Effects of Generalized Loadings on Bond of Reinforcing Bars Embedded in Confined Concrete Blocks

摘要

Under reversing lateral loads, such as occur during a major earthquake, cracks can form at column faces of continuous beams framing into joints of moment-resisting frames. Reinforcement may be strained well into the inelastic range and cracks will tend to remain open. During cyclic loading, continuous longitudinal beam bars can be simultaneously pushed and pulled from opposite sides of a column, creating a severe demand on anchorage. The performance of anchorage under conditions similar to those described above was tested experimentally. Seventeen specimens of single bars embedded in well-confined column stubs were tested under push-pull or only pull loadings. Monotonic as well as cyclic loadings were prescribed. Bar sizes No. 6, No. 8, and No. 10 were tested. The tendency of bond to degrade under cyclic loading was observed. Results obtained from these tests provide essential data from which a mathematical model for predicting the bond behavior that leads to the pull out or push in of a rebar is formulated. Finite element techniques are employed to predict the cracking behavior of the surrounding concrete since this behavior could not be deduced from the experimental data. The superior performance of a bar subjected to a push load is noted. The discrepancy between the predicted and experimental results is evaluated, and the limitations of the material models used in the present analysis are described. A model for the hysteretic behavior of a bond element when subjected to generalized loading histories is established from the experimental results. The reliability of the model for monotonic and full reversal loading histories is encouraging.