Experimental and numerical investigation of concrete-filled hot-finished and cold-formed steel elliptical tubular stub columns

Abstract The structural behavior of concrete-filled hot-finished (HF) and cold-formed (CF) steel elliptical tubular stub columns was investigated and is presented in this paper. A series of tests was conducted on HF and CF steel elliptical tubular sections infilled with three different concrete grades, namely C40, C80 and C100. The tested HF and CF steel elliptical hollow sections (EHS) had an aspect ratio of 2 with the same nominal section dimension of 200 × 100 × 6.5 mm. The test specimens were subjected to uniform axial compression. The initial local geometric imperfection measurements, ultimate loads and failure modes of the concrete-filled HF and CF EHS stub columns are presented. An extensive numerical study accounting for the confinement effect, as well as the non-linearities of materials, geometry and contacts was also performed. After a successful model validation against test results, a parametric investigation was conducted by considering a wide range of the cross-section dimensions and section slenderness of HF and CF EHS with different grades of the infilled concrete. A total of 111 concrete-filled HF and CF EHS specimens were carefully designed and analyzed by using the validated numerical model. The behavior of concrete-filled HF and CF EHS stub columns was investigated, including the maximum load, end shortening, strength enhancement index and ductility index. Effects of section strength factor and column sectional characteristics on the stub-column behavior were also investigated. Furthermore, the experimental and numerical results were used to assess the suitability of the design equations specified in the current American Specifications (AISC and ACI) and European Code (EC4) for the compressive resistance of the concrete-filled HF and CF EHS stub columns. It was found that the predictions from the current international design specifications were overall conservative for both concrete-filled HF and CF EHS stub columns. Generally, the predictions by EC4 were less conservative but more scattered than those predicted by AISC and ACI specifications for the concrete-filled HF and CF EHS stub columns.