Walking Columns - How Much is Too Much 8

No, I don't like these monstrosities either, for all the reasons you listed. As well, I just hate the look of it. Saw that thing in Vancouver recently, and to see it described as "an examplar new urban typology" raised my blood pressure. It depends on which angle you view it from, and your picture isn't even from the worst viewpoint.

I can't define how much is too much, but I know it when I see it.

City Hall
Tempe, Arizona

- 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.

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That was exactly my reasoning for begging off to do something similar for a far shorter structure. Not sure what ASCE's ideas on this are since even with torsional irregularities, you can still build it if you do a dynamic analysis.

Unfortunately, if an Architect can dream it, there's a structural engineer with a black box who thinks they can defy gravity and design it.
No one puts pictures of three story concrete frame building in the magazines.

I've always been fascinated by the building that cvg posted. It is the library at UC San Diego, about the worst possible place to place an inverted pyramid in a seismic zone.

And when we build it, it's painful as well.


I was looking over the shoulder of draftsman today, and saying - that can't be right - but its nearly identical to the first picture.

The same group will have a transfer beam sized to carry the load above with no deflection, but only overlap a stepped column a inch or two on a 5" slab.

hokie66 said:

Saw that thing in Vancouver recently

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What's that now?? The next time that you find yourself anywhere within a short range nuclear launch of western Canada, I want to know about it in advance damn it. I won't quite fly to the south pacific to have a beer with you but I'll damn well high tail it out to Vancouver.

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.

Watching this building in Mexico City whip & twist during the Sept 20, 2017 Puebla Earthquake, it struck me that the acceleration of any large pieces of furniture that were not nailed down could be extremely dangerous to anyone in the building on the higher floors. It might even be difficult to stand while in a doorway. Maybe it is a life safety issue even before it is a structural issue? You could have lots of occupants unable to walk & no elevators.

I'd actually argue that cvg's building is not nearly so bad. It's short and, unless I'm mistaken, largely symmetrical. That eliminates all of my concerns other than the inverted pendulum stuff.

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,
Thought about you and some of my other friends here, but I was doing the tourist thing with my wife, daughter, and son-in-law. They already think I neglect them for Eng-Tips at times.

Next time, make it happen. Just tell me where you'll be and when and I'll tail you like a crazy nutter. I wont' be the worst that your family will see on Robson street.

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.

I'd do it because I like a challenge, but I've also never designed high-seismic, high-rise so I'd probably regret it.

It seems to me that "too much" is the point when you start combining extremes and pushing the limits. Inverted pendulum; okay. Extreme torsional irregularity; okay. Combined extreme torsional irregularity and inverted pendulum and offset column irregularity and complex structural analysis and detailing; no way.

Short answer is I'd keep the types of irregularities to only one, or two; I'd make sure all the normal design conditions for modal analysis are not violated, and I'd make sure the detailing was simple and robust. If anything pushed me to the limits of "normal" analysis tools I'd pass. I'd also envelope the design like crazy to ensure that failure of joints and unanticipated distributions of forces were all considered. I'd budget a ton of time to preparing multiple analysis to ensure that all practical methods of analysis were utilized to envelope the design.

Finally, I'd remind myself about the Citicorp Tower design flaw. Maybe post a picture of the Citicorp Tower on the wall to remind myself each day not to miss anything.

All that said; this got built and seems to have managed well enough:



Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

Also, don't forget wind. While high seismic will certainly control, something like what you posted for a picture almost certainly will require wind tunnel testing to ensure you don't get any strange effects (vortex shedding will almost certainly be a problem).

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

I'm not opposed to walking columns here or there. I've done a building with a 6 degree tilt on one side. But it was symmetric, easily understood with simple statics, and had a good lateral layout. You could come up with the static horizontal load with a pen, calculator, and a napkin.

This one is nuts though! My real concern is how do you deal with all the lateral seismic load that gets dumped in these walls. Do you design them all as special shear walls? All the diaphragms are getting locked together at so many points. If you treat them as columns, even the relatively small ones, how do you possibly get the slab to work for Mpr??

Looking at other photos of the building it looks like there are many, many of these walls pretending to be columns. Crazy.

TME said:

All that said; this got built and seems to have managed well enough:

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Again though, I'd argue that is not nearly as bad. Diagrid perimeter tubes. Nice, discrete load paths and gobs of torsional resistance. Additionally, an aspect of it that often gets over looked is that it's essentially a giant, single bay moment frame with a kink. You shed much of that cantilever action typical of high rises.

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 said:

Again though, I'd argue that is not nearly as bad.

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True, but I guess that's kind of my point. Crazy looking things can be done, but they need to be a lot simpler than they look. If you are getting into the realm of things that are actually crazy to design then I'd say you've gone too far.

Perhaps what this needs to be is you need to tell the architect what their building shape can be rather than the other way around.
_{When you figure out how to do this let me know...}

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

ajh1 said:

I've always been fascinated by the building that cvg posted. It is the library at UC San Diego, about the worst possible place to place an inverted pyramid in a seismic zone.

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Not sure what that building is, but it is NOT the UCSD library. For us proud UCSD grads, we know the library looks like below.


Same basic concept though. Though I think the UCSD one is both more appealing aesthetically and appears more robust structurally. We used to ask our professors about what they thought of it. They would politely decline to comment. LOL.

cvg's building looks like the one in Tempe, AZ.