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RE: ASCE 7-05 Cantilevered Column System vs. Inverted Pendulum-Type Structures

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The intent of the nonbuilding structures section was to stand alone.  We have many sytems that are not allowed of they were categorized as buildings, but are a reality in the nonbuilding structure world.  We just take the hits from low R values and height limits and carry on. 
 
The buildings people don't look at it quite that way.  I would suggest reading the ASCE 7 Sections 12.2.5.2 and 12.2.5.3.  The NEHRP commentary does shed some light that occured in the development process. 
 
The thought process was that with an R factor approaching a linear response, we could back off a bit on the overstrength factor.  Just stay lower than 35 ft tall "building" structures.  That would kill a lot of "nonbuilding structures" that are designed as cantilever columns. 
 
Regards,
Harold Sprague



From: Jnapd(--nospam--at)aol.com
Date: Tue, 11 Mar 2008 15:58:41 -0400
Subject: Re: ASCE 7-05 Cantilevered Column System vs. Inverted Pendulum-Type Structures
To: seaint(--nospam--at)seaint.org

Bill
I use line G.  1. in table 12.2-1 and design base plate as moment connection.
 
The ASCE committee people must not design buildings with patio areas or widow walls in a smaller scale than the main building, and especially not residential.
The Inverted Pendulum column is present in most residential where there is a view in one if not several directions even to your own yard.
 
The Inverted Pendulum column as indicated in table 15.4-2 should be in table 12.2-1.
If the intent was there the English is terrible. If in Section G of table 12.2-1 the intent of items 1-7 is to describe the type of connection at the joints, which is the way we interrupt it to be, it could have been worded such that engineers do not have to figure out what the real intent is. 
 
If you read 2003 NEHRP Commentary section 4.6.1.5 it suggest you design the base connection for 1.5 x actual moment and .5 x actual moment at top.
 
 
 
In a message dated 3/11/2008 10:59:15 AM Pacific Standard Time, t.w.allen(--nospam--at)cox.net writes:

What’s the difference?

 

My (current) situation is a two story SFR. One edge of the second floor is supported by a beam supported by three steel columns. This allows room for a car port. Yes, it sounds like the typical tuck-under scenario.

 

I’m not sure I can take the loads back to the next SW (only 10’-4” away) due to the second floor condition. I would rather take the tributary load out in the three steel columns and design them accordingly. However, I’m in Seismic Category D and it appears Cantilevered Columns is NP. There are no seismic coefficients for Inverted Pendulums in Table 12.2-1 but there are in Table 15.4-2. However 15.4-2 refers to “nonbuilding structures not similar to buildings”.

 

Can someone clear this up for me?

 

 
Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA





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