Bond stress distribution in adhesive anchor systems: Interplay of concrete and mortar creep. (1st January 2022) - Boumakis, Ioannis
Abstract: The safe design of fastening systems, especially considering the multi-decade performance, relies on a thorough understanding of mechanisms and processes that lead to excessive deformations or even failure in course of time. According to current design guidelines and standards, adhesive anchor system are designed based on the uniform bond model. The uniform bond model is a generally good approximation of the real stress distribution during short-term testing and for loads close to the pull-out capacity of the system. However, both concrete and adhesive mortar are characterized by pronounced time-dependent deformation, especially at elevated temperatures. Thus, noteworthy shear stress redistributions are expected due to creep in course of a structure's life-time. Depending on the level of stress redistributions potentially critical stress levels may be reached locally, triggering progressive failure. Therefore, it is quintessential to understand bond stress redistribution phenomena in adhesive anchor systems under sustained load. Unfortunately, it is experimentally impossible to decouple the intertwined effects of concrete and adhesive creep. Thus, in this study a numerical approach is adopted. The response of concrete is modeled by a discrete meso-scale damage model in combination with the micro-prestress solidification theory coupled to a hygro-thermal chemical analysis while the adhesive layer is represented by a visco-elastic shear stress–slip law. After separate calibration of concrete creep and creep of the visco-elastic interface the obtained model is validated on independent experimental data on anchor systems. Finally, the established computational framework is utilized to virtually isolate concrete creep, adhesive creep and study their mutual interaction. Results show strong antagonistic redistribution mechanisms driven by concrete and adhesive creep with varying dominance depending on the investigated time-scale. Highlights: Concrete creep causes redistribution of bond stress towards surface. Mortar creep tends to equilibriate bond stresses along anchor. In interacation mortar creep is the initially dominant process. In interaction concrete creep dominates the long-term response larger 1 year. Growing micro-damage contributes to redistributions even at low load levels.