Time-dependent modelling of steel-tube confined concrete columns considering confining and bonding effects

Abstract

Steel tube confined reinforced concrete (STCRC) columns have been applied in high-rise buildings with a promising future due to its high load-bearing capacity and excellent seismic behaviour. Different from traditional reinforced concrete (RC) and concrete-filled steel tubular (CFST) columns, the concrete of STCRC columns is subjected to triaxial time-dependent varying stresses even at low sustained loads, and the stresses of the tube and concrete are non-uniformly distributed along the column length due to the interfacial bonding effects. In this context, available long-term research outcomes for RC or CFST columns cannot be implemented to STCRC columns directly. Hence, a confined concrete creep model for STCRC columns was determined based on the collected 56 creep tests on sealed confined concrete under multiaxial stress states. Subsequently, accounting for the time-dependent varying confinement effects and the influence of the non-uniform interfacial stress distribution, a refined numerical analysis method was established for the long-term behaviour prediction. A parametric study was then conducted with particular attention to the difference in the long-term behaviour of STCRC, RC and CFST columns and the determination of the key parameters. Results indicate that the uniaxial creep model (i.e. Eurocode 2) can be extended to the creep prediction of confined concrete with the effective Poisson's ratio of 0.187. Due to the longitudinal bonding effects, the slenderness ratio would significantly influence the long-term deformation of STCRC columns. The influence of the steel tube on the time effects is less noticeable when compared with the concrete strength, loading age and slenderness ratio.