Combined compression-bending-torsion behaviour of corrosion damaged reinforced concrete columns

Abstract

The corrosion of reinforcement due to pre-existed or infiltrated chloride ion is a major concern for the durability and structural integrity of reinforced concrete (RC) structures. In order to investigate the seismic behaviour of RC columns under combined loads of compression, bending, shear and torsion, a series of reversed cyclic tests were conducted on nine identical column specimens in the laboratory. Experiments were designed for the square RC column samples having 200x200mm section dimensions. Two of them were kept in as build condition as reference and seven of them were subjected to different levels of corrosions from slight to severe. Three of the corroded specimens were then strengthened by using Carbon Fiber Reinforced Polymer sheets (CFRP). The main variables studied in this program included level of reinforcement corrosion, axial load ratio and the use of the CFRP strengthening. The failure modes, hysteretic curves, ductility and energy dissipation were analysed and compared. The results revealed that the failure modes of the columns were mainly governed by the presence and the level of corrosion, which can be classified into bending failure, bending-shear, bending-shear-torsion failure, and shear failure. Effect of corrosion on lateral load-carrying capacity and ductility appear to be positive within a specific range. However, as the corrosion ratio increases further, its effect turns to be negative. In addition, higher axial load and strengthening increases lateral load resisting capacity considerably. It was noticed that the ductility is increased under higher axial load alone whereas the presence of corrosion accompanied with higher axial load leads to a decrease in both ductility and energy dissipation. The strengthening noticeably improves the ductility and energy dissipation of specimens and especially decreases the negative effects of corrosion.