Tall Shear Wall

TimmyH76 · Mar 6, 2007

Has anyone here ever had any experience designig very tall shear walls? I have walls on a private airplane hanger that we are designing that are 20' x '5'3" wide. The framing is 2" x 6" SYP. We have structural sheathing on both sides. The chords have been the problem. I decided to use steel tubes as the chords. I have bearing plate on the top and bottom to spread the load out on the top and sill plates. On the outsite of either tube I have 3" framing to nail to. The anchors for the chords are being tied directly to the foundation.....Any thoughts or anything your would specifically look at?

NKT · Mar 6, 2007

I would look at the wall's aspect ratio... The UBC limits the ratio to 2:1 for shearwalls, with some exceptions up to 3.5:1 (not sure about the IBC). Your wall has a ratio of 3.8:1. It seems that calculated deflections would be unacceptable.

A couple of alternatives to think about:

1) Moment frame(s)

2) Ignore the slender panels and perform a rigid diaphragm analysis to transfer the loads to the other three sides of the building, assuming you have some solid panels to work with there.

TimmyH76 · Mar 6, 2007

Actually the wall is 18' tall. So yes if they were 20' I would have been out of the 3.5 limit. The aspect ratios are the same for IBC 2:1 and 3.5 to 1 max with special provisions. The deflections were ok...mostly due to the steel tubes.

Thanks

csd72 · Mar 6, 2007

NKT,

I am sure you are right, but it sounds crazy to me.

A portal frame will be much more flexible than the 3.8 to 1 shear wall with steel tube chords.

This is the problem when you try to have codes that cover everything, you end up with inconsistencies.

NKT · Mar 6, 2007

cds72: I actually meant to present the option of a steel moment frame rather than a wood portal frame.

My concern is with inconsistencies between strength and rigidity: I assume the other sides of the building have mostly solid walls. If that is the case, much of the lateral load will distribute to the other more rigid walls before the slender shearwalls deflect enough (rigidity) to take the load they were designed for (strength). When the roof diaphragm is not designed for this action, you can end up with portions of the diaphragm being overloaded.

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