Mixed Formulation of Bond-Slip Problems under Cyclic Loads

The stress transfer mechanism between reinforcing steel and surrounding concrete through bond and the resulting slip plays an important role in the hysteretic behavior of reinforced concrete structures. Earlier models of the stress transfer problem were based on a displacement formulation. Recent models, however, have demonstrated the significant advantages of a flexibility formulation on account of its accuracy and numerical stability under large inelastic strains in the reinforcing steel and bond damage in the surrounding concrete. This paper presents a critical evaluation of existing anchored reinforcing bar models and proposes a new model based on a two-field mixed formulation in which independent interpolation functions are used for the relative slip and the reinforcing steel forces. The advantages of this approach over existing models are assessed by numerical studies of anchored reinforcing bars under monotonic loads. The accuracy of the proposed model is established by correlation of analytical results with experimental data of an anchored reinforcing bar under severe cyclic loading.