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

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Mark,

You have a good point.  Canopies are not specifically listed in table 16-P,
the inference is that the default values apply.  But Section 1634.2 allows
the designer to use Section 1629.

Regards,
Harold Sprague
The Neenan Company


-----Original Message-----
From: Mark D. Anderson [mailto:mda(--nospam--at)alaska.net]
Sent: Monday, September 27, 1999 12:24 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: 1997 UBC Section 1634 - Non-building Structures question


Regarding non-building structures, how does 1629.8.3 Item 2 fit into this
subject?  If the structure has a lateral force resisting system covered by
Table 16-N, then Section 1630 is applicable, in accordance with 1629.8.3.
Does the code language necessarily invoke Section 1634 for non-building
structures that are previously covered by Section 1630?

Unfortunately, 1629.8.3 is written as a permissive provision, and 1634 as a
mandate.

Detached roof canopies are an example of a structure type that appear to be
addressed by both Sections 1630 and 1634.  For the case of roof canopies
which are not of the cantilevered column type system, the difference between
the design requirements of the two sections is substantial, since nothing in
Table 16-P is directly applicable, and apparently line 11 is the default.

Mark D. Anderson
Anchorage, AK


-----Original Message-----
From: Harold Sprague <harold.sprague(--nospam--at)neenan.com>
To: 'seaint(--nospam--at)seaint.org' <seaint(--nospam--at)seaint.org>
Date: Thursday, September 23, 1999 9:45 AM
Subject: RE: 1997 UBC Section 1634 - Non-building Structures question


>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
>