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FW: Redundancy Factor

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One minor correction to the rho calculation below.  The shear assigned to a
bay is divided by the story shear under consideration.  The maximum shear
assigned to a bay is .7*2*4 kips=5.6 kips.  The story shear at the base is
46.2 kips and so r max =5.6/46.2=.12.  Using the other numbers provided, rho
is now -1.43 which still indicates that you have a very redundant building.
Use rho=1.

>From a cursory look at the facts, this seems to be a very unsual building.
By the assignment of shears, it looks like a 4 bay by 3 bay building which
assuming even bays in all directions yields about a 14 ft. bay spacing.
Unusual, even for semiconductor work.

Let me know if I'm in the ballpark.

Curt La Count
Jacobs Engineering
Portland, OR

From: Dan Connell
To: seaint(--nospam--at)
Subject: Re: Redundancy Factor
Date: Tuesday, June 08, 1999 10:00PM

I am just finishing a course at UCI which included this subject so I'll tell
you what I have learned:

The rho factor is a penalty factor for a non redundant system.
When calculating the rmax factor, you use two adjacent columns.  70% may
only be used on interior columns only.
So say that you have a 4 column frame with the exterior columns taking 2.1 k
ea and the interior ones 4 k ea and the total story shear is 20.2 kips.
r1 = (2.1+.7*4)/49 = 0.1
r2 = (.7*4+.7*4) = 0.11
rmax = 0.11 for this frame at this story
you must find rmax for ea frame at ea story.
note that only the bottom 2/3 of the building need to be considered.
if rmax = .11 and Ab = 2312,
rho = 2-(20/(rmax(Ab)^1/2)) = -1.78
tne negative number says that you have a redundant system and you should use
rho = 1.

let me know if this is correct,
 -Dan Connell

>From: rlewis(--nospam--at) (Richard Lewis)
>Reply-To: seaint(--nospam--at)
>To: seaint(--nospam--at)
>Subject: Redundancy Factor
>Date: 09 Jun 1999 01:45:38 GMT
>I would like to start a new thread on the Redundancy Factor, Rho, of the
>I have a 2 story concrete framed building.  Total base shear is 46.2 kips.
>Worst case shear in a frame line is 12.2 kips, with 4 columns.  Ground
>area is 2312 SF.  Now for a multi bay frame I use 70% of 2 columns to
>calculate Rho.  I get
>ri=0.7*(12.2*(2/4)/46.3 = 0.092  (from paragraph in 1630.1)
>Rho = 2-20/(0.092*sqrt(2312)) = -2.5 (eq. 30-3)
>Now this Rho is less than 1.0 so Rho min = 1.0  (paragraph in 1630.1)
>My question is, did I do this right?  Can I calculate a Rho value less than