Static flexural behaviour of concrete-filled spiral-welded stainless-steel tubes

Abstract

Abstract Durability and maintenance considerations may necessitate the use of stainless-steel for concrete-filled steel tube structural elements. The cost-effectiveness of such concrete-filled stainless-steel tubes (CFSSTs) can be improved by utilising spiral-welded tubes compared to their longitudinally welded counterparts. Spiral-welded stainless-steel tubes (SWSSTs) are fabricated by helically bending a continuous length of steel plate and welding the resulting abutting edges. The flexural behaviour under static loading of such hollow as well as concrete-filled spiral-welded stainless-steel tubes (CF-SWSSTs) has not been investigated to date, unlike for other stainless-steel tube types. To address this research gap, an experimental program was conducted consisting of four-point bending tests on twelve self-compacting CF-SWSST specimens. Tube geometries of nominal outside diameter 152 mm, 203 mm and 229 mm with wall thicknesses of 2 mm and 3 mm each were considered for the tests, together with infill concrete strengths of 20 MPa and 50 MPa. Six hollow SWSSTs corresponding to each of the six tube geometries were also tested for reference. The study showed that the ultimate limit state (ULS) deformation mode of CFSSTs was similar, irrespective of the tube fabrication method. The same was found to be true for hollow stainless-steel tubes as well. However, for hollow SWSSTs, it appears that there is greater probability for local buckling to occur at the spiral-weld seam, unlike for CF-SWSSTs. Nonetheless, for both hollow and CF-SWSSTs, existing codified guidelines were found to provide considerably conservative estimates of the respective ULS moment capacities. The prediction conservativeness was comparable to that reported for other tube types. For the tested CF-SWSSTs, the existence of non-uniform concrete core confinement at the ULS was confirmed experimentally. Explicit consideration of such effects may lead to improved predictions of the ULS flexural capacity compared to existing methods.