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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 4
A. E. P. G. A. JACINTHO | V. P. SILVA | J. A. V. REQUENA | R. C. C. LINTZ
| L. A. G. BARBOSA | L. L. PIMENTEL
the tests, in comparison with the ISO 834 curve for the 30 and 60
min. test times. It is noted that the curves obtained were very simi-
lar to the standard ISO 834 curve.
5. Computational results
The SuperTempcalc Program (ANDERBERG [2]) was used to
determine the temperature distribution in the cross-section of the
columns and to compare the measurements from the physical ex-
perimental tests.
The actual temperature elevation curves obtained for the oven dur-
ing the experimental tests were used for computational analysis.
The thermal conductivity and specific heat values for the steel and
the concrete as a function of temperature were based on the BS
EN 1994 standard [7] and [8]. The values adopted for the emissiv-
ity and convection factor were 0.7 and 25 W/m
2
, respectively. The
density of the concrete was 25 kN/m
3
.
Figure 16 shows the temperature distribution in the cross-section
of model C6-30-1 as an example of what was performed for all of
the models.
In Figures 17 and 18, the graphs for temperature increases are
shown for the models with a 6 mm tube thickness, for 30 and 60
minutes of exposure to the high temperatures, respectively.
Figure 19 shows the temperatures achieved on the steel, at the
steel-concrete interface and in the concrete core through compu-
tational analysis.
The influence of the thickness of the tube on the final temperature
of the concrete core can also be observed in this graph.
6. Conclusion
The load bearing capacity of the composite columns suffered a
small reduction when they were subjected to high temperatures.
This effect only occurred for the models that were heated for 60
minutes, for which the temperatures in the concrete core reached
300 to 400ºC. The load bearing capacity for the columns that re-
mained in the oven for 30 minutes was very similar to that of the
columns that were left at room temperature.
The stress-strain behavior of the composite columns was altered
after exposure to high temperatures relative to the same columns
at room temperature. This effect was most evident for the 60-min-
ute exposure tests, which achieved higher temperatures. When
these tests were compared to those conducted at room tempera-
ture, the yield strength and proportionality limit were lower for the
columns that were subjected to high temperatures compared to
those that remained at room temperature; however, the ultimate
strength of the former group increased slightly to compensate for
these reductions.
With regards to the application of a load to the columns inside of
the oven, it can be concluded that the level of applied load did not
affect the final temperatures achieved by the concrete core or its
residual load bearing capacity.
In the tests where the diameter of the tube remained constant
while the thickness varied, the maximum temperature at the inter-
face between the metallic tube and concrete was lower for larger
thicknesses. This effect was also observed in the computational
analysis for all of the C6 and C8 models, with a diameter of 114.3
mm. Comparing the results of the same cited models revealed that
the diameter influenced the final temperature of the concrete core.
The composite columns with steel tubes of larger diameter (141.3
mm) showed lower yield strengths compared to those with steel
tubes of smaller diameter (114.3 mm) but the same thickness. This
Figure 17 – Cross-sectional temperature
distribution of model C6-30-1
Figure 18 – Temperature elevation curves
for the models with a 6-mm-thick
tube and 30-minute exposure time
Figure 19 – Temperature elevation curves
for the models with a 6-mm-thick
tube and 60-minute exposure time