Axial Compression Tests on Elliptical High Strength Steel Tubes Filled with Self-Compacting Concrete of Different Mix Proportions

Abstract The compaction state and the paste volume of concrete may significantly influence the compressive behaviour of concrete-filled steel tube (CFST) columns. This study presents an experimental investigation to the axial compressive behaviour of elliptical CFST (ECFST) column consisting of a high-strength steel (HSS) tube and a self-compacting concrete (SCC) core with different mix proportions. Eighteen ECFST column specimens, fabricated with high-strength elliptical steel tubes in three different cross-sections and three batches of concrete with different mix proportions, were tested under axial compression. The parameters under investigation are the concrete paste volumes (41%, 37% and 32.5%), the cross-sectional aspect ratios (1, 1.5 and 2) and the compaction conditions (with and without mechanical compaction). The standard cylinder tests reveal that SCC without mechanical compaction has a better filling ability and thus a better self-compaction capability when the paste volume is larger than 37%, while SCC with mechanical compaction has the highest strength when the paste volume is the lowest. The axial compression tests show that the peak axial load capacities of ECFST columns are dependent on the paste and aggregate contents in concrete. The compaction state also affects the performance ECFST columns because compaction usually increases concrete strength especially when the aggregate content is high. In addition, it is found that key performance parameters (e.g., strain enhancement ratio, ductility and strength index) all decrease with the increase of cross-sectional aspect ratio due to the non-uniform confinement provided by elliptical steel tubes.