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[SEAOC] wood panel shear wall/frames

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With regard to Dennis Wish's question regarding deflection of
a shear wall with an opening, and various responses....


Issue #1

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

Various messages on this mailing list have said it can't be done, but...

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 truss.
See, for example, pg 8.35 of the "Wood Engineering
and Construction Handbook," Faherty and Williamson,
pg13 of "Guidelines for the Design of Horizontal Wood
Diaphragms," Applied Technology Council, Pub. No. ATC-7,
and Appendix E of "Research Report 138," American
Plywood Association.

That is to say, moments are developed in the portions of the
diaphragm adjacent to the opening, and  one provides
framing members tangent to the opening, and extending
beyond,  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 the framing in an opening in a horizontal
diaphragm.  And, of course, moments
would be developed at the base of the columns
by the hold-downs.


Issue #2

How do the Code proportion limits apply to
moment resisting frames constructed of
panel-sheathed 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, more generally, of a diaphragm with an opening...

The deflection of the moment resisting frame
(Mr. Wish's goal) could
be determined analytically, with some tedium,
by breaking the system into its parts and computing
deflections and rotations for each.   

ATC-7, page 21, puts it another way, for horizontal
diaphragms with openings:  "The effect of an opening on the
deflection is determined from the classical analysis
used to derive the second term of the equation, 
using integration over segments of the diaphragm."


Dave Evans, PE


>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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