Li, Han and Chan 2014

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Experimental Study, Results, and Discussion

This paper discusses circular CFDST members under both concentric and eccentric tension with parameters eccentricity, and steel and concrete ratio. CFDST columns display traits of typical CFTs, however display lighter self-weight, and higher fire resistance. The steel plates were cold formed, with cover plates welded to both ends. A combination of .079, and .12 in steel tubes were used, for both the inner and outer tubing. The concrete was compacted continuously as it was placed into the cavity between inner and outer steel plates. Strain gauges were placed on the specimen to measure both longitudinal and transverse strain. Load intervals of 1/10 of the load capacity was applied, until the specimen yielded. After yielding, an unloading program was run. The specimens tested under eccentric tension displayed linear behavior until yielding, and the specimens exhibited elasto-plastic behavior after yielding. There was no obvious cracking on the outer steel tubes, and large bending deformation was seen on the eccentric tubes. However, on the concentric tubes, there was some cracking on the outer tube, and the inner concrete displayed evenly distributed cracks, displaying failure due to axial elongation and bending. Generally, as the eccentricity increases, the ultimate strength and stiffness decreased. The moment vs. rotation graphs display similar results to the load vs. deformation graphs. Both the transverse and longitudinal strains were measured at different locations along the specimen, and the longitudinal strain for eccentric columns were not uniform as bending moment increases. A slight difficulty was seen in calculating the ultimate strength, and was later defined as the load when the longitudinal tensile strain reaches 5000 με.

References

Li, W., Han, L-H., Chan, T-M. (2014). “Tensile behaviour of concrete-filled double-skin steel tubular members.” Journal of Constructional Steel Research, 99, August, pp. 35-46. doi:10.1016/j.jcsr.2014.03.011