Li, Han and Zhao 2012

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Experimental Study and Results

In this paper, concrete-filled double skin steel tubular columns (CFDST) are tested, in which there are two layers of steel, with a concrete tube in between the steel layers. For this experiment, the steel columns are installed prior to the placement of the concrete, and the steel columns are subjected to preload, thus bringing pre-stress and deformation. In some cases, preload is only applied to the outer tube, yet in other cases, preload is applied to both steel tubes. Both square and circular outer tubes are investigated in this paper, both specimens having circular inner and concrete tube. It is seen that the outer tube behaves similar to a CFT, whereas the inner tubes behaves like a hollow tube. If the preload is applied on both the inner and outer tubes however, both tubes will resist the preload proportionally, based on the cross sectional area. When they are both loaded, an interaction stress develops between the steel and concrete layers. The interaction stress is smaller for the circular tube than that of the square tube, and in both cases, when there is preload, the strength of the columns is significantly decreased. It is concluded that for the hollow tubes, a preload brings initial stress as well as deformation, and a CFDST with preload has significantly less strength.

Analytical Study and Discussions

A finite element analysis model was created prior to testing, which could then be verified during the testing. It was found that the residual stress and deformations that occurred during the manufacturing process had little effect on the axial compressive strength when the maximum imperfection was less than that allowable imperfection. For columns with preload, there were two preload stages: the constructional preload was applied, followed by testing until failure. The results from this study were then compared to other research performed prior.

References

Li, W., Han, L., and Zhao, X. (2012). “Axial Strength of Concrete-Filled Double Skin Steel Tubular (CFDST) Columns with Preload on Steel Tubes.” Thin-Walled Structures, 56, July, pp. 9–20. doi:10.1016/j.tws.2012.03.004