Sakumoto, Osaka, Yoshida, and Tasaka 1994
Experimental Study, Results, and Discussion
Square specimens were created with equal length and cross section dimensions to be tested under fire conditions. 26 holes were created in the steel tube in order to prevent a steam explosion in the concrete center. The effects of the type of steel used (fire resistant vs. ordinary), type of fire protection, lod, method of loading (central and eccentric). Thermocouples and displacement gauges were placed along the length of the columns. A 3,000 kN capacity loading apparatus was used to apply the load, and failure was determined as the time at which the rate of axial shortening sharply increases, and thus the heating is terminated. JIS A 1304 for standard time-temperature curves was used to apply fire conditions to the members. A ceramic rod was used in addition to displacement gauges to measure the horizontal deflection in the cases of eccentric loading. The specimens failed between temperatures of 350 and 600°C. The specimens that had fire protection increased temperature at a slower rate than the specimens without, however the increase in temperature of the specimens with fire protection slowed down significantly due to the heat capacity of the concrete core. Specimens without protection exhibited significant damage to the steel tubes. The temperature of the concrete remained low, and exhibited the highest temperature of 441°C close to the steel tube, and 134°C at the concrete center. The deformation of the specimens can be divided into 4 stages. The first is thermal elongation of the steel tube, and when the elongation stops it enters the next phase: local buckling of the steel tube and shortening of the column. In the third stage, the loading shifts from the outer steel tube to the inner concrete core due to local buckling of the steel. In the final stage, abrupt shortening occurs due to compressional failure of the concrete. The elongations were measured at each corner of the base plate, and stayed constant up to failure. The column fails due to compressional failure of the concrete. For eccentrically loaded specimens, the specimens did not exhibit stage three, and failure was caused solely by the local buckling of the steel tube. Overall, the fire resistant steel has a greater strength at higher temperature and can support loading for more time, as compared to the conventional concrete.
Sakumoto, Y., Okada, T., Yoshida, M., and Tasaka, S.(1994). “Fire Resistance of Concrete‐Filled, Fire‐Resistant Steel‐Tube Columns.” Journal of Materials in Civil Engineering, 6 (2), May, pp. 169-184 doi:10.1061/(ASCE)0899-1561(1994)6:2(169)