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Electronic Journal of Structural Engineering, 1 ( 2001) 38
Fire behaviour of steel members penetrating
concrete walls
I. D. Bennetts and C. C. Goh
Centre for Environmental Safety and Risk Engineering, Victoria University of Technology,
Werribee Campus, Victoria, Australia
Email: ian.bennetts@vu.edu.au; chongchee.goh@vu.edu.au
ABSTRACT
In steel construction it is often desirable for a steel member to pass through a concrete fire wall rather
than being curtailed at the wall. In situations where a steel member penetrates a fire wall, the member
will usually be fire protected for a certain length on each side of the wall so as to minimise the heat flow
through the steel member and reduce the likelihood of ignition of combustibles on the non-fire
(unexposed) side within the adjacent compartment. The testing reported in this paper suggests that it is
not necessary to apply fire protection to each side of a penetrating steel member since the resulting
temperature rise of the member is insufficient to cause ignition.
KEYWORDS
Steel members; fire wall
1. Introduction
It is often desirable for structural steel members to pass through a fire wall or common wall
rather than being curtailed on each side of the wall. In such cases, the penetrating member will
often be fire protected for a certain length on each side of the wall so as to minimise the
possibility of fire spread through heat conduction and excessive temperature rise of the member
on the unexposed side of the wall. This latter aspect is necessary to ensure that lateral restraint
will continue to be provided to the top of the wall by the member on the unexposed side of the
wall, as illustrated in Fig.1. This lateral restraint is necessary to maintain the structural
adequacy of the wall.
exposed face
concrete fire wall
steel member
unexposed face
restraint forces
deforming
member
Fig. 1 - Lateral restraint from member on the unexposed side of the wall
Such fire protection can be costly and it is not clear that it is necessary. The reasons for this is
that although a steel member is heated intensely on one side of a wall, this heat will be readily
conducted to the unexposed side where it will be lost by radiation and convection to the
surroundings. Some heat will also be conducted into the concrete wall. These mechanisms are
illustrated in Fig.2. Transient heat flow analysis can be used to demonstrate dramatic
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Electronic Journal of Structural Engineering, 1 ( 2001) 39
temperature drop across the width of the wall but such calculations need to be confirmed
experimentally.
exposed face
concrete fire wall
steel member
unexposed face
radiation and convection
conduction
conduction
conduction
radiation and convection
Fig. 2 - Mechanisms of heat transfer
The ability of a penetrating member to act as an effective bracing member depends on the
temperature of the member on the unexposed side of the wall: if the member is too hot, it will
have insufficient stiffness to provide effective restraint. Similarly, high temperatures could lead
to ignition of combustibles should these be in contact with the members on the unexposed side.
The tests [1] described in this paper were undertaken to better assess the above situation. The
tests were conducted at the Centre for Environmental Safety and Risk Engineering of Victoria
University of Technology.
ig 1
2. Test set-up, test specimens and instrumentations
2.1 Test Set-up
The tests were conducted in a standard fire test furnace which internally measures 2.1 m width
×
1.8 m depth
×
2.1 m height. Fig.3 shows an overall view of the furnace with two test
specimens mounted in the side walls of the furnace.
Fig. 3 - Overall view of test set-up
Electronic Journal of Structural Engineering, 1 ( 2001) 40
Fig. 4 shows details of test specimen mounted in the side walls of the furnace.
ceramic fibre
furnace wall
100 x 2 steel plate
100 x 20 steel plate
160
120 or 200
500
exposed face
concrete block
100 x 20 steel plate
100 x 2 steel plate
500
unexposed face
Fig. 4 - Layout of test set-up
2.2 Test Specimens
A total of eight specimens were tested in a series of four tests, each test having two specimens,
with one specimen placed in one wall of the furnace and the other in the opposite wall. Each
test specimen contained two steel plates, one with dimensions of 2 mm thick x 100 mm wide x
1200 mm long and the other having dimensions of 20 mm thick x 100 mm wide x 1200 mm
long. A concrete block of dimensions 365 mm x 385 mm x 120 mm (or 200 mm) thick was cast
around the middle section of the length of the steel plates. The concrete block was considered
to simulate a fire wall, and the plates chosen simulate the web or flange of a rolled section (in
the case of the 20 mm plate) and a purlin penetrating the wall (in the case of the 2 mm plate).
Four specimens were cast in the horizontal position (i.e. with the steel plate vertical) so good
compaction of the concrete was obtained. The concrete blocks for the other four specimens
were cast with holes to allow grouting of the steel plates once they were located. For two of
these specimens, the voids were grouted when the blocks were in the vertical position to
simulate a situation that may occur on site. The other two specimens were grouted with the
blocks in the horizontal position. Fig. 5 shows the dimensions of a typical specimen with the
position of the steel plates and voids in relation to the concrete block. Photographs of the test
specimens are given in Table 1.
Electronic Journal of Structural Engineering, 1 ( 2001) 41
365
385
200
60
105
40
120
60
200
165
165
120 / 200
500
500
concrete
block
100 x 2
steel plate
100 x 20
steel plate
Fig. 5- Details of test specimens
Table 1 gives a summary of the configuration of the test specimens. A general layout of the test
specimens is given in Fig. 6.
Table 1 - Configuration of test specimens
Specimen No. Specimen Configuration Remarks
VUT033A Voids filled insitu with concrete block.
Steel members positioned, and voids grouted with
concrete mix with concrete block placed
horizontally.
Thickness of concrete block = 120 mm.
VUT033B Voids filled insitu with concrete block.
Steel members positioned, and voids grouted with
concrete mix with concrete block placed
vertically.
Thickness of concrete block = 120 mm.
VUT034A Voids filled insitu with concrete block.
Steel members positioned, and voids grouted with
concrete mix with concrete block placed
horizontally.
Thickness of concrete block = 200 mm.
Electronic Journal of Structural Engineering, 1 ( 2001) 42
VUT034B
Voids filled insitu with concrete block.
Steel members positioned, and voids grouted with
concrete mix with concrete block placed
vertically.
Thickness of concrete block = 200 mm.
VUT035A No voids.
Steel members cast insitu with the concrete block.
Thickness of concrete block = 120 mm.
VUT035B No voids.
Steel members cast insitu with the concrete block.
Thickness of concrete block = 120 mm.
VUT036A No voids.
Steel members cast insitu with the concrete block.
Thickness of concrete block = 200 mm.
VUT036B No voids.
Steel members cast insitu with the concrete block.
Thickness of concrete block = 200 mm.
(a) Voids grouted vertically (b) Voids grouted horizontally
Fig. 6 - Grouting of voids in test specimens
2.3 Instrumentation
Type K mineral insulated thermocouples were used to measure furnace temperatures
throughout the tests. The steel temperatures were measured using spot-welded thermocouples
attached to the sides and edges of the steel plates. The thermocouple positions are shown in Fig.
7. The positions of furnace thermocouples are also shown in Fig. 7. Copper-disc thermocouples
were also attached to the unexposed face of the concrete block to measure the temperatures of
the concrete.
Electronic Journal of Structural Engineering, 1 ( 2001) 43
120 / 200
500
500
25
100
100
100
100
(1)
25
(2)
26
(3)
27
(4)
28
(5)
29
(6)
30
(12)
36
(11)
35
(10)
34
(9)
33
(8)
32
(7)
31
(13)
37
(14)
38
(15)
39
(16)
40
(17)
41
(18)
42
(24)
48
(23)
47
(22)
46
(21)
45
(20)
44
(19)
43
365
385
200
60
105
40120
60
200
165
165
25
25
(1)
25
(7)
31
(13)
37
(19)
43
(14-18)
38-42
(20-24)
44-48
(8-12)
32-36
(2-6)
26-30
100
100
( ) denotesthermocouple numbers in specimen A
copper disc
spot welded
furnace air
Fig. 7 - Thermocouples Positions
Electronic Journal of Structural Engineering, 1 ( 2001) 44
Figs 8(a) and (b) show the unexposed and exposed faces of a test specimen positioned on one
side of the furnace wall with its associated thermocouples.
(a) Thermocouples at unexposed face of test
specimen
(b) Thermocouples at exposed face of test
specimen
Fig. 8 - View of thermocouples on test specimen
3. The tests
3.1 Introduction
Table 2 gives a summary of all tests, test dates, concrete compressive strengths of the
specimens at the day of testing, and the duration of the standard fire. Specimens with concrete
block thicknesses of 120 mm and 200 mm were subjected to 120 minute and 180 minute
standard fire test exposure [2], respectively.
Table 2 - Summary of tests
Test No. Test Specimens Test Date Compressive
Strength (MPa)
Duration of
Standard Fire
VUT033 VUT033A 21/10/99 30.5 120 min
VUT033B " " "
VUT034 VUT034A 29/10/99 30.5 180 min
VUT034B " " "
VUT035 VUT035A 05/11/99 29.0 120 min
VUT035B " " "
VUT036 VUT036A 10/11/99 29.0 180 min
VUT036B " " "
Notes: (i) All test specimens were cast on 24/08/99.
(ii) Vertical and horizontal voids were filled on 15/09/99 and 16/09/99 respectively.
(iii) 28 day concrete cylinder compressive strength = 25.5MPa.
Fig. 9 shows an overall view of the furnace. The unexposed face of the steel plates of one of the
specimens can be seen at the right-hand side of the furnace.
Electronic Journal of Structural Engineering, 1 ( 2001) 45
Fig. 9 - View of furnace during test
Non-fire-retarded PVC cabling and a piece of cardboard were attached to the thicker of the
steel plates next to the unexposed face of the concrete wall. These were attached close to the
end of the test for 12-13 minutes to investigate if ignition would occur.
3.2 Results
Fig.10 shows the time-temperature relationships as recorded by the air temperature
thermocouples in the furnace. Alongside these points is the standard time temperature fire curve
(STTC) for 180 minutes duration.
Furnace Temperature
0
200
400
600
800
1000
1200
0 20 40 60 80 100 120 140 160 180
Time (min)
Temperature (°C)
STTC
Average
Minimum
Maximum
Fig. 10 - Time-temperature relationships in the furnace (Test VUT034)
Electronic Journal of Structural Engineering, 1 ( 2001) 46
Figures 11 to 14 show maximum temperatures along the length of the steel plates on the
unexposed face of concrete wall. Figures 11 and 13 show snap shots of the steel temperatures at
times of 60 and 120 minutes for concrete wall thickness of 120 mm. In the case of the 200 mm
wall, temperatures are also given for 180 minutes, and the graphs are shown in Figs 12 and 14.
It can be seen from Figs 11 (Test VUT033) and 13 (Test VUT035) that the steel temperatures
for 20 mm thick steel plate are generally less than 200
°
C and 280
°
C at times 60 and 120
minutes respectively. As for steel plate thickness of 2 mm, the maximum steel temperatures are
below 95
°
C and 155
°
C at times 60 and 120 minutes respectively. The maximum temperatures
and shape of the temperature distribution along the length of the steel plate suggest that the
performance of the concrete is very similar irrespective of how it is cast. That is, whether the
concrete was cast insitu or at a later stage, cast vertically or horizontally appears to make little
difference.
Similar observations can be drawn for tests VUT034 and VUT036 which incorporated concrete
wall of thickness 200 mm. From Figs 12 and 14, it can be seen that at times 60, 120 and 180
minutes, the maximum steel temperatures are generally less than 85
°
C, 140
°
C and 185
°
C
respectively, for a steel plate of thickness 20 mm; and 45
°
C, 70
°
C and 85
°
C respectively, for a
steel plate of thickness 2 mm.
A summary of the maximum temperatures reached for each test is given in Table 3 below. The
maximum steel temperatures on the unexposed side of the concrete was recorded at the first
row of thermocouples next to the face of the concrete.
Table 3 - Summary of test results
Test Specimen Steel plate
thickness
Concrete wall
thickness
Maximum temperature (°C) of
steel plate on unexposed side
(mm) (mm) 60 min 120 min 180 min
VUT033 VUT033A 20 120 193 278 -
2 " 91 153 -
VUT033B 20 " 181 268 -
2 " 97 144 -
VUT034 VUT034A 20 200 80 137 179
2 " 41 66 83
VUT034B 20 " 81 139 183
2 " 45 67 85
VUT035 VUT035A 20 120 182 265 -
2 " 92 141 -
VUT035B 20 " 176 259 -
2 " 83 132 -
VUT036 VUT036A 20 200 79 134 170
2 " 38 62 78
VUT036B 20 " 80 134 171
2 " 38 62 79
Electronic Journal of Structural Engineering, 1 ( 2001) 47
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
0 100 200 300 400 500 600 700 800
Distance along Steel Plate (mm)
Temperature (ºC)
VUT033A: 20 mm thick steel plate, time=120 mins
VUT033A: 20 mm thick steel plate, time=60 mins
VUT033A: 2 mm thick steel plate, time=120 mins
VUT033A: 2 mm thick steel plate, time=60 mins
VUT033B: 20 mm thick steel plate, time=120 mins
VUT033B: 20 mm thick steel plate, time=60 mins
VUT033B: 2 mm thick steel plate, time=120 mins
VUT033B: 2 mm thick steel plate, time=60 mins
steel plate
120 mm thick
concrete wall
Exposed to
standard fire
Unexposed face
(ambient)
25
steel plate
Thermocouples
500
100
FURNACE
Fig. 11 - Steel plate temperatures for various exposure periods to standard fire
(Test VUT033)
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
0 100 200 300 400 500 600 700 800
Distance along Steel Plate (mm)
Temperature (ºC)
VUT034A: 20 mm thick steel plate, time=180 mins
VUT034A: 20 mm thick steel plate, time=120 mins
VUT034A: 20 mm thick steel plate, time=60 mins
VUT034A: 2 mm thick steel plate, time=180 mins
VUT034A: 2 mm thick steel plate, time=120 mins
VUT034A: 2 mm thick steel plate, time=60 mins
VUT034B: 20 mm thick steel plate, time=180 mins
VUT034B: 20 mm thick steel plate, time=120 mins
VUT034B: 20 mm thick steel plate, time=60 mins
VUT034B: 2 mm thick steel plate, time=180 mins
VUT034B: 2 mm thick steel plate, time=120 mins
VUT034B: 2 mm thick steel plate, time=60 mins
steel plate
200 mm thick
concrete wall
Exposed to
standard fire
Unexposed face
(ambient)
25
steel plate
Thermocouples
500
100
FURNACE
Fig. 12 - Steel plate temperatures for various exposure periods to standard fire
(Test VUT034)
Electronic Journal of Structural Engineering, 1 ( 2001) 48
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
0 100 200 300 400 500 600 700 800
Distance along Steel Plate (mm)
Temperature (ºC)
VUT035A: 20 mm thick steel plate, time=120 mins
VUT035A: 20 mm thick steel plate, time=60 mins
VUT035A: 2 mm thick steel plate, time=120 mins
VUT035A: 2 mm thick steel plate, time=60 mins
VUT035B: 20 mm thick steel plate, time=120 mins
VUT035B: 20 mm thick steel plate, time=60 mins
VUT035B: 2 mm thick steel plate, time=120 mins
VUT035B: 2 mm thick steel plate, time=60 mins
steel plate
120 mm thick
concrete wall
Exposed to
standard fire
Unexposed face
(ambient)
25
steel plate
Thermocouples
500
100
FURNACE
Fig. 13 - Steel plate temperatures for various exposure periods to standard fire
(Test VUT035)
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
0 100 200 300 400 500 600 700 800
Distance along Steel Plate (mm)
Temperature (ºC)
VUT036A: 20 mm thick steel plate, time=180 mins
VUT036A: 20 mm thick steel plate, time=120 mins
VUT036A: 20 mm thick steel plate, time=60 mins
VUT036A: 2 mm thick steel plate, time=180 mins
VUT036A: 2 mm thick steel plate, time=120 mins
VUT036A: 2 mm thick steel plate, time=60 mins
VUT036B: 20 mm thick steel plate, time=180 mins
VUT036B: 20 mm thick steel plate, time=120 mins
VUT036B: 20 mm thick steel plate, time=60 mins
VUT036B: 2 mm thick steel plate, time=180 mins
VUT036B: 2 mm thick steel plate, time=120 mins
VUT036B: 2 mm thick steel plate, time=60 mins
steel plate
200 mm thick
concrete wall
Exposed to
standard fire
Unexposed face
(ambient)
25
steel plate
Thermocouples
500
100
FURNACE
Fig. 14 - Steel plate temperatures for various exposure periods to standard fire
(Test VUT036)
Electronic Journal of Structural Engineering, 1 ( 2001) 49
3.3 Observations
Figures 15 to 18 show photographs of specimens on the unexposed and exposed sides of the
concrete block at the end of the tests. The steel plates directly exposed to the fire showed signs
of oxidation (blistering) and the 2 mm plates have also distorted. However, this effect is not
evident at all on the unexposed side.
(a) Unexposed side (b) Exposed side
Fig. 15 - Test VUT033
(a) Unexposed side (b) Exposed side
Fig. 16 - Test VUT034
(a) Unexposed side (b) Exposed side
Fig. 17 - Test VUT035
Electronic Journal of Structural Engineering, 1 ( 2001) 50
(a) Unexposed side (b) Exposed side
Fig. 18 - Test VUT036
As described earlier, non-fire-retarded PVC cables and a piece of cardboard were attached to
the hottest steel plate next to the unexposed side of the concrete wall towards the end of each
test (see Figs 19 and 20). In this test (VUT035), the temperatures of the steel plates near the
unexposed side of the concrete wall were about 265
°
C and 259
°
C for specimens VUT035a and
VUT035b respectively. After about 12-13 minutes of exposure, no ignition occurred except that
the PVC cable melted and the cardboard lightly scorched, as shown in Fig. 21.
Fig. 19 - PVC cable hung from steel plate
Fig. 20 - Cardboard attached to steel plate Fig. 21 - Conditions of PVC cable and
cardboard after 12-13 minutes of exposure
Electronic Journal of Structural Engineering, 1 ( 2001) 51
3.4 Discussion
In all tests, the maximum steel temperatures recorded on the unexposed side of the test
specimens were less than 280
°
C for concrete walls of 120 mm thick (after 120 minutes of fire
exposure), and less than 185
°
C for walls of 200 mm thick (after 180 minutes of fire exposure).
The tests also showed that regardless of the voids cast vertically, horizontally or in-situ, the
maximum temperatures reached were similar. These temperatures will have little effect on the
strength and stiffness of the steel member [3] and it can therefore be assumed, that on the
unexposed side of the wall, the ability of the member to maintain lateral support will not be
impaired. However, it is necessary for the concrete wall to be designed to resist the vertical
loads imposed due to sagging of the steel member on the heated (exposed) side, as shown in
Fig. 22.
exposed face
concrete fire wall
steel member
unexposed face
load due to
deforming
member
Fig. 22 - Imposed vertical load due to sagging steel member
The temperatures noted above were not sufficient to cause ignition of non-fire-retarded PVC
cabling or cardboard. This is not surprising as testing conducted by Lie [4] has demonstrated
that the temperatures required for ignition are much higher than the insulation failure criteria
given in AS1530.4. Furthermore, experience suggests that it is very unlikely that combustibles
will be stored directly in contact with the penetrating steel member at the junction of the wall. It
is therefore argued that protection of a penetrating steel member is not required provided the
gaps around the steel member are fire stopped to prevent the flow of hot gases and flames to the
other side of the wall.
4. Conclusions
The tests reported in this paper illustrate the dramatic reduction in steel temperatures from the
exposed to unexposed sides of a steel member penetrating a wall. The resulting temperatures
are unlikely to reduce the stiffness and strength of the steel member on the non-fire side of the
wall and are unlikely to lead to fire spread through ignition of combustible materials located on
the unexposed side of the wall.
REFERENCES
1.
Bennetts I.D., Culton, M., and Goh, C.C., Behaviour of Steel Members When Penetrating
Fire Walls, CESARE, VUT Report No. VUT/CESARE/BHP/2000/002, March 2000.
2.
Standards Australia, AS 1530.4, Methods for Fire Tests on Building Materials, Components
and Structures, Part 4: Fire-resistance Tests of Elements of Building Construction, 1997.
3.
Poh, K. W., Modelling Elevated Temperature Properties of Structural Steel, BHP Research
Report No. BHPR/SM/R/055, September 1996.
4.
Schwatz, K. J., and Lie, T. T., Investigating the Unexposed Surface Temperature Criteria
of Standard ASTM E119, Fire Technology, 21, February 1985, pp. 169-180.
