Tests of reinforced concrete short columns laterally strengthened with wire rope units and steel elements

The current paper presents a simple unbonded-type column strengthening technique with wire rope units and few steel elements. Eleven short columns were strengthened using the proposed procedure and tested under monotonic concentric axial loads. The main variables investigated to evaluate the confinement effectiveness of strengthened concrete columns were the volume ratio, prestress, diameter, spacing and configuration of wire rope units. The strength gain factor and ductility ratio increased with the increase of volume ratio of wire ropes. The prestress applied to wire ropes had little influence on the strength gain factor but the ductility ratio decreased with the increase of prestress in the wire ropes, owing to earlier rupture of wire ropes. At the same volume ratio of wire ropes, the maximum strength of columns was nearly independent on the configuration of the wire ropes, but higher ductility was exhibited by columns strengthened with rectangular spiral-type wire ropes than by columns strengthened with hoop-type wire ropes, until rupture of the wire ropes. The strength gain factor and ductility ratio of strengthened columns were compared with those of tied columns tested in a previous study. The load capacity of strengthened columns was also predicted using the ACI 318-05 equation modified to reflect the load-carrying effect of steel elements. A much higher strength gain factor and ductility ratio were exhibited by strengthened columns than tied columns having the same lateral reinforcement, except for strengthened columns with wire rope spacing above 0·5 times core width. The axial load capacity of strengthened columns was higher than that of unstrengthened columns by 5–20%, and could be reasonably predicted using the modified ACI 318-05 equation.