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Re: Wood Fr-Upgr : What I'll do and two more questions

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In a message dated 10/30/98 9:01:17 AM, rjbossi(--nospam--at)sonic.net writes:

>1.  calculate the EQ load the existing structure would deliver to the common
>wall using the current code tributary area methods and compareit to the
>capacity
>of the existing roof diaphragm.  Use whichever is less (most likely the
>diaphragm capacity) since the wall won't see more load from the original
>structure than the existing diaphragm can deliver.
>
That's true for now, but what if they upgrade the existing house in the
future?  

We're faced with a similar situation in the Bay Area right now.  Bicyclists
want a bike lane included on the planned new east half of the Bay Bridge.
Opponents say there's no bike lane on the existing west half, so you'll only
be able to get halfway to San Francisco.  Supporters respond that if we don't
include a bike lane on the east half it will preclude bikes for a hundred
years, even if the west half is eventually rebuilt or retrofitted.  It's all
in how far ahead one looks. 

Does anyone else assume full tributary area to new shear walls, assuming that
they might be able to receive the load in the future even if they can't right
now?  

Ralph Hueston Kratz, S.E.
Richmond CA