Strength and ductility performance of concrete-filled steel tubular columns after long-term service loading

Abstract

Concrete-filled steel tubular (CFST) columns are widely used in infrastructure applications and thus usually are subject to long-term service loading. However, understanding the influence of sustained loading on the ultimate performance of these structural members is still lacking. The objective of this work is to develop a constitutive model to account for strength and ductility change of CFST columns under sustained loading, validated by experimental data reported in the literature.In this framework, a simplified analytical method equipped with a monolithic iterative scheme is developed to efficiently estimate the creep deformation of these composite columns at any designated target time. Based on the calculated creep status, an analytical stress–strain curve is proposed to characterize the post-creep mechanical behavior of steel-confined concrete. This stress–strain behavior incorporates the combined effects of enhanced compressive strength of plain concrete and reduced confining strength provided by steel tube, both of which are caused by sustained load. Finite element based numerical study together with the available test database are used to validate the mechanical analysis and to assess the performance of the proposed constitutive model. The predicted post-creep response is found to be in good agreement with the experimental results for CFST columns with circular and square cross-sections. Finally, an extensive parametric study based on a pushover analysis is conducted to examine the influence of individual critical design parameters on structural ultimate strength and ductility due to long-term service loading.