Workers rescued after construction site collapse in Glendale

[JAE]

Looks like poor roof joist bracing during erection.
6 workers rescued after construction site collapse in Glendale, CA.

 

[dold]

Looking at google street view it appears that it's all new construction.

1239 S Glendale Ave, Glendale, CA 91205

 

[Sym P. le]

It appears that corrugated roof decking was loaded on the joists. Inadequate bracing would be a good call.

 

[sbisteel]

Too many bundles of deck stacked too early. Trusses look like custom fabrications as well, not a typical SJI bar joist.

 

[Sym P. le]

I see at least two broken lower chords, possibly bolted on site? Although these two highlighted examples do not look to be a cause they may indicate assembly/design issues.

(Edit: also bottom chord section sitting on upper hoist with bolted connections broken at each end.)

 

[hokie66]

What a mess. I don't know how you know which is top and bottom. But no matter, the poor things were not braced, then overloaded. Those breaks look very clean, would be interesting to know the member properties and connection details.

 

[Sym P. le]

I don't know how you know which is top and bottom.

The vertical elements meet the diagonals on the bottom chord.

I see a hint of X bracing between the trusses but nothing that's plainly obvious to me. A failed bolt connection in the lower chord would also make a mess. It would only take one and it might not be identifiable from a distance. If that were the case, a sharp bend would likely occur in the upper chord above the break.

 

[SWComposites]

Looks like a brittle fracture in the chords.

 

[Sym P. le]

Bolted connections, possibly welded on the top chord as well.

I see a lot of tacked tab connections. Perhaps that was how they were temporarily secured. I suspect the foreman will have a lot to answer for.

Also, the bolted connections require field welding of a diagonal in each instance.

 

[Sym P. le]

One truss is missing its end tension web. That can't be good!

Edit: The broken truss could also explain why the trusses to the west were pulled east so as to miss the row of parked vehicles.

Edit 2: There was a "thunderous sound" (FOXY newsh11 LA, report near end of video) immediately preceding the collapse.

 

[Sym P. le]

The "broken truss" is unique in that it sits atop the columnar reinforcing for the passageway and would have to have its seat altered accordingly.

The 3D stereo view helps to illustrate that the similar truss on the east side of the passageway sits just to the east of the columnar reinforcement and would only require a typical seat.

(view facing south)

 

[JLNJ]

Double angle chords 0" back to back with butt joints for the web connection plates? Never seen it done that way.

 

[Sym P. le]

Calamity was obviously not factored into the service capacity of the connecting bolts.

 

[DAVIDSTECKER]

Years ago, a buddy of mine that was an Iron Worker rode one of those decking bundles to the ground when the trusses' failed due to over loading.
Fortunately, it was a single-story strip mall roof and he survived, although his leg required a lot of steel and screws to put his leg back together.

 

[Sym P. le]

It's a difficult jump to say the trusses were overloaded given the design should also support additional roofing materials plus contingencies. The decking was evenly distributed and it's final resting place towards center span may be a result of the collapse. There are a few bundles near the perimeter that may have tipped off their perch rather than start to slide.

I find the broken truss and its conflicted support detail to be of much greater interest. Though mistakes can be made, this is not likely the crew's first install. Fortunately they get to go home and can answer questions later.

 

[IRstuff]

Seems likely to me that one of the multiple cranes in operation crashed into one of the trusses near the center of the space and caused it to fail, which dragged the rest of the trusses with it.

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[Sym P. le]

Seems likely to me that one of the multiple cranes in operation crashed into one of the trusses ...

That's a possibility.

The "broken truss" is also broken mid-span on the top chord (that's got to be difficult to achieve) and wrenched or broken on the bottom chord, again a condition that seems unique to this truss. Other breaks seem limited to bolt fractures at connections on the bottom chord. Otherwise, they just bend like the pretzels they are.

Another possibility is that they moved the truss off the layout grid at the south end to install it beside the obstruction. My understanding is these joists lose capacity quickly when not installed straight.

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