Metal Ceiling - partial collapse

Just run the numbers on smooth-shanked nail withdrawal to see what’s plausible. It doesn’t matter whether the ceiling itself can bear the insulation if the connections themselves are inadequate. You don’t mention a truss spacing, but if it is truly the case that only 3 nails affix the furring at each truss in sustained tension, then this failure is unsurprising. Insulation doesn’t look blown about, so there must be something else that’s making you think about wind. Are the downspouts ripped off? Is the roof covering removed at the corners, etc? Are there any large windward openings that make you think the building was inflated?

ANE91 said:

Just run the numbers on smooth-shanked nail withdrawal to see what’s plausible. It doesn’t matter whether the ceiling itself can bear the insulation if the connections themselves are inadequate. You don’t mention a truss spacing, but if it is truly the case that only 3 nails affix the furring at each truss in sustained tension, then this failure is unsurprising. Insulation doesn’t look blown about, so there must be something else that’s making you think about wind. Are the downspouts ripped off? Is the roof covering removed at the corners, etc? Are there any large windward openings that make you think the building was inflated?

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Thank you, ANE91. I have no reason to believe it is wind. Good observation on your point that the insulation is not disheveled. I definitely saw no signs of wind on outside of building. Trusses are 6 feet apart so I highly anticipate failure in nail withdrawal once I run the numbers. Thanks again!

Well if I'm looking at this correctly, some of your bits of 2 x 4 battens were jointed at a truss by your three nails both into the same truss butting up to each other.

The whole installation looks very poor and how anyone expected that to last is just asking for it. You've actually got a decent dead load so add on any wind load this will be your weak point. Lose one connections and the rest will fail rapidly.

Use screws.

While is not my specialty.
#1) what is the main cause of failure.
List of possibilities.
I not a fan of nails worked on projects bearing load would be lag screws.
Or bolted joints . I talking out my rear end but
Lost pre load added to loss of friction and appling loads to the nails shear and tension.
Is there possibility of wind causing vibration and moments on the joints?

If those are 10d nails, that would be my first concern. They look bigger to me in the pictures but if they are 10d, they also look like 10d CC rather than 10d Bright Common, so not a lot of diameter. I still have to wrap my head around Box Nails, CC Nails and Bright Common all having different diameters for a given penny weight.

Also, there is a little extra collateral load from fixtures, lighting and other items. Add just a little wind intrusion as mentioned before and all these little pieces add up. The marginal nail size most likely could not handle it. It would not have to be a lot of wind to create an additional pressure of 4 to 5 psf. It probably pulled one or more of the 2-nail areas loose, then load transfer took it from there.

Your 5th picture has 3 nails, but one of them looks like a Bright Common and the other 2 look like CC. Note the difference in the diameter. Wonder if they already had a problem before and the Common was the repair.

One other oddity and poor practice was making joints on the same truss, not staggering them. They must have done a poor job of joining them because each 2x4 at a joint would have the same number of nails holding half they weight as compared to a continuous joint with just 2 or 3 nails for twice the load. I assume the lumber was 12' since the trusses were spaced 6' oc.