Balcony Collapse in Berkley, CA 37

[MJB315]

See link:

http://www.latimes.com/local/lanow/la-me-berkeley-balcony-collapse-20150616-story.html#page=1

"We shape our buildings, thereafter they shape us." -WSC

 

[boo1]

looked like the joists were rotten

 

[Robbiee]

The reports say: they were 13 people on the balcony and the balcony is 5ftx10ft, so the live load is about 40-50psf. Normally, balconies are designed for 100 psf, so overloading was not the problem. Were they jumping? or was the structure deficient?

 

[jayrod12]

The reports say: they were 13 people on the balcony and the balcony is 5ftx10ft, so the live load is about 40-50psf. Normally, balconies are designed for 100 psf, so overloading was not the problem. Were they jumping? or was the structure deficient?

Key word, normally, I've also heard more than one engineer argue that since they are off of a 40psf design load suite that the balconies can be designed for 40psf. I don't do that, but I know some who do.

 

[BUGGAR]

Another engineer said water penetration caused dry rot in the framing. I thought dry rot was fungal and not water caused?

 

[manstrom]

Damn shame.

These wood cantilever balconies scare the crap out of me for this reason. All developers want to do them, but there is no redundancy and a failure is sudden.

To avoid water infiltration issues, we typically just cantilever 2 PT beams, one at each end. No repetitive for redundancy.

And that would be a 60 psf live load per code. Not 100. You could argue 40.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[jimstructures]

Buggar,

Speaking as a non-botanist or biologist, but as a 6 year forestry student, all rot is fungal in one way or another. All rot needs water to become established, some les some more, but dry rot after it is established will proper and continue to grow and spread and degrade the wood with just a little moisture in the air or frequent applications of environmental moisture.

Jim

p.s. Those broken wood ends looked wetter than dry rot but may have been dry rot anyway. Hard to tell with out close examination. the lawyers will have a field day and well they should.

 

[tstructural]

I think the code allows 60 psf in residential but I always use 100 psf for all balconies. We don't know the size of the people but if we assume 175 lbs/person it's still only 45.5 psf. Bouncing up and down in unison can of course amplify the loads but it still doesn't seem like it was overloaded per code. I'm sure we'll find out after the investigation is complete.

So sad for their families.

 

[Jerehmy]

Dry rot is a misnomer. Wood doesn't rot when it's dry.

Shouldn't have failed if it was designed for 40psf. Wood has an average safety factor of 2.5.

Bouncing up and down would be like an impact loading. Wood is 2x stronger for impact loads. They'd have to bounce up and down with the same frequency as the floor joists to get some resonance.

Regardless, what a shame. Someone f'd up and 6 people had to pay the price with their lives.

 

[boo1]

substandard waterproofing
Why would PT joists and decking not be specified?

 

[SteelPE]

How can you tell the joists were rotted in a photos taken from 200' away? Has there been any reports saying that the joists were rotted?

 

[cvg]

yes, fox news this morning indicated that rotten joists (with a close up photo) might have been to blame

 

[boo1]

http://news.yahoo.com/6-killed-california-balcony-collapse-during-party-063649164.html#

joist breaks appears irregular and discolored (dark, not fresh wood)

loading 2007 required the balcony to hold at least 60 pounds per square foot
4'x6' = 24 square feet
24 x 60 = 1140 pound design capacity
13 people on balcony = ???

 

[CTW]

 

[JedClampett]

In retrospect, it looks like an iffy detail. The maximum tension stress is on the top of the member, which is also the portion that would be exposed to the most storm runoff. If it isn't well sealed, it makes matters worse.
But there's probably thousands of balconies that are designed the exact same way.
Very sad. People send their kids to the US to get more education and this happens.

 

[TehMightyEngineer]

I'm with boo1; why weren't the joists PT? Even if they were covered it seems like very cheap insurance to prevent exactly what happened.

Maine Professional and Structural Engineer.

http://www.fepc.us

 

[boo1]

looked like the decked was deteriorated to mush

 

[S3Engineers]

The picture posted shows white deposits on the joists- probably calcium carbonate from water intrusion. There is OSB sheathing on top and what appears to be the remnants of a stucco covered gypsum board soffit.

The moisture barrier on top of the deck could have failed quite a while ago, allowing water intrusion over an extended period of time. This deck probably gets a lot of sun and rain as well, which sets up a wetting and drying cycle. There has probably not been much if any waterproofing maintenance which allowed the wood deterioration to advance to the point that the joists had only a fraction of their original capacity.

The building owner should inspect all other decks, particularly on this face of the building and initiate immediate structural and waterproofing repairs.

 

[manstrom]

I would guess non P.T. wood

Must have saved hundreds of dollars. I wonder if it was worth it?

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[boo1]

I would like to see the header below the joist too. I suspect water intrusion into the wall.
Grace Bitumen pan failed. 40 mil PVC pan might have performed better.