A new confinement configuration of conventional steel hoops with carbon fiber mesh for HSC columns

The implementation of high-strength concrete (HSC) to reduce the dimensions of the columns in highrise buildings depends, among other things, on a practical solution to the concrete confinement of these elements. Confinement in concrete increases the strength and ductility of the column and is usually provided by steel hoops. The required amount of hoops increases with the increase of the concrete strength. In many cases, for high strength concrete columns subjected to high compressive loading, the required amount of steel hoops is difficult to apply due to their large density (small spacing). Previously proposed methods to solve this problem, such as external wrapping of FRP sheets around the column, may be disqualified due to their sensitivity to fire. This research presents an innovative hybrid confinement method of combining conventional steel hoops with carbon fibers wrapped internally around the steel reinforcement cage. The study presents experiments on high-strength concrete column specimens with a length of 950 mm and a diameter of 250 mm with the hybrid confinement system. The experiments were performed on columns at both ambient temperature and during heating to a high temperature, simulating a fire. The experimental results show the performance of the proposed hybrid confining system, which indicates its feasible implementation both in a non-fire situation and in a fire scenario.