Stress relaxation analysis of adhesively bonded anchorages for CFRP tendons

An adhesively bonded anchor for Carbon Fibre Reinforced Polymer (CFRP) tendons was investigated under the stress relaxation phenomenon. Experimental stress relaxation tests were undertaken on anchorages with four different adhesive thicknesses. Ten specimens were prestressed at three different initial tensioning forces and the displacement was kept constant. In addition, seven specimens were restressed when the loss load was stabilised and constant. The stress relaxation test setup used in this work is proposed for long term tests for anchors. Moreover, a viscoelastic theory was used to predict the stress relaxation of the anchors through the Bailey-Norton law (creep power law). The model was numerically implemented in Abaqus and the load loss of each anchor was simulated during the relaxation process before restressing. The predicted load loss results were found to be in good agreement with the experimental results recorded. It was also found that the restressing technique allows for increasing the working load of the composite tendon by successive restressing. Finally, the most relevant recommendations for a potential use in prestressing applications are presented in the conclusions section.