Retrofitting damaged subway station columns with CFRP grid-reinforced ECC jackets for improved seismic performance

In seismically active regions, many reinforced concrete (RC) columns are vulnerable to damage, reducing their seismic performance and requiring necessary repairs. Meanwhile, the seismic vulnerability of underground structures has become a critical concern, but research on the seismic performance of central columns in underground structures remains relatively limited. Therefore, this study introduced a retrofit method using an engineered cementitious composite (ECC) with a carbon fiber-reinforced polymer (CFRP) grid to improve the seismic performance of pre-damaged central columns. Cyclic loading tests were performed on an intact RC column and two retrofitted columns subjected to different pre-damage levels. The failure modes, load-bearing capacity, deformation capacity, energy dissipation and ductility of retrofitted columns were evaluated. Finite element (FE) models of CFRP-ECC retrofitting columns subjected to cyclic loading were developed and verified against the experimental results, and the effects of the pre-damage level and number of CFRP grid layers on the seismic performance of central columns were further investigated. The results showed that CFRP-ECC retrofitting shifted the seismic failure mode of RC columns from brittle to ductile. The bearing capacity of both moderately and severely damaged columns was fully restored, with variations within ±2 %. Compared with the control column, the ultimate displacement of moderately and severely damaged columns increased by 26.4 % and 53.6 %, while their ductility coefficients improved by 30.6 % and 15.6 %, respectively. Furthermore, two layers of CFRP grids achieved an optimal balance between improved performance and material efficiency. These findings provide practical guidelines for the seismic retrofitting of underground structures. • A retrofitting method using CFRP-reinforced ECC was developed for pre-damaged central columns. • Seismic tests on the CFRP-ECC retrofitting columns with pre-damage were conducted. • The CFRP-ECC jackets changed the failure mode of RC columns from brittle to more ductile. • The CFRP-ECC jackets can significantly enhance the seismic behavior of pre-damaged columns.