Saskatoon Hollow-Core Building Collapses during Construction

[Craig_H]

Link: CTV News

Looks like a bit of confusion in the news about this one. The above article lists the building as "industrial", yet it looks a lot like an apartment to me. The video seems to show a failed connection between the stair/elevator core (tilt-up?) and a steel beam, which precipitated the progressive collapse of the hollow-core planks down five stories.

 

[Sym P. le]

The empty bolt holes suggest the connection was not completed before the beam was loaded. The beam web also look torn, which is odd.

 

[Cool_Controls]

Are those Nelson studs on the top of the beam?

 

[Sym P. le]

Yes. It looks like something dropped down from the top level and punched out the lower levels, thus the damaged beam. I've no experience with these but I believe the system is tied together with a combination of rebar, grout and a topping mix.

 

[Tomfh]

The empty bolt holes suggest the connection was not completed before the beam was loaded.

Could be, however they often drill holes at beam ends regardless, for the sake of repetition. Judging by the torn web and damaged concrete, it is possible that an extended cleat was welded to the web, which reached across and was anchored to the concrete structure?

 

[Sym P. le]

That makes sense. It looks like it experienced some unintended loading.

 

[Craig_H]

Most interesting to me was that the failure precipitated a progressive collapse. Perhaps it makes sense if all the steel was hanging on its erection-only connections and hadn't been fully bolted up, and none of the lower stories had been grouted. Progressive type collapse is supposed to be mitigated (NBCC 4.1.1.3), and if I'm not mistasken, the failure of one beam end connection would be considered sufficiently minor that alternate load paths should mitigate the progressive collapse.

I haven't worked with hollow-core, so I am interested to learn whether it's routine to go up five stories without grouting the panels? I should think that if the lower stories had been grouted, that the resulting bond beams and composite action with the supporting steel might have prevented the collapse of the lower floors.

 

[jayrod12]

In our hollowcore projects, going up multiple floors without grouting has been requested, but never approved. I believe the most we've allowed them to go up without grouting was 2 floors. Otherwise you have no path for the lateral loading to move around to the resisting systems.