Thread: Deck Collapse

I don't know if this is appropriate to post in this fashion, however, credit is given to the photographer and all involved in this catastrophe.
And, seeing as how this is (in my view) an educational forum, I feel that we can all bebefit from this situation and possibly fine tune our radar when evaluating similar structures.
This collapse happened over the Memorial day week end when about 70 guests of a wedding reception rehersal gathered on the deck. Two are still hospitalized and fortunately there were no fatalities.

The link to the news story is here
No structural problems in Pawleys Island porch collapse
The link to the slideshow is here.
PHOTOS: Pawleys Island deck collapse

I uploaded the pictures as follows:

1. Danny Mercer of the structural engineering firm Stantec examines the condition of the deck at 304 Atlantic Avenue in Pawleys Island. Temporary steel columns have been installed for support.

2. Danny Mercer of the structural engineering firm Stantec examines the condition of the deck at 304 Atlantic Avenue in Pawleys Island. Temporary steel columns have been installed for support.

3. Temporary steel columns have been installed for support to stablize the remaining deck and railing.

4. Jeff Tanner a structural engineer with Stantec points out a weakness in the way the deck support beams were anchored to the framing.

5. Floor boards from the collapsed deck can be seen hanging down on the south side of the house at 304 Atlantic Avenue in Pawleys Island.

6. The street-side view of 304 Atlantic Avenue in Pawleys Island. The deck that collapsed is on the right side of the house.

7. Georgetown County Building Inspector Robert Cox points to rusted bolts in the center of the deck support beam that broke causing the deck to collapse at 304 Atlantic Avenue in Pawleys Island. He suspects that the bolts may have weakened the beam and contributed its failing.

8. Robert Cox, Georgetown County building inspector, pointed out that the deck had been nailed to the framing of the house instead of bolted through it.

All pictures are credited to TOM MURRAY tmurray@thesunnews.com

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Victor,

Interesting comments, based on the headline of no structural problems:

(underlining is mine)
"Georgetown County building inspector Robert Cox told The Sun News of Myrtle Beach on Wednesday that the report showed there were no structural problems with the house, built in the 1950s."

"Jeff Tanner a structural engineer with Stantec points out a weakness in the way the deck support beams were anchored to the framing."

"Georgetown County Building Inspector Robert Cox points to rusted bolts in the center of the deck support beam that broke causing the deck to collapse at 304 Atlantic Avenue in Pawleys Island. He suspects that the bolts may have weakened the beam and contributed its failing."

"Robert Cox, Georgetown County building inspector, pointed out that the deck had been nailed to the framing of the house instead of bolted through it."

Here is the headline "No structural problems in Pawleys Island porch collapse."

Am I missing something, or do the statements reflect a different headline should have been used?

Maybe they meant "no structural problems found in the part of the deck that did not collapse."

Headlines are frequently truncated by editors for a variety of reasons, including reasons that make no sense.

Dom.

It seems that the AHJs are attributing the collapse to factors such as;

At the time of construction, the '50s, approved methods of construction were used.

The proximity of the structure to a "salt air" environment accelerated the wood decaying process.

Of course, the official reason being given is the 40Lb PSF load design and the 70+ people on the deck at the time.

Salt air does not decay wood, Nor does salt water. Thats why you find drift wood on salt water and none on fresh water.
It does however cause heavy rust. As indicated by the rusted bolts.

Originally Posted by Victor DaGraca

Of course, the official reason being given is the 40Lb PSF load design and the 70+ people on the deck at the time.

That looked like about a 10' x 20' section.

That's 200 sf x 40 pounds load per sf, or 8,000 pounds load divided by 70 people equals 114 pounds per person average.

Let's same an average between men and women is 140 pounds, that would put the load at 9,800 pounds.

You mean the 40 pounds per sf was not the safe building capacity, but the failure point capacity? No safety factor built into that code?

The local official probably know the owners, and, it they said there were structural problems, the attorneys would be on them like flies on $hit, which, of course, they will be anyway. The attorneys will simply start by pointing out what I did, and it will go downhill from there, with the homeowners in$urance footing the bill to the maximum coverage limit.

When you rent a house like that out to parties like that, you need to make sure your in$urance coverage has a high limit, least you have to dip into your wallet and your future income.

I have to go with 'attachment' being a primary problem.
- I looks like the deck collapsed for the outside (railing) end first down towards the house.
- I also looks like the entire system was built as sections. "let's build this one section because the lumber size is easy to handle, then another and another and nail them together". I see this method sometimes on larger decks. It's a good method when covering a roof that may needs servicing at some point but I am absolutely against it in decks as depicted.
- Each deck section tends to 'float' somewhat independently of the others because no one ever properly bolts the sections together to make one continuous run.
- It looks like support and attachment at the railing end are the real culprits here.
- I can't tell what size the joists are from the picture.
How many more news stories do we have to see like this before people stop cheaping out on deck design and maintenance? Every year there's a few.

Porch safety concerns - Local - Myrtle Beach Sun News

"The breaking point was the extra weight of about 50 people standing in one area of the porch, Cox said.
"It gave way like a trap door in the middle point," Cox said. "The age [of the lumber] and the weight on top were contributing factors."
Cox estimated that the area that collapsed could hold about 4,000 pounds.
The combined weight of people and porch furniture would have brought the weight in one area to around 10,000 pounds, he said.
Other remaining support beams under the porch are beginning to crack, and there are more rusty nails in the boards, according to engineers inspecting the house."

"The outside wall began to twist when the porch collapsed, Cox explained.
Metal braces are now supporting the outside wall and the structure is not in danger of falling, Tanner said."


From looking at picture #5, it looks like the porch roof is being supported by columns that rest on the porch's rim joist. From the way one of the porch support columns splintered (pic#7) It looks like these people were extremely lucky that the roof didn't come down on them.

There are a lot of these homes built on piers around here, everyone wants a deck. One of the engineers is recommending that homeowners have their homes evaluated twice a year.


"Cox is urging homeowners and renters to have their homes inspected by an engineer at least twice a year to ensure the structural integrity.
"You can get too many people and this is what can happen," he said. "An engineer could come close to giving you a maximum weight limit for your porch."

Sounds like overkill to me......

Nobody asked but those red steel posts are rescue equipment. They are not steel but rather air craft grade aluminum. They are rated for 40,000 lbs in a vertical orientation and 18,000 pounds in a horizontal orientation.

They are extended by pressurized air and then a pin is inserted. The air is released and the pin holds the two portions of the post. There are a wide variety of ends that can be put on the posts depending on the particular use. The ends are held in place with a pin similar to the pin to hold your trailer hitch to the receiver hitch. Ends include swivels, flat, u clamp, spikes, and etc.

They posts come in a variety of lengths as short as 18 inches up to 8 feet in closed position. They open to about 6 inches less than double their closed position.

They are known as "Airshores" and the FEMA USAR (Urban Search and Rescue) teams that respond to such events as 911 have a wide assortment of them.

Rescue squads use them in a horizontal position to support the walls during a trench rescue. They are used in a vertical position to support buildings during building collapse rescue. They are used in a diagonal position to support cars and truck during vehicle rescue.

They are not your standard steel columns from the box store.


Picture from inside of rescue trailer. Airshores stored on right side


Airshores in use during a trench rescue. These are older models and are not red, just natural aluminum.


Here is an example of how they might be used in vehicle stabilization


3 airshores with a special adapter plate used to form a tripod during a confined space rescue training inside a fuel tanker.

The way that deck collapsed leads me to believe the deck boards had rotted with age, especially the ones near the exposed to the weather outer edge, plus the ledger does not appear to be bolted. Deck construction has always been a Darwinian example of thinning the gene pool of folks who fail to see any danger in over loading wooden balcony decks, cocktails in hand, no matter what age or condition the deck may be?

I'm pretty sure, by the pictures, everything was undersized as well. Old building codes/standards, as well as beach construction contributed as well. Notice it was only a 2x4 attaching the deck to the house...and with 50 people on it, all it needed was 1 board to break and the rest go easier. Just like tearing a phone book in half, it only take a small start.
On a "lighter" note, Jerry, I'd like to know where you find the average weight of men and women in a mixed crowd to be 140 lbs.! In South Carolina too? I'm thinking by one trip to the local Walmart you'd up that by about 30 lbs. Europeans may be in shape, we Americans are all getting fat and lazy (on the average.)

That deck looks rotted just by looking at the deck boards.

To say "salt" water does not rot wood? Water and age rot wood. Gets wet, dries out, gets wet, dries out. The salt rust nails and bolts and hangers.

Just nailed to the house framing. Gees. This is a prime example of a combination of shoddy workmanship, age and poor maintenance all rolled into one.

It's hard to analyze looking at a few dinky pics, but I find it telling that the section of the deck attached to the home stayed put, and the failure occurred near the outer edge. I don't exactly buy into the weathering theory as regards the rim joist since the outer support appears relatively intact. In other words, the damage there appears to be more likely "collateral damage" than the cause of the collapse. I suspect that the crowd gathered near the outer edge (maybe to look at something) and added more concentrated weight there than the structure could handle. Since the joists ran parallel to the outer support posts, they were not much help transferring the load to the support columns or rim joist. So what you were left with was only the floor joists under the (over)loaded outer section to bear all the load -- a bad thing only exacerbated by poor connections to the adjoining sections.

Hey...it's just a guess. I'm no engineer.