Failure analysis of a ropeway accident focussing on the wire rope's fracture load under lateral pressure

摘要

AbstractThe bi-cable reversible aerial ropeway had been built as a winch system exclusively for goods transport. During upwards transport the winch was brusquely stopped by the operator. This caused the winch rope to slack and eventually to fracture at the moment of the jerky stretching by the backward rolling carriage. The brakeless carriage sped downhill along the track rope and finally crashed into the lower station leading to the unfortunate death of the farmer sitting unlawfully in the carriage. The steel wire rope (?6mm, type 6×7-FC) showed no indication of the typical failure mechanism of moving ropes, i.e. fretting fatigue. The single wires were broken in almost the same cross section showing a mixture of conical and shear fractures. This unusual fracture pattern could have been either the consequence of a local pre-damage or of an excessive lateral pressure and bending at the cross point of two windings on the winch. The latter alternative was evaluated by a test setup, allowing continuous increase of the deflection angle β until fracture of the rope.As a rule of thumb for β<25°, the deflection angle in degree is numerically roughly equal to the caused load capacity reduction of the rope in percentage, e.g. a deflection angle of 10° reduces the load capacity by approximately 10%. Based on this empiric relationship, along with the calculated critical back-roll velocity of the carriage, it could be proven that the jerkily stretched rope could have fractured without being necessarily pre-damaged.The quantified susceptibility of the rope's ultimate load to lateral pressure at sharp bending can also support future investigations of similar failure cases and risk analyses.Highlights?The failure analysis of a fatal ropeway accident is presented.?The failure mechanism of the winch rope was not typical: fast fracture but not fretting fatigue.?The residual fracture load of the wire rope under lateral pressure due to sharp bending was quantified experimentally.?For the investigated rope type, the deflection angle in degree and the resulting load capacity reduction in percentage are roughly equal numerically.?The dynamic load peak in the jerkily stretched rope was calculated.]]>