Experimental Study on Axially Loaded Reinforced Concrete Columns Strengthened with Steel Cage

The presented study investigates the structural behavior of reinforced concrete (RC) columns strengthened using an external steel cage and an additional concrete infill layer. An experimental program was conducted on short RC columns subjected to axial compressive force. A total of eleven columns were tested, including five plain RC and six strengthened specimens. The objective of the research was to evaluate the load-bearing capacity, failure mechanisms, and composite interaction between the steel cage, the infill concrete, and the original RC column. Two different distances between battens were considered in order to evaluate whether the number of batten plates significantly influences the efficiency of strengthening. The experimental results show that the proposed strengthening technique leads to an increase in axial capacity compared to unstrengthened specimens. Also, the variation in batten spacing within the investigated range has a negligible effect on the ultimate load. Failure was governed by cracking and bond deterioration in the infill layer, followed by progressive loss of composite action. The results indicate that the strengthening performance is primarily controlled by the properties of the infill concrete and the confinement mechanism, rather than by the spacing of the steel battens. The application of EN 1994-1-1 and EN 1998-3 in predicting the axial capacity of strengthened columns showed a good relation between experimental results and code calculations.