Experimental Study of Square and Rectangular CFDST Sections with Stainless Steel Outer Tubes under Axial Compression

Abstract

A comprehensive experimental investigation into the axial compressive response of concretefilled double skin tubular (CFDST) sections with stainless steel square and rectangular outer tubes is presented. A total of 28 tests was carried out. The experimental setup and procedures are described, and the test observations are fully reported. The test results are employed to assess the applicability of the current European and North American design provisions for composite carbon steel members to the design of the studied CFDST cross-sections.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 and a reduction factor η to account for the effective compressive strength of high strength concrete. Overall, the comparisons revealed that the existing design rules may generally be safely applied to the prediction of the compressive resistance of CFDST cross-sections with stainless steel outer tubes, while the modified design rules offered greater accuracy and consistency.

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

“…In general, the design methods provide rather conservative predictions for specimens with grade C40 concrete, but the conservatism reduces for those with higher concrete grades (C80 and C120), particularly for cross-sections of low slenderness. This observation mirrors previous findings for CFST sections [14][15][16][17][18] and CFDST sections [8,20];…”

“…The ductility of the CFDST stub columns was assessed through the ductility index (DI) [8,18,20], which is defined as the ratio of the axial displacement when the load dropped to 85% of the ultimate load (Δ85%) to the axial displacement at the ultimate load (Δu), as presented in Table 1. In cases where the load did not drop to 0.85Pexp, the DI values was calculated on the basis of the maximum obtained displacement, as indicated by a '>' symbol in Table 1.…”

“…Three cross-sections were chosen for the high strength steel inner tubes-hot-rolled CHS 22×4 mm (diameter × thickness) and CHS 32×6 profiles and a cold-formed CHS 89×4. The nominal stub column length (L) was chosen to be 2.5 times the nominal cross-section depth, which was deemed appropriately short to prevent global buckling, yet adequately long to avoid end effects [8,14,18,20,26].…”

“…The load versus true axial deformation curves are employed in Section 3 for the validation of the FE models. A constant 0.4 mm/min displacement rate was used to drive the bottom end platen of the testing machine upwards in order to apply the load to the stub columns [8,20].…”

“…Uy et al [13] documented a rather more rounded and ductile load-deformation response of stainless steel CFST stub columns compared to that of carbon steel CFST stub columns. A limited number of tests has been performed in recent years on CFDST sections utilising stainless steel for the outer tubes [7,8,19,20]. Comparisons were made to assess the applicability of existing design rules, and the resistance predictions were found to be rather scattered.…”