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RE: 3-D Loading

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It makes perfect sense.  Scott described an analysis done for wind 
loading which does not specifically require consideration of 
orthogonal effects.  The building in question is the Citicorp Center. 
The engineer is Bill LeMessurier.  An interesting article was 
published in The New Yorker, May 29, 1995.

In this case diagonal loading was more severe than either of the 
orthogonal loads because of the unique characteristics of the 
building.  (In case you don't remember what's unique, see the sketch 
below.)  Unlike normal square buildings with four columns at the 
corners, the four columns in the lowest story are at the middle of 
the sides.  The available moment arm is much smaller for diagonal 
loading than for orthogonal loading.  Therefore the forces in the 
columns and superdiagonals are larger.

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> From:          "Bill Allen" <Bill(--nospam--at)AllenDesigns.com>
> Subject:       RE: 3-D Loading
> Date:          Thu, 18 Nov 1999 17:00:08 -0800

> This doesn't make any sense at all, unless I am missing something. If you
> design a building for loads at 45* (assuming a square building), then that's
> like designing for 71% concurrently in each direction. Is that more severe
> than 100% in one and 30% in the other? It would seem to me that the only
> elements that are critical in these conditions are those who are
> participating in the lateral force resisting system for both directions,
> i.e., common columns, etc. in which case it would appear to me that 1.3 is
> greater than 1.0. But maybe, once again, I am oversimplifying the problem.
> 
> Regards,
> 
> Bill Allen, S.E.
> ALLEN DESIGNS
> Laguna Niguel, CA
> 
> 
> ||-----Original Message-----
> ||From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> ||Sent: Thursday, November 18, 1999 3:28 PM
> ||To: seaint(--nospam--at)seaint.org
> ||Subject: Re: 3-D Loading
> ||
> ||
> <snip>
> ||Either during
> ||construction or after occupied (I can't remember), he for some reason
> ||decided to look at it with wind at 45 degrees and ALL the
> ||lateral braces
> ||were overstressed...to the point that there was a concern of
> ||a collapse
> ||that could result in several blocks being destroyed...so a
> ||fix was developed.
> ||
> ||I guess that is what I get for watching too much Discovery channel...I
> ||actually learn interesting things.
> ||
> ||Scott
> 
> <snip>

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Michael Valley                                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201