Residential Shear Wall Design Problem 1

[markreme_pe]

Hi All,

I have come across an interesting residential braced wall problem. This is a new residential project on the NJ coast (120 mph wind) where the home will be elevated on wood piles. There is a rear 14' deep x 30' long enclosed porch (again about 10' off grade on piles). The architect/homeowner wants windows (6' high windows) along the whole rear wall leaving only 1'-4" on the wall ends and only 1' adjacent to exit door. The wall height is about 10' (9' ceilings). The architect worked with another structural engineer to design the majority of the structure and is now no longer on the project. My scope is to design the rear braced wall. My problem is the space at the ends and adjacent to the door is less than the minimums for the various sheathing/bracing methods allowed by IRC 2015. I tried using a steel frame (design calcs call for HSS 8 x 3 x 3/8" columns and beam), but have concerns about attaching the columns to the lower wood girder (the loads are quite high (~9.5 ft-kips moment). I suggested using a steel beam atop the piles, but the owners want to try and keep as much of the original design as possible.

Ive been spinning my wheels looking at the IRC and playing with steel details. Im also thinking of talking to Simpson about some of their solutions, however based on the information on their website it does not seem that their products will work with the space available.

I can ask the architect to shorten the windows but i am for now keeping that as a last resort. Any thoughts or suggestions?

Thanks for the help.

Mark E. Reme, PE
Reme and Associates, LLC

 

[DaveAtkins]

Can you do a three sided diaphragm, and ignore the rear wall?

DaveAtkins

 

[PengStruct]

Ditto what Dave Atkins said. Check the criteria in ASCE7 to see if you can use a 3 sided diaphragm. Or go back to the owner with a list of proposed changes to the design such as longer shear walls or introducing the steel beam and frames and let them decide which way to go. You could spend a lot of time designing your own wood shear walls with straps, double sides, holdowns, etc. For a single family house the fees never seem to be high enough to warrant such detail.

 

[JoshPlumSE]

You might check to see if you can do a simpson strong wall or something in those limited spaces. Giving their reps a call is probably a good idea. They may know about solutions to odd cases like this. If not, then I would go with steel framing of some kind (moment frame or cantilever columns).

Three sided diaphragms are possible, but problematic (at least here in seismic country). If you use them in non-seismic country, just make sure the open side can take all the additional deformation and P-Delta effect that you'll get during a design event.

 

[KootK]

Were it not for three sided buildings with solid glass non-sides, the one percenters would be homeless.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[racookpe1978]

What if you doubled the floor thickness - if there is a basement, or put plywood under the ceiling rafters instead of drywall if there is not - and use that membrane across the top of the three walls to prevent twisting? If a high raised interior V-roof, that would not work as well though.