Behavior of partially encased composite members under various load conditions: Experimental and analytical models

Abstract

This study addresses the experimental behavior of octagonal partially encased composite column under axial and bending load conditions. The complementary study on axial and combined axial–torsional behavior is done through finite element analysis. The main parameters for the experiment part are reinforcement details and failure modes. The six parameters of this analytical analysis include width-to-thickness ratio of flange, transverse links spacing and diameter, welding line arrangements, and different types of retrofit of cross-shaped steel (concrete encasement, use of stiffener plates and transverse links). To verify accuracy of the proposed three-dimensional finite element model, the axial behavior of the numerical models was compared with test specimens. Experimental results of the axial study show that concrete crushing phenomena and local buckling behavior occurred for all specimens under ultimate stage of loading. It should be noted that local buckling behavior occurred after crushing phenomena. The analysis of bending assessment demonstrated that the use of stirrups has no remarkable effect on increasing the effective bending moment strength of octagonal partially encased composite columns. Meanwhile, an equation was developed based on comprehensive parametric study of octagonal partially encased composite column using detailed finite element analyses. Under axial–torsional load conditions, one could conclude that steel shear plates should be placed at the end zones of column to heighten torsional resistance of member. Meanwhile, transverse links were found to exert marginal effect on torsional behavior of octagonal partially encased composite column.