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Integration of Structural
Engineering into Fire
Engineering Design
LEUNG Siu-man
Chief Structural Engineer
Buildings Department
Building (Construction) Regulation 90 –
Fire Resisting Construction
Every building shall be designed and constructed so as to –
(a)
(b)
(c)
(d)
Inhibit the spread of fire within the building and to nearby buildings by dividing the building into
compartments;
Provide adequate resistance to the spread of fire and smoke by the separation of different uses in
a building by compartment walls and floors and by the separation of the building from any
adjoining building or site;
Maintain the stability of the building in case of fire; and
Provide adequate resistance to the spread of fire over the roof of one building to another having
regard to the position of the building.
In other words, every building shall be designed and constructed so
as to provide adequate resistance to spread of fire and smoke and
to maintain its stability.
High casualty fire incidents in HK
- Garley Building (1996) : 40 fatalities
- Mei Foo Sun Chuen (1997) : 9 fatalities
Practice Note for AP & RSE 204 issued in 1998 :
- to provide guidance on fire engineering approach
to meet the fire safety objective and performance
requirements of B(C)R90
Fire Engineering Design
Active Fire Services Installation
Passive Fire Design
Fire Safety Management System
Total Fire Safety in Buildings
Smoke: A deadly hazard to life in a fire
Fire hazard chart
Some measures in Fire Engineering Design to
minimize the hazard caused by smoke
Active Fire Services
Installation
Smoke control system
- to control the spread of smoke
- difficult to ignite
Passive Fire Design
Appropriate selection
of building lining
materials
- do not release vast quantity
of heat and smoke
- have low rate of flame spread
- to ensure escape routes are
Fire Safety
Management System
Fire Safety Manager
known by all occupants and
free from obstructions
- that fire drills are practiced on
a regular basis
Three dominant criteria to ensure that the fire resistant compartment
is maintained so as to allow sufficient time for safe evacuation and
rescue operation – The “Fire Resistance Period” concept
•
•
•
Insulation (I) to prevent developing excessive temperature on the unexposed
surface of the building element;
structural Integrity (E) to maintain the separating function in preventing spread
of flame and smoke;
ability for Load-Bearing (R) structural element to support the load under fire.
Structural Fire Engineering generally
comprises the consideration of three aspects :
 Modeling of possible fire scenarios
 Calculation of heat transfer to the structure
 Assessment of the structural response at
elevated temperatures
Example of a restrained partition compartment wall
The 3m high concrete compartment partition wall, which is
constructed of d=100mm thick and restrained both at the top by a
fire protected steel beam and the bottom by the concrete floor slab,
is subjected to a natural fire condition with the fire exposed wall
surface at a temperature T0 higher than the fire unexposed wall
surface.
Assuming there is negligible flexible movement at the top and bottom
restraints, the restrained bow (or lateral thermal displacement) yR [1]
2H

T0
gap
H
For T0 = 900 C ;  = 9.0 x 10-6 /C; E = 20,000 N/mm2
H = 3000mm ; the gap at the top of compartment wall = 10mm
yR = 132mm
The restraint stress R
E ( T0 gap )
H
R = 95 MPa
(i.e. which is much greater than the crushing strength of partition wall of 20 MPa)
[1]
O’Connor D J, Structural Engineering design for fire safety in buildings. The Structural Engineer/ Volume
73/ No. 4, 21 February 1995
Sensitivity study of parameter on integrity of compartment wall under fire condition
Parameter
Gap
H
T0
Variation/ % change
YR(mm)/ % change
R (MPa)/% change
10mm
132
95
20mm (+100%)
72 (-45%)
29 (-69%)
30mm
-
-
3m
132
95
6m (+100%)
306 (+132%)
129 (+36%)
9m (+200%)
479 (+263%)
140 (+47%)
12m (+300%)
651 (+393%)
145 (+53%)
600 oC (-33%)
87 (-34%)
41 (-57%)
900 oC
132
95
1200 oC (+33%)
165 (+25%)
149 (+57%)
(N.B. The basic case in bold : Gap = 10mm, L = 3m and T0 = 900 oC)
From the sensitivity analysis, the following findings are observed: a.
Sufficient gap size would significantly reduce the restraint stress in the compartment wall
b.
The increase in compartment wall height would increase the restraint stress mildly whereas
the increase in bow deflection is much greater
c.
The change in temperature would significantly change the restraint stress in the
compartment wall
Example of a platform supported by steel hanger rods
According to BS 5950 Part 8, the limiting temperature of steel
members in tension is as follow:
Description
of member
Members in
tension: all
cases
Limiting temperature(oC) at a load ratio of
0.7
0.6
0.5
0.4
0.3
0.2
0.1
460
510
545
590
635
690
770
Table 1
The forces taken by each steel rod at fire limit state calculated by
using a finite element program SAFE, the structural capacities of
steel rods at ambient temperature provided by the manufactures,
the calculated load ratio of the steel rods, and the respective
limiting temperatures derived by interpolation of Table 1 are as
follow:
Size of
steel rods
Forces taken
by each rod at
fire limit state
(A)
Structural
capacities at
ambient
temperature (B)
Load ratio
= (A)/(B)
Limiting
temperature
76mm
560 kN
1725 kN
0.33
622oC
95mm
1210 kN
2695 kN
0.45
568oC
Deficiency
The platform is supported by hanger rods which can
only take tensile loads. Excessive relative elongation
of individual rods heated up under fire may render
these affected rods losing their supporting action (i.e.
no longer in tension). This will cause a load
redistribution and increase the load on the other
remaining hanger rods jeopardizing their original fire
limit state designed for.
Common Problems
FRP ratings are mainly evaluated for individual
building elements only
Structural aspect concentrated on strength and relied
on FRP ratings as guideline on the use of respective
element and material types
Large deformation and plastic strains allowed in fire
limit state design, but may hinder the overall fire
performance of the compartment
Thermal analysis relating to structural response of
building elements ignored or not properly considered
Structural
Fire
Engineering
Engineering
Gap
Factors to consider for Fire Engineer & Structural Engineer
(a)
(b)
(c)
(d)
(e)
(f)
(g)
The selected fire cases should be critically reviewed to ascertain if they generally
cover the worst scenario.
The derivation of the fire load should be conversant with the local condition rather
than simply refer to overseas fire load data.
Some unprotected steel members might be subjected to a temperature close to the
limiting temperature in case of fire. However, the structural design of the steel
structure should take into account the stress reduction factor of steel at elevated
temperature.
The derived surface temperature of the material subjected to elevated temperature has
to account for the heat effects of thermal conductivity of materials, which may further
raise the surface temperature.
The behaviour of natural fire set up of an open frame structure in the laboratory may
be different from the real fire on the spot. In particular, the prevailing wind and other
actual building layout, which may accelerate and increase the temperature of the
structural material, have to be taken into consideration.
Calculation of fire resistance ratings, based on full compartment burn-out.
Development of suitable acceptance criteria for the design and use of timber, steel,
concrete and glazing and their material limitation.
Conclusion
 Importance of other design parameters
affecting the structural design in
performance base approach to be observed
 Design criteria should be incorporated in
the coming Code of Practice (Fire
Engineering Design)
- Thank You -
Q&A