Investigation of cyclic behavior of full-scale tree-like hollow structural section columns with infilled concrete

Abstract

The cyclic behavior of tree-like hollow structural section (HSS) columns with infilled concrete was experimentally and numerically investigated. A full-scale column, with the height of 3.7 m and the treetop plan dimension of 4 m × 3 m, was designed and manufactured according to a practical engineering prototype. The column was composed of a petal-shaped trunk using a concrete-filled steel tubular (CFST) section, four primary branches using a circular CFST section, and twelve secondary branches using a circular HSS. The column with a capacity protected reinforced concrete foundation was tested under combined constant axial compression and cyclic lateral loading through a specifically designed setup. The cracking and spalling of the reinforced concrete foundation were observed initially, followed by yielding of the bottom end of the primary branches when the story drift ratio reached 1.00%. The specimen failed by fracture of the full penetration groove welded splices in the petal-shaped trunk embedded in the foundation when the story drift ratio reached 3.00%. A detailed finite element analysis model for the tree-like column was then established and verified. Parametric studies were conducted to investigate the influence of the axial load level (0.016–0.3), filling range of concrete (including no filling, partial filling, and overall filling), steel yield strength (235–460 MPa), and the height to width ratio of the petal-shaped trunk (0.75–3.14). The results showed that the higher the filling height of concrete was, the greater the lateral load-carrying capacity and stiffness of the specimen were, but the filling height after reaching the secondary branches hardly affected the mechanical properties of the specimen. With the increase of the axial load level, the load-carrying capacity and deformation capacity decreased. Both the filling range and the height to width ratio of the petal-shaped trunk could change the failure mode of the tree-like column. Finally, some design considerations were proposed.