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

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Issue #1

Can you accomplish a moment connection between shear walls
and the panel above the walls....

When one designs a horizontal wood panel diaphragm with an opening,
one usually bases the analysis on the assumption that 
the diaphragm behaves similar to a vierendeel girder
(for example, pg 8.35 of the "Wood Engineering
and Construction Handbook," Faherty and Williamson),
and one provides framing members tangent to the
opening to develop the required forces into the surrounding
diaphragm.

Mr. Wish's system is only different in that it is
oriented vertically, and the opening happens
to be at the diaphragm periphery.  Moments
could be developed between Mr. Wish's columns
(shearwalls at the opening sides) and the
beam (panel over the shearwalls and door),
much like those in a horizontal diaphragm
with an opening.  And, of course, moments
would be developed at the base of the columns
by the hold-downs.


Issue #2

How do you apply the Code proportion limits to
moment resisting frames constructed of
wood sheathing shear walls...

If one does make a "moment resisting frame"
out of this system, perhaps one could argue that
the 2:1 ratio applies not to the full height of the shear
wall  but to the height at the point of 
inflection of the "column."


Issue #3

How do you calculate the deflection of such a frame
or a diaphragm with an opening...

The deflection of the moment resisting frame
(the original poster's goal) could
be determined analytically, with some tedium,
by breaking the system into its parts and computing
deflections and rotations for each.   But I've never
done it.

Dave Evans, PE


At 01:03 PM 7/3/96 PDT, you wrote:
>Dennis,
>
>From what I read, it would be more appropriate to call your system a wood
>frame. The two shearwalls acting as columns, and the connection above the
>door header acting as a beam.
>
>Now, the question is, will this frame work? I don't think so. Primarily
>because you can not accomplish a moment connection in wood members. A pin
>frame will not work.
>
>I recommend that you look at the whole wall. Consider moving the door such
>that you get at least one shear panel that meets the h/d requirements.
>
>Hope that helps.
>
>Shafat
>
>
>
>
>>A friend that lives in Los Angels recently contacted me to see if I could
>>help him with this problem. I would like some input on the following
>>hypothetical problem:
>>
>>The L.A. City building department increased the H/b ratio of 2:1 for
>>plywood shear panels - where, prior to the Northridge earthquake the ratio
>>was 3.5:1. The height of the panel was twelve feet from foundation to
>>lateral restraint at the roof diaphragm.  The design has a three foot
>>shear panel on either side of a four foot by seven foot door. The panels
>>don't make the 2:1 ratio required by the ordinance.
>>I responded by explaining that I thought you could exceed the 2:1 ratio if
>>you design the panel for deflection based upon the 1991 UBC standard. He
>>indicated that he did not feel comfortable with this based upon the
>>current ordinance. He further explained that as far as he knew, there was
>>no new testing on wall deflection.
>>
>>Classically, the tow panels can be combined across the opening as long as
>>each pier is adequately anchored and braced. The question came as to how
>>to determine the deflection of the two piers when tied across the opening
>>and acting together.
>>
>>Does anyone have a method for determining shear wall deflection with an
>>opening in the shear panel?
>>
>>Dennis Wish PE
>>
>>...
>>
>>
>
>...
>
>
>

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