Resistance of a Space Frame subjected to a Localized Travelling Fire

Hongxia Yu Arup (Beijing)

2

Purpose of the work

3

Functions

Dinning

Sight-view

Dinning Hotel lobby

Gym F&B and Swimming pool

Outdoor sight-view

Ourdoor swimming pool

4

Fire Risk Analysis

•  Maximum roof height 12m

•  Open space within the entire bridge

•  Flashover unlikely to happen

•  Fire spread may happen as fire loads can be very close to each other.

32m

12m

A fire spread model should be used for the dinning area.

5

Fire Spread Model

a.  Realistic fire spread mode b.  Simplified fire spread mode 18m 18m

Each table (including 12 chairs) takes an area of 3.5m×3.5m. Average Heat Release Rate : 500kW/m2. Fire Load: 652MJ/m2.

6

Heat Release Rate of One Table

6.125MW

6.2min 21.5min

17.4min

•  Peak Heat Release Rate

0.5×3.5×3.5=6.125MW

•  Total fire load

652×3.5×3.5=7987 MJ

•  Use fast t-square fire, fire development time is 6.2min. Steady burning phase is 15.3min.

•  Ignore the fire development phase, a steady burning would last for 17.4min.

7

Fire Travelling

0

17.4min

6.2 12.4 18.6 24.8

17.4min

17.4min

17.4min

17.4min

42.2 Time (min)

Row 1

Row 2

Row 3

Row 4

Row 5

8

Heat Transfer to Steel Members

Convection with the air hc

Radiation to the air hr,a

Radiation from the flame hr,f

arcfr hhhh ,, −−=

•  Net heat absorbed by the steel member

•  Temperature increase of the steel member

ssss CV

thTρΔ×

=Δ

)( 44, msssar TTAh −×= σε

( )msc TTAh −= αsc

( )44s, sfcfr TTAh −×Φ= σε

9

Calculation of the view factor

•  Flame size, including the fire diameter and flame height is calculated according to SFPE Handbook.

•  Flame then simplified to a block with all external panels radiating heat.

•  View factor for a steel member is calculated as the sum of these panels.

Top panel 14×3.5

Side panel 3.5×3.5

Side panel 3.5×3.5

10

Calculation of the view factor

•  In case of a travelling fire, the view factors from several fires may need to be considered at the same time.

0

17.4min

6.2 12.4 18.6 24.8

17.4min 17.4min

17.4min

17.4min

42.2 Time (min)

Row 1

Row 2 Row 3

Row 4

Row 5

11

Steel Temperatures

0 100 200 300 400 500 600 700 800 900

0 20 40 60 80 100

N1 N3 N6 N9

time (min)

Temperature (

°C)

Temperature development during a complete travelling procedure

12

Simplification of the Temperature Distribution

0 100 200 300 400 500 600 700 800 900

0 5 10 15 20 Node ID

Temperature (

°C)

Node Numbering and zone division

Simplify the non-uniform temperature distribution along half of the frame to four groups.

13

Temperature development for the frame

•  Each segment of 3.5m width of the frame is subjected to the travelling fire at a 6.2min interval. At time=40min….

Fire travelling direction

1

2 3 4 5 6

Fire zone

14

Structural Response

•  All steel members that were in contact with the flame showed residual plastic strain and visible plastic deformation after the fire.

15

Load Bearing Principle •  Structure remained stable by load-redistribution

-600

-500

-400

-300

-200

-100

0

100

200

0 10 20 30 40 50 60 70 80 90

time (min) Axial force (kN

)

heated members adjacent members

1 2

3

4 5 6

16

Conclusions and Design Suggestions

•  Conclusion: the structure maintained stable by load-redistribution. •  Design Suggestion: