Lu, Zhao, and Han 2010

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Experimental Study, Results, and Discussion

This paper discusses the fire performance of tubular stub CFDST columns with self consolidating concrete. In order to increase the workability of the concrete, a superplasticizer, steel or polypropylene fiber was added. Both the inner and outer columns have the same shape, either circular or square. The concrete was placed into the cavity without vibrations, and three thermocouples were placed on each specimen. The specimens were tested in the Civil Engineering Laboratory at Monash University, according to the procedures in AS 1530.4 in order to measure the temperature vs. axial deformation plots. The maximum temperature recorded on the outer and inner tubes ranged from 400-963oC, and 59-197oC, respectively. The axial deformation of CFDST columns can be described in three stages. During the first stage, there is little deformation, as the specimen is only just exposed to the heat. During the second stage, the tensile deformation changes to compressive deformation, and deformation increases. The final stage consists of a dramatic increase in deformation, until the stub can no longer support the load. The fire resistance varies from 18-138 minutes, where the larger columns have a greater fire resistance than the smaller columns. The failure mode for the entire specimen is typically compressive failure, without buckling. Small longitudinal cracking can be seen in the concrete, and there is slight color change in the longer specimens, due to longer fire exposure. The steel fibre reinforced concrete is much more ductile than the unreinforced concrete. The polypropylene fibre reinforced concrete increases crack resistance within the concrete. Overall, the fire resistance and load level are inversely proportional.

References

Lu, H., Zhao, X. L., and Han, L. H. (2010). “Testing of self-consolidating concrete-filled double skin tubular stub columns exposed to fire.” Journal of Construction Steel Research, 66 (8-9), August- September, pp. 1069-1080. doi:10.1016/j.jcsr.2010.03.004