Balcony Collapse in Berkley, CA 37

[MJB315]

See link:

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

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

 

[IDS]

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/

 

[hokie66]

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.

 

[IDS]

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/

 

[MacGruber22]

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."

 

[ChiefInspectorJeff]

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

 

[MacGruber22]

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."

 

[itsmoked]

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.

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Keith Cress
kcress -

http://www.flaminsystems.com

 

[IDS]

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/

 

[IRstuff]

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.

TTFN
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[IDS]

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
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[MacGruber22]

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."

 

[IRstuff]

"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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[ChiefInspectorJeff]

I guess the point is moot if galvanized steel and venting is used.
The blocking between the floor joist would not connect to them so they could act as the web of a T beam with the flange being 2- 3/4" plywood.Is this possible?

Inspector Jeff

 

[IDS]

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.

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.

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

http://newtonexcelbach.wordpress.com/

 

[MacGruber22]

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."

 

[hokie66]

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.

 

[MacGruber22]

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."

 

[ChiefInspectorJeff]

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

 

[MacGruber22]

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."

 

[MacGruber22]

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."