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[SEAOC] Re: [SEAOC] Re: [SEAOC] Plywood Shearwall Deflection

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I, too, have used the UBC Standard's design criteria for plywood shearwall
deflection and have found that the story drift on narrow panels exceeds
the allowable story deflection by as much as 300 percent. 
My question, though, is if there is a design criteria for a shear panel
that spans across an opening. In other words, how do you determine the
story drift on a ten foot wide shearwall that has a 4 foot x 7 foot high
opening in the middle of it? This makes the assumption that the area above
the opening is part of the panel (also assuming that it is adequately
straped both top and bottom to the adjacent panels). How do you determine
the deflection of the combined system without isolating the individual
panels.
Tom's recommendation is valid and is the customary method of using the
panel above the opening to reduce the effective hight of the shear pier
and thus the H/b ratio of the panel under consideration. In this example,
the panel is still too narrow to comply. The only reasonable solution
(other than provideing a stiffer element such as a frame) is to combing
the piers and analyze the entire system for deflection. 

This leads to another question. Will the City of Los Angeles (or any other
building department that complies with the same design criteria) allow the
use of a narrower panel width if the engineer designs the panel for story
drift in accordance with the UBC Standard? If they allow the design and a
problem occurs in the future, is the engineer liable for "errors" based
upon his design assumption and the acceptance of the city?

Your input is greatly appreciated on this issue. 

Dennis Wish PE

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