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Re: URM

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Mark D. Baker wrote:
> 
> Thanks to Dennis for responding to my earlier post. I am suprised no one
> else has an opinion regarding collectors for crosswalls.
> 
> By definition (see UCBC commentary) "A crosswall is not considered as a
> shear wall in that it need not be designed for the tributary loads of
> the flexible diaphragm or diaphragms. The crosswall decreases the
> displacement of the center of the diaphragm relative to the shear walls
> and wil provide damping of the response of the diaphragm to earthquake
> shaking."
> 
> My take on this is that installation of collector elements would not be
> appropriate in that the crosswall is not carrying (collecting) trubutary
> load of the diaphragm. The code requirement for the connection of these
> walls to the diaphragm is only that they be connected for the crosswall
> capacity. In most cases this can be achieved within the length of the
> crosswall.
> 
> Have I sufficiently baited anyone else to respond ? :)
> 
> Regards,
> 
> Mark D. Baker
> Baker Engineering
> 


Mark:

I agree with Frank Lew, and also beleive your interpretation is correct.
If you look in your SEAOC commentary on Appendix Chapter 1 of the UCBC  
(the one Frank Lew was on the committee for)
it will also further differentiate crosswalls based on whether they are
new or existing.  If they are new they must be attached according to
their capacity as you stated.  If they are existing, you only need to
verify that it is attached to the diaphragm and not just the ceiling
joists, if so, then you don't need to check the connection to the
diaphragm.

Mickey Estey, P.E.
Robert Lawson Structural Engineers