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Re: Finishing a curved ceiling - need some advice

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Nels, 
This is possible since the home is exposed and on a level property up in the 
mountains. 
I found the most useful information on the USG website. It appears that their 
1/4" high strength gypsum is intended for this type of installation and 
should have been installed in multiple layers.
Although the "s" occurs in the great room, there are sufficient blocks 
surrounding the greatroom and designed to resist lateral loads in each 
direction. In orther words, I over-compensated and applied lateral loads 
equivalent to the full base shear in each of four directions and designed 
each of the four blocks surrounding the greatroom for the full load. I doubt 
that this is due to deflection caused by lateral wind forces since the winds 
have not been unusually high in the last three or four months in this area.

All preliminary research indicates that the contractor used the wrong board 
and the tensile strength of the backing was not sufficient to handle the 
stress of the curved surface. 

The contractor tried to pass the responsiblity back to me yesterday and the 
owner, after receiving some 20 pages of information from me that I collected 
from USG and the responses on this list, was convinced that the contractor 
should have used his resources and contacted USG and the GLB supplier (who 
designed the curved beams) before installing the ceiling.

The architect, who had been out of town for the last week, called me from New 
York to tell me that I had defused the potential problem with the owner by 
supplying suggestions for correcting the problem while the contractor had 
simply spent the last three months patching.

With this said, I wish to express my gratitude to all on the list who took 
the time to respond publically or privately. 

Dennis

In a message dated 10/14/1999 7:37:52 AM Pacific Daylight Time, NRoselund 
writes:

<< Dennis,
 
 Could the cracking have something to do with the action of the GLB as a 
seismic strut or collector delivering the lateral loads accumulated from one 
end to the beam to a shear resisting element at the other end of the beam, 
tending to straighten the S?  Have you been getting winds lately that would 
account such lateral loads?
 
 I've found the Plastering Information Bureau to be very helpful in 
identifying plaster and drywall problems.  It seems like they've seen it all. 
 I've talked with Dick Gorman 818-340-6767.
 
 Nels Roselund
 Structural Engineer >>