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[SEAOC] Re: Gyp. board shear walls in LA

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As a young engineer, who didn't know any better, I one time attempted to use
gypsum board in my calcualtions for the wind resisting system of a 6 stroy 
condominum. I very carfully subtracted about 15 psi for the boards
contribution to the overall lateral resistance of the structure.

My then boss, and later partner told me someting have never forgotten: "Never
confuse stiffness with strenth."

He explained the the gypsum walls would fail long before the reinforced
masonry infilled walls shear walls and the somewhat (but not very) moment
resistant flat plate/column system and therefore would not be avliable at
the ultimate level for strength.

He further explainted that the frame would not be worth much either since it
was quite limber, (not stiff) in relation to the walls, and that it would
pick up up very little in relation to the walls at ultimate. He said it was
better to let the frame handle the P-delta effects of the vertical load and
forget about it.

After many years of designing structures, many with finite element
teciniques and shear wall frame interaction, I still find him right.

Mabey it the gyp board was the main system, it should be considered, but if
there are many plywood or other walls, I take a careful look at where each
items would fail, based on the load that its stiffness would give it in the
loading cycle.

John Pepper
The Pepper Engineering Group, Inc.
20895 East Dixie Highway
Aventura, FL 33180