Axial compressive behavior of reactive powder concrete-filled circular steel tube stub columns

Reactive powder concrete (RPC) is a type of ultra-high strength concrete that has a relatively high brittleness. However, its ductility can be enhanced by enclosure in a steel tube. This paper presents an experimental study of the axial compressive behavior of RPC-filled circular steel tube stub columns. Twenty short composite columns under axial compression are tested and information on their load-deformation behavior, axial load capacity, failure modes and confinement mechanism are presented. The effects of tube thickness, mix design, loading and curing conditions on the compressive strength of these columns are discussed. The experimental results show that: (1) confinement increases the load capacity of the test specimens by 3% to 38%, (2) the increase in load capacity is more pronounced when the confinement coefficient (defined as the ratio of axial load capacity of the steel tube to the RPC core) is high, (3) the load capacity also increases when the steel tube is not subjected to any direct axial stress, when a larger amount of steel fibers is added, or when a higher curing temperature is used, (4) the transverse to axial strain ratio can be used as an indicator to determine when the effect of confinement develops. Using the measured strains and theories of elasticity and plasticity, the stresses in the steel tube and the PRC core are calculated, from which expressions for the peak stress of confined RPC are proposed. Equations for stress-strain curves that can be used to describe the behavior of confined RPC are derived.