CFDST sections with square stainless steel outer tubes under axial compression: Experimental investigation, numerical modelling and design

Abstract

The use of concrete-filled double skin tubular (CFDST) cross-sections for compression members has become increasingly popular in construction. A recently proposed innovative form of CFDST cross-section, ultilising stainless steel for the outer tube, offers the combined advantages of the composite action seen in CFDST member alongside the durability and ductility associated with stainless steel. CFDST sections with stainless steel outer tubes, for which there are currently little experimental data, are the focus of the present study. A comprehensive experimental and numerical investigation into the compressive behaviour of CFDST sections with square stainless steel outer tubes is presented in this paper. A total of 19 specimens was tested under uniform axial compression, and the test observations are fully reported. The ultimate loads, load-displacement curves and failure modes from the tests were used for the validation of finite element (FE) models. Parametric finite element analyses were then performed. The combined set of experimentally and numerically derived data was employed to assess the applicability of the existing European, Australian and American design 2 provisions for composite carbon steel members to the design of the studied CFDST crosssections. Overall, the existing design rules are shown to provide generally safe-sided (less so for the higher concrete grades) but rather scattered capacity predictions. Modifications to the current design codes are also considered-a higher buckling coefficient k of 10.67 to consider the beneficial restraining effect of the concrete on the local buckling of the stainless steel outer tubes, as well as a reduction factor η to reflect the reduced relative effectiveness of higher concrete grades. Overall, the comparisons demonstrated that improved accuracy and consistency were achieved when the modified design rules were applied.

Compressive behaviour and design of CFDST cross-sections with stainless steel outer tubes

“…A number of experimental investigation into the compressive behaviour of CFDST crosssections with stainless steel outer tubes have been carried out [9][10][11][12], but the only previous experiments on CFDST cross-sections with SHS carbon steel inner tubes and SHS/RHS lean duplex and ferritic stainless steel outer tubes (see Fig. 1), which are the focus of the present study, were reported in Wang et al [10].…”

“…FE models of all test specimens presented in Section 2 were established employing C3D8R [25] solid elements for the concrete and S4R [25] shell elements for the metal tubes, in line with previous numerical modelling of concrete-filled tubular members [11,12,[26][27][28][29]. A systematic mesh sensitivity study was undertaken to decide upon suitable mesh settings for the FE models, in order to produce accurate yet computationally efficient results.…”

“…Stainless steel members possess a unique combination of excellent mechanical properties for structural applications and corrosion resistance, and have been utilised in construction increasingly over the past few decades [8]. An innovative form of CFDST cross-section, utilising stainless steel for the outer tube, was recently proposed [9][10][11][12], with the aim of exploiting the most favourable properties of the constituent materials to the greatest possible extent. CFDST columns using stainless steel for the outer tubes were found to exhibit a rather more rounded and ductile load-deformation response compared to their carbon steel counterparts [10][11][12].…”

“…An innovative form of CFDST cross-section, utilising stainless steel for the outer tube, was recently proposed [9][10][11][12], with the aim of exploiting the most favourable properties of the constituent materials to the greatest possible extent. CFDST columns using stainless steel for the outer tubes were found to exhibit a rather more rounded and ductile load-deformation response compared to their carbon steel counterparts [10][11][12]. These observations mirror the findings for concrete-filled stainless steel tubular stub columns in a number of recent studies, including concrete-filled stainless steel stub columns with circular [13], rectangular [14][15][16] and square [14][15][16][17] cross-sections.…”

“…Further tests were conducted by the authors of the present paper [10] to examine the cross-sectional behaviour and resistances of CFDST stub columns with lean duplex and ferritic stainless steel outer tubes in pure compression. Meanwhile, the authors [11,12] also examined CFDST stub columns comprising austenitic stainless steel outer tubes and high strength steel inner tubes experimentally and numerically. FE analyses were employed by Hassanein and Kharoob [19] and Wang et al [20] with the focus on CFDST cross-sections with circular hollow section (CHS) inner tubes.…”