)

Cal

cual

ted

failu

re ti

me

(sec

onds

)

SCR44

SCR43

SCR53

SCR54

SCR41SCR52

SCR42

SCR51

Occurrence of Local Buckling

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60

Actual D/t or B/t

Loca

l buc

klin

g lim

it

Composite limit, LBSteel limit, LBComposite limit, NLBSteel limit, NLB

Recommendations for Design

• Bending moments = beam reaction load times eccentricity

• Effective length:(1) Steel columns and concrete filled columns

without local buckling: use Eurocode(2) Concrete filled columns with local

buckling: column height

Acknowledgements

EPSRCCorus