The presence of supplementary reinforcement has a significant influence on the load-carrying capacity of anchorages subjected to tension loads. The load-bearing capacity of an anchorage with supplementary reinforcement results from the anchorage in the concrete breakout body achieved by means of bond and bearing of a hook or bend. When the anchorage is loaded in tension, first the concrete cracks forming the breakout body, and then the stirrups get activated. If the anchorage length of the stirrups within the concrete breakout body is small, they might reach bond failure prior to yielding resulting in lower resistance than potentially achievable. For stirrups with relatively large anchorage lengths, as in case of closely spaced stirrups, resistance equal to the yield resistance of the stirrup can develop resulting in enhanced load and deformation capacity of the anchorage. However, beyond a certain level of reinforcement, the failure of concrete struts can limit the failure load for the anchorage.

The models included in the current standards and guidelines to evaluate the failure loads for anchorages with supplementary reinforcement subjected to either tension or shear forces are generally very conservative. The existing models do not explicitly consider all three major components that provide resistance to applied forces for anchorages with supplementary reinforcement namely the concrete struts, the tension ties and the nodes. The consideration of only concrete “or” reinforcement resistance as the anchorage resistance generally leads to a very conservative estimate of the failure loads for the anchorage. On the other hand, not recognizing concrete strut failure as a possible failure mode might lead to an over-estimation of the failure loads for anchorages of certain configurations with relatively high amount of supplementary reinforcement.

This project deals with investigating the behavior of anchorages with supplementary reinforcement subjected to tension forces and to develop an analytical model for them. Based on well-instrumented tests, a new model has been developed to predict the failure load and the failure mode for anchorages with supplementary reinforcement under tension loads. The model considers separate contribution of the hook and the bond length of the stirrup to calculate the reinforcement resistance based on modifications to the Schmid model. The concrete and reinforcement resistance is combined based on the readings of strain gauges. The increase in the anchorage resistance due to supplementary reinforcement is capped by the strut failure load based on the modifications to the Berger model.

The research has been funded by Peikko Group Corporation and the work has been carried out along with Prof. Rolf Eligehausen and Dr. Jörg Asmus. Further details of the tests and analytical model can be obtained from the following publications:

Paper Experiments

Paper Analytical model