Custom lake home with tall wall great room 2

[TroyD]

(Seismic Category A, Northern Minnesota, Exp. category 'B' assumed). A client needs engineering for this custom lake home (example image) with tall wall great room. Lots of glass, and the peak is approx. 25' tall. Also the roof cantilevers out ~6' at the peak. I have not put pencil to paper but this looks like a challenge to satisfy the shear wall design with LSL framing and OSB sheathing. The 6' wall segments at the ends are probably adequate, and the slender tall wall segments between the windows support glulam beams holding up the cathedral roof, so I have some roof dead load to consider for resisting uplift.

At initial glance, is this something that might warrant a steel moment frame? I am somewhat familiar with Simpson Strong-Wall moment frame products. Or perhaps I should evaluate this wall as FTAO (Force Transfer Around Openings) method with some Simpson coil straps to hold these panels together and distribute the in-plane lateral loads to the end wall segments.

Any advice/input is appreciated!

 

[Pmtottawa]

Sure looks like the Timberblock projects I used to do...

 

[driftLimiter]

@TroyD. This type of building needs frames a lot of the times. That lakefront window is often too much to get the walls to work. That being said it definitely depends on the loading and what you've got to work with. If you do need to look into frames I would definitely investigate the prefabricated options. Most of them are designed to overcome the beam and column bracing requirements that come along with IMF and SMF configurations and are notoriously difficult to achieve in wood framed buildings.

Typically I investigate all possibilities and eliminate them before moving to steel frames but alas many times they are needed where I am, high seismic, high wind, and high snow loads make for a lot of fun.

 

[TroyD]

driftLimiter,

I'm reading some discussions on 3-sided roof diaphragms and also considering an interior shear wall along the stairs to the upper level to possibly provide some rigidity, and reduce the tributary area to this gable wall. This design is a near replica of this example photo, and they apparently built that gable wall with wood/LSL stud framing. Whether it satisfies the design wind loads, however, is unknown.

Wall will certainly need to be 2x8 LSL studs to satisfy out-of-plan C&C loads.

On a similar custom home with tall, slender great room walls, I spec'd out 18" wide Simpson Strong-Wall High-Strength Wood Shearwalls at the corners, anchored into the foundation wall with 1" diameter rods. Something like that might be appropriate here...

 

[driftLimiter]

@TroyD yes the strong walls help with narrow aspect ratio applications. Sounds like your taking the right steps to design that wall to me. Lucky you don't have to worry about seismic .
The three sided diaphragm idea is interesting I have thought about it for similar scenarios but I haven't seen anyone doing it in practice (doesn't mean that people out there aren't using it).

There are limitations to the 3-sided diap. approach for wood, you can check out NDS wind and seismic for that.

I'd be interested to see what your preliminary thinking is on the basement retaining wall. Are you planning to use the building to support that? How are you going to think about the lateral system there as well.

 

[Pmtottawa]

I had psl columns as well as Simpson eccq / ccq caps and hdu5 at the bottom.
Intermediate I used a 9 1/2 2 ply lvl.

And used 3 sided diaphragm/ shear walls. With bracing to back wall

 

[msquared48]

No moment frame needed. Done several of these homes over the years. You have two good shear walls to either side of the window wall to use, log or plywood.

The vertical angle at the center of the window wall reduces the l/r ration of the central column at the angle.

Don't make this more complicated than it is. KISS...

Mike McCann, PE, SE (WA, HI)