Deck Collapse in North Carolina 6

[Ron]

Another wood structure collapse. This one has clean drop at joist buckets. Hmmmm.....fastening issue perhaps?

News story notes it as a "balcony collapse"; however, it is an elevated deck.

Deck Collapse

A photo is attached as well.

 

[charliealphabravo]

The ledger looks like a 2x8 laid flat against the bottom of the beam. It looks like the ledger is toenailed to the beam since no fasteners are visible in the bottom face of the ledger.

 

[msquared48]

Considering the first picture posted and slider less comment about the left rim...

1. Where is the left rim in the first picture? Had it already been removed or lost?

2. I wondering if the lower corner was hit looking at the vertical misalignment of the top to bottom columns. May have been constructed that way though.

3. If the section just dropped vertically, why is the handrail damaged?

Something else happened.

Mike McCann, PE, SE (WA)

 

[charliealphabravo]

The story says as many as 24 people were injured. It also says that they were posing for a picture which means that they were all probably crowded into the corner or one end of the deck. Ignoring the construction issues that is getting pretty close to the load capacity for a residential deck. When I see that first photo that sliderule posted and imagine it supporting 25 people I get a little sick inside.

 

[msquared48]

So, are you saying that 24 people got decked at once?

Seems ridiculous that posting the deck capacity in terms of the number of people would become necessary to shift liability from the designer, but maybe it has come to that with idiots presently in this system of things. It most certainly not have prevented this accident, but certainly have distributed the liability.

Mike McCann, PE, SE (WA)

 

[SlideRuleEra]

The Town of Emerald Isle has issued their final report. Most of it concerns the first responders performance. There is a letter
from the County Building Codes Administrator that has his investigation results:

Double 2 x 10 Beams, 10' Long​

2 x 8 Joists @ 16" o.c., 8' 6" Long​

2 x 2 Ledgers Nailed to the 2 x 10 Beams​

"Collapse is a Result of corroded fasteners"​

The complete report is attached below (.pdf, 19 pages, 8.8 MB)

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[wannabeSE]

Thank you SlideRuleEra
The Building Codes Administrator reported that the nails appeared to be galvanized. Would this typically indicate hot dipped galvanized, or could it mean electro-galvanized nails?

 

[SlideRuleEra]

wannabeSE - Since the incident took place in coastal NC, he was referring to hot dip galvanized.
HDG nails are widely used there, because of corrosion, and more available than inland.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Guastavino]

I vacation at the beach in NC once a year. A couple years ago a deck collapsed at Ocean Isle beach (not far from this one). The environment out there is harsh. You should see people's outside air handlers. They, and really everything that is outside gets corroded quickly. I remember that the zipper on a bocce ball set that was stored inside, albeit not in a conditioned space was corroded. I don't know the solution for this type of environment other than providing a mechanism of failure that is visually evident prior to failure. I think Simpson hanger connections (top flange ones) would be a better solution. Maybe even coat the fastener's with a better coating than the hanger. That way when you see the hanger corroding you know it's time to do something. Because you won't see the fasteners fail, but you might see excessive corrosion on a hanger.

Honestly, I don't know how you engineer this. I think this is like the folks that have a water heater in their attic. You replace it every 10 years whether you need to or not, because you sure don't want to wait for it to break. Problem is that most all of the houses in the worst environments in these areas are rental properties where the owner wants to do as little as possible in maintenance, and I can't blame them for that.

 

[hokie66]

As SRE pointed out in the other thread, 316 stainless for connectors and fasteners is a big step up from what has been done in the past.

 

[boo1]

Hokie66 316 fasteners were very rare in residential construction 30 years ago.

Comments:
Looking at the pictures I don't see how anyone can determine what was galv was used (if any). In the 1980s Hot dip Galv was not always used on coastal decks.
Loading 24-26 people on the 1/3 western corner of a 8'6x10' deck overloads the structure (I believe the SBC used 40 PSF in the 1980s)

 

[charliealphabravo]

Isn't that black stain in the wood at the fasteners caused by leaching/oxidation of the zinc coating?

 

[IRstuff]

http://www.usplastic.com/catalog/files/charts/LG CC.pdf

seems to suggest that 316 is not particularly good against salt

TTFN
faq731-376

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[boo1]

Charlie, looked like they were rusted away in the ledger
IR, 316 is very good in marine environment, chart has mistakes

 

[hokie66]

boo1 is correct. The chart says that 304 is better than 316, which is obviously incorrect.

boo1, I know that stainless fasteners are relatively new. I was just making a suggestion to the poster before me.