Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Period Calculation for One Story Building with Flexible Diaphragm, FE

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I guess you really want an answer, Frank.   Well, OK.

Let's do it the Navy way according to Herman Wouk, who put these words into
Lt. Keefer's mouth in advice to newly arrived Ens. Keith aboard USS Caine,
in The Caine Mutiny:  "The Navy is a master plan designed by geniuses for
execution by idiots. If you're not an idiot, but find yourself in the Navy,
you can only operate well by pretending to be one. All the shortcuts and
economies and common-sense changes that your native intelligence suggests to
you are mistakes. Learn to quash them. Constantly ask yourself, 'How would I
do this if I were a fool?' Throttle down your mind to a crawl. Then you'll
never go wrong."

On that basis, use whatever method FEMA 310 gives for determining diaphragm
deflection. If none is given, as seems to be the case, then use a method in
other standards, if any, referenced in FEMA 310. If none, use a method in
any reference or code you believe is well-accepted by those geniuses who
designed FEMA 310 and by everybody else. (You have. It is the UBC provision
you cited.)  
The question as you pose it is, how do we follow that UBC provision with
respect to the chord component and its area of cross-section and elastic
modulus?  And the answer is:  As fools would, quashing any common-sense
changes that your native intelligence suggests. 

In your poured-closure tilt-up, use only those specially provided horizontal
bars that the original engineer envisioned as chords, forsaking all other
elements. Maybe it is two no.6 bars. That continuous 4x4x1/4 steel angle?
Forget it, unless it is obvious that the original designer meant it to be
the only chord. The routine horizontal bars that splice in the closures?
Ignore them; they are there for other reasons. Area of concrete in the
vicinity of the compression chord? It wasn't called the chord, so it isn't.

Remember, FEMA 310 came from the government and it is here to help you. 

You don't think your result will be realistic if you do it like a fool?
There you go, thinking again. For your purposes, the result isn't supposed
to be realistic, it is supposed to be in accordance with FEMA 310. That's
the genius in it.

Hope this helps. If not, put two steel balls in your coat pocket and reply
by e-mail in the morning.

Charles O. Greenlaw, SE, and former Lt(jg) CEC USNR   
(Thanks to past SEAOC president Jack Barrish for long ago reminding me of
that passage in The Caine Mutiny in response to my own building code laments.)

At 03:51 PM 6/13/98 EDT, you wrote:
> it would seem to be a very simple problem how to calculate
>the "actual" fundamental period, T, of a one story building with a flexible
>roof diaphragm, using FEMA 310, page 4-3, Section, Equation (4-1).
>FEMA 310 will be - or more accurately is now - the "de facto" standard for the
>seismic evaluation of buildings, because of the premature release by FEMA as
>FEMA 310 in one of its "yellow" covered documents, despite the fact that it
>has not been carefully reviewed and "approved" following the ASCE Standards
>Frank E. McClure    FEMCCLURE(--nospam--at)