Research On The Axial Compression Performance Of High-strength Concrete Columns Double-confined By Steel Pipe-CFRP Stirrups

Concrete filled steel tubular(CFST)columns have been widely used in large-span structures and high-rise buildings.The interaction between steel tube and concrete core delays the local buckling of steel tube,enhances the strength of concrete core and improves ductility of it.Circular and square tubes can be used in CFST columns in terms of the shape of crosssection.Also,normal and high strength concrete can be used in terms of concrete strength.High strength concrete produces high load-carrying capacity for the column but poor ductility as a result.Square CFST columns possess high convenience for constructing beam-column joints,but their compressive performance is inferior compared with the circular CFST columns because the confinement provided the square tube to concrete core is rather low.To fully utilize the compressive strength of concrete core in the CFST columns and improve the ductility of high strength concrete,carbon fiber reinforced polymer(CFRP)stirrups are proposed in this study to additionally confine the concrete core,in such a way,the load-carrying and deformation capacities can be enhanced.The compressive load-carrying capacity of the steel-tube CFRP-stirrup double confined high strength concrete columns were tested.The test results showed that the said capacity is highly improved compared to CFST columns without CFRP stirrups,indicating the CFRP stirrups have provided effective confinement to the concrete core.In addition,on the basis of strength equivalence,a unified design-oriented calculation formula for both circular and square steel tube-CFRP stirrup double confined concrete columns is proposed,by considering the double confinement of steel tube and CFRP stirrups as well as the effective and non-effective confinement areas on section.