Behavior of Composite Columns Subjected to Lateral Cyclic Loading

ABSTRACT: Nonlinear 3-D finite element models were developed to investigate the cumulative damage of composite columns subjected to cyclic loading by comparing the effects of different levels of axial loads on the cyclic capacity of steel, reinforced concrete, and composite beam-columns. The beam-column specimens were modeled as fixed cantilever beam-columns with an axial load level of 10%, 15%, and 20% of their axial load capacity as well as cyclic loading similar to that suggested by Applied Technology Council (ATC) guidelines (ATC 1992 - ATC 24). The FEM output was then examined to determine the effect of different levels of axial loads on behavior of beam-columns under cyclic loading. Assessing whether the prototype elastic stiffness had changed, identifying the high stress and strain zones, and evaluating the effects of the level of axial load on stiffness, strength, and ductility of beam-column prototypes were facilitated. The finite element analysis results demonstrate that the encased composite beamcolumns reached the highest ductility among beam-columns specimens due to confinement effect of concrete. The results indicate that local buckling plays a crucial role in curvature ductility for the cyclic beam columns whereas extensive local buckling of steel section leads to significant reduction in stiffness and strength (softening damage). Moreover, the elastic flexural stiffness as well as ductility decreases significantly with an increase in the axial loads level. Keywords: Cyclic Capacity, Confinement Effect, Finite Element Method, Local Buckling, Ductility …………………………………………………………………………………………………………………………