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# Re: Rho in Diaphragms

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Rho in Diaphragms
• From: Darrell Hambley <dth(--nospam--at)red.primextech.com>
• Date: Tue, 02 Nov 1999 13:05:23 -0800

```Gerard,

Thank you for the insight. I was way off base when I was refering to
and Shakespear requiring cliff notes!
Back to the diaphragms on a 1-1/2 story, it looks like when I get my value
of Fp (equ 33-1 from 1630.2.9 and 1630.2.3.4) then I use that value without
any other multiplication and make sure the diaphrgams are designed for
that. The term "Fp" is what's confusing me. 1620.1.1 refers to Fp from 1632
(a Different Fp!!) and then goes on to say use this for Eh and thus E,
etc..etc... but the diaphragm "Fp" from 33-1 isn't mentioned in 1630.1.1.

a slight change of subject, About the 1.4 factor you noted in item 4)
below; If you calculate E in 30-1, then 1630.1.1 says to use this in the
load combinations of 1612 which is E/1.4 (12-9). Isn't this correct? If
Mark Swingle is reading this, Mark, I'm looking at a post of yours from a
few months ago....Where does the UBC say to "put the 1.4 factor back in"?
Boy, I think I need a road map!

>
>	I think you have a many issues here.
>	1) You are using the SIMPLIFIED method, requiring the 3*Ca/R value
>for diaphragms.
>	2) You are describing a transfer diaphragm, where the vertical
>resisting elements are parallel but have an offset. That is a Plan
>structural irregularity per table 16-M item 4. You need to look at those
>sections as well.
>	3) Rho does not apply to collector design (Section 1633.2.6). You
>need to determine the force demand to the shear walls and multiply that by
>omega or determine the limiting force parameter to your shearwall (or brace)
>that may allow you to use a force significantly lower than that obtained by
>using the omega. Examples of limiting factors are overturning, diaphragm
>yield, shearwall or brace capacity.
>	4) I don't think you can divide by 1.4 even in ASD. There were
>be true.
>	5) NO WHERE in the code does it say that E applies to diaphragms, Fp
>does. For the diaphragm itself, you do not have to consider RHO. Look at it
>this way, How can you improve the redundancy of a diaphragm? I don't know
>either.
>	6) The code needs refinement in its wording, we need the Seismic
>Design Handbook Volumes II & III to be published immediately, and we need a
>1"997 UBC for Dummies" to be published or "1997 UBC Cliff Notes" that says
>the intent of the code in plain english. I know these really helped me
>learning DOS and Shakespear respectively.
>
>	I guess I better add a disclaimer to my posts, It seems to be the
>right thing to do and also a funny anecdote.
>
>Civil Engineer, Associate
>CRJ Associates, Inc.
>email: gerardm(--nospam--at)crjarch.com
>tel: 650.324.0691
>fax: 650.324.0927
>web: www.crjarch.com
>
>	DISCLAIMER:
>	1st the Funny one (At least to me):
>
>	The following post is property of the National Football League. Any
>Broadcast or re-transmission without the expressed written consent of the
>NFL and the San Francisco 49ers is Strictly prohibited.
>
>	Now the Real One:
>
>	These views are mine alone. These opinions should not be construed
>to be policy at or the opinion of CRJ Associates.
>
>	AND FINALLY THE QUOTE:
>
>	"It's looks like one huge shit sandwich, and we are all gonna have
>to take a bite"
>	From the movie Full Metal jacket (Scene where the reporters from
>Stars and Stripes are meeting to discuss the turn of events in the Vietnam
>War at the TET Cease Fire) .
>
>	p.s.: Sorry for the foul language, but it kind of sums up some of
>the frustrations interpreting these changes.
>
>

```