Seismic Strengthening of Bond-critical Regions in Rectangular RC Columns Using External FRP Jackets

The use of external fiber reinforced polymer (FRP) wraps for bond strengthening of spliced reinforcement in rectangular reinforced concrete (RC) columns and the consequent effect on the seismic response of the columns is experimentally inve stigated. Full scale unconfined and FRP confined column specimens with lap-splic ed reinforcement at the base were tested. Also, companion columns with continuou s reinforcement and with internal steel confinement to satisfy the ACI Building code requirements for regions of high seismic hazard (earthquake resistant colum ns) were tested for comparison. It was found that confining the spliced zone wit h FRP wraps increased the bond strength of the spliced bars, reduced the bond de terioration and pinching under cyclic loading, and increased the lateral load re sistance and ductility of the columns. The corresponding improvements approached those of the earthquake resistant columns. The lateral strain developed in the FRP increased with decreasing ratio of concrete cover to splice diameter and wit h increasing area of FRP wraps. The predictions of bond strength of spliced bar s in FRP confined concrete using available design expressions were in good agree ment with the test data.