The Interfacial Friction Loss of Prestressed Carbon-Fiber Tendons in a Bending State

Carbon-fiber reinforced plastic (CFRP) is ideal for bridge reinforcement due to its high strength, light weight, and corrosion resistance. Studies on the friction loss of CFRP tendons in a bending state form an important part of advancing the application of CFRP materials to external prestressing strengthening technology. To understand the magnitude and variation of interfacial friction loss of prestressed CFRP tendons under bending conditions, 12 single-bending prestressing tension tests and 4 three-consecutive-bending prestressing tension tests were conducted in this study. Two bending radii of 1.5 m and 2 m, two bending angles of 20° and 30°, and three contact surfaces with different friction coefficients were selected for the steering block condition to measure the friction loss under each stage of tensioning prestress. On this basis, a model for calculating the friction loss rate on the surface of prestressed CFRP tendons was derived for the change of contact stress between CFRP tendons and deflectors during the installation and tensioning stages. The results show that the friction loss of external prestressed CFRP tendons is mainly related to four external factors: bending radius, steering angle, friction coefficient, and the magnitude of tensioning prestress; with the increase of prestress, the friction loss rate goes through three stages, the rising stage, the falling stage, and the stable stage; in the process of friction loss rate change, the main influencing factor controlling the magnitude of friction loss rate changes from bending radius to steering angle. In the theoretical calculation model of friction loss rate, the calculation model of the prestressed CFRP tendons under multiple successive bends can be simplified to a combination of several calculation models for a single bend. This study provides a reference for the engineering field of strengthening reinforced concrete (RC) beams using external prestressed CFRP tendons.

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