AbstractReinforcing old bridges with corrugated steel (CS) is gaining interest due to outstanding reinforcement effects and relative ease of implementation. The approach consists of positioning the CS member under an old bridge and joining the two components by postcast concrete. However, the current design approach ignores the supporting effect of postcast concrete and the old bridges, which is overly conservative. This paper studies experimentally the static performance of the reinforced concrete (RC) arches reinforced with CS, mainly considering the influence of damage degree of the original structure. Two RC arches were prepared and loaded up to 60% and 100% of their ultimate bearing capacity, respectively. After reinforcing and reloading, failure modes, bearing capacity, and ductility of the reinforced specimens were obtained. The results show that when reinforcing the arches with CS, the ultimate bearing capacity increased by 172.8% and 194.0%, respectively. Comparison of the two reinforced specimens shows that the damage degree has only a small effect (8.2%) on the ultimate bearing capacity. Besides, the original structure, postcast concrete and CS were well bonded based on the strain analysis, proving the reinforced structure has the composite effect.