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RE: R=3 Application for Non-building Structures

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Dmitri,

Thank you for the confirmation. That is how I read the ASCE 7-05 as it
pertain to non-building structure (i.e piperack). 
You made a statement that "AISC 341 does not generally apply to building
structures" (same statement is also made by the professor when I
attended the Seismic design Manual Seminar), yet in order to use a R=3.5
in table 15.4-1 the detailing requirement states that AISC 341 to be
used. 

In AISC 341 page 1-7, section on R Equal to 3 Applications starts with
the word "Building"....then it continues with "Seismic provisions are
not intended....... structures"....

Thanks again for the reply.

KP

-----Original Message-----
From: Dmitri Wright [mailto:dmitri(--nospam--at)cascade-structural.com] 
Sent: Friday, June 27, 2008 4:50 PM
To: Seaint
Subject: R=3 Application for Non-building Structures

KP,

In my experience, pipe racks are not typically considered building
structures, and therefore AISC 341 does not generally apply to them.  I
think I have heard rumors that AISC has started work on developing a
standard for non-building structures (anybody from AISC can feel free to
squash or confirm the rumors!).  To be consistent with the IBC, ASCE7
and AISC, this appears to limit the R to 3.0 for most cases.  If the
pipe rack is inside and can be considered a component of the building,
it is covered in ASCE7 section 13.6.  If it is an exterior freestanding
structure, it is covered by ASCE7 section 15.5.2, which references Table
15.4-1.  On this table, the designer can choose different R values, each
with different limits and requirements.  If you are in SDC B, you can
use an R=1, and design with AISC 360, with no restrictions.

Dmitri Wright



All,
=20
We have a pipe rack that is SDC B, Ordinary Moment Frame (OMF) in the
transverse and Ordinary Concentrically Brace Frame (OCBF) in the
longitudinal direction. The question is can we use Table 12.2-1 (page
122) ASCE 7-05, H. STEEL SYSTEMS NOT SPECIFICALLY DETAILED FOR SEISMIC
RESISTANCE, EXCLUDING CANTILEVER COLUMN SYSTEMS, R =3D 3 and avoid using
the AISC 341 - Seismic Design Manual?
=20
Table 12.2-1 (pg 122) may not be applicable for pipe rack design
(non-building structure similar to building) because chapter 12 in ASCE
7-05 is designed for building application only. Therefore section H for
"steel systems not specifically detailed for seismic resistance", may
not be applicable.
Pipe rack is covered under Table 15.4-1 - Non-Building Structures
Similar to Building, and the detailing requirements for ordinary moment
frame spell out AISC 341, so special detailing is required using a R =3D
3.5. If the use of R=3D3 is allowed a section similar to section H on
table 12.2-1 will be placed on Table 15.4-1? So unless we use R =3D 1.0
(unlimited height), we have to go by the AISC 341 with special seismic
detailing.
=20
Does anybody have experience on this issue before? please advise.
=20
Thank you in advance.
KP



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