Steel and carbon fiber textile reinforced high-strength-concrete columns

High strength concrete (HSC) usage is spreading in reinforced concrete (RC) structures in the past few decades. Conventional RC columns, made by steel-reinforced HSC, require a large amount of confining transverse steel to provide sufficient ductility and strength. This leads to transverse reinforcement congestion, and in turn-to application issues of the fresh concrete. Carbon fiber-reinforced polymer (CFRP) wrappings can provide another solution for the required confinement in columns; however, its fire resistance is low because of the fire sensitivity of the polymer and the fact that FRP is wrapped on the external surface of the column. Furthermore, the behavior of CFRP-only confined columns is more brittle than the steel-confined columns. This paper describes a new hybrid steel-carbon fiber textile confinement applied to HSC circular columns. The HSC columns are reinforced by dual layers: steel and carbon fibers mesh. The carbon-fibers mesh is wrapped around the steel hoops of the column before concrete casting and they are protected by the concrete cover. The behavior of the hybrid confined HSC columns combines the ductile behavior of the steel with the stiffness of the CFRP and provides the required confinement level for HSC columns. Initial results that comprise column-confinement analysis and their experimental examination are presented. The analysis focuses on the uniaxial load-displace-ment behavior of the circular columns and compares different amounts of steel and carbon fibers to explain the role of each component. Initial experimental results are also presented, and they demonstrate the advantages of the hybrid confining system and its effectiveness when used in high-strength concrete columns.