CMU block and Hollow Plank Building

[Engin1]

Hello,
We have a block and plank hotel project about 180ft x 70 ft, 5 story. It will have CMU walls as bearing and shear walls for the shorter direction. The other direction has light gauge stud wall as non- bearing walls. I am thinking to use the light gauge stud walls as shearing walls. Anyone done similar jobs? What's the connection detail between light gauge shear wall and diaphragm (hollow core plank)? The plank may have more than 1" camber. thanks!

 

[dik]

Can you use the stair cores and the elevator shaft in the long direction with the narrow wind exposure? Are you in a seismic area?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Engin1]

dik, it's in seismic design category B. Stair and elevator shaft in that direction is short, they won't be enough.

 

[dik]

Can you use strap X-bracing with the CFS wall construction? or introduce some masonry shear walls?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[milkshakelake]

5 story cold formed steel walls can work if you detail it correctly. There's a lot of intricate details and calculations. Do you have experience in this? It's a deep subject.

You can use strap bracing for shear if there are a ton of shear walls that go all the way down. You might need gusset plates and holdowns for tension. Calculate each connection for screw/weld, gusset plate, and column/post/jamb. Stiffness might need to be calculated with a non-linear response because the straps only work in tension.

 

[XR250]

There's a lot of intricate details and calculations

....and a lot of intricate details to construct. At the end of the day, it will not be designed and/or constructed properly. (based on my 20 years of light gage design) I would use masonry for shearwalls in the long direction as well.

 

[Engin1]

dik, ARCH wants to use CFS wall, so it will be strap X-bracing or CFS with sheathing, I have not checked the shear load yet.

 

[Engin1]

milkshakelake, this is my first project using light gauge shear walls for block and plank building. there will be a 5ft shear wall every 27ft. It will need hold downs for tension.

 

[Engin1]

XR250, thanks for your suggestions. The ARCH does not want to use CMU in the long direction. Have you done some similar jobs using cfs shear wall for cmu and plank building?

 

[dik]

Can you do it with a continuous 'threaded rod' going full height, and tying your cross-bracing anchors to it. I've not done one, but doesn't seem too difficult.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[XR250]

XR250, thanks for your suggestions. The ARCH does not want to use CMU in the long direction. Have you done some similar jobs using cfs shear wall for cmu and plank building?

Only for light framed buildings. Most engineers struggle to get shearwall details correct for 1 story buildings. 5 story is not for the faint of heart. If you go that route, I would have an experienced LGS designer review your work. Might also consider some steel frames instead.

 

[dik]

I've dealt with architects before, too... only a couple of times have there been issues. I would think the loads were relatively small and a continuous threaded rod would make a good anchor. You can use hight strength threaded rod.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[jayrod12]

The architect may want to use the CFS, but you're the engineer, be the engineer. If CFS isn't going to work, tell them that.

How are you going to isolate your masonry walls in that direction from your CFS walls? I'd bet the masonry walls will be so stiff in comparison that they take the lion's share of the load. May as well try to design them to take it all,and if you're short a bit of capacity find a couple of discrete locations to add some block wall lengths. Shouldn't be impossible.

I'd bet that the stair end elevator short walls are good on their own for a fair bit of the building height, maybe just the lower floor or two you need some additional wall length.

 

[KootK]

...there will be a 5ft shear wall every 27ft. It will need hold downs for tension.

5' x 5 story CFM shear walls? I'm pretty skeptical that can be made to work reasonably for what will be a pretty heavy building. If the front and back of the building are mostly windows and doors and your shaft walls can't get the job done, you might be headed for hot rolled steel moment frames across those faces. Or something proprietary in CFM as shown below, although I 'm not sure how well that system would play with multi-story.

Be sure to consider your plank to CFM details carefully. Those can be tricky, particularly given plank camber.

 

[Engin1]

jayrod12, thanks for your suggestion! I can use CMU if it has to be. Most of the front and back walls have window and door openings. The elevator shaft has 2x 8ft wall in that direction and stair has 10 ft. I will check if that is enough. From my experience, that won't be enough for a 5-sotry plank building.

 

[Engin1]

KootK, yes, most of front and back walls have window and door openings. That's pretty heavy for 5ft CFS shear wall. I will take a look at this CFS moment frame. The camber location is tricky, may need some kind of shim?

 

[milkshakelake]

Quote: this is my first project using light gauge shear walls for block and plank building. there will be a 5ft shear wall every 27ft

5' of shear wall every 27' is sus. It probably won't work with a 5 story plank building. Even if it does work, like XR250 said, there's no way it's going to be built correctly. And you're going to be the one to blame. I agree with everything XR250 says.

Try to find an alternate method, like CMU or concrete shear walls. 5' of CFS strap bracing for 5 stories at 27' has almost no stiffness at all.

 

[phamENG]

I'd also advise against using CFS, non-bearing shear walls. Non-bearing cold form typically employs slip tracks (it's what prevents them from being load bearing). I've detailed single story slip track walls to take shear - it was a nightmare that I'll never try to do again. I can't imagine a 5 story hotel working.

Do you have a central corridor? Those usually have limited openings (just a door for each room). Can you make those walls CMU and bring them up and put your shear walls down the middle? That'll take a lot of load off of the exterior walls, maybe all of it depending on how you lay it out. Of course this gets hard when they put a big lobby on the first floor.

 

[Engin1]

milkshakelake and phamENG, thanks! I am going to try to use CMU wall at the corners of the building and couple locations of the corridor to see if that works.