The stress-strain relationship of concrete confined with corroded transverse reinforcements

Abstract

As service years increase, the corrosion of steel rebar stands out as a major problem for existing reinforced concrete (RC) structures in corrosion-inducing environment. The mechanism of steel corrosion in concrete is an electro chemical process, which is often accelerated by the ingress of aggressive chemicals, for example chloride ion. The accumulation of corrosion products on steel rebar is able to generate circular stress which could result in cover cracking. Corrosion of steel rebar will degrade the physical appearance and reduce its original cross section. Corrosion often appears to be non-uniform and localized. Corrosion damaged RC elements displayed smaller yield strength, ductility, energy dissipation capacity, etc. Corrosion level of stirrup tends to be higher than longitudinal rebar due to smaller diameter and less cover protection. Stirrup corrosion decreased confinement behaviour on concrete, thus exacerbating the degeneration of the deformation capacity and the ductility of the RC structures. Experimental studies on the concentric loading behaviour of reinforced concrete column with corroded stirrup and residual confined concrete strengths are presented. Based on maximum pit depth and nominal average pit depth, localization level is proposed to quantify the degree of pit corrosion. Experimental results prove that localization level is not strongly correlated with weight loss level. Columns with highly corroded stirrup have compromised compressive capacity and axial deformation capacity, which both are more related with weight loss level than localization. Analysis reveals that the mere reduction of cross section area can not sufficiently account for the effect of corrosion on the maximum lateral pressure of transverse reinforcement. Based on Mander confined concrete model, a new model is proposed by introducing correction factors to quantify the variations. Regression analysis has helped establish relationships between correction factors and weight loss level or localization level of stirrups.