E0

where E0 is Young's modulus of the straight cable, g is the weight of the unit length cable, I is the horizontally projected length of the cable, and a is the tensile stress in the cable [1]. Although this

TABLE 26.2 Types of Suspension Bridge Cables

Name

Shape of section

Structure

Parallel wire strand

Wires are hexagonally bundled in parallel

Strand rope

Six strands made of several wires are closed around a core strand

Spiral rope

Wires are stranded in several layers mainly in opposite lay directions

Locked coil rope

Deformed wires are used for the outside layers of spiral rope

Source: Okukawa, A., Suzuki, S., and Harazaki, I., in Bridge Engineering Handbook, CRC Press, Boca Raton, FL, 2000, with permission.

TABLE 26.3 Mechanical Properties of Steel Wire Cable

Type Void ratio (%) P/NSa Elastic modulus (MPa)

Strand rope 35-42b 0.80-0.85 1.35 x 105

Spiral rope 23-25b 0.9 1.55 x 105

Locked-coil rope 10-14b 0.9 1.55 x 105

Parallel wire strand 11-14b 0.95-0.98 1.95 x 105

a P rupture load of strand, S: tensile strength of a wire, N: number of wire. b Value for a circumscribed hexagon.

reduction of the stiffness is practically negligible in most cases, it must be properly considered for a very long cable or during some construction stage.

The sectional area of cables is determined on the basis of the maximum cable tension. The safety factor of structural cables has been normally 2.0 to 2.5 for the guaranteed tensile strength, while that of main cables of long-span suspension bridges may be a little lower. This depends on the ratio of the dead load stress to the total stress, the nature of secondary stress, and the existence of fatigue stress.

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