Simplified Analytical Model of Local Instability of the Outer Steel Tube of the Concrete-Filled Double-Skin Steel Tube Stub Columns under Axial Compression
The formula for calculating the critical stress of the local instability of outer steel tube of concrete-filled double-skin steel tube stub column under axial compression is not perfect enough.According to the analysis,the stress of the outer steel pipe of the concrete-filled double-skin steel tube stub column is basically the same as that of the solid concrete-filled steel tube stub column.Therefore,based on the theoretical model of Zhang Yaochun et al.,the local instability of outer steel tube of the concrete-filled double-skin steel tube stub column is studied.The interaction model between the sandwich concrete and the outer steel tube strip element is taken as the model of long beam on the Winkel elastic foundation,and then the calculation formula of the bending wavelength λ in the Wenkel elastic foundation beam is introduced.According to the fact that the ratio of the thickness t of the steel tube to the cross-sectional radius r of the cylindrical component in the actual engineering is much less than 1:t/r«1,and the wavelength of the instability of the outer steel pipe is about the bending wavelength λ,the theoretical derivation in the model of Zhang Yaochun et al.is simplified.By analogy with the model of Zhang Yaochun et al.,a simplified calculation formula for the critical stress of local instability of the concrete-filled double-skin steel tube stub outer steel tube is derived.Compared with the experimental data of other scholars,the average error of the local instability wavelength in the simplified calculation model is 7.7%,and the relative error value of the calculated value of critical stress is 2.7%,which indicates that the simplified calculation formula is feasible and can provide reference for engineering practice.