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- Subject: [SEAOC] wood panel shear wall/frames
- From: "Tryck Nyman Hayes, Inc." <tnhanc(--nospam--at)alaska.net>
- Date: Mon, 8 Jul 1996 13:35:15 -0800
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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