Study On Mechanical Behavior Of Reactive Powder Concrete Filled Steel Tubular Columns

Reactive powder concrete (RPC) is a new type of ultra high performance cementitious composite, but the brittleness limits its application in engineering. It is promising to get a structural type with good bearing capacity and ductility via combining RPC and steel tubes.RPC with the compression strength higher than 170 MPa was prepared using PO 42.5 ordinary Portland cement, mineral admixture, steel fiber, sand and superplasticizer. It is also studied the mechanical behaviors of RPC, such as strengths, stress-strain curves, elastic modulus and Poisson's ratio. RPC shows enormous compressive brittleness and steel fiber plays little act in improving compressive ductility of RPC, so it is necessary to utilize steel tubes to alleviate the brittleness of RPC.Based on the study on mechanical behaviours of RPC, it is also studied the interaction between steel tubes and the RPC core as well as the interaction's influence on the bearing capacity and deformability of RPC filled steel tubular (RPCFT) stub columns when the columns are subjected to axial load. The results indicate that: (1) RPCFT stub columns get tremendous ductility and alleviate RPC's disadvantage of brittle failure. (2) RPC's mechanical properties, such as large compression peak strain, constant Poisson's ratio, high autogenous shrinkage and high brittleness, limit the confinement effect between RPC and steel tubes. (3) The common failure mode of RPCFT stub columns under axial compression is shearing failure. The residual strength of RPCFT stub columns is mainly independent from RPC strength.Axial compression test results of 86 RPCFT stub columns acquired from the experimental investigation and literatures are compared with the existing design codes from China, America, Japan and Europe. The comparison indicates that most of the current design codes for normal strength concrete filled steel tubular columns are not safe for RPCFT columns. The confinement between RPC and tubes is suggested to be neglected in the design for convenience and safety, just as the ACI code does.Impact compression tests of RPC and the RPCFT specimens are performed with a split Hopkinson pressure bar (SHPB). RPC specimens with steel fibers show good impact resistance and the impact resistance can be improved furthermore by steel tubes'confinement.Because of the similarity between RPC and traditional high strength concrete, conclusions derived from this study can also be adopted by researches on high strength filled steel tubular columns.