Preventing debonding at the steel to concrete interface through strain localization

For composite structures with externally bonded reinforcement, debonding at the interface is one of the most difficult problems. This paper presents the application of a nanotechnology - surface mechanical attrition treatment (SMAT), which produces nanostructured steel plates, to overcome this critical debonding problem through strain localization. The nanostructured steel plates can have tensile strength comparable to that of fiber reinforced polymer (FRP) while retaining high ductility. When used for structural strengthening, the plates retain the advantages of FRP and steel, and avoid their disadvantages. By locally treating a steel plate with SMAT to increase its tensile strength in certain parts, the plate's yielding is diverted and localized to certain relatively weaker zones when the strengthened beam is loaded to yield, leaving the stronger zones under elastic and much smaller strain conditions. As debonding is closely related to the tensile strain of the externally bonded reinforcement, the small strain condition in the stronger regions inhibits the debonding from spreading. As a result, the global detachment of the externally bonded reinforcement can be delayed or even avoided. The effectiveness of this new technology has been substantiated by beam testing. The anti-debonding mechanism is also studied using numerical simulations. © 2012 Elsevier Ltd. All rights reserved.