Walking Columns - How Much is Too Much 8

[KootK]

I'm polling the gang here to get a sense of everyone's opinion regarding the business of seriously walking columns as shown below. The project is a high rise building in a high seismic region. I get the whole walking column concept but feel that, at some point, there should be a rational limit. Some potential seismic consequences of this:

- you've got a significant, permanent lateral load on on the building that will ratchet under seismic yielding.

- you've got a significant, permanent torsion acting on your core that will ratchet under seismic yielding. I'm not sure that anybody even really knows how cores respond to torsion when they're already yielded as plastic hinges.

- vertical seismic accelerations are going to exacerbate the above concerns.

- the whole thing's got an inverted pendulum character to it.

Yeah, we've got irregularity penalties, ETABS, OpenSEES, PBD, and the rest... To me though, this still seems like hubris even with all of the fancy tools in hand. I'd like to hear how others feel about this kind of thing. Would you really want your kids on the 30th floor of this things start shaking?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Wallache]

Yep, Tempe City Hall

 

[JLNJ]

Eventually we get cocky and venture into the unknown without realizing it (see the FIU bridge failure).

KootK and the like have that educated and intuitive voice of reason lurking inside their heads. Not everyone has (or listens to) that voice.

 

[SnTMan]

Eventually we get cocky and venture into the unknown without realizing it...

This is what Petroski cautions us about.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[KootK]

The litmus test that I apply to my own work is that I imagine a future where something has gone wrong and somebody has gotten hurt. I want to be able to credibly say to myself and to others "I believe that my decisions on this project were aggressive but in accord with good engineering judgement given the state of the art in structural engineering at the time". With something like this, what would you say:

- I allowed the center of mass to needlessly be shifted high on the building.

- I allowed a torsional vibration mode to become one of my dominant vibration modes.

- I allowed my vertical vibration modes to become coupled to my torsional vibration modes.

- I invited a high degree of torsional irregularity into a major structure.

- I knowingly invited permanent lateral and torsional loads into a core made of a material characterized by creep deformation.

- I knowingly invited torsional seismic ratcheting into a concrete box section for which behavior under plastic hinging is poorly understood.

- I did all of this because I've got 4000 pages of CSI Perform output saying that everything was fine.

My eng-soul would be blackened beyond redemption I fear.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[civeng80]

There is a building in my home town very much like cvg's photo. We call it the upside down building. It is in the news every so often and the Government tenants swear that the building moves during high winds.
How the architects and the engineers come up with these boggles me.

 

[Trenno]

"Structural engineering is the art of molding materials we don't wholly understand, into shapes we can't fully analyze, so as to withstand forces we can't really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance."

 

[KootK]

@Trenno: it's a great quote and fitting here but it fails to draw a line in the sand. Does it mean that we should be cautious? Or does it mean than any one wacky structure is really not so much wackier than any other and we should just maintain our facade in all instances? I know you do a lot of large and complex work these days. I'd love to hear your own personal opinion of the matter.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Trenno]

In the relative scheme of things, I'm still very green in the structural engineering sphere, so my opinion doesn't hold much weight.

What I will say however, is that I recommend people listen to Sean Brady's podcasts. He's a brilliant forensic structural engineer, who has been featured in the IStructE magazine many times. In regards to the topic at hand, I find his ideas/comments regarding the progression and development of bridge design/construction techniques very relevant to this discussion. It essentially goes along the lines of... engineers are always pushing the envelope and every now and then a failure happens; will provide not only a reality check but also redefines a limit. This limit changes as we witness failures and then learn from them. It's a harsh but true reality.

[URL unfurl="true"]https://bradyheywood.libsyn.com/[/url]

EDIT: There's even a podcast on the Citicorp Tower Crisis for you, TME.

 

[KootK]

In the relative scheme of things, I'm still very green in the structural engineering sphere, so my opinion doesn't hold much weight.

Pfft. Over the years here I've gotten a good measure of you as an engineer and I respect your intuition. Give me your weightless opinion damnit. You know I'd do it for you.

I certainly agree with Brady, of course, that ours is a reactive profession. And that's weird space. Pushing the envelope reaps great rewards for individual practitioners. And occasionally puts people in harm's way in very real sense.

I can't name names but I'm friendly with one of the dominant academic thinkers in seismic engineering, formerly a professor at the university of British Columbia in Vancouver. I recall sitting in his office a few years back and asking his opinion of some other things I don't love in Vancouver. I think it was transfer slab punching shear, the "wallumn" issue that DETstru mentioned, and a one sided coupling beam detail often used when there's hardly any return wall left on one side of the opening (it's atrocious). All of these trouble me in high seismic regions. He leaned in and said something to the tune of "if people here had experienced an earthquake in their lifetimes, or understood any of the recent developments in NZ, I can't imagine any of them wanting to live in any of these terrible 30 story...". He then cut himself off and said that there are limits to what he ought to be saying given the close ties that the university has to local developers and engineering firms. I could see the concern on his face and it was, truly, a very sobering moment for me.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Agent666]

While we are quoting, I'm quite fond of this one which I think sums up engineering and the engineer's burden.

“It is a great profession. There is the fascination of watching a figment of the imagination emerge through the aid of science to a plan on paper. Then it moves to realization in stone or metal or energy. Then it brings jobs and homes to men. Then it elevates the standards of living and adds to the comforts of life. That is the engineer’s high privilege.

The great liability of the engineer compared to men of other professions is that his works are out in the open where all can see them. His acts, step by step, are in hard substance. He cannot bury his mistakes in the grave like the doctors. He cannot argue them into thin air or blame the judge like the lawyers. He cannot, like the architects, cover his failures with trees and vines. He cannot, like the politicians, screen his shortcomings by blaming his opponents and hope the people will forget. The engineer simply cannot deny he did it. If his works do not work, he is damned…

On the other hand, unlike the doctor his is not a life among the weak. Unlike the soldier, destruction is not his purpose. Unlike the lawyer, quarrels are not his daily bread. To the engineer falls the job of clothing the bare bones of science with life, comfort, and hope. No doubt as years go by the people forget which engineer did it, even if they ever knew. Or some politician puts his name on it. Or they credit it to some promoter who used other people’s money . . . But the engineer himself looks back at the unending stream of goodness which flows from his successes with satisfactions that few professions may know. And the verdict of his fellow professionals is all the accolade he wants

Don't forget in terms of the building response that you have active/passive seismic controls up your sleeve, things like tuned mass dampers can work wonders to improve undesirable responses.

I'm not to worried about people/companies who understand and address all the risks involved (kootk's list among other things), what really worries me is people/companies who really don't understand or appreciate the risks. I seem to see this all the time as a reviewer, some fundamental thing being missed or treated in an overly simplistic manner.

 

[Trenno]

Give me your weightless opinion damnit. You know I'd do it for you.

I would like to think the profession as a whole should aim to rephrase a few words in your list. "I made allowance for..." and "I acknowledged and designed/detailed accordingly for..." It'd be quite a task to curtail mankind's pursuit of progression. However we should keep in mind, as I alluded to previously, perhaps some of the limits of our structural designs aren't quite known yet.

However I'll never forget something my mentor told me... if it looks wrong, it probably is.

 

[KootK]

You may have missed your true calling as a lawyer Trenno. You're displaying some seriously skillful straight answer dodging here. Fine, remain non-committal.

Don't forget in terms of the building response that you have active/passive seismic controls up your sleeve, things like tuned mass dampers can work wonders to improve undesirable responses.

Yeah, I'm happy to acknowledge that there may be some excellent engineering voodoo going on that I simply can't see. And I'd love to hear of it if anyone knows what the heck it is. An example of something that I simply don't know enough about to understand is shown below. Gotta be something going on there? Column transfer to the interior? Maybe they're not actually structural columns after all?

I also have a problem with supplemental control devices and, in a broader sense, performance based concepts in general. It'll be the subject of another thread eventually. Seems to me that all that stuff is based on the statistically infused "knowing" of things. I think that this is headed in the wrong direction and that the true genius of capacity design was always that you weren't really relying on knowing much. Nature tends to frown upon over-clever engineers who think that they know things.

I'm not to worried about people/companies who understand and address all the risks involved

I know the firm. They have experience with passive control systems and performance based design. They're as competent as anyone outside academia in that regard I'd say.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Agent666]

I'm sure that is just the Façade being expressed? Not the actual columns and transfers at each level. If it is the columns I'd be very surprised.

 

[DETstru]

Koot that's probably just the facade. You can tell which ones are the columns (which are really walls) because you see shadow of the overhanging slab at their top. The ones without shadow are facade elements.

I still want to know what they do with all the shear and flexure that ends up in those walls...

 

[TLHS]

For the record, I hate that building every time I look at it.

I wonder, though, if those offset walls are to avoid providing vertical stiffness there. If you had a direct load path, it would presumably be the stiffest part of the structure, since it's furthest from the center of gravity. Making sure that you control the load paths is pretty important if you're going to do a complicated analysis and try to control the seismic response. Controlling vertical stiffness makes sense both if they're part of the shear system or if they're just façade.

 

[KootK]

Yeah, I feel as though the general proportions are anathema to most people's sensibilities. I suspect that's actually part of the architectural intent. You know, to evoke an emotional response etc. The sister building is in Calgary and I find it nearly as unappealing aesthetically. The fact that the top heavy one ought to have been in Calgary and Calgary's in Vancouver is just more fuel on the KootK emotional response fire.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

And then there's this one that I discovered shortly after initiating this thread. Sometimes I feel as though the universe is just mocking me. Although, again, I can think of several factors that actually make this not so bad. It's bottom heavy, largely symmetrical, torsionally not so bad, and obviously endowed with an intentionally stocky shear wall system. And, technically, I suppose that those are not actually walked columns. I'd be curious to know how the detailing of the column/slab joints went for the curvy ones. I'd almost think you'd have to just stick some central dowels in there and call 'em all pinned.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[RickyTickyTavi]

Where is that guitar structure? I find that hilarious for some reason.

Also, great use/location of the shear wall.

 

[jayrod12]

That last one is sure going to be a sweet looking guitar when it's done.

 

[DETstru]

Your scientists engineers were so preoccupied with whether or not they could, they didn’t stop to think if they should...