Compact and slender box concrete-filled stainless steel tubes under compression, bending, and combined loading

Abstract An extensive investigation on the behaviour of compact and slender box concrete-filled stainless steel tubular (CFSST) members is carried out studying their response under compression, bending, and combined compression and bending, with the main aim of developing comprehensive design procedures. Under this objective, an experimental programme is first conducted comprising compact and slender CFSSTs fabricated from austenitic and lean duplex stainless steel plates. Stub columns under axial compression as well as combined compression and bending, CFSST beams under pure bending, and long CFSST columns under axial force are all included in the experiments in order to investigate both the section and member responses. Specimens with high width-to-thickness ratios, high length-to-width ratios, and those under combined compression and bending are particularly considered in the experiments as test data is very scarce for such CFSSTs in the literature. A special technique is used to estimate the loads carried individually by the stainless steel section and the concrete infill to assist with the development of design recommendations. The experiments are followed by an extensive numerical study comprising over two hundred three-dimensional nonlinear finite element simulations. Outcomes of the experimental and numerical programmes are presented, analysed, and discussed thoroughly. Comprehensive procedures are then developed for the design of compact and slender CFSSTs under compression, bending, and combined loading which incorporate the effects of local and global buckling in strength predictions. Such procedures have not yet been established for CFSSTs in international design standards. The validity of the recommendations is demonstrated through comparison with the results of the present study as well as the test data available in the literature.