A CAPACITY PREDICTION PROCEDURE FOR CONCRETE-FILLED STEEL COLUMNS

A seismic design procedure for partially concrete-filled box-shaped steel columns is presented in this paper. To determine the ultimate state of such columns, concrete and steel segments are modelled using beam-column elements and a pushover analysis procedure is adopted. This is done by means of a new failure criterion based on the average strain of concrete and steel at critical regions. The proposed procedure is applicable to columns having thin- and thick-walled sections, which are longitudinally stiffened or not. An uniaxial constitutive relation recently developed is employed for concrete filled in the thick-walled unstiffened section columns. Modifications are introduced to this model for other types of columns. Subsequently, the strength and ductility predictions obtained using the present and previous procedures are compared with the corresponding experimental results. Comparisons show that the present procedure yields better predictions. It is revealed that the inclusion of the confinement effects and softening behaviour of concrete is important in the present kind of prediction procedures. Furthermore, an extensive parametric study is carried out to examine the effects of procedures and geometrical and material properties on capacity predictions.