Second International Workshop « Structures in Fire » – Christchurch – March 2002
MECHANICAL PROPERTIES OF STRUCTURAL STEEL AT
ELEVATED TEMPERATURES AND AFTER COOLING
DOWN
Jyri OUTINEN and Pentti MÄKELÄINEN
Laboratory of Steel Structures,
Department of Civil and Environmental Engineering,
Helsinki University of Technology
P.O. Box 2100, FIN-02015 HUT, Finland
[email protected]
http://www.hut.fi/Units/Civil/Steel/
ABSTRACT
Experimental research program has been carried out during the years 1994-2001 in the
Laboratory of Steel Structures at Helsinki University of Technology in order to investigate
mechanical properties of several structural steels at elevated temperatures by using mainly
transient state tensile test method. The aim is to produce accurate material data for the use in
different structural analyses. The main test results are public and they are available for other
researchers.
In this paper the experimental test results for the mechanical properties of the studied steel
grades S350GD+Z, S355 and S460M at fire temperatures are presented with a short
description of the testing facilities. A test series was also carried out for cold-formed
material taken from rectangular hollow sections of structural steel S355J2H and these test
results are also given in this report.
The mechanical properties of structural steel after cooling down have also been shortly
examined and these test results are given in this report.
The test results were used to determine the temperature dependencies of the mechanical
properties, i.e. yield strength, modulus of elasticity and thermal elongation, of the studied
steel material at temperatures up to 950°C. The test results are compared with the material
model for steel according to Eurocode 3: Part 1.2.
KEYWORDS: mechanical properties, strength, high-temperature testing, structural steel
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Second International Workshop « Structures in Fire » – Christchurch – March 2002
INTRODUCTION
The behaviour of mechanical properties of different steel grades at elevated temperatures
should be well known to understand the behaviour of steel and composite structures at fire.
Quite commonly simplified material models are used to estimate e.g. the structural fire
resistance of steel structures. In more advanced methods, for example in finite element or
finite strip analyses, it is important to use accurate material data to obtain reliable results.
To study thoroughly the behaviour of certain steel structure at elevated temperatures, one
should use the material data of the used steel material obtained by testing. The tests have to
be carried out so, that the results can be used to evaluate the behaviour of the structure, i.e.
the temperature rate e.g. should be about the same that is used in the modelling assumptions.
Extensive experimental research has been carried out since 1994 in the Laboratory of Steel
Structures at Helsinki University of Technology in order to investigate mechanical properties
of several structural steels at elevated temperatures by using mainly the transient state tensile
test method. The basic material research programme is still going on, but the main test
results so far were published in 2001 in the Laboratory of steel structures’ publication series
[1]. The publication is freely available from the laboratory’s website:
http://www.hut.fi/Units/Civil/Steel/Publications/jsarj.html. Some of the test results were also
presented in the previous ‘Structures in Fire’ –workshop in Copenhagen [2].
The test results have recently been used in some research projects studying the behaviour of
e.g. cold-formed steel members in fire [3] [4]. The results seem to work quite well with the
structural analyses carried out within these projects.
In this paper the transient state test results of structural steel grades S355, S355J2H, S460M
and S350GD+Z are presented with a short description of the testing facilities and
comparisons with ENV1993-1-2 [5].
In addition to the original plan, some tests were also carried out for structural steel material
taken from that have been tested at elevated temperatures. This was to find out the
remaining strength of the material after fire. The preliminary test results are presented in this
paper.
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Second International Workshop « Structures in Fire » – Christchurch – March 2002
STUDIED MATERIALS
The studied materials were common structural steel grades with nominal yield strength
varying from 350N/mm2 to 460N/mm2. The actual yield strength varied significantly from
the nominal values and this has to be taken into account. The materials are listed in the Table
1 below with the nominal and measured values at room temperature.
Steel Grade
S350GD+Z
S355
S460M
S355J2H
Nominal fy
[N/mm2]
350
355
460*
355
Measured fy
[N/mm2]
402
406
445*
539-566**
Material Standard
SFS-EN 10 147
SFS-EN 10 025
SFS-EN 10113
SFS-EN 10219-1
Table 1: Studied steel grades
* The nominal yield strength is dependent on plate thickness. The nominal yield strength for steel plates with
20mm thickness that was studied in this research is 440N/mm2.
** The measured yield strength values are for test specimen taken from the face of square hollow sections
50x50x3, 80x80x3 and 100x100x3.
TEST METHODS
Two types of test methods are commonly used in the small-scale tensile tests of steel at high
temperatures; transient-state and steady-state test methods. The steady state tests are easier to
carry out than the transient state tests and therefore that method is more commonly used than
the transient state method. However, the transient state method seems to give more realistic
test results especially for low-carbon structural steel and that is why it is used in this research
project as the main test method. A series of steady state tests were also carried out in this
project.
Transient-state test method
In transient-state tests, the test specimen is under a constant load and under a constant
temperature rise. Temperature and strain are measured during the test. As a result, a
temperature-strain curve is recorded during the test. Thermal elongation is subtracted from
the total strain. The results are then converted into stress-strain curves as shown in Figure 1.
T1
σ2
Stress
T2
σ1
σ1
Strain
σ2
σ3
T3
T3
Temperature
σ3
T2
T1
Strain
FIGURE 1: Converting the stress-strain curves from the transient state test results.
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The mechanical material properties i.e. elasticity modulus and yield strength, can be
determined from the stress-strain curves. This is illustrated in Figure 2. The strain value of
εy,θ stands for 2 % total strain.
Stress σ
fy
f p,0.2
f p,θ
E a,θ = tan α
α
ε = 0.2%
εp,θ
ε y,θ
ε t,θ
ε u,θ
Strain ε
FIGURE 2: Stress-strain relationship for steel at elevated temperatures.
The transient-state test method gives quite a realistic basis for predicting the material’s
behaviour under fire conditions. The transient-state tests were conducted with two identical
tests at different stress levels. Heating rate in the transient state tests was 20°C min-1. Some
tests were also carried out using heating rates 10°C min-1 and 30°C min-1. In addition some
tests were carried out with a high heating rate close to the ISO-curve to compare the real
behaviour of the material with this heating rate. Temperature was measured accurately from
the test specimen during the heating.
Steady-state test method
In the steady-state tests, the test specimen was heated up to a specific temperature. After that
a tensile test was carried out. In the steady state tests, stress and strain values were first
recorded and from the stress-strain curves the mechanical material properties could be
determined. The steady state tests can be carried out either as strain- or as load-controlled. In
the strain-controlled tests, the strain rate is kept constant and in the load-controlled tests the
loading rate is kept constant.
TESTING DEVICE
The tensile testing machine used in the tests is verified in accordance with the standard EN
10 002-2 [6]. The extensometer is in accordance with the standard EN 10 002-4 [6]. The
oven in which the test specimen is situated during the tests was heated by using three
separately controlled resistor elements. The air temperature in the oven was measured with
three separate temperature-detecting elements. The steel temperature was measured
accurately from the test specimen using temperature-detecting element that was fastened to
the specimen during the heating. The testing device is illustrated in Figure 3.
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FIGURE 3: High-temperature tensile testing device.
TEST RESULTS OF STRUCTURAL STEEL S350GD+Z
The behaviour of structural steel S350GD+Z at elevated temperatures was studied with 30
high-temperature tests. The test results were combined with an earlier test series of 60 tests
that were carried out in the same laboratory. The aim was to add the test results of the
mechanical properties at temperatures from 700°C to 950°C to the earlier test results. On the
basis of these test results a suggestion concerning the mechanical properties of the studied
material was made to the Finnish national norm concerning the material models used in
structural fire design of unprotected steel members. The test results were fitted to ENV19931-2 material model and the results are illustrated in Table 2.
In Figure 4 the experimentally determined yield strength fy is compared with ENV1993-1-2
material model. In Eurocode, the nominal yield strength is assumed to be the constant until
400°C, but in the real behaviour of the studied steel it starts to decrease earlier.
Additionally room-temperature tests were also carried out for material taken from members
that have been tested at elevated temperatures. This was to find out the remaining strength of
the material after fire. In Figure 5 the tensile test results are compared with the test results for
unheated material.
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Second International Workshop « Structures in Fire » – Christchurch – March 2002
Steel
Temp.
Reduction factor
for satisfying
deformation criteria
(informative only)
Reduction factor Reduction factor
for the slope of the for proportional
linear elastic range
limit
θa
[°C]
kE,θ = Ea,θ / Ea
kp,θ = fp,θ / fy
kx,θ = fx,θ / fy
20
100
200
300
400
500
600
700
800
900
950
1000
1.000
1.000
0.900
0.800
0.700
0.600
0.310
0.130
0.090
0.068
0.056
0.045
1.000
0.970
0.807
0.613
0.420
0.360
0.180
0.075
0.000
0.000
0.000
0.000
1.000
0.970
0.910
0.854
0.790
0.580
0.348
0.132
0.089
0.057
0.055
0.025
Reduction
factor
for yield strength
Reduction
factor
for yield
strength
kp0,2,,θ = fp0,2,θ / fy ky,θ = fy,θ / fy
1.000
1.000
0.863
0.743
0.623
0.483
0.271
0.106
0.077
0.031
0.023
0.014
1.000
0.970
0.932
0.895
0.857
0.619
0.381
0.143
0.105
0.067
0.048
0.029
TABLE 2: Reduction factors for mechanical properties of structural steel S350GD+Z at
temperatures 20°C-1000°C. Values based on transient state test results.
Reduction factor for yield strength ky,θ = fy,θ /fy
1.2
1.0
Model based on test results
EC3: Part 1.2
0.8
0.6
0.4
0.2
0.0
0
100
200
300
400
500
600
700
800
900
1000
Temperature [°C]
FIGURE 4: The reduction factor for effective yield strength f y,θ of structural steel
S350GD+Z determined from test results compared with the values given in Eurocode
3: Part 1.2.
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550
Test pieces taken before high-temperaure tests
500
450
Test pieces taken after high-temperature tests
2
Stress [N/mm ]
400
350
300
250
200
150
100
50
0
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Strain [%]
FIGURE 5: Tensile test results for structural steel S350GD+Z. Test pieces taken before
and after high-temperature compression tests.
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From Figure 5 it can be seen that the increased yield strength of the material due coldforming has decreased back to the nominal yield strength level of the material. It has to be
noted that the material has reached temperatures up to 950C in the compression tests. The
temperature histories from the compression tests are illustrated in Figure 6. The tensile test
specimen were taken from compression members 24,27 and 30. The compression tests were
carried in a research project of VTT, the Techcnical Research Centre of Finland.
1000
900
compression
members
24,27 and 30
800
700
600
500
400
300
200
100
0
0
10
20
30
40
50
60
70
80
90
TIME (min)
TC_22
TC_23
TC_29
TC_30
TC_24
TC_25
TC_26
TC_27
TC_28
FIGURE 6: Temperature histories of the compression test specimens, from which the
tensile test specimens were taken after cooling down.
The members that were in the compression tests were quite distorted after the tests. Despite
this, the mechanical properties of the steel material were preserved in the nominal strength
level of the material. This kind of phenomenon should be taken into account when
considering the load bearing capacity of steel structures that have been in fire and are
otherwise still usable, i.e. not too badly distorted.
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TEST RESULTS OF STRUCTURAL STEEL S355J2H
Normal tensile tests according standard SFS-EN 10002-1 were carried out for the coldformed material. The test results for yield strength are illustrated in Table 3. It can be seen
from the test results that the increased strength caused by cold-forming is significant for all
studied hollow sections. The nominal yield strength for the material is 355N/mm2. The
tensile tests at room temperature were carried out for the specimens taken from the corner
part of SHS 50x50x3. The average yield strength fy for these specimens was 601 N/mm2.
50x50x3
80x80x3
100x100x3
Yield strength
fy [N/mm2]
Yield strength
Rp0.2 [N/mm2]
Yield strength
Rt0.5 [N/mm2]
566
544
539
520
495
490
526
502
497
Table 3: Tensile test results for structural steel S355J2H at room temperature.
Test pieces from SHS cross-sections.
A test series of over 100 tensile tests was conducted for the material taken from SHS-tubes
50x50x3, 80x80x3 and 100x100x3. The heating rate in the tests was 20°C/minute. Some
tests were also carried out with a heating rate 10°C/minute and 30°C/minute. A small test
series was also carried out with a heating rate 45°C/minute.
The tensile tests for structural steel S355J2H were carried out using test specimens that were
cut out from SHS-tubes 50x50x3, 80x80x3 and 100x100x3 longitudinally from the middle of
the face opposite to the welded seam. A small test series with test specimen taken from the
corner parts of the SHS-tube 50x50x3 was also carried out as an addition to the original
project plan. The test results have been fitted into the EC3: Part 1.2 material model using the
calculation parameters determined from the transient state tests.
The high-temperature tensile testing has to be carried out using the rules given in testing
standard SFS-EN 10002 : Metallic materials. Tensile testing. Parts 1-5. In this standard there
are limitations for the strain rate and the loading rate used in high temperature tensile testing.
The test results that are given in this report are based on tests carried out according this
testing standard.
From the test results it was clearly seen, that with this used heating rate 20°C/minute the
increased strength caused by cold forming starts to vanish in temperatures 600°C-700°C. For
the test specimen with a higher heating rate the increased strength seems to remain to higher
temperatures. The test results at temperatures 20°C – 1000°C are illustrated in the following
tables.
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Temp.
[°C]
20
100
200
300
400
500
600
700
750
800
850
900
950
1000
Modulus of
Elasticity E [N/mm2]
210000
210000
189000
168000
147000
126000
65100
27300
23100
18900
16537.5
14175
11812.5
9450
Proportional limit
fp [N/mm2]
481.1
481.1
441.48
367.9
311.3
169.8
67.92
39.62
28.3
19.81
11.32
6.792
5.66
4.528
Yield strength
fy [N/mm2]
566
566
549.02
537.7
481.1
367.9
181.12
101.88
67.92
42.45
31.13
22.64
19.81
22.64
Yield strength
Rp0.2 [N/mm2]
520
520
485
439
381
255
118
66
46
29
20
13
12
10
Yield strength Rt0.5
[N/mm2]
526
526
496
455
399
280
132
72
51
33
23
17
14
11
Reduction factors relative to the values at temperature 20°C:
Temp
[°C]
20
100
200
300
400
500
600
700
750
800
850
900
950
1000
Modulus of
Elasticity
kE,θ = Ea,θ / Ea
1,000
1,000
0,900
0,800
0,700
0,600
0,310
0,130
0,110
0,090
0,079
0,068
0,056
0,045
Proportional limit
fp
kp,θ = fp,θ / fy
0,850
0,850
0,780
0,650
0,550
0,300
0,120
0,070
0,050
0,035
0,020
0,012
0,010
0,008
Yield strength
fy
ky,θ = fy,θ / fy
1,000
1,000
0,970
0,950
0,850
0,650
0,320
0,180
0,120
0,075
0,055
0,040
0,035
0,030
Yield strength
Rp0.2
kp0,2,,θ = fp0,2,θ / fy
0,919
0,919
0,867
0,795
0,693
0,468
0,217
0,124
0,088
0,053
0,039
0,025
0,021
0,018
Yield strength
Rt0.5
kt0.5,θ = ft0.5,θ / fy
0,929
0,929
0,876
0,804
0,705
0,495
0,233
0,127
0,090
0,058
0,041
0,030
0,025
0,019
Table 4: Mechanical properties of structural steel S355J2H at elevated temperatures. Test
pieces from SHS 50x50x3
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Second International Workshop « Structures in Fire » – Christchurch – March 2002
Temp
[°C]
20
100
200
300
400
500
600
700
750
800
850
900
950
Modulus of
Elasticity E [N/mm2]
210000
210000
189000
168000
147000
126000
65100
27300
23100
18900
16537,5
14175
11812,5
Proportional limit
fp [N/mm2]
462,4
462,4
424,32
353,6
299,2
163,2
65,28
38,08
27,2
8,16
7,344
6,528
5,44
Yield strength
fy [N/mm2]
544
544
527,68
516,8
462,4
353,6
174,08
97,92
65,28
35,36
29,92
16,32
13,6
Yield strength
Rp0.2 [N/mm2]
500
500
473
432
379
255
117
67
44
21
16
11
Yield strength
Rt0.5 [N/mm2]
525
505,4882
478,1146
438,4486
384,3109
270,426
128,1229
70,38595
48,80605
24,87326
22,46505
12,67555
Reduction factors relative to the values at temperature 20°C:
Temp
[°C]
20
100
200
300
400
500
600
700
750
800
850
900
950
1000
Modulus of
Elasticity
kE,θ = Ea,θ / Ea
1,000
1,000
0,900
0,800
0,700
0,600
0,310
0,130
0,110
0,090
0,079
0,068
0,056
0,045
Proportional limit
fp
kp,θ = fp,θ / fy
0,850
0,850
0,780
0,650
0,550
0,300
0,120
0,070
0,050
0,015
0,014
0,012
0,010
0,008
Yield strength
fy
ky,θ = fy,θ / fy
1,000
1,000
0,970
0,950
0,850
0,650
0,320
0,180
0,120
0,065
0,055
0,030
0,025
0,020
Yield strength
Rp0.2
kp0,2,,θ = fp0,2,θ / fy
1,016
1,016
0,961
0,878
0,770
0,518
0,238
0,136
0,089
0,043
0,033
0,022
Yield strength
Rt0.5
kt0.5,θ = ft0.5,θ / fy
1,000
0,963
0,911
0,835
0,732
0,515
0,244
0,134
0,093
0,047
0,043
0,024
Table 5: Mechanical properties of structural steel S355J2H at elevated temperatures. Test
pieces from SHS 80x80x3
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Second International Workshop « Structures in Fire » – Christchurch – March 2002
Temp
[°C]
20
100
200
300
400
500
600
700
750
800
850
900
950
Modulus of
Elasticity E [N/mm2]
210000
210000
189000
168000
147000
126000
65100
27300
23100
18900
16537,5
14175
11812,5
Proportional limit
fp [N/mm2]
458,15
458,15
420,42
350,35
296,45
161,7
64,68
37,73
26,95
18,865
10,78
6,468
5,39
Yield strength
fy [N/mm2]
539
539
522,83
512,05
458,15
350,35
172,48
86,24
59,29
40,425
29,645
16,17
13,475
Yield strength
Rp0.2 [N/mm2]
496
496
469
427
373
252
117
53
38
23
17
11
Yield strength Rt0.5
[N/mm2]
500,9744
500,9744
473,8989
434,6986
381,0532
268,1464
127,0427
64,46188
45,50802
25,24635
22,26879
12,56227
Reduction factors relative to the values at temperature 20°C:
Temp Modulus of
[°C] Elasticity
kE,θ = Ea,θ / Ea
20
1,000
100
1,000
200
0,900
300
0,800
400
0,700
500
0,600
600
0,310
700
0,130
750
0,110
800
0,090
850
0,079
900
0,068
950
0,056
1000 0,045
Proportional limit
fp
kp,θ = fp,θ / fy
0,850
0,850
0,780
0,650
0,550
0,300
0,120
0,070
0,050
0,035
0,020
0,012
0,010
0,008
Yield strength
fy
ky,θ = fy,θ / fy
1,000
1,000
0,970
0,950
0,850
0,650
0,320
0,160
0,110
0,075
0,055
0,030
0,025
0,020
Yield strength
Rp0.2
kp0,2,,θ = fp0,2,θ / fy
1,012
1,012
0,957
0,871
0,761
0,514
0,239
0,108
0,078
0,047
0,035
0,022
Yield strength
Rt0.5
kt0.5,θ = ft0.5,θ / fy
1,008
1,008
0,954
0,875
0,767
0,540
0,256
0,130
0,092
0,051
0,045
0,025
Table 6: Mechanical properties of structural steel S355J2H at elevated temperatures. Test
pieces from SHS 100x100x3
The test results with heating rates 10°C/minute and 20°C/minute don’t differ from each
other, but the heating rate 30°C/min seemed to give higher test results. This is illustrated in
Figure 6 This led to the decision to carry out additional tests with a higher heating rate. Also
the behaviour of the corner parts of the profile was studied.
Three small test series were carried out. One with corner specimens with a heating rate
20°C/minute, one with corner specimen with a heating rate 45°C/minute and one with flat
specimen with a heating rate 45°C/minute. The used temperature history of this new test
series is illustrated in Figure 7. The test results at temperatures 600C and 700 are illustrated
in Figures 8 and 9.
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Second International Workshop « Structures in Fire » – Christchurch – March 2002
800
700
30°C/min
20°C/min
10°C/min
Temperature [°C]
600
500
400
300
200
100
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Strain [%]
FIGURE 6: Temperature-strain curves of structural steel S355J2H at stress level
100N/mm2 with heating rates 10°C, 20°C and 30°C/min. Test pieces taken from SHS
50x50x3.
900
Calculated temperature of SHS 50x50x3
according to EC3: Part 1.2, using ISO-curve.
Measured air temperature
800
Temperature [°C]
700
Measured steel temperature
600
500
400
300
200
100
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Time [min]
FIGURE 7: Temperature history of the new test series compared with the ISO-curve.
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Second International Workshop « Structures in Fire » – Christchurch – March 2002
280
260
240
220
2
Stress [N/mm ]
200
180
160
140
120
100
80
Corner pieces 45°C/min
Corner pieces 20°C/min
Flat pieces 45°C/min
Flat pieces 20°C/min
Model based on transient state tests 20°C/min
60
40
20
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Strain [%]
FIGURE 8: Stress-strain curves of structural steel S355J2H. Test results with different
specimens and different heating rates at temperature 600°C.
160
140
2
Stress [N/mm ]
120
100
80
60
Corner pieces, 45°C/min
40
Flat pieces 45°C/min
Flat pieces 20°C/min
20
Model based on transient state tests 20°C/min
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Strain [%]
FIGURE 9: Stress-strain curves of structural steel S355J2H. Test results with different
specimens and different heating rates at temperature 700°C.
The difference between the test results with heating rates 20°C/minute and 45°C/minute
seems not to be as big as was assumed before for the specimens taken from the face of the
square hollow section. Also the difference between the test results with flat specimens and
corner specimens with a heating rate 20C/minute was not very big. The test results for the
corner pieces are significantly higher with heating rate 45°C/minute. In Figure 10 the yield
strength fy determined from these test results is illustrated.
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Second International Workshop « Structures in Fire » – Christchurch – March 2002
Yield strength fy [N/mm2]
600
Model based on transient state
test results, 20C/minute
500
EC 3: Part 1.2 (fy=355N/mm2)
Corner pieces, 45°C/min
400
Flat pieces 45°C/min
300
200
100
0
0
100
200
300
400 500 600 700
Steel temperature [°C]
800
900
1000
FIGURE 10: Yield strength fy of structural steel S355J2H. Test results with different
specimens and different heating rates at temperatures 20-700°C.
Some tests for structural steel S355J2H were carried out at room temperature with test
specimens that had been heated unloaded up until temperature 950°C and let cool down to
ambient temperature after that. The mechanical properties of the material seemed to return
back to the nominal values of structural steel S355. In Figure 11 the test results of these tests
are compared with the normal room temperature test results.
600
SHS 50x50x3
Stress [N/mm2]
500
SHS 80x80x3
SHS 100x100x3
400
Heated test specimen
300
200
100
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Strain [%]
FIGURE 11: Comparison between the tensile test results of heated and non-heated test
specimen on structural steel S355J2H at room temperature.
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In addition to this project a small tensile test series was carried out to determine the yield
strength of the material used in high-temperature stub column tests. The specimens were
taken out from SHS 50x50x3 tubes after they had been tested at elevated temperatures. The
average yield strength of the material before high-temperature tests was 529N/mm2 and the
nominal yield strength 355N/mm2. The test results are illustrated in Table 6 and in Figure 12.
specimen
Max. temperature during
stub column test
[°C]
602
674
611
611
498
498
532
532
369
658
710
643
569
617
334
A1
A2
A3Y
A3A
A4Y
A4A
A5A
A5Aa
A6A
Y1
Y2
Y3
Y4
Y5
Y6
Yield strength
fy
[N/mm2]
478
527
482
497
469
465
520
499
520
----464
474
508
492
538
Modulus of
Elasticity, E
[N/mm2]
148942
186318
201951
185999
323808
214593
179985
210465
184878
225715
213532
181901
184246
164970
224360
Table 6: Tensile test results at temperature 20°C for structural steel S355J2H. Test pieces
from SHS 50x50x3 after high-temperature stub column tests.
650
600
550
500
2
Stress [N/mm ]
450
400
350
300
250
200
150
100
50
0
0
2
4
6
8
10
12
14
16
18
20
22
24
Strain [%]
FIGURE 12: Tensile test results at ambient temperature for structural steel S355J2H.
Test coupons taken from SHS 50x50x3 tubes after high-temperature stub column tests.
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The temperatures used in the column tests are given in the table. It can clearly be seen that
the tested yield strength of the specimen is more than the nominal yield strength of the used
material.
CONCLUSIONS
An overview of the test results for structural steels S350GD+z and S355J2H were given in
this paper. The high temperature test results were fitted to the ‘Eurocode 3 model’ to
provide the data in a useful form to be used in e.g. finite element modeling of steel
structures. The aim of this research is mainly to get accurate information of the behaviour of
the studied steel grades and to provide useful information for other researchers.The test data
is presented more accurately in Ref.[1], which can be downloaded from:
http://www.hut.fi/Units/Civil/Steel/Publications/jsarj.html.
The behaviour of structural steel S350GD+Z differed from the EC3 model and a new
suggestion was made on the basis of the high-temperature tests. The mechanical properties
after heating seemed to be near the nominal values of the material, which is good, when
thinking of the remaining strength of steel structures after fire.
The behaviour of steel S355J2H seemed also to be very promising. The increase of strength
due to cold-forming seemed to remain quite well at elevated temperatures. This should
naturally be taken into account when estimating the behaviour of cold-formed steel
structures. Also the strength after high-temperature tests seemed to remain quite well.
ACKNOWLEDGEMENTS
The authors wish to acknowledge the support of the company Rautaruukki Oyj, and the
National Technology Agency (TEKES) and also the co-operative work of VTT Building and
Transport, Finnish Constructional Steelwork Association and Tampere University of
Technology making this work possible.
REFERENCES
[1] Outinen, J., Kaitila, O., Mäkeläinen, P., High-Temperature Testing of Structural Steel
and Modelling of Structures at Fire Temperatures, Laboratory of steel structures
publications, TKK-TER-23, Finland, 2001.
[2] Outinen J., Kaitila O., Mäkeläinen P., A Study for the Development of the Design of
Steel Structures in Fire Conditions, 1st International Workshop of Structures in Fire,
Copenhagen, Denmark, 2000.
[3] Feng,M., Wang,Y.C., Davies,J.M., Behaviour of cold-formed thin-walled steel short
columns under uniform high temperatures, Proceedings of the International Seminar on Steel
Structures in Fire, pp.300-312, Tongji University, China, 2001.
[4] Kaitila, Olli, Imperfection sensivity analysis of lipped channel columnsat high
temperatures, Journal of Constructional Steel Research, vol.58, no.3, pp. 333-351, 2002.
[5] EN1993-1-2 European Committee for Standardisation (CEN), Eurocode 3: Design of
steel structures, Part 1.2 : Structural fire design, Brussels 1993.
[6] SFS-EN 10002 : Metallic materials. Tensile testing. Parts 1-5
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