Bond role in strut-and-tie systems modelling reinforced-concrete members

The unknown a priori position of bond-related joints in the strut-and-tie systems used in reinforced-concrete modelling is determined in this paper by developing a simple model concerning a single stiff and strong deformed bar (tie), that is embedded in a reinforced concrete member. The model takes into account the bonded length, the bond-stress profile and the nature of the bond along the tie (basically by interlock due to the formation of microcracks and microstruts, as well as by adhesion). The interaction between the position of the joint and the yielding of the reinforcement around the bonded tie, as well as the shares of the pull-out force resisted by interlock and by adhesion, are dealt with in detail, in order to maximize the bearing capacity of the tie within the static approach to limit analysis. Any tie, like those found in the strut-and-tie systems used in representing 2D regions, can be treated in accordance with the proposed model, provided that no direct confinement be applied by the supports or by the loads. The model may be a useful tool to evaluate the bearing capacity of reinforcedconcrete structural systems.