Failure of giant wheel ride at an amusement park

Abstract

A Giant-Wheel ride at an amusement Park in Lahore (Pakistan) fell on the ground killing three school children and injuring twice as many. It was of great concern that the giant wheel ride, after its installation, was operational for only two months before it broke. The unfortunate incident took place when the central cantilever shaft, which held and drove the giant-wheel in a vertical plane, was catastrophically broken. The examination of the broken shaft showed that it was a typical Fatigue fracture that had initiated at a ‘step’ on the outer diameter of the hollow shaft. This step which was basically a sharp change in the outer diameter of the shaft, machined out to match the size of ball-bearing, had acted as a stress-raiser. A closer visual examination of the fracture surface further indicated that the shaft had primarily been subjected to high nominal loading. Detailed calculations showed that even if no stress raiser step was present, the section of the shaft was ‘merely sufficient’ to stand the bending loads applied on the shaft when the ride was fully loaded.