15 December 2010

Why you need to check the bearing capacity – the Waikato crane accident video

Posted by Dave Petley

This accident occurred last week in Waikato, near to Auckland in New Zealand.  The crane is a 200 tonne Terex All Terrain machine.  It was lifting one of the sections of a new foot and cycle bridge into place when the embankment upon which one of the crane footings was located slipped under the load, sending the crane toppling over:

A series of photos before and after are available here. This one in particular shows the slip after the event:

The morphology of the slide is interesting.  Note the extensional cracks running across the surface.  This is quite unusual, probably resulting from the rather unusual failure mode of essentially point loading at the top of the slope.  Second, the materials look weak and wet, such that I am surprised that the footing was located so close to the crest of the slope.  Locating the footings in such situations is always difficult though.  Finally, the bridge section was swinging, which will have applied a dynamic load.

The driver was not seriously hurt.  His final actions as the crane tipped of turning the crane so that he facing upwards were well-judged.

Comments and thoughts?