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RE: 1997 UBC Section 1634 - Non-building Structures question

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Ed,
 
I don't know why the exclusion is not extended to the nonbuilding structures
that are structurally similar to buildings.  I would say that it is an
oversight.  The begotting began with the NEHRP, and I am not aware of any
discussion departing from the intent contained in the NEHRP.
 
Harold Sprague
The Neenan Company 
 

-----Original Message-----
From: Ed Marshall [mailto:elmarshall(--nospam--at)HASimons.com]
Sent: Tuesday, September 21, 1999 5:18 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: 1997 UBC Section 1634 - Non-building Structures question



Section 1634.5 of the 1997 UBC specifies increased minimum seismic loads for
"Other Nonbuilding Structures" relative to those for buildings.  It says
that nonbuilding structures not covered by Sections 1634.3 & 1634.4 shall be
so designed.  Section 1634.3 covers rigid structures and Section 1634.4
covers tanks with supported bottoms.  Section 1630.2 (non-building
structures with structural systems similar to buildings) appears not to be
exempted from the increased minimum.

In contrast, in the 1994 NEHRP Recommended Provisions and in ASCE 7-95, the
exception applies to all three categories (rigid structures, tanks with
supported bottoms, and non-building structures with structural systems
similar to buildings).   See NEHRP section 2.7.5 and ASCE 7-95 section
9.2.7.5.

It seems that logically the exception should apply non-building structures
with structural systems similar to buildings since the R factor is typically
coming from UBC Table 16-N rather than Table 16-P.   I'm inclined to assume
this is a typo in the code (although I don't find it corrected in the
Errata).  Does anyone know of any other reason why the 1997 UBC deviates
from the 1994 NEHRP Recommended Provisions in this regard?

Ed Marshall, PE