Church Roof Collapse 1

[azcats]

This happened in my neighborhood. Came upon it just after it occurred. Fire alarm was activated and could hear sprinklers pouring water.

Appears the building was unoccupied. I'd seen no recent construction there.

Map Link

 

[Alistair_Heaton]

was there any wind blowing?

 

[TugboatEng]

Is terra cotta roofing substantially more heavy than shingle roofing? Is that something that must be taken into consideration when selecting rafters?

 

[azcats]

Virtually no wind - maybe a light breeze under 10 mph if that.

 

[Alistair_Heaton]

tug they would have included the roofing type in the dead load calculations for rafter specification.

close ups of the rafters and spacing at the failure ends would be nice

 

[azcats]

Let's see if this attachment gives a better pic...

 

[azcats]

#2

 

[azcats]

#3

Not the best pics. All I have

 

[phamENG]

tug - yes, real terracotta is significantly heavier than asphalt roofing and plays a big part in selecting rafters or designing roof trusses. There are synthetic versions, though, that are very light. Judging by the way some of those are hanging there I suspect they may have used a synthetic version...

 

[Alistair_Heaton]

looks like it was a curved internal ceiling.

Thanks for posting the bigger pics.

I am just going to wait with interest for those that have a proper clue what they are talking about to comment.

 

[azcats]

The clay or concrete tile roofs are super common here.

 

[Alistair_Heaton]

I would be very surprised if they don't include it in the dead load calculations.

The lighting rig might not be.....

 

[JohnRBaker]

Is terra cotta roofing substantially more heavy than shingle roofing?

Yes, we have a terracotta roof...

...and in the attic you can see that the roof joists are on narrower spacing than you'd expect and are made from wider boards:

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[EdStainless]

The two light trusses cause me concern.
We have a few of these at my church.
Before we went all digital on the lighting, we were very careful about how many lights we hung.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Alistair_Heaton]

You have beefie Purlins as well John.

Just looked it up.

Clay tiles are @ 50 kg/m2 or 10 lb/ft2

My metal sheet roof I used 10 kg/m2 but turns out its 6kg/m2 or 1.2 lbs/ft2. Me being lazy wanting easy numbers yet again.... And using 245mm x 48mm C24 600mm spacing and greater than 45 deg pitch it was well within limits just looking at them.

Point load in the middle of the rafter from the lighting is not going to be pretty... And above that might cause issues with eigen buckling max span length.

 

[Sym P. le]

Let's see if this attachment gives a better pic...

Excellent pics azcats! I believe they point straight to the problem, which, as Alistair suggests, is buckling.

FWIW, the trusses are parallel chord type (see first truss to the north) with an eave extension. The end of the extensions have pushed hard to the north in a small group of trusses and buckled the sheathing against the northern solid truss (which may be a double truss or could have benefited from additional framing). The seat of the trusses on the west wall appear to remain fixed suggesting appropriate blocking or other connection at that point.

On the ridge beam, a deep steel member with a backing spacer at mid height to stop the truss bottom, a double top plate was applied which held top mounted truss hangers. The top plate appears torn centered on one truss (asterisk), the same truss which oddly has relief cut into the back stop. The torn top plate landed on the truss backing. It seems there is a tab at the bottom of the hangers to fix the truss bottom, there doesn't appear to be any blocking between trusses at that level (and I don't know if there should be). One of the backing blocks is torn (circle) as though there was a vertical load on it or perhaps split as the truss buckled.

The trusses to the south appear to have rotated downward out of their hangars as though they snapped mid span.

 

[Alistair_Heaton]

Everything seems to be pointed towards the lighting rig....

 

[dik]

I'm not in an area where blowing sand is an issue. Do they actually have design loads to accommodate this?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Alistair_Heaton]

I will freely admit 30 years ago I really didn't get buckling...

But 12 months ago I revisited structures for building this bloody barn and went through it all again for designing the roof. And buckling strangely enough, just was logical and relatively uncomplicated to run the numbers on. Not anywhere near the mind screw I remember it as. Just Izz and Iyy and a stability factor with geometry.

Maybe when I am 90 Naiver Stokes will become logical and back of a fag packet....

 

[Sym P. le]

Everything seems to be pointed towards the lighting rig....

It's close to the rig, but not right on it. Modern spots don't abuse structures like legacy spots. Even so, the rigs are hung very close to the truss end at the ridge beam. The ridge beam is boxed out beneath the trusses and may provide the mount point for the rig. I tend to believe a more innocuous flaw reared its ugly head.

Edit: Having said that, I now notice the two truss hangars at the rig locations were also ripped off the top plate and disappeared. I don't see the hanger cables though.