Han and Yang 2005
Constant axial load, cyclic transverse load tests were performed on eight circular CFT specimens. An analytical model was developed to replicate the behavior observed during the test. Further, simplified models were developed from the analytical model to predict the hysteretic behavior of circular CFT columns with a wide range of parameters.
Experimental Study, Results, and Discussion
Cyclic lateral loads were applied to eight CFT and two HT specimens. There were two varieties of CFTs, each with four different axial load levels. The first set of CFTs had diameters of 4.25 in, tube thicknesses of 0.157 in, steel yield strengths of 51.6 ksi, and concrete compressive strengths of 3.2 ksi. The second set of tubes had diameters of 4.49 in, tube thicknesses of 0.118 in, steel yield strengths of 44.7 ksi, and concrete compressive strengths of 5.6 ksi. The two HT specimens were of the same tube as the second set of CFTs. The specimens were 59 in long and supported at the ends with cylindrical bearings. The specimens were loaded through a 6 in rigid stub attached at midheight. An increasing amplitude cyclic loading protocol was utilized and the specimens were tested to failure.
Load-deflection response was plotted for all specimens. Additional plots displaying the envelope of response for the tests varied by axial load level as well as those comparing the HT specimens to corresponding CFTs were presented. The peak results were also plotted against several design and mechanistic predictions of the interaction surface.
Analytical Study
An analytical model for predicting behavior of CFTs under cyclic load was also created as part of this research. The stress-strain relationship used for the steel tube consisted of a number of linear segments and accounted for strain hardening as well as the Bauschinger effect. The stress-strain relationship for the concrete core followed a set of nonlinear equations and took into account the confinement provided by the steel tube and tensile strength of concrete. The deflection of the members was assumed to be a sine wave. Results from the model were overlaid with the experimental results presented previously as well as with results from previous research.
A parametric study was performed to examine the effect of axial load level, ratio of steel area to concrete area, steel strength, and concrete strength on the envelope curves of the moment-curvature response. A simplified model for the moment-curvature response was created based on the parametric study and further studies were conducted using the simplified model. Among the main conclusions was that the ductility of CFT columns decreased with increasing axial load level, slenderness, and concrete strength and increased with increased ratio of steel area to concrete area. Steel strength had less effect on the ductility.
Reference
Han, L. H., and Yang, Y. F. (2005). “Cyclic Performance of Concrete-Filled Steel CHS Columns Under Flexural Loading,” Journal of Constructional Steel Research, Vol. 61 No. 4, pp. 423-452.