Compressive testing and numerical modelling of concrete-filled double skin CHS with austenitic stainless steel outer tubes

A comprehensive experimental and numerical study of concrete-filled double skin tubular (CFDST) stub columns is presented in this paper. A total of 23 tests was carried out on CFDST specimens with austenitic stainless steel circular hollow section (CHS) outer tubes, high strength steel CHS inner tubes, and three different grades of concrete infill (C40, C80 and C120). The ultimate load, load-deflection histories and failure modes of the stub columns are reported. The test results were employed in a parallel numerical simulation programme for the validation of the finite element (FE) model, by means of which an extensive parametric study was undertaken to extend the available results over a wide range of cross-section slendernesses, inner tube strengths and concrete grades. The experimentally and numerically derived data were then employed to assess the applicability of the existing European, Australian and North American design provisions for composite carbon steel members to the design of the studied CFDST cross-sections. Overall, the existing design rules are shown to provide generally safe sided (less so for the higher concrete grades) but rather scattered capacity predictions. Use of an effective concrete strength is recommended for the higher concrete grades and shown to improve the consistency of the design capacity predictions.