Influence of Bond Behavior on the Cross Sectional Forces in Flexural RC Members Strengthened with CFRP

Synopsis: In strengthened RC members the distribution of cross sectional tensile forces is affected by the significant differences in bond behavior of the reinforcement layers. As the tensile forces in the externally bonded reinforcement is the essential input value for bond verification for example at the end anchorage, the detailed knowledge of the distribution of forces in cracked sections is of fundamental importance. In this paper the common models to describe the interactions in tensile members are summarized and an advanced numerical model based on nonlinear bond stress-slip relationships for strengthened flexural members is presented. On the basis of experimental results combined with parametric studies, the effects of various parameters – for example the axial stiffness of CFRP, the diameter of internal rebars or the concrete compressive strength – on the interactions between the different reinforcement layers are examined. For practical design bond coefficients for a simplified calculation of cross sectional tensile forces are proposed.