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RE: 1958 UBC Seismic

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Mark,

This was a very transparent attempt to dredge up more '61 Volkswagen
stories, but I will resist.

I have had the occasion to check several older structures with the code
being the inferred standard of care.  Load combinations and local practices
varied much more in the olden days than they do currently.  The codes of
days gone by were also more vague ("...snow drift load shall be
considered...").  The design professional (engineer, architect, ...
pharmacist) in the first half of the 20th century, was not a strong seeker
of consensus.  Practices also varied with the size and height of the
building.

1.  I would imagine the practice was to just do the DL + seismic.  That
seems to be what was practiced at the time, if lateral loads were considered
at all.  

2.  Orthogonal load consideration was the rule (one direction at a time) was
the practice throughout most of the U.S. until relatively recently.  This
was true of wind and seismic.  Wind and seismic were generally treated the
same until the mid to late '80's.

Regional practice was highly variable.  Lateral load consideration was not
prevalent in most buildings.  I have evaluated schools (not in CA) that had
no consideration for lateral loads and were constructed in the mid '70's.

If you tell me the size and type of the building, and where it is, I or
someone else on the list might be able to be more definitive about the local
practice at the time it was constructed.

Nation wide consideration of lateral loads started becoming more uniform in
the 1970's, but there were many exceptions. 

I would also try to determine from the owner, what the point of this
exercise is.  Code compliance to a '50's vintage code might be valid for an
academic study, but is by no means assurance of performance.

Regards,
Harold Sprague

> -----Original Message-----
> From:	Mark Ketchum [SMTP:mark(--nospam--at)ketchum.org]
> Sent:	Thursday, January 27, 2000 2:11 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	1958 UBC Seismic
> 
> A client has asked me to review an existing building for compliance with
> the building code that was in effect at the time it was designed and
> built.
> In this case, that would be the 1958 UBC. Most of the code requirements
> are
> fairly clear and I believe my interpretations are ok, but a few issues
> have
> come up with respect to seismic loadings:
> 
> 1. Load combinations. Do I check (a) DL + LL + Seismic, or (b) just DL +
> Seismic? This is not stated in the 1958 UBC document. Therefore I would
> assume that (a) would be checked, but somehow this would surprise me.
> 
> 2. Direction combinations on EQ. The code lateral loads are
> straightforward
> to calculate for E-W loading and for N-S loading. However, do I check for
> combined E-W and N-S, or just for one at a time? This also is not stated
> in
> the 1958 UBC.
> 
> I am fairly cognizant of how these issues should be addressed to meet
> today's codes and other guidelines, but I am not sure of what was done 40
> years ago. I am somewhat concerned about using a "standard of care" in
> this
> re analysis that is compatible with 1960 practice. My dad once made a
> statement to me on the order of "give me enough analysis and I can show
> you
> that any building is overstressed." I am sure I could do that in this
> case,
> and don't want to.
> 
> Thanks in advance for any advice or recollections.
> 
> Mark Ketchum
>