Local bond stress-slip model for reinforced concrete joints and anchorages with moderate confinement

This paper presents a summary of an experimental investigation and the derivation of a bond-slip model for reinforcing steel embedded in moderately confined concrete under monotonic and cyclic loadings. Moderately confined concrete encompasses the domain between unconfined and well-confined concrete, the limits of which are defined in the paper. The proposed constitutive law adapts and extends the well-known Eligehausen-Filippou model for well-confined concrete to moderately confined concrete. It is described by an envelope curve and degradation rules. The former is obtained through a confinement index, defined in this study as a function of the amount of confining steel and concrete, distance between confining steel and the rebar, and concrete segregation effect. It is proposed to adopt the same degradation rules used for well-confined concrete. These rules are validated through statistical tests for moderately confined concrete. They are found to predict correctly the main features of reduced envelope response under increasing cycling amplitudes but to underestimate response degradation under constant cycling limits for the subsequent cycles to the first cycle. To demonstrate the validity and limitations of the proposed model, its predictions under monotonic loading are compared with experimental results and analytical predictions from other studies.