TENSION-STIFFNESS MODEL FOR REINFORCED-CONCRETE BARS

An analytical formulation for modeling the tension-stiffness phenomenon in cracked reinforced concrete bars is presented. It is assumed that the bond stress-slip relationship is bilinear, and remains linear throughout the bar in the initial stages of the cracking. At the later stages, the bond stress becomes constant. Unlike in the reinforced concrete models currently in use, it is shown that the tension-stiffness phenomenon is a function of the parameters of the problem, viz., the area parameter, the bond parameter, and the strength parameter. A simplified model is also presented in which the bond parameter is eliminated. Results from the present model are compared with those from some test results. Various implications related to the assumptions and the conclusions are reviewed. The experimental results show a marked reduction in the tensile capacity of concrete at higher deformations that cannot be explained by the proposed relationships. A possible solution is to use a variable concrete tensile strength that diminishes exponentially as a function of the average tensile strain and a damage parameter. Future investigations may show that this parameter is related to the property of the materials, geometry of the structural member, the loading level, and so on. The present formulation represents a significant improvement over the models currently in use. © ASCE.