Stress redistribution along the mortar-concrete interface in bonded anchor systems under sustained load

In structural engineering bonded anchor systems are widely used as connectors of different structural members, or/and for assembling of precast elements. All fastening systems have to undergo rigorous testing in course of an approval process to ensure their compliance with the established short-term and long-term performance criteria. In case of the sustained load behavior current guidelines require sustained load tests of typically 3 months lengths. The actual check is based on a semi-empirical approach. According to this, a simple power law is fitted to the structural deformation data of bonded anchors. Finally, the projection of the creep deformation to the service life time, e.g. 50 years, and it’s comparison to a set displacement criterion serves as an approval criterion. From a scientific perspective the current approach is, although simple and practical, insufficient as it is unable to account for the contribution of each material, i.e. concrete, steel, and polymer-based mortars, potential stress redistributions in course of time, and evolving damage. This contribution studies systematically the creep effect of each material on the system long-term response as well as the development of the bond stress distribution along the anchor, i.e. the stress of the concrete/adhesive mortar interface. This investigation is performed by using a physically-based computational framework for concrete that couples hydration, diffusion, and heat transport processes. The response of the adhesive is calibrated inversely in terms of a visco-elastic bond law utilizing available pull-out tests and sustained load anchor tests at low and high load levels. The model is validated on sustained load tests of different geometries, with a very good predictive capacity. Finally, numerical parameter studies are presented that reveal the relationship between the evolving bond stress distribution and the interacting visco-elastic materials complemented by a sensitivity study on the material model input parameters