Axial Behavior of Reinforced Concrete Columns Strengthened with New Section Enlargement Approaches

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Title: Axial Behavior of Reinforced Concrete Columns Strengthened with New Section Enlargement Approaches

Author(s): Keun-Hyeok Yang

Publication: Structural Journal

Volume: 116

Issue: 5

Appears on pages(s): 87-96

Keywords: axial performance; column; prefabricated bar unit; section enlargement; strengthening; V-ties

Date: 9/1/2019

Abstract:
This paper presents a new section enlargement strengthening technique based on prefabricated steel arrangement approach employing V-ties as a supplementary transverse reinforcement in the jacket section to enhance the structural performance of nonseismic or deteriorated columns. Nine full-scale columns were tested to failure under concentric axial loads to explore the significance and shortcomings of the proposed strengthening technique. The test parameters included the arrangement method of closed peripheral hoops and amount of transverse reinforcement in the jacket section. Thus, the strengthened columns were classified into two groups as follows: 1) the L-group for overlapped channel-shape bar hoops; and 2) the P-group for prefabricated bar unit hoops. The test results confirmed that the axial strength of the strengthened columns is conservatively determined using the nominal design equation of the ACI 318-14 provision. The supplementary V-ties are effective in preventing the premature failure of longitudinal bars in the jacket section and the sudden decreases in the load-transfer capacity of the strengthened columns, indicating that the strengthened P-group columns had an axial ductility more than 1.39 times higher than that of the existing column. Therefore, the developed technique exhibits significant potential for seismic section enlargement strengthening of columns by providing core concrete with a high lateral confinement and preventing the premature buckling of longitudinal bars.