Abstract:
In this paper, 6 short columns of ultra-high performance concrete filled stainless steel tubes (UFCSST), 3 short columns of ordinary concrete filled stainless steel tubes (CFSST), and 3 stainless steel tubes are tested under axial compression. The test parameters were stainless steel tube wall thickness and core concrete strength. The failure process and morphology of the specimen was observed, and the load-displacement curves were obtained. The axial-compressive properties of UFCSST were analyzed through the failure morphology, load-displacement curve, load-strain curve, concrete contribution rate and strength improvement coefficient of the specimen. The results show that the failure model of UFCSST short columns is related to the confinement coefficient. When the confinement coefficient is greater than 1.03, the core concrete changes from shear failure to lateral expansion. The change trend of load-displacement curve after the peak load can be divided into three categories according to the value of confinement coefficient: an initial descending section followed by slow increase to the peak load, stable development, and slow increase. When the thickness of stainless steel tube is fixed, the UHPC grade has little influence on the bearing capacity, and the maximum bearing capacity can be increased by 14.8%. The high strength of UHPC and the inclusion of steel fibers inside would slow down the development of cracks and inside deformation, causing the concrete contribution rate of UHPC 81.6% higher than that of ordinary concrete; however, due to the autogenous shrinkage of UHPC and the multiaxial mechanical properties of concrete, the strength improvement coefficient of UHPC is 46.4% lower than that of ordinary concrete. The calculation results of some foreign codes are more conservative than the test results, with the maximum deviation of 22.4%, while the calculation results of CECS 28: 2012 in China are 10.4% higher than the test bearing capacity. Based on the unified strength theory, a theoretical calculation model of UFCSST bearing capacity is proposed.