Unified Bond Model for Externally Bonded Reinforcement

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This study presents a unified local bond stress-slip model for interface between concrete and externally bonded reinforcing material (shear bond model). The shear bond model was derived based on a reinforcing material stress-slip relationship at loaded end of pullout bond test, so that necessary measurement was simplified and the data scatter problem was minimized. The shear bond model needs only two material constants, interfacial fracture energy and interfacial ductility factor. The shear bond model was expanded to be bond stress-slip-reinforcing material strain model to express cases with a short bond length. Both original and expanded shear bond models consider effects of mechanical properties of reinforcing materials, adhesive materials and concrete substrate. Besides the shear band model, the prediction formula for interfacial fracture energy, effective bond length and bond strength for given anchorage length are presented. Reliability of the proposed unified shear bond model together with the proposed formula for interfacial fracture energy, effective bond length and bond strength for a given bond length is presented by comparing the calculated results with experimental results.Tension bond model is examined experimentally and it is disclosed that the bond strength (or interfacial fracture energy) is not affected by stiffness of adhesive materials, which is different from the cases of shear bond model. A test method to represent a mixed mode for bond (shear and tension bond) is newly developed. Using this method, an interaction diagram of shear bond strength and tension bond strength is presented, which shows that the shear bond strength is reduced only by 10% even under tension bond stress equal to 90% of the tension bond strength. The theoretical method to calculate punching out capacity of reinforcing material externally bonded in orthogonal direction is also presented.