February 8th, 2012

Picture from RMF24.pl

Rzeszow, Poland. A tower crane with the classic Potain Arrow on the counter jib suffered a structural failure between jib section #1 and 2, possibly exclusively on jib section #2. The cause of the failure is not noted. Fortunately no one was injured in the accident. I find it incredibly important to note that the operator was "sober" as noted in the article. (I find this amusing as if drunkenness would be normal or a likely cause of a crane accident as if he were driving on snow. Not that it's likely as a cause, but I suppose a lapse in judgement has been known to occur during alcohol consumption.)

This is an interesting accident. The pendent is fully connected still. Jib section #1 is still aloft. Yet when you look at the end of it, you can see that the chord splices have ripped, presumably at their welds or just adjacent to them. Chord construction is commonly large angle iron pieces welded together for form a square member. At the ends, the splice connections, be they male or female, are welded on. If the welds at this point were not looked at since they are not obviously noted as welds in a cursory glance, a strong load sitting on this splice could easily cause a fracture of the lower chord splice welds which would then rip the top chord, as it has done, and the trolley would be missing from these pictures as nothing would be present to hold it up to be visible. Additionally, note the cables (ropes) appear to be broken near the weld failures indicating trolley placement.

Certainly wind could have played a role, as well as side loading. Side loading is less likely to be a cause this far in on the boom as leverage is severely reduced and the slewing motors would have a difficult time causing this damage at a 10 meter radius. Wind is also commonly caused with the trolley farther out. See this South African accident as an example.

I feel confident that this was simply a structural failure. We have an older model of crane and I would ask, who is looking at this crane? When they inspected the boom, did they look at those welds, especially underneath the chords? Normally these jibs are flat on the ground and a mirror would be necessary to do this. Inspect your welds regularly. I have my jib walked monthly at a minimum. We spend an hour going through the jib, trolley and ropes. Obviously I look that the easily reachable items daily. You too should take the time to look over each weld. You'll find nothing 99 times, but that 100th time you may save your own life.