Application of fracture mechanics to reinforced concrete beams under bending

In the present paper application of Fracture Mechanics to reinforced concrete beams, under bending, theoretically and experimentally is investigated. During the increasing loading (force) of a three point bend reinforced concrete beam, the crack reaches the reinforcement, passes it, and then the crack along the reinforcement develops, causing debonding. Simultaneously vertical crack continues to develop. This crack is propagating with the driving force at the crack tip due to externally applied load. At the same time the reinforcement behaves as elasto-plastic spring decreasing the stress intensity factor at the crack tip. Theoretical model allows calculation of collapse load, crack length and crack opening displacement. It is based on Carpinteri's approach in which the debonding is implemented. Experimental investigation is comprised of measurements of all theoretically obtained results.. Special attention is focused on the determination of vertical crack size. This is achieved using graphite and optical fibers.