Date of Award

May 2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Habib Tabatabai

Committee Members

Rani Elhajjar, Devendra Misra, Yongjin Sung, Hua Liu

Keywords

7-Wire Strand, Bending Stress, Finite Difference Method, Finite Element Analysis, Stay Cables

Abstract

Stay cables are the most important structural elements that support a cable-stayed bridge span. Although stay cables are primarily tension elements, they are also subjected to bending stresses due to the application of transverse loads on the cable, end rotations due to the deck and tower movements, and cable vibrations. Due to their potential impact on fatigue, bending stresses are an important design consideration for stay cables. Most modern stay cables are composed of parallel 7-wire greased-and-sheathed strands that are bundled together. The individual 7-wire strands are splayed out near the anchor heads at the ends of the cable, and each strand is terminated at a specially designed wedge-socket system at the anchorage plate. Traditionally, designers have assumed that the strands form a non-composite bundle due to a lack of sufficient bond between strands along the length of the cable. This assumption ignores the fact that relative slippage between strands (needed for full non-composite action) cannot occur at the anchorage (i.e., compatibility of deformations is enforced at the cable ends even though the strands are not in contact with each other in the transition zone). The governing design standard for parallel strand stay cables in the U.S. (PTI DC-45), as well as industry practice, considers the apparent angular rotation as the only parameter influencing bending stresses in stay cables, while the influence of cable size and length is not considered. In this study, the development of bending stresses in stay cables is examined through experimental and computational models. Simplified calculation procedures for bending stresses are proposed. The computational models and the proposed calculation procedures are verified using laboratory experiments performed on single-and 5-strand cables. The bending-induced stress generated in each strand is proportional to the average eccentricity of that strand from the centroid of the cable within the transition zone (between anchorage and tension ring). Bending stress is also proportional to the rotation angle within the transition zone (θ) and is inversely proportional to the cable length (L). Furthermore, there is an axial stress increment due to the elongation of the cable under load. Therefore, the commonly made assumption that rotation angle alone can represent the bending stresses in a stay cable is not valid. Bending stresses for a given angle change can be substantially higher in shorter cables with many strands.

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