Performance of carbon fiber reinforced polymer (CFRP) tendons and their use for strengthening of prestressed concrete beams

The purpose of this study has been to investigate the performance of Carbon Fiber Reinforced Polymer (CFRP) tendons in the exterior post-tension strengthening of prestressed concrete beams. The first phase of this study involved the testing of 0.32 in. (8 mm) diameter CFRP tendons subjected to uni-axial loading, combined axial loading and harping, bending-tension fatigue loading, and sustained loading under combined axial load and harping. Test results indicate that increased strains associated with harping are confined to a length of about 12 in. (305 mm) of the tendon. Failure at the tendon harping point is associated with a maximum fiber strain of 0.0216, which greatly exceeds the highest reported uni-axial ultimate strain of 0.015. Based on the tendon strength tests, an analytical model was developed that accurately predicts the conditions at failure for tendons subjected to combined axial load and harping.;The second phase of research included both experimental and analytical evaluation of steel prestressed concrete beams subjected to exterior post-tensioning using CFRP tendons. Experimental work included ultimate strength tests of six 8 x 16 x 216 in. (203 x 406 x 5490 mm) steel prestressed concrete beams. Four of the beams included two 0.32 in. (8 mm) diameter CFRP tendons that were externally post-tensioned between each end of the concrete beam and draped at two locations symmetric about the midspan of the beam. The analytical evaluation included the development of an iterative computer analysis that predicts the exterior post-tensioned beam performance. This analytical model is used in a limited parametric study that investigated the influence of material and geometric properties on the performance of prestressed concrete beams subjected to exterior post-tensioning with CFRP tendons. Results indicate a substantial increase in ultimate strength and stiffness of beams resulting from the addition of external post-tensioning.