Seismic control of plastic mechanism of steel reinforced concrete columns by the use of GFRP bars

In order to limit the cost of seismic retrofit following an earthquake, it is recommended to shift the locations of potential plastic hinge regions away from the beam-column joints and foundation-column joints. Formation of a plastic hinge at the bottom end of a bridge column causes damage to the supporting foundation. Post-earthquake retrofit of bridge foundation is very difficult and expensive. In recent years, several techniques have been introduced to move the location of potential plastic hinge regions away from the joints. This has been done by the use of additional steel control reinforcing bars (rebars) extended over a certain length from the beam-column or the foundation-column joints. When used as control rebars, Glass fiber reinforced polymer (GFRP) rebars are superior to steel rebars in relocating plastic hinge regions, as they have lower modulus. In a steel reinforced concrete column, GFRP rebars could be used as control rebars, only. The primary advantage of the use of GFRP rebars is low bond stresses at the interface between the control rebars and the surrounding concrete, as a result, they cause significantly less damage to the column's concrete core during a seismic event. This paper presents guidelines for the use of GFRP rebars for controlling the location of plastic hinge regions in steel reinforced concrete bridge columns. The recommendations are based on extensive study of the properties of concrete columns reinforced with hybrid reinforcements. These reinforcements consist of primary steel bars and auxiliary GFRP control bars. The results of this investigation suggest that GFRP bars are effective in shifting the plastic hinge regions in bridge columns subjected to axial load stress below 10 MPa.