Develpoment of time dependent bond model between steel bar and concrete

为了分析钢筋混凝土结构的变形性能，有必要了解钢筋与混凝土之间的相互作用。这种相互作用一般由杆件的局部粘结应力-局部滑移关系来表示。一些局部粘结应力滑移模型已经提出。然而，这些模型大多是通过静力试验获得的，并不总是适用于TQ静载或持续荷载作用下的结构分析。本研究旨在阐明持续荷载作用下时间传递对粘结性能的影响，并提出混凝土与钢筋的时变粘结模型。混凝土与钢筋的粘结机理是位于钢筋库前方的混凝土抵抗钢筋库的作用。在这种情况下，三轴下的极高应力会对拱顶前方的混凝土产生影响。因此，为了建立精确的粘结徐变模型，有必要了解混凝土在三轴高应力条件下的徐变特性。进行了混凝土大砌块内嵌钢筋在持续荷载作用下的轴向拉拔试验，以测量加载后内嵌钢筋的应变分布随时间的变化。讨论了加载后时间对局部粘结应力-滑移关系的影响。结果表明，在局部滑移较大的地方，混凝土砌块内嵌钢筋的应变随时间增加，粘结应力随时间显着降低。

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.