| Summary: | The purpose of this paper is to study the behavior and efficiency of reinforced concrete square columns strengthened by steel angles and strips (steel cage). An experimental program was conducted on ten axially loaded column’s specimens till failure. Size of the steel angles, strip spacing, grout material between column sides and angles, and the connection between the steel cage to the specimen head, were the main studied parameters in this paper. Also, an analytical model was developed using a simple stress mechanics and strain compatibility to obtain the ultimate loads of the strengthened columns including the effect of the confining stress due to the steel cage and axial forces in the vertical angles considering both directly and indirectly connected cases. It was concluded that using this strengthening method is very efficient and a gain in the axial load capacity of the strengthened columns was obtained. This gain was due to the confinement effect of the external steel cage, and the ability of the steel angle to resist an extensive part of the applied axial load. The failure in most of the strengthened specimens was due to the buckling of the steel angle followed by crushing of the original columns.
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