timber shed 1

[struengineer]

I need to design a timber shed (50’x 40’x15’(h)) located on the top of a mountain. The mountain is 600’ high from ground. Basic wind speed for this area is 120 m/hr. The uplift pressure therefore could come to 85#/sf. Is any one familiar with this situation and can give me suggestions as for what kind of Simpson tie I should use to prevent roof from blowing away?

Since it is a open shed. There is no shear wall. What kind of bracing system is the best here to provide lateral resistance and, in the other hand, it does not block the opening?

Please advice and thank you very much.

 

[AggieYank]

Simpson would be glad to send you a manual full of their products. Its not too hard to figure out the uplift in each roof rafter and to size a tiedown based on that.

Shear walls are the way to go. Assuming you have one side mostly open (like a garage), you'll have a torsional effect. Reference a code like the IBC 2003, or ASCE 7 to get the different load combinations and factors for wind analysis. I highly recommend the book "Design of Wood Structures - ASD" 5th edition by Breyer. If you read the whole thing, you'll be able to design this shed.

 

[struengineer]

Hi,AggieYank,

Thanks for response.

I cannot build a shear wall because four sides of this shed are supposed to installed big windows. There is no interior wall in this shed also. I guess that a moment frame at each end of shed is needed to provide lateral resistance

The Book by Breyer does not talk about timber framing design. Especially I would like to know how to design a moment connection for laminated framing. Can you help?

Meng

 

[DaveAtkins]

It's difficult to create a moment frame out of timber. If you can't use knee braces for your timber moment frame, I would think about using a steel moment frame.

DaveAtkins

 

[AggieYank]

I agree with DaveAtkins on not using a timber moment frame, but using a steel moment frame in its place.

I apologize if you bought the Breyer book on my recommendation and it wasn't what you needed. I assumed when you said timber that you meant conventional wood framing or glulam members (which it has both). I'm not aware of a good timber design book.

An idea which I have never used (I don't work with timber, and haven't done this with typical stick framing) is to set the posts in a concrete pier, so that they will cantilever up, meaning you won't have to create a moment frame at the top of the column. You will obviously have to design both the post and the pier for the lateral loading, as well as check your local building code to see the requirements for embedding wood in concrete. In the IBC 2003, it requires the wood to be preservative-treated wood.

 

[boo1]

Consider structural steel posts and frame...

 

[UcfSE]

Can you put x-bracing above the windows? Have you tried embedding the posts so they act like cantilevers? How about a combination of the two?

 

[boo1]

Its an open shed....

 

[struengineer]

Thanks guys!

Steel frame was my first choice originally. However, my contractor told me he could not lift the steel beam because he could not drive truck to the top of mountain.

Using concrete fixed footing is a good idea. I will try it if I cannot get a timber frame. Conc. can be hand mixed anyway.

When timber embedded in concrete, will it create a corrosion problem even it is treated?

Mark

 

[RHB51]

The idea of embedding the columns in concrete is the
best idea if you want wood.
AITC has a straight forward method of designing a "pole barn", which this construction would be classified.

If it is a simple shed you don't even need to embedd the posts in concrete; you can embedd in a large hole and
tamp in crusher run. As the poles move it will actually compact the crusher run (with fines) tighter.

 

[RareBugTX]

I know that some jurisdictions do not allow wood directly embeded in concrete.i.e. posts.
In regards to a moment frame using wood, I have seen a few new details here in the midwest where they use for the connection angles with through bolts that tie together the members and they create a "semi-rigid connection" Analysis of the bearing due to the lateral forces is posible and not that complicated.

Good Luck and hopefully brings up more ideas.

RareBug

 

[TFL]

one thing i have done in the past is cast a steel tube or pipe into the concrete with an inside clear dimension that matches your posts. Thatmwill keep the post from contacting the concrete and at least seperate the two. the theer option is to embed 4 steel posts into concrete and do the rest out of wood.