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

 

[gte447f]

wannabeSE,
Thanks for the heads up on the 2015 IBC loading. I have the ASCE 7-10 back at the office but I didn't cross check it vs the 2012 IBC, which is what is currently in effect in my state, so it's what I typically default to. It's interesting to note the difference between IBC and ASCE 7, thanks for pointing that out. Personally, I think I will default to 100psf for cantilevered balconies in the future, which is what I was used to from the 2006 IBC before my state's last code cycle.

In the case of this particular Berkley balcony the design live load may well have been a mute point because of the wood rot resulted from inadequate waterproofing, but in general the difference between 40psf and 100 psf is massively significant, and even in the case of this Berkley balcony, in the hands of a good lawyer (I am not a lawyer, not even a bad one), if the design live load was in fact exceeded, that could be end of story.

 

[ChiefInspectorJeff]

How did the water get behind the membrane? Either became loose from wall or holes in it? Possible nail holes in flashing like on roof leaks.The membrane should have gone up the entire curb and under the sill.

Inspector Jeff

 

[hokie66]

gte447f,

There is a big difference in 40 PSF and 100 PSF, but in all the building failures I know of or have studied, details and defects have caused them, not overloading.

 

[manstrom]

Note that balcony loading in IBC and ASCE 7 are NOT the same. IBC lightened up to 40 psf. IBC is the code, ASCE 7 is adopted by the IBC. IBC controls.

ASCE 7-10 says 1.5 times occupancy use. 100 psf max. (60 psf for residential)
ASCE 7-05 say 60psf for 1 and 2 family residences, 100 psf for public.

IBC 2009, 2012 and 2015 say same as occupancy served. (40 psf here)

In 2006 IBC, it was 60 psf for 1 and 2 family, 100 psf for public.

Regardless of loading, what is the capacity of a rotten 2x10?

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

 

[gte447f]

manstrom,
Good summary of design live loads from recent common codes and referenced standards. You have further illustrated precisely the wide variation of design criteria commonly used in practice that I pointed out in my initial post above. Regarding your rhetorical question about the capacity of a rotten 2x10, I don't disagree with your point.

 

[Brad805]

I don't know about others, but the architects I work with are rarely interested in our comments about flashing details. This is an interesting discussion. I believe the problem will track back largely to construction flaws such as incorrect membrane lap, missing membrane, improper membrane bond, nail penetrations, leaks at the railing connection penetrations or some other issue. The fundamental problem is this waterproofing system requires almost perfect execution to be serviceable for 25 - 40years. The typical contractor we see on this type of project is not always the best equipped to ensure perfect implementation and professionals are only doing random field reviews for obvious reasons. I don't believe that the loading is all that germane to the discussion either. 40psf/60psf or 100psf would only affect when the failure occurred and would not have prevented this tragic event. The key takeaway for us should be to avoid cantilever spans for a wood decks and ask questions when the finish is stucco. I believe a stucco finish is one of the worst for trapping moisture and as Ron pointed out many of the trades are of the incorrect opinion that stucco is virtually impermeable. In British Columbia we require a rain screen due to the leaky condo case. Redundancy is our friend with products that can decay.

 

[manstrom]

"The key takeaway for us should be to avoid cantilever spans for a wood decks"

I wish. Developers are loving the look. Wood buildings now don't look like wood buildings. They want them to look like concrete or steel with big cantilevers. Hopefully this instance will help to talk them out of 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

 

[gte447f]

Brad805,
I agree with you that 40/60/100psf design load would only affect when a failure like this might tragically occur. In light of the apparent waterproofing defects in this case, from the perspective of Architecture/Engineering/Construction industry principles and practices, the design live load requirement may indeed be immaterial to a failure analysis of this case. From a logic point of view though, and a perhaps a legal one (I am not a lawyer), the design live load may not be immaterial. For example, answer the question, if a healthy balcony would be permitted to fail under 41psf or 61psf, then why should an identical rotten balcony be required to support 62psf or 102psf or more?

I disagree that the key takeaway for us should be to avoid cantilever spans for wood balconies. There is no fundamental reason why cantilevered wood balconies are any more susceptible to this type of failure than balconies constructed from steel or concrete. I have personally witnessed steel framed balconies with over 50% loss of cross section from corrosion resulted from improper water proofing. Like the wood joists in this Berkley case, the steel framing was completely enclosed by architectural finishes and there was no way to detect the problem visually. That is, until the balconies began to deflect a couple of inches and the rim joist, which in this case was a rolled steel channel, disintegrated to the point that you could easily take a look inside the floor cavity through the fist sized holes!

 

[theonlynamenottaken]

The typical contractor we see on this type of project is not always the best equipped to ensure perfect implementation

I agree - that is the symptom. The problem is that owners/developers want extremely low $/sqft construction costs and then compound that condition further with a lack of maintenance and inspection. When the starting $/sqft value is low, then it undergoes one or more rounds of V.E. a quality waterproofing contractor and/or quality materials aren't affordable. If owners/developers were hit with a giant insurance premium for pursuing cheap construction it mitigate that problem some...

I was an expert witness in an analogous suit a few years ago where the owner/developer (same person) successfully showed that they were oblivious to the fact that severe V.E. cuts compromised the overall integrity and quality of the finished building. The architect's insurance ended up footing the bill because, "the architect should have better communicated to the owner that reducing construction costs so severely would result in a sub-standard quality building".

John Klein, P.E., M.L.S.E.

http://www.johnkleinpe.com

 

[gte447f]

theonlynamenottaken,
That is a very instructive outcome in the case you describe.

 

[theonlynamenottaken]

Yeah, thankfully there were no injuries in that suit. Just millions of dollars of water damage to fix. Where do you draw the line though? I wouldn't sue the manufacturer if a $2 hammer broke after a year of use...

@gte447f
By the way, if I'm correctly assuming the origin of your username I was gte312d once upon a time.

John Klein, P.E., M.L.S.E.

http://www.johnkleinpe.com

 

[IRstuff]

But, in the case of the hammer, you presumably bought with malice and forethought, and duly recognized that if the head fell of and klonked you, there was no one to blame but yourself. As engineers, we strive to keep the rose-colored glasses off, but it seems that non-engineers are more able to do that and then claim, "Nuthing.. I know nuthing..." by buying into the notion that the architect can still do exactly the same job for 1/3 the cost, because they were obviously sandbagging the numbers to start with.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529


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

 

[gte447f]

@theonlynamenottaken, you are correct.

 

[RoopinderTara]

The Balcony Collapse in Berkeley, California: What Can We Learn from This? Article by Richard Flower, PE, ENGINEERING.com, June 26, 2015.

http://www.engineering.com/BIM/Arti...y-California-What-Can-We-Learn-from-This.aspx

I invite your comments, observations and additions.
Roopinder Tara
Director of Content
ENGINEERING.com

 

[IRstuff]

Another issue I have with inspections, particularly where the potential downside is thousands of dollars is regulation. Who's watching the watchers? How can a homeowner be absolutely certain that the inspector isn't simply scamming for the potential of a massive repair job. So, a gigantic bureaucracy would need to be developed to license and monitor all these inspectors.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529


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

 

[hokie66]

Even if you had honest and capable inspectors doing these proposed periodic checks, I think it is wishful thinking to believe that would address issues like the one we are discussing. The defect was hidden, so without doing some removal of finishes, it is doubtful there were signs of the problem.

 

[3DDave]

Three ways to detect this without access to do a visual inspection:

One is that the slope of this balcony would increase as the supporting wood rotted.
Two is that the natural frequency of this balcony would decrease as the supporting wood rotted.
Three is to set an allowable deflection change for an applied load; up to setting a pool on the balcony and filling it to match the allowable load.

The problem for the first two methods is that it requires keeping records of how the item performed initially. The ideal would be that there is no change, but there would be some measurement error and some mass change as the wood and concrete moisture content changed, which would affect the results.

The initial problem for the third is that one needs to keep a record of what the expected deflection is. The next problem is that time and possibly heavy equipment is required. The biggest problem for the third is that the structure might fail during the test and do a lot of damage; people could be safely removed from the area prior to the test, but it might make a simple repair much more complicated. I can imagine a cascade of balcony failures as the top one and its load dropped onto the next and repeated down the side of a building.

Of the methods I like the natural frequency check the best. The change in frequency would be very dramatic for a change in the section properties and not as dramatic for smaller changes like moisture content. Slope change is difficult to measure as the item may not be uniform, making a good comparison a problem. The most certain method is to load the item to the design limit, assuming there is some factor of safety, but it has a high expense and when an item fails the test, has a lot of unwanted side-effects.

 

[TXStructural]

RoopinderTara, I would say that the article is a bit inappropriate and unprofessional. As the author says, we don't have first hand information. If the article was framed as a commentary on the type of construction, rather than what he knows based on one internet forum, it might be useful. I do not want to have my comments on this forum associated with a story that prematurely assesses the situation.
Also, one of the updates says that there was "dry rot". Wood rots only when exposed to moisture and microbes, so I suggest your technically-oriented website stick to proper terminology.

 

[RoopinderTara]

TXStructural - thanks for your comment about "dry rot." It is a commonly used term and may not be technically correct.

In regards to the article, I would have to say it is a commentary based not only on this forum but also draws upon the author's experience, which is considerable and quite relevant to the subject.

I would encourage you, and others, to share your views of this and other subjects outside this forum. I know as an engineer, I take comfort in talking to other engineers and this forum is great for that, but ENGINEERING.com offers a way to get reach a bigger audience, one that can benefit from learning from professionals in active practice. So much of what we read is supplied but non-technical and non-expert authors. Most engineers would like to read on engineering subjects outside their discipline, for example. Also, with any big news story, the public needs to be informed. If there is an engineering angle, such as this balcony disaster, who better to write the article than an actual structural engineer? Sure, we have to be careful we don't speculate but most of us in the engineering professions are not prone to that.

I'm still looking for someone to write more on this subject, as we have not yet covered the maximum load the balcony may have had, compared to what it could be designed for (40/60/100 psf?) And what about dead vs live load? As it has been pointed out, humans crowded on to a balcony is beyond normal for the rest of the dwelling. The pieces of this article are here in the forum but would anyone care to work on an article with me?

best,
Roopinder Tara
Director of Content
ENGINEERING.com

 

[BS2]

I hesitate to post a reply to RoopinderTara as I agree with hokie66 that it would be irresponsible for any of us that do not have direct involvement in the details of this project to write an article as requested. I also agree with TXStructural that the article was inappropriate and unprofessional.

My reason for replying is simply to correct what may be a possible error as presented by the article posted above. The article mentions that the construction type is an "outrigger" balcony and not a "cantilevered" joist balcony. The difference being that the cantilevered beams on each end are the only structural support versus all of the joists being cantilevered supports. It appears to me (although it is hard to tell from the photos) that this is actually a "cantilevered" joist balcony. Can anybody confirm this?