Han and Huo 2003

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Experimental Study, Results, and Analysis

Twelve concrete-filled HSS columns were tested in order to determine the influence of changing strength of material, fire duration time, steel ratio, slenderness ratio, and load eccentricity ratio on composite columns subject to ISO-834 standard fire. Six of the specimens had square cross section while the remainder had circular cross section, and 4 of the 12 specimens had a fire protective coating. Primarily, strips of the steel tubes were taken and tested in tension to determine the yield strength and modulus of elasticity. Prior to testing, all of the specimens were heated in a furnace to follow the ISO-834 fire standard as closely as possible. The fire duration time was 90 minutes, and 180 minutes for specimens with added fire protection. Displacement transducers and strain gauges were attached to specimens, and all specimens were tested in a 5,000kN testing machine in small increments where strain and deflection was measured at each increment. All of the specimens failed at mid height, and it was noted that at between 60 and 70% of the maximum load, lateral deflection at mid height started to increase. It is also seen that the loss of strength for specimens without fire protection was much greater than that of the columns with the protection. The residual strength index (RSI) is defined to quantify the strength of the HSS columns after fire exposure, and is defined as residual strength corresponding to dire duration time, divided by ultimate strength of the composite column at the ambient temperature. It should be noted that no load was applied to the specimens during fire exposure which differs from practice. After exposure, the strength of the column decreased with the duration of exposure, and the deflection increases. Duration time, slenderness ratio, and column size have significant influence on the RSI after fire exposure, while steel ratio, load eccentricity ratio, and strength of steel and concrete have only moderate influence on RSI.

References

Han, L., Huo, J., (2003) “Concrete-Filled Hollow Structural Steel Columns after Exposure to ISO-834 Fire Standard” Journal of Structural Engineering, 129 (1), January.