Ultra-high strength concrete filled composite columns for multi-storey building construction

Abstract

A test programme was carried out to investigate the performance of 27 axially loaded column specimens, including 18 steel tubes infilled with ultra-high strength concrete (UHSC) of compressive strength close to 200 MPa, 4 steel tubes infilled with normal strength concrete (NSC) and 5 hollow steel tubes. Steel fibres were added into the UHSC to study their effect in enhancing the ductility and strength. Concrete filled double-tube columns were also investigated for potential application in multi-storey and high-rise constructions. Test results showed that UHSC filled tubular columns achieved ultra-high load-carrying capacities, but they could become brittle after the maximum load was attained. In addition, the ductility and strength of composite columns infilled with UHSC was improved by applying load only on the concrete core, adding steel fibres into the concrete core or increasing the steel contribution ratio. Comparison of test results with Eurocode 4's predictions indicates that the Eurocode 4 method could be safely extended to predict the compressive resistance of UHSC filled composite stub columns. On average, Eurocode 4 approach underestimated the resistance by 14.6% if the confinement effect was not considered and by 3.5% if the confinement effect was considered for all the specimens involving UHSC. However, to ensure sufficient ductility, it is recommended that a minimum steel contribution ratio of 0.30 or 1% steel fibres should be used. Furthermore, strength enhancement due to confinement effect should be ignored in estimating the ultimate strength of concrete filled composite columns with Class 3 steel sections.