Seismic strengthening of bond-critical regions in rectangular reinforced concrete columns using fiber-reinforced polymer wraps

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 are experimentally investigated. Full-scale-unconfined and FRP-confined column specimens with lapspliced reinforcement at the base were tested. Also, companion columns with continuous reinforcement and with internal steel confinement to satisfy the ACI building code requirements for regions of high seismic hazard (earthquake-resistant columns) were tested for comparison. It was found that confining the spliced zone with FRP wraps increased the bond strength of the spliced bars, reduced the bond deterioration and pinching under cyclic loading, and-increased the lateral load resistance 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 with increasing area of FRP wraps. The predictions of bond strength of spliced bars in FRP-confined concrete using available design expressions were in good agreement with the test data.