Develpoment of time dependent bond model between steel bar and concrete

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For the analysis of deformational behaviors of reinforced concrete structures, it is necessary to know about interaction between steel bars and concrete. The interaction is generally represented by a local bond stress-local slip relationship of the bar. Some local bond stress-slip models have already proposed. However, most of these models were obtained from static tests and can not always be applied to the analysis of structures subjected tQ dead or sustained loads. The subject of this research is to clarify the effect of time passing on bond behavior under sustained load and to propose a time dependent bond model.Mechanism of bond of concrete to steel bar is that concrete in the front of the lib resists against the bar lib. Extremely high stress under three axes causes on the concrete in the front of the lib at this condition. Therefore, it is necessary to find the creep characteristic of concrete under three axes high stress conditions in order to develop a precise bond creep model. Axial pullout test of bar embedded in large concrete block under a sustained load was carried out in order to measure the change of strain distribution along embedded bar with time after loading. The effect of time after loading on the local bond stress-slip relationship was discussed. It was found that the strains of steel bar embedded in concrete block increased wIth time and the bond stress decreased with time remarkably where the local slip was larger.