Collapse and Buckling Behavior of Octagonal Concrete Filled Steel Column Connected to a Beam Under Cyclic Loading

The Octagonal concrete filled steel tubular (CFST) sections offer greater efficiency than square and rectangular tubular sections because of their better local-buckling resistance and flat surfaces that allow easier connection construction compared with circular tubular sections. This paper presents analytical studies on the seismic behavior of steel I-beam to octagonal CFST column assemblies with external diaphragms. Different stiffeners, slenderness ratios and moment capacities were introduced in the external and corner octagonal column-beam model and studied analytically using the software ANSYS 16.1. In the analytical study finite element models are developed to predict the hysteretic behavior and the stress distribution. Steel to concrete interfaces are modelled by hard contact with friction. The loading condition is displacement controlled and the axial load is applied on the top of the column and lateral load is applied on the column by cyclic vertical load on the beam ends. The stress distribution of model components, including steel beams, steel tubes, stiffeners and concrete cores are illustrated. The results indicate that failure modes have significant effects on the characteristic of stress distribution.