Allowable Deflection on Steel Knee Brace

[RareBugTX]

Has anybody dealt with something similar to this?:

This is a simple knee brace to support a shelter shed with the following characteristics.

<--------6'0"------------>

0-----0------------------- ^
/ |
/ 2'-0"
/ |
/ |
0/ v


Snow and Dead load control the design. I have already checked and designed my reactions and pullout forces on 12" clay masonry. I feel that I have to check the brace for deformation (i.e.) detlection from its axial axis but have not found anything on my library nor books.

I would suspect at midspan of brace there should be a limited deflection and allowable stress. maybe L/360? By the way the brace for preliminary purposes is L 4"X4"X5/16" Should I consider it as a column?.

Can anybody shed me some light with this issue.

Best regards

Rarebug

 

[Ron]

At worst, your knee brace will be in compression. Check for buckling, not deflection.

 

[RareBugTX]

Thanks a lot Ron!

 

[RWF7437]

Why not check for both buckling and deflection ?

 

[Ron]

Buckling is a form of deflection, but it doesn't work like bending deflection. When buckling limits are reached, the eccentric instability can be instantaneous, particularly if the axial load is not abated during the initial instability.

 

[kslee1000]

I am more concerned about the fixidity of the connections. Have you checked stability of the framing?

 

[Ron]

Generally, knee braces are pinned. If you could develop the moment transfer between the beam and column, you wouldn't need a knee brace.

 

[kslee1000]

If all connections are pinned, how the horizontal force component to be handled?

 

[RareBugTX]

There is no support to the right of the shed. It was meant to be the vertical dimension line but somewhat the editor shifted it to the left.

My shelter shed is cantilevered from the wall, with two support welded plates anchored to the clay masonry wall. Came up with a pullout force of 4.39 kips at the top connection. according to my calcs, I need [4] 3/4" a.b. with 6" min embedment, I will specify 8" anyway. compression on the bottom plate is not significant.

Thanks for your feedback guys, This exposed me to AISC LRFD 3. single angle compression member design, pretty nice calcs, there are tables tough, but doing the calcs is much more fun.