knee brace to a rafter?

[paisan8]

 i have a 14' by 22' TF shed roof stand alone porch. the 22' length has 6x6 posts supporting a 22' 6x10 beam these two bent are different heights making aprox a #1 pitch. these two bents will be connected by 5 8x8 rafters. i need lateral support for the 14' side.i was considering a half lap dove tail knee brace from the post to the 8x8 rafter. where the rafter meets the beam. 4 of these at the 6x6 corner posts up to the 8x8 #1 pitch rafter. the rafters will be attached to the beam with steel. basically want to forego a tie beam on this 14' side and use the rafter instead.
 also was considering  6" x 3" 90% angle iron bolted to the beam and the rafter, 2 of these per rafter. can i expect this to provide any lateral support? my feeling is maybe a bit but not enough to be relied upon.

thank you
james

[Don P]

Bracing to the rafter is fine if the rafter is secured well enough against jacking as the brace tries to lift it. The angle clips alone won't provide enough lateral, their bolts/lags would simply tear out of the rafter or tear it up as the assembly fails. You can also pick up lateral from floor joist to post if the post is stiff enough or as X'ing in a railing, just putting out more ideas. Also check your proposed roofing, not many are good down to 1/12 pitch.

[paisan8]

Ok yea i see the strength of the brace is only as good as the weakest joint in the triangle. The brace would be pushing up on the rafter and directly up on the bolts and this is not ideal, not working in shear.
 The post goes to the top of the beam, the beam terminates into the side of the post not sitting on top. So the side of the rafter is flush with the beam. What if i ran 12"x4" steel plate from the rafter to the post. with lags working in shear?
the brace wold be to the outside as well, in line with the steel plate. angle iron could be used on the other side of the rafter holding it to the beam keeping it from twisting.
the floor joist option is a good idea but would leave alot of post above the brace.
the structure is getting railings so i could make the top rail a tie beam and run the knee brace up off of this.
my preference is using the rafter though if i can make it work.
i will take some pics today.
the roof is going to be 2x8 tg pine with rubber over that. it matches the house.

thanks for the reply
james

[Don P]

Can you not attach the upper beam to the house, that would take care of the lateral in that direction. Pics and a dimensioned sketch of what you are thinking would help.
Mainly with small end connections of steel to wood keep in mind that if things rotate the steel is rigid and the lags are trying to split the wood. Just as an aside and I'm not advocating, those "flimsy" sheet metal connectors bend but hold, there is more thought going on there than we think at first glance. There is a saying "load goes to stiffness", be mindful that where you make something rigid that it is capable.

[paisan8]

 

 
not a great pic . the member in the center is an 8x8 rafter to run between theses two bents. the rafters at each end is what i would like to brace on. was thinking 12 inch flat steel from the rafter on to the post with lags. and on the other side of the rafter angle iron on top of the beam and the side of the rafter.
 then a brace like this as described by mr. rojers in another post.


 


the structure is free standing so i cannot brace it of existing

2 of these braces at each end of the structure enough?

james

[Don P]

Just gut reaction, you can never have too much bracing. If the beam is full length it is probably ok just braced at the ends. If it is interrupted at the center post I'd want to brace it there all the more. Your roof is creating a diaphragm though, making that a fairly rigid plate. Bracing as part of the railing fill wouldn't hurt a thing. If you need definite answers to any of that, its engineer territory.

[paisan8]

yes more braces are better for sure and i can get 2 more on the middle post to the rafter. it is a continuous beam.
i am def in engineering territory and the customer my brother is one but he just say "i think itll be alright".
this will remain open on all sides, bit worried about the wind getting under it.
thanks for your comments don.
cheers 
james

[paisan8]

 

 

this is what i came up with. 12"x5.5" quarter inch steel plate with half inch lags holding the rafter down. im tempted to put a blind peg at a slight angle in each half lap to hold the brace in but its probably not necessary.
cheers
james