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RE: ASCE 7-05 Cantilevered Columns?

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Per Section 11.2, Inverted Pendulum-Type Structures are defined as structures in which more than 50% of mass is concentrate at top of a slender cantilevered structure and in which stability of the mass at the top of the structure relies on rotational restraint to the top of the cantilevered element.
 
Suresh Acharya, S.E.
 


From: Larry Hauer [mailto:lrhauer(--nospam--at)hotmail.com]
Sent: Monday, February 25, 2008 12:54 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: ASCE 7-05 Cantilevered Columns?

Bill,
 
Good point, but still not sure what would be used- An R of "3" for "distributed mass cantilevered structures", or an R of "2" for "invreted pendulum" structures. Averaging these out comes up with an R of "2.5", which, again, seems reasonable to me, (back to an R of "2.2" for the '97 UBC/'01 CBC).
 
Larry Hauer S.E.



Subject: RE: ASCE 7-05 Cantilevered Columns‏
Date: Mon, 25 Feb 2008 12:25:30 -0700
From: William.Sherman(--nospam--at)CH2M.com
To: seaint(--nospam--at)seaint.org

I suggest looking at Table 15.4-2 for "nonbuilding structures not similar to buildings" - but it still requires some interpretation.
 
Bill Sherman
CH2M HILL / DEN
720-286-2792
 


From: Larry Hauer [mailto:lrhauer(--nospam--at)hotmail.com]
Sent: Monday, February 25, 2008 12:16 PM
To: seaint(--nospam--at)seaint.org
Subject: ASCE 7-05 Cantilevered Columns‏

Michel,
 
I don't think Sec. 12.2.5.6 or .7 is applicable since those would be OMF's with steel beams and moment connections. What I am talking about are "flag pole" structural elements such as cantilevered WF columns out of a grade beam or cantilevered pile foundations. Unless someone can convince me other wise I will be designing them with an "R" of 2.5 per Table 12.2-1 Item "G.1", (Special Steel Moment Frames". My rational is that the columns don't know whether they are "Special" or "Ordinary", (Item "G.3"), since there is no moment connection at the top, and an R of 2.5 equates to approximately an R of 2.2 which was required in the '97 UBC. I feel an R of 1.25 is way to conservative.
 
Any opinions would be appreciated.
 
Thanks in advance,
 
Larry Hauer S.E.



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