From: Mark Ketchum <mark(--nospam--at)ketchum.org>
Date: Thu, 27 Jan 2000 12:11:01 -0800
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.