An analytical method is presented for a complete study of the thermomechanical bending effects in underground HV (high-voltage) cables, confined in individual ducts, during daily temperature cycles. A segment of cable between two successive manholes is isolated, the structural continuity being maintained by equivalent axial springs at both ends. Up to a certain temperature, the central part of the segment remains completely restrained in the axial direction by the end forces added to the friction between the moving end sections of the cable and the supporting duct. Beyond this temperature, the entire segment moves axially. Cables rigid in bending remain straight, but more flexible ones assume a post-buckling deformed shape under the axial thrust. The resulting displacements, strains, and forces are calculated for evaluation of the cable fatigue. Parametric studies are presented for two typical self-contained cables to assist in the optimum design of underground power lines.
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