Seismic behaviour of pre-damaged RC columns strengthened with CFRP grid/sprayed ECC jackets subjected to horizontal reversed cyclic loading and constant axial force

A new seismic repair method for reinforced concrete columns, which uses carbon fiber reinforced polymer (CFRP) grids and sprayed engineered cementitious composite (ECC) to form a composite reinforcement jacket, was proposed to improve the seismic performance of concrete columns damaged by earthquakes. Five specimen columns with 250 mm×250 mm cross section and 1160 mm height were prepared and four different damage degree (no-damage, minor damage, moderate damage and severe damage) was controlled by the comparative specimen under the same amplitude-increasing lateral loading protocol and constant axial load. The pre-damaged columns were repaired and strengthened with three layers of CFRP grids and 25 mm thickness of sprayed ECC. The repaired columns were tested to failure and the effectiveness of the repairing schemes was evaluated by comparing load-carrying capacities, ductility, and energy dissipation. Based on the OpenSees seismic analysis software, a finite element model has been proposed to predict the seismic performance of the strengthened columns. The experimental results showed that the yield load, peak load, and ultimate load of the strengthened RC columns with no damage and slightly damage have significantly increased compared to the control specimen, with an increase range of 15% to 18%. For moderately damaged and severely damaged strengthened columns, the increase in the three characteristic load values is very small, or even reduced. Except for the severely damaged strengthened column, the ductility and energy consumption of other specimens have been improved to varying degrees. The analysis results indicated that the simulated values are in good agreement with the experimental ones, and the established finite element analysis model can be used to predict the seismic performance of strengthened columns.