Calculating the useful life of a multistrand spiral rope

The DSB Wire Rope Regulations require that rope fatigue strength be calculated on the basis of the highest stress to which the outer strands or wires are subjected. However, in the case of multistrand spiral ropes we know from experience that the high pressure between outer and inner strands results in greater stress upon the wires of the inner strand layer than upon those of the outer and thus premature fracturing of these. To allow for this the track cable is paid out slightly at fixed intervals from the mountain terminal, so that those sections lying on saddles and round deflection sheaves are shifted from the region of added strain, in which the required fatigue resistance cannot be guaranteed .Calculation of rope fatigue strength is not fully covered in the DSB. In assessing total dynamic stress, however, the engineer may take into account any number of stresses occurring, provided these cannot be avoided by other measures, e.g. choice of a different rope design [1].