Another deck collapse

[IRstuff]

https://www.yahoo.com/gma/deck-coll...e-injured-043006189--abc-news-topstories.html

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[JoelTXCive]

There was a deck failure in Montana over the weekend with many injuries.

I’m looking at the photo and trying to determine possible failure modes. Here are the observations I see:

1) The joists are running left to right so it’s okay that we don’t see joist hangers on the house ledger board.

2) Why is there a column on the ground? I’m guessing that it was not embedded in the ground. Was it even connected to a footing and was there any lateral restraint? The furthest right column appears ‘kicked out’ at the base, which makes me think the columns are not attached to footings at all.

3) The beams on the furthest right do not appear to be notched into the columns, which makes me think they were mechanically fastened somehow.

Perhaps some sort of shear failure of connectors at the beam column connection led to the collapse? I’m thinking a punching shear type failure at the column?

What do ya’ll think?

 

[IRstuff]

The article mentions sponginess in one corner. I suspect it's the near right corner, whose post appears to be out of alignment with the others.

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[hokie66]

It definitely looks like the connection between the beams and columns failed, possibly because the columns moved away from the deck. Because they wanted the decking to run in the same direction all around, the beam to column connections would have been different from the ones on the left of the picture. Those on the left do seem to be notched into the columns, but I can't see any bolts through the columns, which would be essential to hold it all together.

More pictures would help.

 

[BigInch]

I don't see enough framing (left-right) wreckage under the flooring. If it was there, somebody's done a good job of hiding it. For that span very deep joists would be needed. Were there joists spanning between what appear to look like trusses framing from wall to columms? Looks like the right truss connection to the fallen column broke and the column rotated from top out about its base, falling towards the left. Then the left truss' connection to column broke and it went down.

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1. Write down the problem.
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[Toby43]

Another angle

 

[itsmoked]

Toby's link DIRECTLY POSTED USING THE

.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[hokie66]

BigInch,

They are not trusses, they are timber beams with joist hangers still in place. The joists have been dislodged, but are still mostly still attached to the decking boards.

I can't figure how the beams were connected to the columns, but obviously quite tenuously.

 

[BigInch]

Well that's a lot clearer. Long span for those shallow depth beams.

Some discoloration around the connection. Glue?

Can you walk up a little closer before you take the next picture.

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1. Write down the problem.
2. Think very hard.
3. Write down the answer.

 

[IRstuff]

Another picture

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[BigInch]

Now it looks like the bracing posts are going to fall down.

You don't happen to have a tape measure do you?

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1. Write down the problem.
2. Think very hard.
3. Write down the answer.

 

[John2025]

No visible connectors on the outside of the columns. Beams let in to columns and then what, lagged from the inside because they didn't want to see the fasteners?
The columns are restrained from moving outward by the roof on the section to the left, but not on the section that failed?

 

[Spartan5]

How likely is it that this was just built, and not designed by an engineer?

 

[LionelHutz]

The missing column separated from the beam and all hell broke loose. I'd agree that the columns and beams don't appear to be fastened together properly. The railings are a rather poor design too. The horizontal supports are just "spindled" into holes in the columns and railing posts.

Just glad to read there were no casualties in the linked story.

 

[hokie66]

Spartan5,
I'm guessing 99%.

 

[Ingenuity]

Internal corner connection detail:

 

[LionelHutz]

Is that a ledger board over top of the old ledger board which still has the joist hangers on it? It might have more issues even though it still appears the deck falling off the missing post was the cause.

 

[racookpe1978]

Using the convention established in the original photo for left-right framing members under the deck.

There are three near-square deck sections in the first picture. the primary failure appears to be the right deck square of those three squares. The center and left-hand deck square remain attached at one side, but have also fallen as their beams moved to the viewer's right when the furthest-right deck square failed. All three deck squares remained "near intact" as they fell = The deck boards were sutiably fastened to the deck joists, but the joist-to-beam connections failed.

Now, look at the furthest right deck square in the lower pictures.

The left sides of the left-right under-deck joists are fastened into a series of box-store "standard" deck joist attachments to the deck beams. The right side of those same joists are attached with "nothing visible" (no pulled out nails, no screws, no joist hangers, no tenons, no cut-in notches ...

What is the UBC Code rating for "magic" fasteners?

I suspect the right-most deck square was held by the deck boards being supported by the small board still attached to the deck beam. The load was carried from (unattached) deck joists to rightmost deck board, which was held up by the board still nailed to the beam.

 

[hokie66]

racookpe,
A chain of optometrists here has a commercial "Should have gone to Specsavers".

The joist hangers are still on the beam.

 

[LionelHutz]

The left sides of the left-right under-deck joists are fastened into a series of box-store "standard" deck joist attachments to the deck beams. The right side of those same joists are attached with "nothing visible" (no pulled out nails, no screws, no joist hangers, no tenons, no cut-in notches ...

Joist hangers are clearly visible on both the left and right beams of that deck section in the last picture IRstuff posted.