Debonding failure mechanisms in prestressed CFRP/epoxy/concrete connections

•Prestress force-release tests with CFRP strips bonded to concrete have been performed.•The overall debonding process is strongly influenced by Mode I.•Cracks penetrate deeper in the concrete substrate compared to classic lap-shear.•FE calculations with cohesive elements are used to simulate the debonding process.•A mixed-mode failure over the strip width is revealed.

This paper presents an investigation on the failure mode in prestress force-release tests of CFRP strips bonded to concrete substrates. Background of the study is the gradient anchorage technique. Firstly, experimental test series are presented. It is shown that considerable differences in failure mechanisms between lap-shear and the before mentioned release tests exist. The study reveals a strong Mode I-influence in the debonding process, compared to a Mode II for lap-shear tests. Secondly, FE simulations with a commercially available software are introduced. It is demonstrated that delamination in a force-release test occurs by a mixed-mode failure over the strip width.