Experimental research and finite element analysis on the seismic behavior of CFRP-strengthened severely seismic-damaged RC columns

This study describes a new strengthening technique that involves the combination of CFRP jackets, CFRP sheets and high- strength grouting material. Three different strengthening alternatives were employed to strengthen three severely damaged RC columns. Based on the experimental results, the failure mode, hysteresis curve, skeleton curve, ductility, energy dissipation ability, stiffness degradation and strength degradation of both the original and strengthened test specimens were compared and discussed. All three strengthened test specimens exhibited similar damaging processes, yielding of longitudinal reinforcement, cracks on CFRP jackets, rupture of CFRP sheets and collapse of high-strength grouting material were successively observed in the loading procedure. The results showed that the three strengthened seismic damaged concrete columns all presented a bending failure mode and met the "strong shear, weak bending" design attributes. Compared with the original columns, the ductility and energy dissipation capacity of the three strengthened test specimens were significantly improved, while the capacity and stiffness were not fully restored. Strengthened test specimen Z3-R, which was strengthened by the combination of CFRP jackets, CFRP sheets and high-strength grouting material, showed the best seismic performance among all three strengthened test specimens. A finite element model based on OpenSees was developed and validated by a comparison with experimental results. The effects of the axial compression ratio and thickness of CFRP sheets were also discussed through parametric studies.