Behavior of axially loaded L-shaped RC columns strengthened using steel jacketing

Abstract

Other than rectangular and circular columns, the most commonly used sections in reinforced concrete (RC) buildings in Saudi Arabia are L-shaped columns with a re-entrant angle of 90° or more. The structural designers are using L-shaped columns to meet the architectural and functional constraints of the building without obstructing the movement. Strengthening of such L-shaped RC columns is required to increase their load capacity for a number of reasons, such as an increase in the number of stories, the change of building use, design error(s), or construction defect(s). This research studied experimentally and analytically the behavior of strengthened L-shaped RC columns. The test matrix comprised two groups of six half-scale L-shaped RC columns. In the first and second groups, respectively, columns had 90° and 135° re-entrant corners. Each group had three columns: one unstrengthened control specimen used as a baseline for comparison and two steel-jacketed columns. In the first strengthened specimen, there was a 25 mm gap at the interface of the steel jacket with the ends (bottom base and top box), whereas, in the second specimen, the jacket was connected with the ends. The column specimens were concentrically loaded in compression until failure. It is demonstrated that strengthening of L-shaped columns with disconnected steel jackets had limited improvement in the axial load capacity ranging from 26% to 29% over the unstrengthened ones, while upgrading the columns with connected steel jackets had major enhancement in the axial load capacity varying from 68% to 79% over the control specimens. Furthermore, an analytical model that considers concrete confinement and axial load contributed by connected steel jacket was developed for assessing the axial capacity of tested specimens. Good agreement was achieved between the experimental and analytical peak loads with errors in prediction ranging from 1% to 6%.