Experimental study on behavior of circular concrete-filled high- strength steel tubular stub columns under compression

To investigate the mechanical behavior of concrete filled high-strength steel tube (CFHST) stub columns, the tests on 13 CFHST stub columns under axial load were carried out. Analysis and comparisons were performed between circular high-strength steel tube filled with normal strength concrete and ultra-high-performance concrete (UHPC), in terms of failure mode, load-displacement curve, bearing capacity, residual bearing capacity and ductility, mutually and respectively. And the effects of the yield strength of steel, the compressive strength of concrete and diameter-to-thickness ratio of the steel tube on the axial compressive performance of the two kinds of CFST stub columns were explored. The test results show that the failure modes of CFST stub columns are related to the equivalent diameter-to-thickness ratio, which can be divided into two types, waist drum-shaped failure and shear failure. For steel tubes with the same strength and diameter-to-thickness ratio, the stub column filled with normal strength concrete shows higher resistance enhancement index, residual bearing capacity ratio and ductility index than those of the stub column filled with UHPC. The tested bearing capacity results were compared with the theoretical results calculated according to Chinese code GB 50936—2014, European code EC4, and American code AISC 360-16. And the results show that current codes overestimate the bearing capacity of the ultra-high-performance concrete-filled high-strength steel tube stub columns to a certain extent. Based on existing test statistics and the test results in this study, the design formulas of axial compressive bearing capacity of CFST stub columns infilled with high-strength and ultra-high-strength concrete were modified to obtain conservative calculation results.