I prefer to keep the crane outside the building!!! I don't do these types of projects that often, but to park a crane of that size on a bar joist floor system with a thin conc topping seems a bit crazy.
I recently saw this. What I can't fathom is how there are no spreaders. Even when a crane is used on the ground, you have spreaders under the outriggers.
What is even more baffling to me is that the shore does not seem to have buckled. I don't know if it was a case of the shore not being under the outrigger.
The slab looks paper thin to carry anything so monstrous. Does anyone know what really happened?
This is from an email sent out 1 week after the incident (and included the photos in the link):
"Incident: Friday Morning 26/09/08 - Castle Hill/Sydney
- 9 Day Old 250t Leibherr Crane (never used before)
- $4mill price tag
- Failure of back propping beneath the 200mm thick concrete deck
- Crane support outrigger punches through slab causing crane to lose balance and collapse across the site and onto adjoining property
- Crane balanced in the air for approx 1 hour before entire rig & boom collapse completely across site and rigs falls through to the basement level."
Perhaps 'Failure of back propping' means the outrigger loads weren't located over the props, or the props fell over due to slab movement.
I work close to that area, well about an hours drive. Anyway
The slab was a PT slab, it failed in punching shear.I remember when that happened, we were actualy checking another slab for that same purpose! I'll tell you what we doubled checked our calc then added some just to be sure!
From the first picture of the crane on the slab (2nd picture in the article), I thought it was a slab-on-grade.
Then I scrolled down. It appears that the crane fell into the basement area. You can see a basement retaining wall in the background. It seems possible that the operator thought he was on the retained soil side of the basement wall but drove the crane past that into the elevated slab area.
According to a magazine I read recently about this crane punching through the floor,the crane company rep who went to assess the job instructed the client not to use rigger pads so that the load was spread directly onto the supporting columns underneath,wonder if he still works there?
Well, when parked on a slab on metal deck (looks like long span Epic-style deck), the spreader pads wouldn't really do any good, since you want the load to go directly through the concrete into the shoring towers below. From my perspective, this was crazy idea from the begining. But it still could have worked. I find it very surprising that the shoring towers were not laterally restrained in any way. I would have constructed fully braced towers under the crane, with x-bracing in 2 directions to ensure that the shoring towers were fully restrained. This way, any slight movement would not be an issue.
Also, it could very well be that the outriggers were not located directly over the shoring towers, which caused the outriggers to punch through the slab.
Somebody seems to have forgotten to do some basic engineering work. Anybody interested in doing this type of engineering should study Shapiro's "Cranes and Derricks".
