Behaviour of circular concrete-filled lean duplex stainless steel tubular short columns

• FE models are developed for circular concrete-filled stainless steel short columns.
• The accuracy of the models is established by comparisons with experimental results.
• Parametric studies on the behaviour of axially loaded CFSST columns are conducted.
• The results are used to examine the accuracy of various design codes and models.

Lean duplex stainless steel material (EN 1.4162) has recently gained significant attention for its higher structural performance and corrosion resistance compared to the austenitic type. Circular lean duplex stainless steel tubes filled with concrete are innovative composite columns which have not been studied experimentally or numerically. This paper presents the fundamental behaviour of circular concrete-filled lean duplex stainless steel tubular (CFSST) short columns under axial compression. Three dimensional finite element (FE) models for CFSST columns subjected to axial compression are developed using the FE package ABAQUS. The lean duplex stainless steel material is modelled using the two-stage constitutive laws while the concrete is simulated using accurate concrete confinement models. The FE models are verified by comparisons with existing experimental results on hollow stainless steel columns, concrete-filled steel tubular columns and CFSST columns. Parametric studies are undertaken to investigate the effects of concrete compressive strength and diameter-to-thickness (D/t) ratio on the behaviour of CFSST columns. The results show that the ultimate axial strength of circular CFSST columns increases with increasing the concrete compressive strength but decreases with an increase in the D/t   ratio. Circular CFSST columns with different D/tD/t ratios exhibit the same initial stiffness. The lean duplex stainless steel tubes cannot provide good confinement on the concrete when D/tD/t ratio is large. The ultimate axial strengths of CFSST columns predicted by the FE models are also compared with those calculated by the Eurocode 4, ACI code, the continuous strength method (CSM) by Lam and Gardner and Liang and Fragomeni's design formulas. The comparative study shows that Eurocode 4 and the CSM give good estimates of the ultimate axial strengths of CFSST columns with D/t<40D/t<40 but overestimates the strengths of columns with D/t≥40D/t≥40. The ACI code gives too conservative estimates of the ultimate loads of CFSST columns as it does not consider the concrete confinement effects. Finally, it was found that the modified Liang and Fragomeni's design formulas yield the best predictions of the ultimate axial strengths of CFSST columns over the entire range of D/tD/t ratios.