Bending-Induced Stresses in Parallel Seven-Wire Strand Stay Cables

The bundled parallel strand stay cables are important structural components of modern cable-stayed bridges. Strands commonly used in modern stay cables are seven-wire greased-and-sheathed strands. Stay cables primarily resist tension loads imposed by various loads, but they also resist bending stresses due to wind loads, vibration, and any traverse load applied on the cable. The movements of the deck and towers (at termination points of stay cables) also impose rotations at the cable ends, which will induce bending stresses in the strand bundles. Calculating and analyzing a stay cable’s bending-induced stresses is an important consideration, especially regarding fatigue resistance. Traditionally, designers have assumed a noncomposite moment of inertia for the bundle of parallel strands because of the presumed lack of sufficient interstrand bond along the length of cables. Therefore, the composite effect is generally not considered, and the moment of inertia is typically assumed to be equal to the number of strands times the moment of inertia of an individual strand. This assumption neglects the fact that unrestrained relative slippage between strands cannot occur because the anchorage plates enforce displacement compatibility at cable ends. Also, deviation clamps and periodic cable bands (tying of the strand bundle together) along the free length of the cable may provide some degree of composite action. This study examines the global bending-induced stresses developed near the termination points of stay cables due to the application of transverse loads on the cable. Experiments and computational analyses are conducted to assess these stresses. The computational models are verified using laboratory experiments performed on a five-strand cable. Detailed and simplified finite-element models are developed. Bending-induced stress calculation procedures are developed using a simplified stay cable model.