Research on axial compressive behavior of lightweight concrete-filled cold-formed elliptical hollow section steel stub columns

To study the axial compression performance of elliptical steel tubular stub column, this paper presents an experimental investigation on lightweight concrete-filled circular and elliptical hollow section steel tubular columns under axial compression at cross-section level. The lightweight aggregate concrete and elliptical tube material properties, bearing capacity, failure mode and ductility of stub column were analyzed. The elliptical hollow section (EHS) was cold-formed from the hot-rolled circular hollow section (CHS). Comparison based on experimental findings in particular between the hot-rolled CHS and cold-formed EHS were made. The results indicate the cold-forming process reduces the load carrying capacity and ductility; being filled with concrete can significantly improve the bearing capacity and ductility of stub column; contribution of filling concrete is larger in the concrete-filled hot-rolled CHS stub columns than that in the concrete-filled cold-formed EHS stub columns; the level of enhancement due to concrete in-filling is more significant for the thinner EHS and CHS tubes (about 10%). Design rules based on Chinese and foreign standards were also assessed: the prediction of cold-formed EHS compressive resistance based on the hot-finished formulations is adequate; design equations based on Eurocode 4 can be adopted for the lightweight concrete-filled hot-rolled circular hollow sections; CECS 28-2012, the code for design of concrete-filled steel tubular structures can be used for the compressive bearing capacity calculation of thinner lightweight concrete-filled EHS, but the compressive bearing capacity calculation method for thicker lightweight concrete-filled EHS needs further study.