Lu, Han, and Zhao 2010

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Experimental Study, Results, and Discussion

Six CFDSTs with self consolidating concrete (SCC) are used in this experiment and tested for fire performance. SCC is used because vibration is not necessary, therefore is cheaper and eliminates noise associated with vibration. The parameters for this experiment were load ratio, cavity ratio, and load case. All the specimens had a length of 150 inches, and a fire protection thickness of 0 of .39 inches, which was applied in layer a few weeks before the testing. The specimens had a combination of square and circular inner and outer tubes. Three thermocouples were added to each specimen to measure change in temperature. The specimens were tested at Structural Fire Resistance Laboratory in Tianjin Fire Research Institute, China. There are three burners along the testing rig, which allows air and fuel circulation. Specific testing conditions such as temperature, pressure, and loading conditions can be specified in the testing facility. The boundary conditions for these specimens are fixed-pinned. The load was applied 30 minutes prior to the fire conditions, and an initial deformation was recorded. Fire conditions were applied according to ISO-834. The general failure seen was buckling, however specimens with eccentric loading displayed lateral deflection as well. For the circular specimens, there was slight cracking on the outer tube, and a bulge at mid-height, where the spray coating cracked off after 80 minutes of fire exposure. For specimens with square cross sections, there was much more obvious local buckling, as well as cracking on the corners of the outer tubes. Most of the inner concrete was intact and little cracking was seen on all of the specimens. In terms of temperature, the temperature of the outer steel tube increased rapidly at the beginning of the test, however is much more stable in the inner tube as well as the concrete. The maximum temperature after 4 hours of fire exposure of the inner and outer tube are 450oC, and 940oC, respectively. In general, CFST have a better fire resistance than CFDST columns, due to a thicker concrete tube. For CFDST, there is a longer load transfer path, as the load moves from outer tube, to concrete, to inner tube, rather than just from steel tube to concrete with a CFST. Similarly, the concrete acts as a ‘heat sink’, and absorbs some of the energy from the temperature elevation, thus delaying temperature elevation of the steel tubes. The fire resistance for the columns with spray coating ranges from 165-240 minutes, and 40-115 minutes for the columns without spray coating.

Reerences

Lu, H., Han, L. H., and Zhao, X. L. (2010). “Fire performance of self-consolidating concrete filled double skin steel tubular columns: Experiments.” Fire Safety Journal, 45 (2), February, pp. 106-111. doi:10.1016/j.firesaf.2009.12.001