×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Deck Collapse in North Carolina
6

Deck Collapse in North Carolina

RE: Deck Collapse in North Carolina

Ron - I believe you have named the cause - fastener failure. The house is 29 years old (per www.zillow.com) and ocean front. Looks like a typical Carolina style beach house. Fasteners used in the 1980's would be hot dipped galvanized nails - nominal useful life of say 20 to 25 years with the harsh salt air exposure.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Deck Collapse in North Carolina

Not knowing anything it seems a fastening issue just given the clean break with no remaining joist structure.

Maine Professional and Structural Engineer. www.fepc.us

RE: Deck Collapse in North Carolina

Quote (ABC News)

Preliminary findings reveal the floor joists and fasteners failed to hold the deck together, Emerald Island Town Manager Frank Rush told ABC News today. Results from the investigation could be released as early as Monday, he said.
http://abcnews.go.com/US/inspectors-investigating-...

Looks like the floor joists and deck all came down together:



Bay that collapsed before photo:

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Deck Collapse in North Carolina

I'm guessing that the joists were sitting on small ledgers which were in turn nailed to the beams. When the nails corroded away or failed in end grain tension, the beam moved laterally to the outside, and the joists just fell off.

RE: Deck Collapse in North Carolina

Hokie - Right you are about the ledgers:



Hot dipped galvanized nails in this salt air / spray environment typically corrode at the junction of the wood members. They will "neck down" at this spot to almost nothing as years go by. Emerald Isle is on the lower end of the Outer Banks, the land is an isthmus only a couple of blocks wide, from the Atlantic Ocean to the (salt water) Bogue Sound. That part of North Carolina gets many close calls from hurricanes and other storms - a constant barrage of salt spray from all sides.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Deck Collapse in North Carolina

It seems that we read about at least one of these a year.

RE: Deck Collapse in North Carolina

Unfortunately, we treat decks (and maybe even balconies, another thread) as if they are a Saturday afternoon, keg of beer with the guys, all owning a hammer and knowing everything, as if they where a simple DIY’er. project. Well... they can fail and hurt people, just like any other structure if not properly designed and maintained. Interior structures need some less maintenance becuase they are protected from the weather. Otherwise, these deck structures need no less attention to design, detail and maintenance than any other structure. We can not keep codifying everything so that just any damn fool can do it, if only he can read the convoluted code and follow it. Building and designing any structure is serious business, and just anyone who owns a hammer and a cordless drill motor may not be qualified to do that work. I don’t have a great deal of sympathy for the know- it-all DIY’er. who builds an insufficiently strong or improperly connected deck, we have determined/allowed that any damn fool should be able to do anything, as long as they pretend to follow the code and pay a fee to the city so they can get a building permit. I think the city should be held more accountable when they supposedly review the plans, collect a fee for doing same, and issue a building permit. I think the old Hannibal rule should apply to these DIY’ers, if you hurt or kill someone, they to join them in their fate. I also think the big box stores should be held more accountable, when they provide some nifty software program which shows the DIY’er. exactly what lumber and hardware the store wants to sell them, and then the fine print says, ‘but we are not responsible for anything.’ I can’t imagine why people don’t shop for heart transplant operations or knee replacements the same way.

RE: Deck Collapse in North Carolina

Hammurabi, dhengr.

RE: Deck Collapse in North Carolina

Construction is like raising kids... you just have to be smarter and have more foresight than your opponent.

Mike McCann, PE, SE (WA)


RE: Deck Collapse in North Carolina

The photo shows nails still attached to the beam, which suggests that the nails didn't fail, and might suggest that it was the wood that failed, particularly if the wood wasn't properly sealed or maintained.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: Deck Collapse in North Carolina

if this continuous the building codes should be revisited

RE: Deck Collapse in North Carolina

IRstuff,
I can't really see the nails, but my eyes are not too good. But nails in the end grain of wood are not very effective even when new. With a bit of corrosion, and a bit of splitting of the wood, they are no good. What I am guessing that happened is that the edge beam rotated due to the eccentric loading and perhaps some lateral load from the people, and the joists just dropped off the ledger. To prevent this type rotation, tension ties are required, and the nails were not good enough.

RE: Deck Collapse in North Carolina

I believe we will know for sure by Monday. This incident was the lead story on NBC's nationally televised news in the USA this evening.

I'm puzzled why the news media continually calls the structure a "deck". In the Carolina's we call what I see a "screen porch". A screen porch has a roof... a deck does not. An ocean front screen porch roof is of no value protecting the fasteners from corrosion by salt air / spray, but does shelter the lumber somewhat. In the 1980's, in the Carolinas, the stringers and decking would typically be treated (0.25 PCF CCA) southern pine. If so, the lumber should be in reasonably good condition.

From the photos, I would say the original 1986 design and construction were above average for the time and location. Meaningful building codes in NC and SC small towns, like Emerald Isle, are an ongoing 21st century development.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Deck Collapse in North Carolina

a bit off topic - I talked to one of my fickle clients (contractor) the other day about the progress of his work re-building the floor framing of a church which had a serious case of the termites. I wanted him to hire us to inspect the work, because I knew it wouldn't be done otherwise. In the midst of that conversation, he had the gall to tell me that he didn't need a building permit because it wasn't residential construction, and that they (the code officials) wouldn't care about the church as much. (!!!!)

Point being: these types of residential structures get build after the initial home construction on such a frequent basis without a permit. Not sure how beefing up prescriptive code will mitigate impromptu decks/porches/balconies without a competent contractor, no permit, and no independent inspection.

Personally, I think the strengthening of criminal statutes in this matter is warranted.

"It is imperative Cunth doesn't get his hands on those codes."

RE: Deck Collapse in North Carolina

Here are 2 solutions.
1.Insurance companies employ inspectors.
2.Homeowners hire inspectors who work for an agency that employes Lawyers.
Otherwise the corruption will continue, through government officials coerced to pass illegal thing just to keep their jobs.
I put up with it for 17 years.If you only knew!!

Inspector Jeff

RE: Deck Collapse in North Carolina

I like your number 1 as an addition to a more comprehensive solution, Jeff. I believe that the solution to these collapses need to come via "small" changes from numerous angles. I think we have a tendency to pick one aspect (design, construction, etc.) and throw all of our weight into it.

"It is imperative Cunth doesn't get his hands on those codes."

RE: Deck Collapse in North Carolina

Hokie:
Thanks, I knew it was one of them thar guys. I’m not quite sure were that came from, what with all the elephants, Alps mountains and all that stuff. I’ll wake up some time later today. I’m still suffering from shell shock from the fireworks yesterday. It sounds like you got it right on the rusted nails.

RE: Deck Collapse in North Carolina

That deck does not look like it has had an ounce of maintenance in years.

RE: Deck Collapse in North Carolina

This appears to the the best picture I've seen: https://lintvksnw.files.wordpress.com/2015/07/58ff... Nails appear on the right side beam, but not the left.


TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: Deck Collapse in North Carolina

So the better detail would have been to bear the joists on the beams, not set them in hangers or nailers.

Mike McCann, PE, SE (WA)


RE: Deck Collapse in North Carolina

Agreed, msquared48. I ask myself: why didn't they simply drop the beam below the joists and pass the joists over the beam in a conventional manner with lap-splices?

Richard L. Flower, P. E., LEED Green Associate
Senior Structural Engineer
Complere Engineering Group, Inc.

RE: Deck Collapse in North Carolina

Here's a close up of a joist end - taken from this video: Video Link - go to the 30 second mark



With nails sticking out up above - it seems like the bond between the nail and joist was such that many simply pulled out of the end grain.
This may not be the initial cause of the collapse - perhaps something gave way in shear and that started a domino effect as the deck joists pulled away from the supporting beam.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

RE: Deck Collapse in North Carolina

Interesting comments made on this thread regarding the use of galvanized nails in this situation. The attachment indicates a recent (2004) change in how pressure treated lumber is manufactured and how this change affects the proper fasteners to be used.

Richard L. Flower, P. E., LEED Green Associate
Senior Structural Engineer
Complere Engineering Group, Inc.

RE: Deck Collapse in North Carolina

>>>It seems that we read about at least one of these a year.<<<

Years ago I made that very comment to a representative of Simpson Strong-tie. He, being more directly involved in that specific corner of our industry, replied, "More like every week." And I didn't get any sense that he was joking or using hyperbole.

RE: Deck Collapse in North Carolina

The ledgers seem to have stayed attached. Maybe they were fixed with different fasteners.

The edge beam rolled when loaded, and there were no nails left to resist.

RE: Deck Collapse in North Carolina

Hokie - I believe the left ledger is gone. Take a look at the enlargement of IRstuff's photo below.

I propose all the corroded nail on the left side sheared (the nails into the ends of the joist and the nails holding the ledger in place).
As the left side of the floor descended the joists rotated downward... pulling away from nails remaining in place on the right.
This explains why no full length nails are visible on the left side, yet the right ledger and full length nails are visible on the right.
The photo JAE furnished, showing nail holes, must be of the right end of the joists.

Here is the enlargement of the left side:


www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Deck Collapse in North Carolina

Continuing with the adventure regarding proper usage of fasteners and connectors engaged with pressure treated wood: I just spoke with a technical rep for Simpson Strong-tie. The general synopsis is that except for more extreme marine environments, they would be satisfied with the specification of "Z-Max or hot dipped galvanized equivalent" for all their connectors and fasteners that are engaged with PT wood and are exposed to such an environment.

Richard L. Flower, P. E., LEED Green Associate
Senior Structural Engineer
Complere Engineering Group, Inc.

RE: Deck Collapse in North Carolina

Seems to be another case where < $100 worth of joist hangers would have kept the thing from coming apart that way.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: Deck Collapse in North Carolina

SRE,
Yes, I agree. That stands to reason, as the exterior one is the most susceptible to the weather.

IRstuff,
No, joist hangers are nailed, so the same corrosion problems exist.

rlflower,
The outer islands of North Carolina, as well as all barrier islands, are an extreme marine environment. Simpson's satisfaction would not satisy me.

RE: Deck Collapse in North Carolina

I will concede to your assessment with regards to the location, hokie66.

Richard L. Flower, P. E., LEED Green Associate
Senior Structural Engineer
Complere Engineering Group, Inc.

RE: Deck Collapse in North Carolina

There is another consideration to look at that can contribute to the fastener corrosion. After manufacturers switched to ACQ instead of CCA for lumber treatment most lumber was treated with ACQD as it was probably cheaper. What most people including reputable contractors weren't made aware of for several years after the switch, was how corrosive ACQD is to fasteners and connectors. While this house is older it is harder to tell the age of the deck, but the lumber doesn't appear to be weathered that bad. Also the story makes mention of 24 family members injured. Overloading may be a contributing factor, with the joists being toe nailed instead of hangered or supported on beams its hard to say if the deck would have held without the corrosion.

RE: Deck Collapse in North Carolina

The connections at the end of the joist shows as two side toenails and one top toenail. Proof not to rely on toenails.

Mike McCann, PE, SE (WA)


RE: Deck Collapse in North Carolina

(OP)
Much better photos!
Looks like the left ledger dropped and allowed rotation that pulled the right side of the joists out from the beam.

The ledgers were installed on the bottom of a double beam, with all the fasteners in tension (however few of them there were). Ledger fasteners should be in shear, not tension. Even if the fasteners did not corrode, it would be easier to overload the pullout in this orientation.

RE: Deck Collapse in North Carolina

I didn't get that, Ron. Looks like to me the ledgers were about 2"x2", nailed to the side of the beams. The one on the right side which was still in place seemed to have nails horizontal.

RE: Deck Collapse in North Carolina

Ron - From everything that I have seen, read, and know (first hand: 50 years+) about SC, NC beach house construction, here's my take on it:

Double 2 x 10 beams, approximately 10' long.
2 x 8 floor joists @ 16" O.C, each approximately 12' long.
2 x 2 ledger with 3 nails under each joist (probably 16d or 20c common). Nails loaded in shear.
Remains of toenails from joists into beams (probably 12d or 16d common).
5/4 x 6 deck boards.

All lumber color and condition (29 years old) consistent with CCA-C treatment.
All nails hot dip galvanized.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Deck Collapse in North Carolina

(OP)
SRE...that's what I would have expected as well except that the right side looks like a solid piece of lumber under the double 2x10's. I see the 3 nails under each joist, as you would expect, but it looks strange. Maybe I'm just not seeing it correctly from the angle or resolution.

I think you'd have to be nuts to construct it as I described above, but considering the amount of bad construction I've investigated over the last 35 years, not much surprises me anymore.

Looking at the band below the sliding glass doors, the left side looks like maybe a 2x12 and the right side narrower and is pieced with a 2x2. Why? That member picks up essentially no load.

RE: Deck Collapse in North Carolina

Ron, I think it is a visual illusion - the 2x2 shadow is farther down the wall, indicating it is protruding farther from the wall than the 2x12. There seems like some anti-pest netting underneath and maybe the little strip was part of that.

RE: Deck Collapse in North Carolina

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.

RE: Deck Collapse in North Carolina

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)


RE: Deck Collapse in North Carolina

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.

RE: Deck Collapse in North Carolina

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)


RE: Deck Collapse in North Carolina

3
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)

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Deck Collapse in North Carolina

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?

RE: Deck Collapse in North Carolina

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.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Deck Collapse in North Carolina

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.

RE: Deck Collapse in North Carolina

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.

RE: Deck Collapse in North Carolina

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)

RE: Deck Collapse in North Carolina

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

RE: Deck Collapse in North Carolina

http://www.usplastic.com/catalog/files/charts/LG%2... seems to suggest that 316 is not particularly good against salt

TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: Deck Collapse in North Carolina

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

RE: Deck Collapse in North Carolina

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources