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Re: Engineers involved with UBC

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Scott, I see what you mean, where there are moment frames for both
orthogonal directions of the structure, and the oblique resultant wind load
makes for bi-axial bending.

I doubt that such a scenario was contemplated in the pre-1982 UBC Wind
provision rewrite; I don't recall it being aired. Much of the research used
at that time was done for the Metal Bldg Mfrs Assn, and two-way moment
frames seemed not to be their concern. ANSI had just compiled a complex wind
code and reportedly pressed for its adoption as is into model codes, and the
UBC effort was to simplify it for ordinary use, like a "short form" in tax
returns, but embracing the long-form ANSI A58.1 version as a fall-back at
the option of the code user. The EIA code for towers was allowed as another
option, as "an approved national standard." Perhaps the complete ANSI
version speaks to side walls concurrent with windward and leeward walls. The
SEA of Washington has an excellent commentary on the UBC wind provisions,
and it says that the ANSI A58 is now ASCE-7.  (Hope I got all the acronyms
right this time.)

Yet the UBC still requires consideration of wind coming from any horizontal
direction, which includes oblique directions. How one does the analysis for
this is not suggested however, unlike for oblique seismic directions. When
the short form doesn't cover one's situation, then resort to the long form
and/or to basic principles is intended.

What's missing in seismic codes is two things: a long-enough simple short
form method for routine situations, like UBC wind provisions, and the spirit
among those who count to allow such a thing to exist, unlarded with grudging
penalties.

Charles Greenlaw SE  Sacramento CA

At 02:25 AM 03/22/2000 -0500, you wrote:
>Charles,
>
>I understand this thinking for do the components and cladding
>design...i.e. either windward or leeward will always govern over a
>"sidewall" pressure, but there are some scenarios that might create
>problems with this method when doing the main force resisting system.  For
>example, say you have a large industrial plant (i.e. an automobile plant
>building) that is rather long and has several expansion joints along the
>length of the building.  The end portions of the building could have a
>wind scenario where there is windward pressure on the one wall, leeward on
>the other side of the building, sidewall pressure on one side, and nothing
>(interal) at the expansion joint.  In the case of an industrial building
>where the trusses are being used a moment frames, this could produce
>bi-axial bending on the columns.  The UBC code does not appear to address
>this type of situation adequately.
>
>Maybe this might help explain why the question was asked.
>
>Scott E. Maxwell, SE, PE
>Structural Engineer