Abstract

Fibre-reinforced polymer (FRP) plates have been widely used to retrofit RC beams to achieve higher strength, however, it is not uncommon to find the retrofitted RC beams fail in a sudden manner by premature debonding before the target flexural capacity. A layer of concrete is usually found attached to the debonded plate, so plate debonding is clearly a fracture event of concrete that is initiated from the inevitable flaws in the concrete cover layer. In the retrofitted RC beams, these small flaws can trigger-off structure collapse, so should be investigated in detail. Although it has been studied for decades, detailed concrete fracture investigation has been considered difficult so far. There is a lack of direct fracture observation for the plate debonding failure that occurs in the concrete cover layer.

Using non-destructive image correlation techniques, which obtain real strain field distributions from digital photographs, it is possible to observed the detailed process and provide estimates for the fracture energy related to FRP plate debonding. This talk will present the experimental observations of a plate debonding fracture propagation in a plated double-cantilever beam specimen, which is designed to simulate the concrete cover layer, and a way of estimating the fracture energy associated to FRP plate debonding.