Prediction and optimization of stress distribution in bonded anchors for CFRP tendons

This study proposed a universal theoretical model for predicting the stress distributions in bonded anchors for carbon fibre reinforced polymer (CFRP) tendons based on the elasticity theory. The proposed model is adaptable for predicting the stress distributions of straight anchors as well as anchors with different conical angles, and it was validated by experimental results. A parametric analysis was conducted to examine the effect of the structural form of anchors, conical degree and bonding material on the stress distributions in the anchor zone based on the developed theoretical model. The results reveal that the resistance against the slippage of the tendon increases with respect to the conical degree. However, by having a high conical degree, serious stress concentrations as well as a high risk of shear and compressive damage appear in the anchor zone. The conical degree from 3° to 4° is suggested for the anchors with a conical length of no less than 200 mm. The straight segment at the free end in a straight-conical-straight anchor has little effect on the stress distributions whereas the straight segment at the loading end reduces significantly the stress concentration and even out the stress distribution in the anchor zone. It is suggested that the length ratio of the conical to the straight segment at the loading end be kept in between 4:1 to 2:1, which has a positive effect on the stress distributions by reducing the maximum stress as well as transferring the tensile load from the loading end towards the free end more efficiently. The bonding medium influences the stress distributions as well. A homogeneous bonding medium with a lower modulus produces better stress distributions in the anchor zone. An improvement in the stress distributions becomes more distinct with the application of a bonding medium with a gradually decreasing modulus from the free end to the loading end. A thicker bonding medium generates a more uniform stress distributions in the anchor zone, but the increase of the thickness has to be limited due to a larger deformation appearing simultaneously in the bonding medium.