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Balcony Collapse in Berkley, CA
37

Balcony Collapse in Berkley, CA

RE: Balcony Collapse in Berkley, CA

looked like the joists were rotten

RE: Balcony Collapse in Berkley, CA

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?

RE: Balcony Collapse in Berkley, CA

Quote (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?

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.

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

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?

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

http://news.yahoo.com/6-killed-california-balcony-...#
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 = ???

RE: Balcony Collapse in Berkley, CA

2

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

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. www.fepc.us

RE: Balcony Collapse in Berkley, CA

looked like the decked was deteriorated to mush

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

24*60=1440, but that's for the deck, as designed, not as it was two days ago.

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RE: Balcony Collapse in Berkley, CA

There was a real victim-blaming tone to the New York Times' story, Ew. As discussed, no way 13 people exceeded (100 PSF + margin) * FOS.

http://www.nytimes.com/2015/06/17/us/balcony-colla...

'Muricans collapse balconies all the time, and no such tone. Perhaps the 1800's and NINA are still with us.

RE: Balcony Collapse in Berkley, CA

The photos imply wood rot. Whether this is conventional stucco, EIFS or one-coat stucco, it appears that the waterproofing was not done correctly. There are several groups in this area that have promoted for years that stucco is waterproof. That's absurd, but they have had the collective ear of the stucco applicators.

RE: Balcony Collapse in Berkley, CA

Maybe 2x10s@12 with 4x10s each side?
Seems increasingly plainly a water issue...
The "decorative" concept is inconceivable to me. I've seen 'decorative balconies' in hotels with less than 12" cantilever and absolutely inaccessible by persons. But a double door with a 4' balcony absolutely invites the party outside. I assume everyone will crowd onto a balcony and lean over the rail to watch the sirens go by....

RE: Balcony Collapse in Berkley, CA

Wondering if the water ponded on the balcony, poor drainage detail, non-ripped to slope joists ... not a lot of rain in California.

RE: Balcony Collapse in Berkley, CA

Reading through the posts above - several very good posts, BTW - I see that no one chose to highlight what was likely the cause: lack of proper drainage of the balcony surface. Several of you cited lack of treatment of the joists (pressure treated), and some of you questioned proper use of the building code design live load. However, if the balcony had drainage properly installed and well maintained, then the serviceable life of the joists supporting the balcony would have been greatly enhanced.

The photo posted above does suggest lack of a proper drainage system. Rainwater was likely allowed to pond on the surface of the balcony, spreading over its surface. I think this is why we see fairly uniform deterioration of all of the joists; if there was localized deterioration, then I would have blamed a leaking drainage system.

To compound the situation, I question whether there was a proper moisture barrier in place that would have prevented - or at least limited - the amount of water infiltration into the joists.

Furthermore, one (or two) of you suggested that the header directly below should also be investigated for possible deterioration due to water infiltration. I agree that this possibility cannot be ruled out. This brings to light something about this type of problem that is so often overlooked: we need to open pandora's box, so to speak, and question the current state of all the other balconies in this structure. After all, the intent of the building code is life safety!

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

RE: Balcony Collapse in Berkley, CA

If you look closely at the balcony below there is what seems to be a small drainage hole with drain marks in the centre and the deck has a small upstand all the way round the edge. The destruction of the beams seems extensive and spread over all the beams. Maybe water entered the void under the decking and just created a moist humid atmosphere allowing fungus and rot to develop.

It could be something as simple as someone nailing on a top surface to the decking and puncturing the rather flimsy plastic sheeting that is evident.

Not building at least the main spars out of steel is simply a recipe for disaster. will be interesting if we ever see what the balcony under looks like once they've stripped off the deck.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Balcony Collapse in Berkley, CA

I heard that in General 80% of litigations in buildings are due to water damage. This is a good example.

RE: Balcony Collapse in Berkley, CA

Ssbatrseh in wood buildings I would bet that number is significantly larger.

RE: Balcony Collapse in Berkley, CA

I am not sure wet and corroded steel would behave differently than wet and rotted wood.

We build plenty of outdoor decks out of wood. I don't see many steel ones.

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

RE: Balcony Collapse in Berkley, CA

Most wood frame houses that have balconies, have wooden supports. In fact my old house had wood cantilever beams supporting a balcony just slightly wider than the one in question, that was about as deep.

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RE: Balcony Collapse in Berkley, CA

With loss of life involved, there could be a change in the building code. It is unfortunate that this is what it takes to motivate changes in the building code.

That being said, what do you think would be an appropriate code modification?

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

RE: Balcony Collapse in Berkley, CA

Quote (rlflower)

That being said, what do you think would be an appropriate code modification?

All balconies or porches 4 feet or more above grade require all structural framing and connections to be moisture resistant (i.e. pressure treated wood and stainless or galvanized metal) and detailed to prevent moisture related failure (proper drainage).

Maine Professional and Structural Engineer. www.fepc.us

RE: Balcony Collapse in Berkley, CA

Quoting from the article you posted, boo1:

"Annual inspections are so important for all balconies and terraces, but particularly for ones made of wood," he said. "In fact, rotting wood is the biggest cause of balcony and terrace failures."

Are annual inspections required by the building code?

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

RE: Balcony Collapse in Berkley, CA

Code reference, TehMightyEngineer?

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

RE: Balcony Collapse in Berkley, CA

rlflower: I was just making up an idea of what I would suggest for a code modification. I don't know of any code requirement that is similar to that, but it seemed like a low cost to value solution to this issue.

I don't know of any required annual inspections, I understood what he said as essentially "annual inspections are a good practice, especially for wood balconies".

Maine Professional and Structural Engineer. www.fepc.us

RE: Balcony Collapse in Berkley, CA

I think the failure was in being able to see the rotten wood. The balcony joists should have been PT out of good practice, but if they were completely sealed, then they wouldn't need to be PT. You can't mandate that all balconies be PT if it is completely enclosed by the building envelope; the (apparent) problem was that there was a hole in the envelope. Maybe add a code modification to allow projections to be easily inspectable or open bottomed.

Regardless, as a good practice these should always be PT, even if covered to avoid failures like this. Even if they are PT wood, my concern is what happens in 20 years when the PT is essentially gone and the wood needs to be replaced?

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

RE: Balcony Collapse in Berkley, CA

...to my way of thinking, a code change is not the issue, at least on the design side. sure it'll make a politician feel good... now if a commercial balconied building owner was required to submit a sealed engineer's balcony inspection report every so often......

RE: Balcony Collapse in Berkley, CA

When the motivation is present to instigate a code change, then by all means it should be pursued. I am inquiring what that change should be. I am leaning towards annual inspection of balconies for structural concerns.

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

RE: Balcony Collapse in Berkley, CA

Quote:

Even if they are PT wood, my concern is what happens in 20 years when the PT is essentially gone and the wood needs to be replaced?

Didn't know PT wore out. Is that true?

RE: Balcony Collapse in Berkley, CA

Quick google. http://www.lumbertalk.com/2008/05/08/life-span-of-...

" the life span of properly treated posts should be at least 20 years"

A residential deck has about a 20 year life span. Longer if not exposed, but a wet piece of wood (or steel) won't last 50 years.

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

RE: Balcony Collapse in Berkley, CA

If code provisions result in collapse and deaths under foreseeable loading, as a result of foreseeable degradation, then of course the code should be changed.

For a platform suspended high above the ground there clearly should be a back-up support to prevent collapse in the event of failure of the main support.

Specifying adjusted load factors, or more stringent durability control is not the answer. It needs a different approach.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

4
A different approach...I would prohibit cantilevered wood balconies. Done.

RE: Balcony Collapse in Berkley, CA

hokie66 - that would be similar to the prohibition in the codes about using wood to support significant concrete or masonry elements.

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RE: Balcony Collapse in Berkley, CA

JAE,
And even more appropriate, methinks.

RE: Balcony Collapse in Berkley, CA

I try to use Parallam Plus on balconies whether they are going to be "water protected" or not. It is rated for greater than 28% moisture content by the American Wood Protection Association. Beams are rated for as high UC4A protection which is good for prolonged wetting and exposure to all weather cycles. Columns are rated as high as UC4B protection which is for high decay potential and saltwater splash applications. The only caveat is that it cannot be resawn in depth or width; it can only be cut to proper length.

The material technical resource sheet is publication TJ-1020 from Weyerhauser.

RE: Balcony Collapse in Berkley, CA

They could implement a higher preservative treatment requirement for wood used in decks. I haven't read the AWPA U1 in a while, so I'm not sure if this is feasible.

RE: Balcony Collapse in Berkley, CA

At least design in some redundancy. Airplane wings don't often fail. Why not?

Why can't ACI come out with an "Appendix D" for decks?

RE: Balcony Collapse in Berkley, CA

ICC CODE cantilevered wood decks:
TABLE R502.3.3(2) CANTILEVER SPANS FOR FLOOR JOISTS SUPPORTING EXTERIOR BALCONYa, b, e, f

Member Size Spacing Maximum Cantilever Span
(Uplift Force at Backspan Support in lb)c, d
Ground Snow Load
≤ 30 psf 50 psf 70 psf
2 × 8 12″ 42″ (139) 39″ (156) 34″ (165)
2 × 8 16″ 36″ (151) 34″ (171) 29″ (180)
2 × 10 12″ 61″ (164) 57″ (189) 49″ (201)
2 × 10 16″ 53″ (180) 49″ (208) 42″ (220)
2 × 10 24″ 43″ (212) 40″ (241) 34″ (255)
2 × 12 16″ 72″ (228) 67″ (260) 57″ (268)
2 × 12 24″ 58″ (279) 54″ (319) 47″ (330)

For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
a. Spans are based on No. 2 Grade lumber of Douglas fir-larch, hem-fir, southern pine and spruce-pine-fir for repetitive (three or more) members.
b.[u] Ratio of backspan to cantilever span shall be at least 2:1.[/u]
c. Connections capable of resisting the indicated uplift force shall be provided at the backspan support.
d. Uplift force is for a backspan to cantilever span ratio of 2:1. Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 2 divided by the actual backspan ratio provided (2/backspan ratio).
e. A full-depth rim joist shall be provided at the unsupported end of the cantilever joists. Solid blocking shall be provided at the supported end.
f. Linear interpolation shall be permitted for ground snow loads other than shown.

Top Previous Section Ne

RE: Balcony Collapse in Berkley, CA

Your friend's photos show 3 views of one corner of the collapsed balcony, and I think it is an exterior corner. So I don't see how these photos support your assessment. If the joists were indeed pinned at the wall, how do you explain the photo which CTW posted above?

RE: Balcony Collapse in Berkley, CA

Jeff....you are quoting a prescriptive provision from the residential code. This is a commercial structure (multi-family is commercial, not residential by code).

RE: Balcony Collapse in Berkley, CA

Based on this article it sounds like the design was ok (not toenailed to a ledger as suggested above), just a water issue as most here have expected.

There are some screen shots of drawing details here as well.

http://www.berkeleyside.com/2015/06/19/no-smoking-...

RE: Balcony Collapse in Berkley, CA

You, are correct.The engineer sent me photos of the end of the balcony and said it was the connected end. P.276 Breyer "design of wood structures": "cantilever beam systems are not recommended for floors".
Do you think anyone would attempt to design a wood cantilever balcony connecting into a face mounted plate?

RE: Balcony Collapse in Berkley, CA

I have a copy of the plans also.Looks like Architect sealed them.

RE: Balcony Collapse in Berkley, CA

If the berkleyside photos are of the balcony pre-collapse then I'd say the design is fundamentally flawed. There is no good that comes from putting a concrete floor over wood and then walling it in from the bottom to prevent inspection of the condition of the structure. I wondered how the people could not feel the sponginess of rotting wood, but it looks like the design was practically created to kill people by preventing any discovery of wood rot, and it was designed to hasten the process.

Why doesn't the membrane extend up and into the dwelling instead of being used to funnel water into the wood? There's no other drain path provided.

RE: Balcony Collapse in Berkley, CA

Article posted by bookowski shows archt details. Would like to see struct framing plan and detais referenced by architectural drawing.
But I am suspecting the ripped to slope joists or maybe the deck topping, something resulting in ponding.

RE: Balcony Collapse in Berkley, CA

From an article in contra costa times:

Childress Engineering Services structural engineer Kevin Liu reviewed the designs and photos, and said the structural design of the wood beams and joists met building codes then in effect. He said the deck's two major cantilever beams -- 1 3/4-inch by 11 7/8-inch each, at each side of the balcony -- appeared to fail, "and then the rest of the joists and beams went down with it."

RE: Balcony Collapse in Berkley, CA

Based on the details of the original design as shown, there is no means of secondary drainage from the balcony. In a proper design, there should be drainage at the membrane level as well as runoff from the surface of the concrete.

Further, it appears that there was a water intrusion line about a foot off the joist attachment. This indicates a linear breach of the membrane. Was the first joint or the counterflashing joint not adequately sealed? Only a proper investigation will determine.

Even though we're not there and can only speculate, it is clear that the balcony waterproofing design and construction were contributing factors.

RE: Balcony Collapse in Berkley, CA

It looked to me like the detail put the flashing under the membrane and called for caulk to prevent water from funneling from the top of the flashing under the membrane. I think that one should never put an uphill-facing joint where water will drain. Membrane should have extended up the wall and under the door frame extrusion. If there is some requirement for metal flashing, that should go over the membrane so the gap faces downhill.

The rot seems to be maximum where the detail indicates the flashing would end. The lower balcony had some leakage but did not look rotted. Maybe the lower balcony had the flashing over the membrane; the membrane extended up the wall; the caulking was better for some reason; the upper balcony deflected the majority of water from that part of the lower balcony.

RE: Balcony Collapse in Berkley, CA

As a professional publication that covers engineering, design and architecture, I feel it is our duty to provide information to the public that provides an understanding of the possible causes of the failure so something like this can this can be avoided in the future. I am reaching out members of this forum to see if they would be able to write an article about the engineering aspects of the balcony collapse.
Requirements: Insightful, engineering analysis, 1200 words, minimum, 2 pictures, minimum. Need by: ASAP
Please reply back if you are available and interested. Any summary or thoughts on what you would like to develop in the article beyond what is suggested above would be appreciated. Also, do estimate how soon you could submit this article. With news stories, time is of the essence and we are already a little late with this one.
Roopinder Tara
Director of Content
ENGINEERING.com
rtara@engineering.com

RE: Balcony Collapse in Berkley, CA

Quote (SFGATE Article)

“It was definitely not large enough to be what the city would call an ‘open space balcony,’ where groups of people could stand outside,” said Carrie Olson, whose 14-year stint on the review committee termed out last year. “This was meant just to be a place where someone could stand out for bit, get a breath of fresh air. Not for something like 13 people.”

Well, that opinion makes me want to pull my hair out. Though, thank God their job title wasn't listed as building "engineer". We don't need more fuel to fan this fire: http://www.eng-tips.com/viewthread.cfm?qid=180126

I look forward to reading the op-ed. Could you provide a link in this thread when it has been posted, RoopinderTara?

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

RE: Balcony Collapse in Berkley, CA

3
RoopinderTara,
It would be irresponsible for any of us here to write the article you want. We can all speculate, and some things are obvious, but any detailed analysis of this collapse will have to be done by the investigators in Berkeley. In case one or more of our members are involved in the investigation, I think they will not be releasing a report any time soon.

RE: Balcony Collapse in Berkley, CA

hokie66....well stated.

RE: Balcony Collapse in Berkley, CA

What we generally find in investigations is that very few people (architects included) understand how water travels in building. They don't even seem to understand the two main principles of water usually-but-not-exclusively flowing downhill and humidity permeating any contained space. Repeatedly, balconies fail and walls rot because "that cut/tear/hole is not big enough to let _much_ water in..." The history of EIFS as one glaring example.

Someone mentioned the white deposits on the wood remnants. That is most likely salts coming out of the wood AND fungus byproducts, it is very commonly seen on wood that has been routinely or repeatedly wet.

RE: Balcony Collapse in Berkley, CA

Be curious to know what the condition of the other balconies on the top floor look like. It seems like from the photos above that the balcony which collapsed was shielding the one directly below, i.e. no signs of decay. Significant amount of roof run off, perhaps.

RE: Balcony Collapse in Berkley, CA

Random thought, did previous occupants have potted plants out there that were watered daily?

RE: Balcony Collapse in Berkley, CA

Proposed new code:
Any wood structure exposed to the elements that is used as a deck, balcony,walkway,or any related purpose shall be constructed of pressure treated wood elements. If enclosed construction it is to be vented by an area of 1/180 s.f.of structure. Vents shall be removable for periodic inspections.

RE: Balcony Collapse in Berkley, CA

Quote (rlflower)

what do you think would be an appropriate code modification?

If a building code modification is in order then I had something in mind that is actually a combination of hokie66 and manstrom's ideas. Maybe something to the effect of:

EOR is to identify and designate any structure, or portion of a structure, that is determinate with respect to structural analysis and that is to be subjected to moisture, exterior exposure, or other conditions conducive of rot and degradation. EOR is to include these areas in the Special Inspection data for the structure. The responsible design professional shall ensure that these designated areas comply with one of the following:
a) The structural members and connections shall not be permanently concealed by architectural finishes and shall be left visible in their final, completed form.
b) Employ hatches, ports or similar devices in the concealing finishes to allow future inspections of structural members and connections.
c) Be designed for 200% of the loads set forth in ASCE 7-XX.

However, I don't believe that code modifications are an effective way to address this issue. At the end of the day the people footing the bill for this collapse will be insurance. There would most likely be more real-world impact if insurance companies required inspections, offered rate discounts for inspections, or at the very least included some very specific smoking-gun questions in their application/questionnaire and seriously hike the rates depending on the answers. Changes won't happen until there is the threat of someone's wallet getting lighter...

RE: Balcony Collapse in Berkley, CA

I would also add that the EOR is usually not the right person to do envelope moisture control. That is the domain of the architect on most jobs.
At a previous employer, I investigated an entire school that was constructed such that the wall cavity held standing water, and in his wisdom, the architect had permitted (in writing) the builder to leave off the waterproofing on the exterior face of the wallboard behind the brick. It was so bad that the steel stud exterior framing was completed rusted through in many places. The entire exterior of the classrooms was removed - brick, stud wall, insulation - and replaced between the last day of spring semester and the first day of fall semester.

I am watching a cheap wood apartment complex going up near my house. (The structure is cheap, not the rent, based on what I see locally.) Not 20 minutes ago, I drove by and observed the balconies in various states of completion. 2x6 or 2x8 framing, a rim joist against the lap siding and/or EIFS, enclosed underneath with solid boards of reconstituted wood. Having watched the job go up from the recently cleared earth, including the spunbound polyolefin moisture barrier go on, I would lay odd that they will have water problems in short order. A lack of diligence in waterproofing is a pet peeve of mine. Shoddy construction costs us all a great deal.

(Now, if they had constructed it of reinforced concrete...winky smile

RE: Balcony Collapse in Berkley, CA

Amen, TX. Part of the problem is that architects have largely abdicated their primary responsibility of vapour and water proofing. They just make it the builder's responsibility, and many builders have no clue. However, many reinforced concrete structures have their problems with water as well. "Water is the greatest enemy of buildings". I forget who said it.

RE: Balcony Collapse in Berkley, CA

Looks like nearly a 1/1 back-span ratio. We certainly never go for that at my firm, regardless of how heavy-duty the uplift connectors are. Though, not sure how any of that really plays into the failure photos.

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

RE: Balcony Collapse in Berkley, CA

About 80 percent of the building failure investigations that I do have a root in poor waterproofing of the building envelope. I routinely see poor detailing and even worse construction. As I mentioned before, for wood framed balconies there is a need to provide drainage at the waterproofing plane of the concrete topping support. There is a nifty design for this using a device known as a "T-bar". It allows drainage at the waterproofing membrane plane and bleeds out the side of the balcony. The problem is that neither the architects nor the contractors seem to understand its function and routinely will specify a detail band around the balcony that the contractors will then proceed to construct incorrectly and block the drainage plane. In the past 4 major condominium envelope failures I've investigated all had similar issues. Fortunately none of them were cantilevered, so life safety was not an issue when found....but could have been in the future.

RE: Balcony Collapse in Berkley, CA

ChiefInspectorJeff
Can you upload a clearer version of that structural plan?

RE: Balcony Collapse in Berkley, CA

Even pressure treated wood has a limited life and will eventually rot. Galvanized steel connectors will eventually corrode. So yes p.t. wood should be used, but irrespective of that, there must be regularly scheduled inspections. Better yet, don't use cantilevered wood balconies.

About 20 years ago I had to recommend that all the cantilevered wood balconies on a 6 year old low rental housing be cut off due to rot found on some of them. I was a very unpopular person at the tenants's meeting called to explain the recommendation. However the recommendation was followed and they had no more balconies. Thank goodness.

RE: Balcony Collapse in Berkley, CA

Having regular inspections sounds great, but this will never happen.

I'd be much more comfortable requiring stainless steel connectors and a higher preservative treatment. There are ones that last a lot longer than 20 years. Per AWPA U1 (Link), decks have a use category of 3B or 4A. They should increase it to 4C or even marine.

Per home depots website, pressure treated lumber has a chemical retention of 0.05 lb/ft3 using MCA. This seems low.

If you look at Table 15-5 in the wood handbook (Link), you can see that there are plenty of treatment options that will last longer than 20 years. Increasing the retention in most of the treatments resulted in NO failures after a substantial amount of time.

I'd rather have a certain level of preservative treatment and stainless connectors in conjunction with the inspections every so often.

RE: Balcony Collapse in Berkley, CA

2
Perhaps Hammurabi had a good idea. Use this law and the problem should take care of itself.

Quote (Hammurabi)

If a builder build a house for some one, and does not construct it properly, and the house which he built fall in and kill its owner, then that builder shall be put to death.

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RE: Balcony Collapse in Berkley, CA

Looking at the flashing detail in the article here, there is an expansion joint that allows water under the slab. The flashing should flow over the balcony, not under it.

http://www.berkeleyside.com/2015/06/19/no-smoking-...

Regarding the backspan of the balcony beams and joists, 2:1 is best practice but not code required. The failure wasn't in the backspan lifting up, the beams and joists sheared off.

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-R. Buckminster Fuller

RE: Balcony Collapse in Berkley, CA

Regarding moisture and building envelopes, maybe it’s time to repost this, a presentation I erroneously poo-pooed before giving it a fair shake when it was first shown to me by way of this site. This one’s worth making the time for, in my opinion…maybe watch it over lunch, or something. It’s Joseph Lstiburek’s lecture at, ironically enough, Berkley. Link

RE: Balcony Collapse in Berkley, CA

From article in paper:

"
Based on their observations, city staff recommended that the Berkeley City Council adopt new and modified regulations to enhance the safety of all current and future buildings in Berkeley.

The recommended changes would make new balconies and other sealed areas that are exposed to weather subject to stricter requirements on materials, inspection and ventilation. The proposed rules would also require regular maintenance inspections for all such spaces for future and existing buildings.

"I'm going to propose, similar to San Francisco, owners get a structural engineer to inspect the buildings every five years," Eric Angstadt, director of Berkeley's Planning and Development Department, said at a press conference Tuesday.
"

RE: Balcony Collapse in Berkley, CA

A few thoughts:

If the balcony was indeed 4ftx6ft as stated somewhere above and the code in force at the time of construction required 60psf design live load, then the balcony was in fact overloaded at the time of the failure if there were 13 people on it as reported in some of the articles linked above, since 4x6x60/13 = 110lbs per person and people weigh more than 110 lbs.

It is interesting to note that the 2012 IBC, currently in effect in many locations, has reduced the balcony live load to "same as occupancy served", which for multifamily buildings like this one, is 40psf for private rooms. The 2006 IBC required 100 psf for balconies serving private rooms of multifamily buildings like this one and allowed the use of 60psf for balconies serving 1 and 2 family dwellings if the balcony was less than 100sf. This reduction from 100psf to 40 psf was quite significant and unconservative in my opinion, and I will not be surprised to see it revert back to 100psf in future editions of IBC. Does anyone know what is required by 2015 IBC on this?

Nevertheless, from the photo posted above, it seems rather obvious that the cantilevered joists were pretty deteriorated from rot caused by water infiltrating into the building envelope and that rot was a significant contributing factor to the collapse of the balcony.

Several of the comments calling for requiring regular inspections seem well intentioned and sound good politically, but a meaningful inspection of this type of construction would be impossible since the framing is all concealed within the building envelope.

RE: Balcony Collapse in Berkley, CA

does anyone believe that the gypcrete was placed at 2% slope per plan and that it might had inadequate slope or even the wrong way? water test might have been useful to see if water actually drains off the balcony.

RE: Balcony Collapse in Berkley, CA

I agree with gte447f. I am all for supplementary reviews, however, a meaningful review would include dismantling the architectural finishes which is rarely done during periodic visual structural reviews. Perhaps for critical components, the architectural finishes would have to be thought out in advance with access ports or other such removable panels.

RE: Balcony Collapse in Berkley, CA

wouldn't a city stipulation imposed upon owners for a sealed engineering survey of balconies every so often, say 5 years as proposed in article, or maybe yearly for 1st five years, make owners think twice about wanting balconies and cause them to require architects to design system facilitating simple routine structural observations?

RE: Balcony Collapse in Berkley, CA

The only thing that will require owners and/or architects to design systems that facilitate simple routine structural observations is a code mandate.

RE: Balcony Collapse in Berkley, CA

"Perhaps Hammurabi had a good idea. Use this law and the problem should take care of itself.

Quote (Hammurabi)
If a builder build a house for some one, and does not construct it properly, and the house which he built fall in and kill its owner, then that builder shall be put to death."

Not really, since it's often more than just a single factor that causes these things; a lazy, or malevolent, owner is not exactly a rare thing.

As for inspections, that's just going to be another tax that will jack up the cost of living. I'm forced to do a backflow valve test every year, which is $25, so not that bad, but a structural exam is going to cost $200?

TTFN
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RE: Balcony Collapse in Berkley, CA

IRstuff - over time all those lazy, malevolent owners will be killed since their balconies would have all fallen and killed someone.
We'd be left with diligent, nice owners. smile

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RE: Balcony Collapse in Berkley, CA

There is a lot wrong with some of the posts here:

1. Periodic inspections would not solve a hidden problem like this. They would just create, as Irstuff said, another tax.
2. Failures rarely occur due to overloading, they occur due to defects. So changing code live loading will have little effect.
3. The statement above that the flashing should have been turned out above the topping slab is wrong. The topping slab is for protection of the membrane, not to serve as such.

RE: Balcony Collapse in Berkley, CA

cvg, Who puts gypcrete on an exterior balcony?

(Despite the somewhat unclear plans photo, I will weight in on what seems to be a problem so designers will avoid it.)
That drawing seems to show a saw cut top chord of the cantilever lumber. This would probably change the grading of the lumber and if pressure treated, would remove the treated wood and open it up to moisture intrusion. It also opens up endgrain right at the area where the flashing most likely leaks at the face of wall.

RE: Balcony Collapse in Berkley, CA

The slab doesn't protect the membrane, which stops a large distance before the wall. In fact, it stops just about where the wood rotted. The slab does serve to funnel water that runs down the wall directly to the open edge of the membrane. Had the membrane been continued and terminated under the door sill above the concrete, there would be no opportunity for water to get under the membrane and from there to the wood.

RE: Balcony Collapse in Berkley, CA

Quote (hokie66)

3. The statement above that the flashing should have been turned out above the topping slab is wrong. The topping slab is for protection of the membrane, not to serve as such.

Exactly!! I wish architects and contractor could understand this!!

RE: Balcony Collapse in Berkley, CA

"over time all those lazy, malevolent owners will be killed since their balconies would have all fallen and killed someone. "

Sure, but there're also be a lot of innocent, but dead, builders. winky smile

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RE: Balcony Collapse in Berkley, CA

Ron,
I wish they would as well, but we continue to get these incorrect comments from engineers, who should know better.

RE: Balcony Collapse in Berkley, CA

Here are a few more pics:






Inspector Jeff

RE: Balcony Collapse in Berkley, CA

gte447f,
The balcony loading did not change in the 2015 IBC. The code is online at http://codes.iccsafe.org/I-Codes.html
ASCE 7--10 lists balcony live load as 1.5 times the load for the area served, not required to exceed 100 psf.

RE: Balcony Collapse in Berkley, CA

hokie66,

You don't think the difference between 40psf and 100psf is significant?

RE: Balcony Collapse in Berkley, CA

Sorry about some upside down pics. They were not like that when I attached them..

Inspector Jeff

RE: Balcony Collapse in Berkley, CA

Here's what I'm looking at - in the first I've exaggerated the positions; I think the filler board will eventually get compressed, and not rebound, leaving a gap and with it a reservoir of water. In any case, it cannot form a bond with the concrete, so water will bypass it and be directed as shown, with the first place it contacts the wood in the offset of the barrier where the moisture barrier doesn't exactly follow the flashing, leaving at least a small reservoir of water that cannot evaporate, but will be consumed by fungus to drive rotting.



The next shows the moisture barrier under the metal flashing, protecting the potentially exposed portion of the barrier. The barrier is continuous and water is prevented from contacting the wood, while being able to be absorbed and evaporated through the concrete.



Some details are omitted from both images - the filler board, the caulk, and the door details.

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

"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

RE: Balcony Collapse in Berkley, CA

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!

RE: Balcony Collapse in Berkley, CA

Quote (Brad805)

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.
www.johnkleinpe.com

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

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.
www.johnkleinpe.com

RE: Balcony Collapse in Berkley, CA

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
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RE: Balcony Collapse in Berkley, CA

@theonlynamenottaken, you are correct.

RE: Balcony Collapse in Berkley, CA

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/ArticleID/10332/The...

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

RE: Balcony Collapse in Berkley, CA

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.

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RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

3
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.

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

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?

RE: Balcony Collapse in Berkley, CA

I think you are right, BS2, but think that is irrelevant. But then I also think the design loading is irrelevant in this case, but some others disagree.

RE: Balcony Collapse in Berkley, CA

ChiefInspectorJeff showed us a framing plan purporting to be of the building in question. It appears that the balcony joists are cantilevered with a fairly small back-span but I tend to agree with hokie66 that it isn't relevant.

BA

RE: Balcony Collapse in Berkley, CA

You may be correct, hokie66, in stating that the design loading is not relevant in this case. However, as was the intent of the article, "What can we learn from this?" I saw an opportunity here to describe two basic methods of framing balconies that are in use today. My claim that this is an "outrigger" method of framing was based primarily upon one photo that showed the cut-away view of the balcony directly below the one that failed. I have searched in vain to recover that one photo, but basically, we can note from the available photos that the perimeter framing is somewhat larger than the joists themselves, and this suggests the outrigger method of framing was employed. The other hint at this was the way in which the balcony failed: it was a "catastrophic" failure - meaning that the entire balcony gave way rather than merely a portion of it. The other common method of framing - where all the joists are cantilevered - would have been a more redundant system which may have allowed a more localized type of failure (one or two joists failing, for example) rather than a total loss of the balcony. In terms of life safety, the difference between these two types of balcony framing should be addressed.

However, I have no intent upon interfering with the investigation. As stated in the article, I give all due respect to the ongoing forensic investigation and I certainly do not intend to interfere with that effort. It is not my intention here to suggest that the failure had anything to do with the chosen method of framing. I think we are all clear on that point and we are looking at cause related to the flashing resulting in deterioration of the wood framing.

The article was presented as an opportunity to learn something from this experience - focusing upon a certain characteristic that will likely be "brushed aside" as not relevant to the investigation.

I also wish to express gratitude to all who have contributed to this thread.

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

RE: Balcony Collapse in Berkley, CA

How could it fail in any other way? Look at the simplified example of two joists with a rigid plate on top. Assume the joists are of equal strength and there is some asymmetric weight that overloads one of them. Either the rigid plate tilts dropping all the people on it or the weight formerly shared is now more concentrated to the remaining one, causing it to fail and dropping all the people on it. There is no condition in which the rigid plate experiences a small, telling motion that gives people on the balcony a warning in time to vacate.

RE: Balcony Collapse in Berkley, CA

For the redundant cantilevers, the end result might have been the same. While there is redundancy, that would only be for as long as the remaining member stay sound. If they were all rotted, then you would get a cascade failure that might happen so quickly that it would be indistinguishable from a sudden catastrophic fail. Moreover, it's likely that the failure was exacerbated by the 13 people on it at the same time. Had there only been, say, 4 people, the balcony might have started to give way slowly, allowing the people to recognize the danger and leave before it collapsed altogether. Certainly, prior to the actual failure, the balcony gave the appearance of being able to support its own weight, which is not inconsiderable, even though the members were already rotted.

While there was some speculation that this balcony shielded the one below, which exhibited, as near as I can tell from photos, almost no rotting, rain water would still have gotten onto the lower balconies. This possibly suggests that the actual construction on that one particular balcony was deficient, which aggravated the less than ideal design. I had that sort of thing happen in my new house; we got some water intrusion, and it turned out that the tar paper had gotten damaged and torn in ONE spot, and water managed to get down to the hole and entered into the wall.

TTFN
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RE: Balcony Collapse in Berkley, CA

My point in asking about the type of construction is that the posted article seems to indicate that a more redundant system (where all of the joists are cantilevered) would be safer. However, from what I can see, all of the joists do appear to be cantilevered. In my opinion, this type of sloppy writing misleads its readers and is not useful in our pursuit of learning from past mistakes.

RE: Balcony Collapse in Berkley, CA

BS2: "All the joists appear to be cantilevered." I would like to know what leads you to that conclusion.

Found the pic I was referring to. This pic is what led me to think that this is an outrigger system. If anyone has more information on the type of framing system employed (a pic of the structural drawings showing the framing system would be ideal), please feel free to post it on this thread.

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

RE: Balcony Collapse in Berkley, CA

Another thought would be NOT to put a finish ceiling on the bottom of the deck.
Leave it open for inspection so it's not "Out of sight - out of mind."

RE: Balcony Collapse in Berkley, CA

rlflowers,

I agree with BS2 that the joists appear to be cantilevered. What leads me to that conclusion is the photo of the failed joists. They all failed at the exact same location along the span as the two edge cantilevered members that are larger in cross section (i.e. the two you refer to as outriggers). In the system you refer to as an outrigger system, I assume that you are implying that only the two edge members are cantilevered, and that the infill joists are simply supported spans between a ledger at the exterior face of the building and an edge beam spanning between and perpendicular to the two cantilevered outriggers at their free ends. If what I have described is an accurate description of what you refer to as an outrigger system, then I don't think that the infill joists would fail in the manner that we see in the photo. Don't you think they would fail at the simple support at the ledger at the face of the building?, especially if it was a toe nailed connection, which it would have had to be since we don't see any joist hangers at the face of the building. I don't think this is the system that we see in the photo. They clearly look like cantilevered joists to me.

RE: Balcony Collapse in Berkley, CA

I agree with gte, they are all more likely than not cantilevered. I often put in a bigger edge beam because it makes other things easier, like connecting guardrails and such.

RE: Balcony Collapse in Berkley, CA

nackra, precisely right. Several commenters have already made the same point. Accessible, visual, hands-on observation is really the only practicable inspection method that can be routinely carried out expeditiously and cost effectively for the tens of thousands (at least) or hundreds of thousands of these types of balconies that exist across the country. Some of the other suggestions of load testing and measuring in-situ natural frequencies and the like would never work in the real world, in my opinion.

RE: Balcony Collapse in Berkley, CA

Some photos show the inside joists extending past the set of horizontal slats(?).

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RE: Balcony Collapse in Berkley, CA

I fail to see how everyone on this thread concludes that these joists are cantilevered. These photos can only give us certainty that these joist bear upon the wall; there has been no means presented on this thread that can suggest that these joists extend beyond the wall - a backspan - to another line of support. Indeed, we are only looking at photos taken from the outside of the wall.

Yes, the stubs remaining of these joists have not significantly rotated as a result of the failure, and that does suggests some measure of restraint to keep them somewhat horizontal; however, there was not much strength left in these members to cause such a rotation at the moment of failure.

We have a lack of information, gentlemen, and we are jumping to conclusions. Again, all I have to go on - as shown on the pic I have posted above - is that the outlying "joists" are thicker than the other joists. This leads me to the likelihood (not certainty of course) that these are outriggers. Why else would these members be thicker than the others?

So, yes, of course I may be incorrect in stating that this is an outrigger system. But the point of my article was NOT to insist on this, rather, to suggest an opportunity to explore two types of balcony construction.

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

RE: Balcony Collapse in Berkley, CA

With respect, I think you are the one who has jumped to conclusions, and placed your conclusions in an article for public consumption. Did you see the framing plan? It seems to show cantilevered joists, but that is just my conclusion. A cantilevered balcony is a cantilevered balcony, no matter how many members cantilever.

RE: Balcony Collapse in Berkley, CA

No I haven't seen the framing plan, hokie66. So, please, if you can, post a pic of the framing plan.

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

RE: Balcony Collapse in Berkley, CA

In this thread, ChiefInspectorJeff posted the framing plan 23/6/15, 2311. Not very clear, but I think it shows all the joists cantilevered.

RE: Balcony Collapse in Berkley, CA

Thank you hokie66. I see that it was posted three days before the article was posted; however, I wrote that article on the 23rd. Had I realized that the floor framing plan was posted, I would have reviewed it before writing the article.

So, yes, that is a true cantilever system rather than an outrigger system. I was fooled by the larger members in the pictures. The joists were "ripped" to allow the shallower depth required for the concrete deck on the balcony.

Anyways, although I have stated in the article that this is an outrigger system, the intent of the article does not hinge upon what this particular system actually is.

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

RE: Balcony Collapse in Berkley, CA

There are 2 balcony framing types. One is joist supported on each end by hangers.
The 2nd is the type that collapsed which consist of cantilevered from an inset inside the floor edge lam beams and between them non p.t. joist.The blocking at the interface of the building makes it hard to see the inset joist.
My theory is that the stucco leaked into the wall from an area about 16' high and with no deck above to block the rain dripped into the wall behind the flashing and floor membrane.Also flashing nails are highly suspect.
I see no weep screed at the base of floor 5 to drain water.
Also the membrane looked short and not going up behind the metal flashing on the detail at the door.It also looks like the decay occurred at the membrane lap.
I'll have info from the man at the scene.

Inspector Jeff

RE: Balcony Collapse in Berkley, CA

I've been following this from the start and is the below a reasonable summary of what the forum has found / posted / noted?

1) The balcony was designed and built from non pressure treated wood as a cantilever design with no significant level of redundancy
2) It was highly unlikely that it was designed to hold 13 people in a 6 x 4 space even at new condition, but no notices existed to that extent
3) The failure of ALL the beams at seeming the same location close to the building indicates a failure of the water proofing, the details of which are seen in posts above
4) Confining the wooden supports within a structure which did not allow either inspection or drainage of any water entering the envelope is poor design
5) Placing a 2 1/2" concrete screed above the beams is not a good idea
6) Similar structures are recommended to be either removed or inspected to show adequate strength of the beams on a regular (1/2 year) basis, especially for those locations where there is no rain cover above them
7) Load limits should be noted / posted on similar balconies
8) More info to come from the scene in due course

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Balcony Collapse in Berkley, CA

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.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

3
I do not agree that the above is an accurate summary of the problem with the balcony in question. Given the likelihood of any conclusions being quoted outside this forum, it might be wiser to avoid stating any conclusions.

BA

RE: Balcony Collapse in Berkley, CA

BAretired: Yup

RE: Balcony Collapse in Berkley, CA

2

Quote (macgruber22)

I look forward to reading the op-ed.

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?

Quote (ASCE Cannon #3)

e. Engineers shall be dignified and modest in explaining their work and merit, and will avoid any act tending to promote their own interests at the expense of the integrity, honor and dignity of the profession.

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

RE: Balcony Collapse in Berkley, CA

Quote:

I do not agree that the above is an accurate summary of the problem with the balcony in question. Given the likelihood of any conclusions being quoted outside this forum, it might be wiser to avoid stating any conclusions.

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
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

I agree with BAretired and MacGruber, as I think I have made plain in this and the other thread about rlflower's article.

Redundancy is great, but this balcony had redundancy. Closely spaced joists provide redundancy...until they all fail.

RE: Balcony Collapse in Berkley, CA

Quote:

I agree with BAretired and MacGruber, as I think I have made plain in this and the other thread about rlflower's article.

Redundancy is great, but this balcony had redundancy. Closely spaced joists provide redundancy...until they all fail.

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
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

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

RE: Balcony Collapse in Berkley, CA

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).

  • Engineers shall issue public statements only in an objective and truthful manner.

  • 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.
  • Engineers may express publicly technical opinions that are founded upon knowledge of the facts and competence in the subject matter.
  • 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.
Maine Professional and Structural Engineer. www.fepc.us

RE: Balcony Collapse in Berkley, CA

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. www.fepc.us

RE: Balcony Collapse in Berkley, CA

Quote (IDS)

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.

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

RE: Balcony Collapse in Berkley, CA

Quote (BAretired)

I am trying in vain to think of an example of a structure where collapse could NOT lead to human death.



So, clearly all structures must now have a height restriction of 4 feet or be designed with 100% redundancy.

Maine Professional and Structural Engineer. www.fepc.us

RE: Balcony Collapse in Berkley, CA

"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.

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RE: Balcony Collapse in Berkley, CA


Quote:

"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.

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
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

The lack of redundancy did not cause the collapse, rotten wood did.

RE: Balcony Collapse in Berkley, CA

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. www.fepc.us

RE: Balcony Collapse in Berkley, CA

Quote:

The lack of redundancy did not cause the collapse, rotten wood did.

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.

Quote:

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.

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
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

Large deflections before they lose strength? You mean like the gusset plates on the lateral braces of the I-35W bridge in Minneapolis?

Thaidavid

RE: Balcony Collapse in Berkley, CA

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
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

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.

RE: Balcony Collapse in Berkley, CA

hokie66 - how can you say that if a structure is designed so that it does not totally collapse as soon as one member fails, this does not assist?

The fact that in this particular case a report does not mention lack of redundancy as a factor just shows that the standard approach to design for collapse needs to be changed.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

I just think redundancy is overrated, sometimes at the expense of making sure that no members or connections fail. I can't think of a way of making a cantilevered wooden balcony more redundant this one was, unless you are going to use hangers or columns.

RE: Balcony Collapse in Berkley, CA

Quote:

I just think redundancy is overrated, sometimes at the expense of making sure that no members or connections fail. I can't think of a way of making a cantilevered wooden balcony more redundant this one was, unless you are going to use hangers or columns.

Connecting the parapet rail to the wall is the third way that has been mentioned.

I don't see anything wrong with any of those options.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

2

Quote (IDS)

Connecting the parapet rail to the wall is the third way that has been mentioned.

I don't know how you could expect that to practically and predictably work.

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

RE: Balcony Collapse in Berkley, CA

I don't see why it would not work. The balcony rail will be fabricated from steel tube stock and be anchored to the host structure and to the wood deck end members with lag bolts or threaded rods. The railing would be a cantilevered braced frame attached to the host stud pack which is attached to the joist or studs below with a HD 7A hold down or similar.The floor would be a fully blocked diaphragm with glued and screwed 2- 3/4 Plywood skin similar to an airplane wing.If the joist rotted the remaining blocking could form a T beam with the subfloor.
Another easier option is use steel floor joist or angle irons.
Or a 2 way slab on junior I beams.
If you look at the photo of the railing it is very heavy duty.

Inspector Jeff

RE: Balcony Collapse in Berkley, CA

Something still doesn't feel right about that scheme - the blocking acting as flexural members...ehhh? Are you proposing your scheme be part of the code? There is a saying that you shouldn't count on structure that doesn't look like structure. Pedestrian guards look like they perform one function, and that one function is not as a secondary structural system for the balcony. At some point in the lifetime of every building renovation, railings are replaced.


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

RE: Balcony Collapse in Berkley, CA

Just a datum: I believe the collapsed balcony and the one directly below it were the ONLY two on the entire building. Probably owing to the "softening" of the "look" mentioned somewhere above and probably implemented at the last minute in the design. (Probably the first step in the Disaster Chain)

The building seems to have an extensive exterior stairway leading down the face of one end of the building. Hmmm, I wonder if it should be checked as it looks to probably have the same sort of drainage needs as the ill fated balcony.

Google Satellite

Keith Cress
kcress - http://www.flaminsystems.com

RE: Balcony Collapse in Berkley, CA

Quote:

I don't know how you could expect that to practically and predictably work.

I really don't see why not, but the point is that even if it only just works it has done its job.

If balcony rails are maintained, that's good. If the connection to the wall is removed (or replaced with one with insufficient strength) during maintenance that's bad, but the resulting system is no worse than the current standard design.

I will make some more general comments in the new thread.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

Railings are typically not structural elements in this type of balcony. In order to completely handle the 1440-lb load that the balcony was supposed to handle will require:
> way more fasteners
> way stronger wall
> way stronger flooring on the balcony
> way stronger railing.

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RE: Balcony Collapse in Berkley, CA

IRstuff - The point is that it should have sufficient strength to prevent total collapse in the event of the main support failing.

I doubt that the changes you listed would be required in the case of the balcony in question, but if they were one of the other options could be adopted.

Are you really suggesting that these structures have no practicable way of providing a secondary support mechanism that would prevent total collapse, or at least substantially reduce the risk?

Doug Jenkins
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RE: Balcony Collapse in Berkley, CA

I mean, don't get me wrong, IDS, I employ "belt and suspenders" frequently without anyone noticing. But, to me, you don't provide suspenders when it can double the cost of the structural system(balcony in this case). Further, without a sketch of these ideas, I still have concern about the load-path of the scheme. If you are explicitly designing a redundant frame, you own all of it. Which means the reliability of the redundant system needs to be greater than or equal to the sub-system you think could fail (good grief that sentence sounds ridiculous).

I think Occam's Razor is being violated...

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

RE: Balcony Collapse in Berkley, CA

"Are you really suggesting that these structures have no practicable way of providing a secondary support mechanism that would prevent total collapse, or at least substantially reduce the risk?"

In some cases, yes. It's not that different that when we demand a certain failure rate, that we essentially have to duplicate the entire suite of hardware. The balcony in question has redundancy; what failed was not the redundancy, but the water intrusion protection; that was the weak link, not the joists. To demand an additional full redundancy would make the balcony way more expensive than it's worth in rent, and we would essentially restrict ourselves to buildings with no balconies, which would be a poor state of affairs.

Note that the lower balcony had ZERO water damage, which is what the design result should have been for the upper balcony. There have been several suggestions as to how that might have been accomplished, without resorting to redundant structures. There are balconies that have existed for centuries without failure, and without redundancy. To immediately demand redundancy seems to me to be a bit of a knee-jerk reaction.

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RE: Balcony Collapse in Berkley, CA

Quote:

In some cases, yes. It's not that different that when we demand a certain failure rate, that we essentially have to duplicate the entire suite of hardware. The balcony in question has redundancy; what failed was not the redundancy, but the water intrusion protection; that was the weak link, not the joists. To demand an additional full redundancy would make the balcony way more expensive than it's worth in rent, and we would essentially restrict ourselves to buildings with no balconies, which would be a poor state of affairs.

The point is that all structural systems have potential for significant degradation over time. Providing a secondary system to prevent total collapse in that eventuality does not need to cost as much as the original system, or anything like it.

As for the balcony having redundancy, I don't see any.

Quote:


Note that the lower balcony had ZERO water damage, which is what the design result should have been for the upper balcony. There have been several suggestions as to how that might have been accomplished, without resorting to redundant structures. There are balconies that have existed for centuries without failure, and without redundancy. To immediately demand redundancy seems to me to be a bit of a knee-jerk reaction
.

To suggest that redundancy is a totally impracticable requirement seems a bit of a knee-jerk reaction to me.

Quote:

Which means the reliability of the redundant system needs to be greater than or equal to the sub-system you think could fail (good grief that sentence sounds ridiculous).

Provided that the redundant system does not reduce the reliability of the sub-system, then the overall reliability will be equal or better than the original system.

Not sure what the Occam's Razor reference is about.

Doug Jenkins
Interactive Design Services
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RE: Balcony Collapse in Berkley, CA

Jeff, possible maybe - but super messy to me. Also, there is going to be a lot of moment introduced into the wall, which will make things worst for detailing. Not sure how the HD7A is doing much of anything - a column will need to resist the moment and then transfer shear to the floor, not tension.

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

RE: Balcony Collapse in Berkley, CA

Just one correction, as I won't argue any more about redundancy. The lower balcony did have water damage, according to the city's report.

RE: Balcony Collapse in Berkley, CA

Quote (IDS)

Provided that the redundant system does not reduce the reliability of the sub-system, then the overall reliability will be equal or better than the original system.

Yes. Though, what I was getting at is that (if you are going to open the can of worms) you have no choice but to assume the base system fails in its entirety (as the subject structure did), or else when something happens you have to explain why your belt and suspenders only has the belt and one suspender.

My reference to Occam's Razor is me suggesting that the redundant cantilever scheme may not be an elegant solution to the problem.

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

RE: Balcony Collapse in Berkley, CA

MacGruber,
Yes, it is messy but uses a few bolts and hold downs and some blocking.
Would not the M be resisted by the HD7A tying into the dead load of the tributary floor and roof? The bolts into the wall might need bearing plates to spread the load.
Wouldn't the braced frame railing resolve into a couple of C=T at the interface of the stud wall, similar to a shear wall?I'd push for galvanized joist with weep holes in the bottom flanges and vent/ inspection holes.Any way you do it wood is messy and difficult to connect properly.

Inspector Jeff

RE: Balcony Collapse in Berkley, CA

Jeff, I don't think so. Based on your sketch, you introduce a couple directly into the wall. The wall will resist the couple via a moment internal to wall studs, a post, etc. The line of action of your tie is right in the middle of the wall, so the moment can only resolve itself into a horizontal shear force at the sole plate (i.e. the base of the wall is pinned).

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

RE: Balcony Collapse in Berkley, CA

Also, along with hokie (I think), I am kind of tired of discussing the redundancy solution. I will end with this - I challenge the redundancy advocates to try it out in real life and report back.

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

RE: Balcony Collapse in Berkley, CA

"As for the balcony having redundancy, I don't see any."

Let's suppose that the balcony was only supported by the outriggers, and further suppose that a sensible design would have made each of the outriggers capable of supporting the entire load of the balcony. Then, by definition, there is redundancy. Since the balcony actually has 5 joists in addition to the outriggers, I think that meets the literal definition of redundancy. The fact that they all failed at the same, or nearly the same, time does not void the redundancy. Even if the railings had been a tertiary support, the same rot that affected the joists could have just as easily been located on whatever the railing might have been anchored upon, since each fastener requires penetration of the outer wall, and runs the risk of water intrusion.

My point is that there are always failure points; they're unavoidable. Even the redundancy professionals get it wrong sometimes, such as in the case of the DC-10 hydraulic systems, which were fully redundant, except at one specific spot in the tail, which was tolerably protected, until the rear mounted turbine developed a catastrophic blade failure, and took out all the hydraulics which had no cable backup, since it was nearly impossible, statistically, for all redundant hydraulics to simultaneously fail.

The issue is that redundancy is a slippery slope; where do you draw the statistical line in the sand, and can you live with the consequences when the line is crossed. Much of redundancy reliability is tied to the statistical analysis of probability of occurrence. So, even in the best case, an unknown probability can be assigned a lower value than what is real. Or, equally likely, the probability is correctly remote, but that probability card just shows up in the deck.

Case in point, and even considering the other balcony failure just reported, what is the statistical likelihood of a balcony failure? Is it one failure per million balcony-hours, or one per billion, or even trillion? Would any seriously contemplate potentially doubling the cost of a balcony to prevent a one in a billion balcony-hour failure probability? What about all the other one in a billion balcony-hour failures? Do we protect against them as well? The balcony-hours as I use it here is the number of actual balconies multiplied by the number of hours, so assume the the US as 70M housing units and 1/100 have a balcony, and assume there is one balcony failure every 2 years would result in 1 per 12 billion balcony-hours as the failure rate.

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RE: Balcony Collapse in Berkley, CA

(OP)
I too am a big fan of redundancy -- especially in places where you can do so easily.

Take a car. It makes a lot of sense to me to have a traction-control system. Divert power from wheels that are slipping to those that aren't. Good redundancy.

But you can't do it everywhere. You wouldn't mandate a fifth wheel just to provide redundancy in case the four wheels stop working. That doesn't make sense. Those first four wheels just need to be engineered to work.

Same with this balcony. Providing a second load path is good when you can do it smartly. But this cantilevered system just needs to be engineered to work.

I agree with much that's said here. A few thoughts:
  1. Making cantilevered joists PT. Why not? Makes sense.
  2. Watertesting some percentage of the balcony water proofing before covering it with finishes. Preferably with a third party. Won't help deferred maintenance items but it should at least keep people on their toes during construction. I don't see why this doesn't make it into Masterspec, if not the codes.
  3. Drilling holes in the sheathing under the waterproofing. This could at least let water drain should it get trapped under a lapped flashing joint. The leak would at least be visible underneath.


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

RE: Balcony Collapse in Berkley, CA

PT does not last forever. Just means the collapse will be some years down the road. Yes PT but that is only a small part of what can never be an entirely satisfactory solution. Annual inspection is another part. It is pretty hard to build redundancy into a cantilever. I like Hokie66's response, namely do not build cantilevered balconies in wood. Don't forget that PT when the lumber is incised as it generally must be, has a big strength reduction factor, but at least that can be accounted for in the design. When the wood eventually does rot, there seems no alternative at that point than to cut the balconies off.

RE: Balcony Collapse in Berkley, CA

Quote:

I too am a big fan of redundancy -- especially in places where you can do so easily.

So, we are all agreed then

On the basic principle, if not the application to a particular class of structures.

I do note however that there is a good deal of what I call either-orism in this thread.

Those who think additional redundancy in balconies is a good idea think the cost would be trivial, and those who think it would be a waste of time think it would be horribly expensive.

Funny that.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Balcony Collapse in Berkley, CA

Quote (undefined)

RE: Balcony Collapse in Berkley, CA

For a structure to be redundant to prevent this type of collapse, it has to last longer than the primary structure, not be affected by whatever might cause the primary to fail, and possibly take a higher load due to energy added to the structure during the failure of the primary support (as in dropping and being suddenly stopped by the back-up.)

If the designer knows all about this, why not use this to design the primary structure so it doesn't fail?

The belt-and-suspenders concept is appealing until the realization that neither belt or suspenders are under much load and that well fitted pants will stay up without either.

Regardless of cost, designing and building a structural back-up is very difficult, particularly to offset a basic deterioration unrelated to structural use. Even designing a structure to fail gracefully under overload when the parts are in like-new condition is hard.

RE: Balcony Collapse in Berkley, CA

Given sufficient time and money, we could all generate a balcony that would not have failed in the same way as this one. But they each may fail in a different way due to the same or different causes. What we do all the time is to make our designs "good enough" because that is the economics of our profession. In this case, we all probably agree that given the outcome, the design and/or construction was not good enough.
It is easy enough to look a failure and determine the cause. How we react as an industry is what matters. There were a series of things leading to the final catastrophe. A fault tree would be useful, but I don't feel like drawing right now, so below is a ludicrously over-simplified assessment of how things got to where they are now:

failure: balcony fails due to deterioration of multiple structural members arising from undetected (or uncontrolled) water intrusion over a period of time.

Anywhere along the road to failure, this could possibly have been avoided. Some controls work better than others:
If the water intrusion had been properly prevented
If the effects of water intrusion had been mitigated
If the materials used were not subject to water damage (treated lumber or other material selection)
If the engineer had recognized that water intrusion was likely and specified appropriate materials
If the water intrusion had been detected and fixed
If the builder and his personnel had known about this issue and been more careful
If the owner or architect had required special inspection of the waterproofing
If the engineer had added separate redundant load path not subject to water damage from the same leak(s)
(aka If the structure was redundant enough, in the right ways)

If the building had not been built because they could not afford to construct a building costing more than one designed to minimum requirements.

RE: Balcony Collapse in Berkley, CA

Some new info on this here if you go down to the bottom. http://www.eng-tips.com/viewthread.cfm?qid=389494

Will be interesting to see how many balconies start disappearing in Berkeley because no one will sign them off as being "free from..."

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