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Design fires for Structural Fire analysis-approving authority status quo
Dr Samantha Foster
Project Example: Heron Tower, London
Cross Section of Building
Compartment floors
Atrium
floors
Building Description
• Heron Tower is a 46 storey building (approx. 200m in height)
• Office accommodation; over 3 storey units or “villages”
• Compartment floors every 3rd floor
• Clear open office areas
• Fully glazed facade
Active Fire Measures
Sprinkler System
• Life Safety sprinkler provision;
• 18 sprinkler heads per floor;
• Highly redundant sprinkler system; duplicate supply
• Provision of smoke detection
• Automatic alarm transmission to fire brigade
Compartmentation
Horizontal Compartmentation:• 90 minutes fire resistance
• All riser, services etc fire stopped/enclosed in 90 minutes fire resisting construction
Vertical Compartmentation:• Fire fighting shaft enclosed within 2 hour fire
resisting core
Compartmentation
• Atrium floor
13m/14m
27m
50m
Compartmentation
• Typical compartment floor
Design fire Scenario 1
25% glazing failure with a fuel load of 695MJ/m²
(65% greater than ave.
characteristic value for use in office buildings)
Design fire Scenario 2
25% glazing failure with a fuel load
of 440MJ/m2
Case 1:
3D single floor model
Case 2:
3D Multi Storey Model
Design Fire ScenariosModelling Case #
Outline of Agreed Work
Design Fire Scenarios
Case 1. Single floor fire
Case 2. Multi storey fire: 3 storeys engulfed
Case 1: Single floor fire•80% fractile value fire load
•Height factor of 2
•25% failure of glazing
•Fire load 695MJ/m2
Case 2: Multi storey fire•Average fire load density
440MJ/m2
25% failure of glazing0
200
400
600
800
1000
1200
0 20 40 60 80 100 120 140 160 180
Time (min)
Te
mp
era
ture
(°C
)
ISO 834 Standard Fire Curve
0
200
400
600
800
1000
1200
0 20 40 60 80 100 120 140 160 180
Time (min)
Te
mp
era
ture
(°C
)
ISO 834 Standard Fire Curve
Modelling Case 1
• 3D Single floor model
(Slab omitted for clarity)
Storey height of 4128mm
Heat Transfer: Case 1
• Slab temperatures
0
200
400
600
800
1000
1200
0 50 100 150 200 250 300 350
Time, min
Tem
pera
ture
, °C
Assumed 25% ventialtion with fire
load 695 MJ/m2
1/4 depth into slab
1/2 depth into slab
3/4 depth into slab
Top of slab
• Unprotected secondary beam temperatures
Heat Transfer: Case 2
0
200
400
600
800
1000
1200
0 50 100 150 200 250 300 350
Time [min]
Te
mp
era
ture
s [
C]
Top Flange Temperature
Web Temperature
Bottom Flange Temperature
Single Floor Fire
Village Fire
Modelling Case 2
• 3D Multi storey model
Heat Transfer: Case 2
• Slab temperatures
0
200
400
600
800
1000
1200
0 20 40 60 80 100 120 140 160 180 200
Time, min
Te
mp
era
ture, °
C
Multi storey fire; fire load 440MJ/m2
25% ventilation
1/4 into slab depth
mid depth
3/4 into slab depth
Top of slab
Heat Transfer: Case 2
• Unprotected secondary beam temperatures
0
200
400
600
800
1000
1200
0 50 100 150 200 250 300 350
Time [min]
Tem
pera
ture
s [C
]
Top Flange Temperature
Web Temperature
Bottom Flange Temperature
Single Floor Fire
Village Fire
• Parametric study undertaken using FDS of typical
compartment temperatures
Comparative studies
0
100
200
300
400
500
600
700
800
900
1000
0 5 10 15 20 25 30
Time [minutes]
Te
mp
era
ture
[C
]
600 MJ/m 2̂
840 MJ/m 2̂
1200 MJ/m 2̂
1800 MJ/m 2̂
• Code requirement
Concluding remarks
Discussion
