Carbon Fiber-Reinforced Polymer (CFRP) Tendons Subjected to Combined Axial Load and Harping

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Title: Carbon Fiber-Reinforced Polymer (CFRP) Tendons Subjected to Combined Axial Load and Harping

Author(s): Shuaib H. Ahmad, Carl V. Jerrett and Paul Zia

Publication: Special Publication

Volume: 172

Issue:

Appears on pages(s): 427-444

Keywords: Anchorage (structural); bending; carbon; fatigue; fibers; plastics, polymers and resins; prestressing

Date: 12/1/1999

Abstract:
The expanded use of fiber reinforced polymer (FRP) tendons as prestressing and post-tensioning tendons requires that these tendons be subjected to high axial loads while bent or harped around a curved surface. This paper describes the behavior of one type of CFRP tendon when subjected to combined axial loading and harping. Four test series to study the tendon fiber strain distribution and seven test series to study the tendon ultimate strength were conducted. The tendons were subjected to various combinations of axial loading and harping around a curved surface. Test parameters for the ultimate strength tests included tendon axial load, bend angle, and curvature of harping point. Harping points were set to either 1 in. (25 mm), 5 in. (127 mm), or 20 in. (508 mm) radius. Ultimate strength tests included static strength tests and fatigue tests. Results of the static tests indicate that at failure, the flexural strains at harped point far exceed the average fiber strain recorded in uni-axial tensile strength tests. The flexural strain is defined as the difference between strain readings from a 0.125 inch (3.2 mm) strain gage placed on the tendon bend outside face and the tendon average axial strain. No flexural strains were observed away from the tendon bend beyond about 6 in. (152 mm). Based on the tests, an expression for the tendon flexural strain at harped point as a function of axial load, bend angle, and harping plate curvature was developed. This expression for flexural strain at harped point was used in a maximum strain failure criteria model that accurately predicts the failure of specimens tested in this research. The results of the fatigue testing indicated no degradation of tensile strength due to fatigue loading.