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Balcony Collapse in Berkley, CA 37
- Thread starter MJB315
- Start date
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3
- #141
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2
- #143
MacGruber22
Structural
macgruber22 said:
I am retracting my previous statement. I am not fond of the engineering.com article, particularly because of the ratio of (potential social good/potential personal gain) I get from reading it.
The Balcony Collapse in Berkeley, California: What Can We Learn from This?
What *was* a layperson supposed to learn from the article? How to be informed/persuaded by conjecture and vagueness?
ASCE Cannon #3 said:
"It is imperative Cunth doesn't get his hands on those codes."
Do you mean points 1-8 or point 9.
I agree that it is premature to decide the exact cause of collapse of the balcony, but it certainly isn't premature to discuss how similar events can be prevented. The fact that we don't know what happened here, or what might happen in the future under similar situations, is the exact reason why structures must be designed with sufficient redundancy to prevent total collapse when the unexpected happens.
Doug Jenkins
Interactive Design Services
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1
- #145
Clearly it did not have enough redundancy.
Multiple members supporting a cantilever subject to a more or less uniform load does not provide redundancy.
Doug Jenkins
Interactive Design Services
ChiefInspectorJeff
Structural
The sad thing is the heavy duty railing was not attached to the wall and could have acted like a braced frame and possibly given the victims time to get of.
Inspector Jeff
Inspector Jeff
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1
- #148
TehMightyEngineer
Structural
I'm going to second MacGruber22. I wanted to see an engineering article written about this that prompts discussion amongst engineers, contractors, and building owners to prevent this failure and provide lessons. However, the takeaway I got reading the article was that it was essentially a summary of this very thread. It didn't teach me anything new as an engineer nor do I feel anyone who is not an engineer would gain anything from it. Obviously being on an engineering website it should be more technical than most articles about this but I just didn't see the true purpose of the article.
The article mentions the building code but fails to provide details on what sections are applicable to this balcony. I'd love to see an article that points out the various code requirements that are there to prevent this failure (or show the lack of such requirements if that's the case). Plus, with the correction that this is a cantilever system the entire section regarding cantilever vs outrigger is not relevant and quite biased. Reading the article you would think that an outrigger system should never be used. But this impression is suddenly opposed in the conclusion which basically seeks to counter all the claims of the first three parts of the article (but the header for this conclusion is "wood not always appropriate" so I'm not sure what the conclusion actually is).
Where are the facts?!
There's also two lines I'm having a lot of issue with:
"I merely wish to point out that the failure of one outrigger beam would cause collapse of the entire balcony whereas failure of one cantilevered joist would not necessarily cause collapse of the entire balcony."
This is 100% conjecture. A very strong outrigger balcony, even with only two outrigger beams, could possibly suffer the loss of an outrigger though unintended paths of support and not collapse. Conversely, a cantilever system could just as easily fail after the loss of a single member if the remaining members were already heavily stressed. Yes, I gather the point was that cantilever systems are typically more redundant than outrigger systems but this sentence does a great job of showing the problems of conjecture and confirmation bias that are found throughout the article.
"Indeed, the structural engineering community should have had the foresight to address this issue before lives had been lost."
No. Just no. This is very much the authors personal opinion AND grossly inaccurate in my opinion (and hopefully to many others). We have no idea what the structural engineer on this project did or did not do unless someone runs the numbers on the design. The balcony could have been well over-designed and still failed due to rot and that's not the engineers fault (unless they also were in charge of the moisture protection). In addition, we don't know if it was the architect, contractor, or owner that caused or exacerbated the moisture damage and failure. Regardless, the structural engineering community had no practical way to prevent this (again in my opinion). Does the article imply that I should go look at the balcony of my apartment, my neighbors apartment, and anyone else who has a balcony in my local area? Does the article imply that no balcony can survive without regular inspections? Obviously as a licensed engineer if I am aware of a unsafe condition then I ethically must address it but how was the engineering community supposed to prevent this failure?
Yes, the engineering community should always strive to identify areas where the building codes do not provide a sufficient minimal level of protection but the article doesn't even address whether the code was sufficient or not.
As MacGruber put it, the article is full of "conjecture and vagueness".
rlflower, I'm being very, very harsh here I know. This isn't personal but I'm also trying to be fair here. This is a high-profile failure and I feel that to not be 100% critical about the things we engineers state publicly would be poor service to the engineering community. We need to be sure our statements publicly are based on facts and well thought conclusions (which is also required by our ethical obligations).
[ul]
[li]Engineers shall issue public statements only in an objective and truthful manner.[/li]
Maine Professional and Structural Engineer.
The article mentions the building code but fails to provide details on what sections are applicable to this balcony. I'd love to see an article that points out the various code requirements that are there to prevent this failure (or show the lack of such requirements if that's the case). Plus, with the correction that this is a cantilever system the entire section regarding cantilever vs outrigger is not relevant and quite biased. Reading the article you would think that an outrigger system should never be used. But this impression is suddenly opposed in the conclusion which basically seeks to counter all the claims of the first three parts of the article (but the header for this conclusion is "wood not always appropriate" so I'm not sure what the conclusion actually is).
Where are the facts?!
There's also two lines I'm having a lot of issue with:
"I merely wish to point out that the failure of one outrigger beam would cause collapse of the entire balcony whereas failure of one cantilevered joist would not necessarily cause collapse of the entire balcony."
This is 100% conjecture. A very strong outrigger balcony, even with only two outrigger beams, could possibly suffer the loss of an outrigger though unintended paths of support and not collapse. Conversely, a cantilever system could just as easily fail after the loss of a single member if the remaining members were already heavily stressed. Yes, I gather the point was that cantilever systems are typically more redundant than outrigger systems but this sentence does a great job of showing the problems of conjecture and confirmation bias that are found throughout the article.
"Indeed, the structural engineering community should have had the foresight to address this issue before lives had been lost."
No. Just no. This is very much the authors personal opinion AND grossly inaccurate in my opinion (and hopefully to many others). We have no idea what the structural engineer on this project did or did not do unless someone runs the numbers on the design. The balcony could have been well over-designed and still failed due to rot and that's not the engineers fault (unless they also were in charge of the moisture protection). In addition, we don't know if it was the architect, contractor, or owner that caused or exacerbated the moisture damage and failure. Regardless, the structural engineering community had no practical way to prevent this (again in my opinion). Does the article imply that I should go look at the balcony of my apartment, my neighbors apartment, and anyone else who has a balcony in my local area? Does the article imply that no balcony can survive without regular inspections? Obviously as a licensed engineer if I am aware of a unsafe condition then I ethically must address it but how was the engineering community supposed to prevent this failure?
Yes, the engineering community should always strive to identify areas where the building codes do not provide a sufficient minimal level of protection but the article doesn't even address whether the code was sufficient or not.
As MacGruber put it, the article is full of "conjecture and vagueness".
rlflower, I'm being very, very harsh here I know. This isn't personal but I'm also trying to be fair here. This is a high-profile failure and I feel that to not be 100% critical about the things we engineers state publicly would be poor service to the engineering community. We need to be sure our statements publicly are based on facts and well thought conclusions (which is also required by our ethical obligations).
[ul]
[li]Engineers shall issue public statements only in an objective and truthful manner.[/li]
[li] Engineers shall be objective and truthful in professional reports, statements, or testimony. They shall include all relevant and pertinent information in such reports, statements, or testimony, which should bear the date indicating when it was current.[/li]
[li] Engineers may express publicly technical opinions that are founded upon knowledge of the facts and competence in the subject matter.[/li]
[li] Engineers shall issue no statements, criticisms, or arguments on technical matters that are inspired or paid for by interested parties, unless they have prefaced their comments by explicitly identifying the interested parties on whose behalf they are speaking, and by revealing the existence of any interest the engineers may have in the matters.[/li]
[/ul]Maine Professional and Structural Engineer.
TehMightyEngineer
Structural
In the spirit of "too long; didn't read":
In my opinion the author of the article violated the engineering ethical requirement that "engineers shall be objective and truthful in professional reports, statements, or testimony. They shall include all relevant and pertinent information in such reports, statements, or testimony, which should bear the date indicating when it was current" and that "engineers may express publicly technical opinions that are founded upon knowledge of the facts and competence in the subject matter."
I don't consider it to be egregious enough to warrant it but I also would not think it improper for this to be brought to an engineering board.
Maine Professional and Structural Engineer.
In my opinion the author of the article violated the engineering ethical requirement that "engineers shall be objective and truthful in professional reports, statements, or testimony. They shall include all relevant and pertinent information in such reports, statements, or testimony, which should bear the date indicating when it was current" and that "engineers may express publicly technical opinions that are founded upon knowledge of the facts and competence in the subject matter."
I don't consider it to be egregious enough to warrant it but I also would not think it improper for this to be brought to an engineering board.
Maine Professional and Structural Engineer.
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1
- #150
IDS said:
My earlier comment applies to items 1) through 8) for reasons I do not particularly wish to discuss at this time, but it applies also to item 9).
I am trying in vain to think of an example of a structure where collapse could NOT lead to human death.
Are you sure you want to make a code provision requiring sufficient redundancy so that a structure does not collapse when any element fails? Where is the redundancy in a simple beam carrying floor or roof members if the simple beam fails or if one of its end connections fails?
BA
TehMightyEngineer
Structural
BAretired said:
So, clearly all structures must now have a height restriction of 4 feet or be designed with 100% redundancy.
Maine Professional and Structural Engineer.
"9) Any structure where collapse could lead to human deaths must be designed with sufficient redundancy so that it does not collapse when any element fails."
I think that already existed. If any single cantilever had failed, the balcony could probably have survived that. ALL the cantilevers failed, and it was overloaded.
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:
I think that already existed. If any single cantilever had failed, the balcony could probably have survived that. ALL the cantilevers failed, and it was overloaded.
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:
It collapsed because there was no effective redundancy.
As has been discussed already, there are several mechanisms by which cantilevers might be constructed so that they don't collapse if the primary support fails, but this balcony did not have any of them, in common with many other balconies in the world.
Doug Jenkins
Interactive Design Services
TehMightyEngineer
Structural
What would happen if the redundant supports also rotted? Just because something is non-redundant doesn't make it unsafe. What was really needed was more ductility in the structure, then failure could be identified before collapse.
Maine Professional and Structural Engineer.
Maine Professional and Structural Engineer.
You can't prevent all deterioration of materials. Structures should not collapse when their materials deteriorate, especially when collapse results in people falling to their death.
By redundant I mean that it should have sufficient strength in some other load path that it doesn't collapse. There are many different ways of doing that, including using materials that will have large deflections before they lose strength.
Doug Jenkins
Interactive Design Services
thaidavid40
Structural
Large deflections before they lose strength? You mean like the gusset plates on the lateral braces of the I-35W bridge in Minneapolis?
Thaidavid
Thaidavid
Either the recent leap second or 4th July has resulted in some posts being inserted out of sequence, or maybe I just missed them.
The statement: "Any structure where collapse could lead to human deaths must be designed with sufficient redundancy so that it does not collapse when any element fails." is supposed to be a statement of a general principle, not a design standard clause.
Certainly it's easy to interpret in such a way that it doesn't make sense, but it is also possible to interpret it in context, in a way that does make sense. The question is, if we do that, does it imply that the design of some structures should be handled differently? I think it does. The questions below relate to all accessible external balconies anywhere in domestic or public buildings:
- What is the maximum load that can be expected over the life of the structure? - As many adults as can squeeze onto it.
- What is the probability of significant deterioration of the supporting materials over the life of the structure? - In many cases high.
- What is the probability that this deterioration will go undetected or untreated? - In many cases high.
- In the event of one supporting member failing what would be the result? - In many cases sudden total collapse, likely to result in multiple deaths.
- Are there any practicable measures that could be taken to significantly reduce the probability of such an event? - Yes, there are several.
So other than a very small increase in the overall construction cost, what is the drawback to a requirement that balconies should be designed to be safer in the event of overloading and/or deterioration?
Doug Jenkins
Interactive Design Services
The statement: "Any structure where collapse could lead to human deaths must be designed with sufficient redundancy so that it does not collapse when any element fails." is supposed to be a statement of a general principle, not a design standard clause.
Certainly it's easy to interpret in such a way that it doesn't make sense, but it is also possible to interpret it in context, in a way that does make sense. The question is, if we do that, does it imply that the design of some structures should be handled differently? I think it does. The questions below relate to all accessible external balconies anywhere in domestic or public buildings:
- What is the maximum load that can be expected over the life of the structure? - As many adults as can squeeze onto it.
- What is the probability of significant deterioration of the supporting materials over the life of the structure? - In many cases high.
- What is the probability that this deterioration will go undetected or untreated? - In many cases high.
- In the event of one supporting member failing what would be the result? - In many cases sudden total collapse, likely to result in multiple deaths.
- Are there any practicable measures that could be taken to significantly reduce the probability of such an event? - Yes, there are several.
So other than a very small increase in the overall construction cost, what is the drawback to a requirement that balconies should be designed to be safer in the event of overloading and/or deterioration?
Doug Jenkins
Interactive Design Services
A June 23rd report by Berkeley's Building and Safety is online at
I don't think that redundancy assists, except perhaps to give a false sense of security. I don't see anything about redundancy in the city's report. The part about mandatory inspections will be soon forgotten, as no engineer in his right mind will be willing to certify these things without proper access. The durable materials part is key, although that too can be abused.
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