EXPERIMENTAL STUDY ON QUASI-STATIC BEHAVIOR OF ULTRA-HIGH STRENGTH CONCRETE FILLED HIGH STRENGTH STEEL TUBULAR COLUMNS

Taking axial compression ratio, steel ratio and steel strength as parameters, eight quasi-static tests on UHSC filled high strength steel tubular columns and one UHSC filled normal strength steel tubular columns were carried out to analyse the effects on failure mode, load displacement hysteretic curve, skeleton curve, as well as the seismic performance indexes such as ductility, energy consumption, strength and stiffness degradation. The results show that overall bending is the main failure mode. The elastic stiffness remains unchanged as axial compression ratio changes, but changes a lot as steel ratio and steel strength change. The ultimate bearing capacity is greatly affected by axial compression ratio, steel content and steel strength, which decreases with the former increases, and increases with the latter two increases. The ductility is greatly affected by axial compression ratio, steel strength and steel strength, which decreases with the increase of the former two, and increases with the increase of the latter. The degradation in stiffness and strength decrease when axial compression ratio increases, but increase as steel ratio increases, while the former increases and the latter decreases when steel strength increases. Comparing the bending stiffness calculation methods of different codes, due to the limitation of material application, the codes are not suitable for this kind of high-strength material composite members.