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Re: rho

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By definition, "Story" is defined as: Space between levels. Story x is the story below level x. (Chapter 16, page 2-10 of 97 UBC)
From this I would use:
Level 1: 10' (Story 1, also Story Level 1)
Level 2: 20' (Story 2, also Story Level 2, roof)
2/3(height) = 13.3'
The maximum element-story shear ratio rmax is defined as the largest of the element story shear ratios, ri, which occurs in any of the STORY LEVELS at or below the 2/3 height level of the building.
My conclusion: At 2/3 height (13.3') you are AT the Story Level 2 shear elements and should therefore check rho in Level 2 elements and all levels below.
Since my initial post it occured to me to see what the Blue Book had to say about this issue. Section C105.1.1.1, 8th paragraph confirms my interpretation.
Now, how to firmly embed this in my mind so that when the question comes up again in our office 3 months from now......
----- Original Message -----
Sent: Thursday, December 13, 2001 9:45 AM
Subject: RE: rho

Assuming the following elevations for a two story building:
Level 1:   0' (Ground)
Level 2: 10'
Roof:     20'
2/3(Height) = 0.67(20') = 13.3'
Of the two elevated decks, Level 2 and Roof, only Level 2 is at or below the 2/3 point.  Hence, I would look at rho based on Level 2 only and not the Roof level.  Of course, if something noteworthy was happening in the structural layout at the Roof, I might look at it there, too, but I don't think the code requires it. 
Paul Crocker, P.E.
-----Original Message-----
From: Mark Baker [mailto:shake4bake(--nospam--at)]
Sent: Wednesday, December 12, 2001 2:48 PM
To: seaint(--nospam--at)
Subject: rho

Seems we revisit this issue every couple months in our office...
Calculating rmax for rho:
rmax is defined as "the largest of the element story shear ratios which occurs in any of the story levels AT OR BELOW the 2/3 height level of the building".
In a 2 story building, "AT OR BELOW the 2/3 height level of the building" would lead one to calculate r at 2nd floor and 1st floor.
Agree or disagree?