Anchorage of plain, naturally corroded reinforcement bars with end-hooks

Abstract

Following the developments since 1960, plain reinforcement bars have been replaced by ribbed reinforcement bars in the design of concrete structures. However, some of the existing old structures with plain reinforcement bars are still in use and there is insufficient knowledge available for the assessment of structures with plain reinforcement bars. The aim of this thesis was to evaluate the anchorage capacity of naturally corroded plain reinforcement bars with end-hooks. The studied specimens were earlier cut from edge beams of a decommissioned bridge. There were two types of beams: with one or two pairs of hooks. Three-point bending tests of the beams had been carried out before this thesis project. Digital Image Correlation was used to monitor deflections and crack developments. In this thesis, the structural behavior of both types of beams was evaluated. The yield penetration and corrosion level of plain reinforcement bars with end-hooks were evaluated from 3D scanned data. Further, the bond stress in the yielded zone and the force anchored by the hooks were assessed. Finally, the experimental results were compared to the design capacity in accordance with two different available codes, BBK 04[3] and ACI[1]. In comparison, the beams with two pairs of hooks showed a larger load-carrying capacity. The end-hook of beams with one pair of hooks managed to carry the yield force in some cases, while for the beams with two pairs of hooks, shear failure limited the deformation capacity of the beams. The results showed that the average corrosion level varied from 0% to 2%. The bond stress in the yielded zone was found to vary between 0 MPa and 4.5 MPa. The force anchored by the hooks varied depending on the assumed value of the bond stress in the unyielded zone. For an assumed bond stress ranging from 1 MPa to 12 MPa, the evaluated force anchored by the hooks was similar in both types of beams and varied between 32 kN and 53 kN. The calculated force anchored by the hooks in the experiments was on average 84% and 64% of the code results according to BBK 04[3] and ACI[1], respectively.