Structural behavior of slender circular steel-concrete composite columns under various means of load application

In an experimental and analytical study on the structural behavior of slender circular steel-concreterncomposite columns, eleven specimens were tested to investigate the effects of three ways to apply arnload to a column. The load was applied eccentrically to the concrete section, to the steel section or to the entirernsection. Three-dimensional nonlinear finite element models were established and verified with the experimentalrnresults. The analytical models were also used to study how the behavior of the column was influenced by thernbond strength between the steel tube and the concrete core and the by confinement of the concrete core offeredrnby the steel tube. The results obtained from the tests and the finite element analyses showed that the behaviorrnof the column was greatly influenced by the method used to apply a load to the column section. When relyingrnon just the natural bond, full composite action was achieved only when the load was applied to the entirernsection of the column. Furthermore, because of the slenderness effects the columns did not exhibit thernbeneficial effects of composite behavior in terms of increased concrete strength due to the confinement.