Seismic behavior of terminal stirrup-confined concrete-filled elliptical steel tube columns: Experimental investigation

Abstract

As a new member of concrete-filled steel tube (CFT) structural families, concrete-filled elliptical steel tubes (CFETs) have great potential to be used as piers and columns in bridges and airport terminals because of its low flow resistance coefficient and reasonable distribution of major–minor axis. Hence, the main objective of this paper presents an experimental investigation on the seismic behavior of terminal stirrup-confined concrete-filled elliptical steel tube (TS-CFET) columns. Pseudo-static tests were tested to investigate the seismic performance of TS-CFET columns, including 3 concrete-filled elliptical steel tube (CFET) columns and 11 terminal stirrup-confined concrete-filled elliptical steel tube (TS-CFET) columns. Those key parameters varied in the experiments included the stirrups, height of terminal stirrup region, equivalent stirrup ratio, loading direction, slenderness ratio and axial load ratio. Then, based on the experimental results, the complete curves analysis on the load (P) vs. deflection (Δ) hysteretic curves were analyzed in detail, and the failure modes and composite action between the steel tube and core concrete were discussed and clarified. Furthermore, six indexes were employed to quantify the effect of varied parameters. The experimental results indicated that using stirrups in the CFET columns can directly confine the core concrete, and then considerably enhance the seismic behavior of CFET columns especially under higher axial load ratio. With the increase of axial load ratio, the energy dissipation capacity increased, while the displacement ductility decreased. The seismic performance of TS-CFET columns under major axis loading was obviously superior to that under minor axis loading. Additionally, the slenderness ratio had significant influence on the ultimate bearing capacity, stiffness and ductility of composite columns.