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# RE: Rho in Diaphragms

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Rho in Diaphragms
• Date: Tue, 2 Nov 1999 14:01:46 -0800

```Darrell,

Glad to see that not all of us engin-NERDS (As my wife calls me) are total
stiffs and can appreciate some humor.

Take a look at section 1630.5 (Vertical distribution of force). I probably
should have labeled Fp as Fpx (So as not to confuse you further about
seismic coefficients). Fpx is the force to a particular floor from the
vertical distribution of the base shear V. Fx per EQT (30-15) is this

Fx= (V-Ft)Wx*hx/(SUM(wi*hi))   at each level. If you have a 1 story building
Fx=V=Eh minus the walls parallel to the direction of the earthquake
tributary to the roof..

It uses V not Eh, but in Eh is defined as equal to V in section 1630.1.
Anyway, Eh doesn't equal E. (Confused Yet?) E has the rho term. Why do they
even use V anymore if V = Eh ? ? ?

To conclude, E is not in the diaphragm equations. The V term is used. Eh
does not have Rho in it either.

If this code was published in Brail, it would be easier to decipher.

Hope this helps. Take it easy.

Civil Engineer, Associate
CRJ Associates, Inc.
email: gerardm(--nospam--at)crjarch.com
tel: 650.324.0691
fax: 650.324.0927
web: www.crjarch.com

These views are mine alone. These opinions should not be construed
to be policy at or the opinion of CRJ Associates.

Was it over when the Germans bombed Pearl Harbor???
(GERMANS ?) Let him go, he's rolling.
NOOOO ! ! !  And it ain't over now ! ! !
(Animal House)

> -----Original Message-----
> From:	Darrell Hambley [SMTP:dth(--nospam--at)red.primextech.com]
> Sent:	Tuesday, November 02, 1999 1:05 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Re: Rho in Diaphragms
>
> Gerard,
>
> Thank you for the insight. I was way off base when I was refering to
> UBC
> 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
> to
> >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.
> >
> >
>
>

```