Roof Cross Bracing/Lateral System for Long and Thin Building 1

[Revv]

Hey Guys so basically I've been assigned to engineer a long thin 1 story storage building. It's around 200' long and 20 wide with 12"X12" square CMU piers between garage doors on one of the long sides and CMU walls on each of the short sides. The roof is metal deck with CFS purlins spanning the long distance over CFS bearing walls @ 10' O.C. I'm trying to work through this without bothering my structural engineer but I'm really confused on what roof bracing does/when to use it.

Can anyone provide guidance on when you know you need to use roof bracing and what it is doing for you?

 

[Enhineyero]

Couple of questions before I give a response.

Hey Guys so basically I've been assigned to engineer a long thin 1 story storage buildin

Are you a structural engineer?

I'm trying to work through this without bothering my structural engineer

What do you mean by the above? I thought you are THE structural engineer.

 

[Revv]

Sorry I meant senior* engineer not structural. I am an EIT working on this.

 

[phamENG]

When you say metal deck are you talking about structural roof deck? SDI Type B sort of metal roof deck? If so, then that's your "roof bracing." Look up diaphragm design. Beyond that...you'll have to get a bit more specific with your questions.

 

[JLNJ]

Load path. You need a load path for your horizontal loads. The load path for vertical loads is usually fairly obvious. Where does the force go when the wind blows?

Determine what load path you desire, and engineer yourself a way to make it happen.

 

[dik]

If you have CFS walls @ 10', I'd look into using each third or fourth one as a 'shear' wall, and use the steel deck as the roof diaphragm taking the loads to the walls.

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

-Dik

 

[Enhineyero]

Bracing in general prevents limits frame movement, without the brace the frame will bend (& rely on joint fixity). Diaphragm action is a another story.

I don't wish to fully answer your question here, as there is a high chance of being misunderstood on such a very essential design principle. Ask you boss, they came in with expectations that you dont know everything. Many design concepts are not taught in university, this being one of them.

 

[BAretired]

I usually find it helpful to draw a Roof Framing Plan. I agree with Dik. You don't need any roof bracing provided the roof deck can act as a diaphragm. Expansion joints at about 40' centers is not mandatory, but seems like a good idea.

Black dashed lines are bearing walls. Red solid lines are roof CFS purlins.

BA

 

[dik]

It may be that if you use each 10' wall, you may not have to do any reinforcing. I'd do a wind check using an increase of 20% for a 10' section and if the walls can accommodate this without reinforcing, I would use it for the entire building. The increase is to accommodate the corner effects of the wind load on the long face.

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

-Dik