Three-Dimensional Modelling of Bond in Reinforced Concrete Theoretical Model, Experiments and Applications

Sammanfattning: The bond mechanism between deformed bars and concrete is known to be influenced by multiple parameters, such as the strength of the surrounding structure, the occurrence of splitting cracks in the concrete and the yielding of the reinforcement. However, when reinforced concrete structures are analysed using the finite element method, it is quite common to assume that the bond stress depends solely on the slip. A new theoretical model which is especially suited for detailed three-dimensional analyses was developed. In the new model, the splitting stresses of the bond action are included; furthermore, the bond stress depends not only on the slip, but also on the radial deformation between the reinforcement bar and the concrete. In addition, this model includes the simulation of cyclic loading. Steel-encased pull-out tests subjected to reversed cyclic loading were carried out. The tangential strain in the steel tubes was measured to investigate how the splitting stresses are affected by cyclic loading. Based on the results of these tests, several improvements of the model were made. Bar pull-out tests with differing geometries and with both monotonic and cyclic loading were analysed, using the new model for the bond action, and non-linear fracture mechanics for the concrete. The results show that the model is capable of dealing with a variety of failure modes, such as pull-out failure, splitting failure, and the loss of bond when the reinforcement is yielding, as well as dealing with cyclic loading in a physically reasonable way.

The new model was used in detailed three-dimensional analyses of frame corners. Until recently, splicing of the reinforcement in frame corners had not been allowed by the Swedish Road Administration. Since this had led to reinforcement detailing that was hard to realise on site, it was of interest to examine how splicing of the reinforcement affects the behaviour of the structure. Tests on frame corners subjected to closing moments were also carried out. It was found that the analyses could describe the test performance in a reasonable way. The tests and analyses showed that splicing the reinforcement in the middle of the corner has advantages over splices placed outside the bend of the reinforcement. They also indicated, in agreement with previous work, that provided the splice length is as long as required in the codes, there are no disadvantages in splicing the reinforcement within the corner of a frame subjected to closing moment.