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dumaszarktek (Structural)
12 Apr 11 18:09
need some help with this. my engineer is not that good with nails

I came up with 785 lbs per rafter for the thrust. please correct me if wrong. Need some strap etc for this, do not want to rely soley on the plate on the floor.

the span of the Bldg is 27' inside, clear spanning the whole thing

the roof pitch is 10/12

rafters are 2x10

TJI is 16" 560...the flange is practially a 2x4

I tried to attach a dwg, but if not visible, the problem here is the
rafter sits on top of the plywood floor on a plate, as i can't notch the TJI floor joist

 
ToadJones (Structural)
12 Apr 11 20:00
Others will know more, but I'm sure Simpson makes a stamped clip for this situation.

Other than that, the detail is a good one. I have used that same exact framing scheme on several homes.

I'm not sure why you'd want to notch the floor joists anyway.
The floor joists should function as a collar tie and with the 2x6 plate resting on the rim board & plywood diaphragm you should have a very stiff system.

Only questionable thing is relying on toe nails in the rafters.

One option there would be to place 2x6 blocking in between each rafter directly on top of the 2x6 sole plate so you can nail at 90 degrees, but I still think a clip of some sort would be easier.  
ToadJones (Structural)
12 Apr 11 20:03
I see what you mean now....

You want to cut the joists to match the roof pitch and rest the rafters on the wall below.

I believe you can do this but the manufacturer of the joist will require that you put blocking in the webs of the joists to compensate for cutting the top flange.  
ToadJones (Structural)
12 Apr 11 20:09
I preferred to build the way your detail shows. It provides a nice uninterrupted diaphragm and a nice deck with the sheeting continuing all the way out to the rim joist rather than stopping short to make way for the rafters.

If you go with the "blocking" idea of my last post, you probably only need a block every-other rafter space with two rafters being nailed to each block.

MSquared....where you at? This is right up your alley, no?  
dumaszarktek (Structural)
12 Apr 11 20:16
No, TJI will not let you taper cut the joists, even tho someone from TJI
sent me a detail as such...my concern is the rafter connection.

Simpson told me to use an A35 which just connects to the plate, and if the plate fails.....
dumaszarktek (Structural)
12 Apr 11 20:19
my snow load is 30 lbs..

And thanks for the comments so far!
ToadJones (Structural)
12 Apr 11 20:19
with the the sheathing glue and nailed and the plate glued and nailed, I dont see the plate failing.

I have seen details for cutting the joists as you describe. I have used the detail in the field. Must have been a different manufacturer.  
a2mfk (Structural)
14 Apr 11 10:27
I don't understand- you said "my engineer is not that good with nails". Are you not the structural engineer here? If not, you need one.

And as Toad said, you will need some type of strap or other connection to tie the roof rafter back into the floor joist to act as a collar tie or bottom chord.
BAretired (Structural)
14 Apr 11 12:20
I would be concerned about the plate failing with a horizontal thrust of 785 pounds per rafter.  The force should be carried by a direct connection between rafter and tie joist.

BA

dumaszarktek (Structural)
14 Apr 11 12:30
The prescriptive code for this bldg size/ roof pitch is only 4 nails
at the heel connection. There are also collar ties.( i know don't do much, but some)

I upped the plate to 2x8 with a row of 3 nails @ 4" o.c. with blocking below and a simpson A35. Nailing the plywood in the eaves at 4" o.c.

We are just going to have to see what happens....
a2mfk (Structural)
14 Apr 11 13:20
So you are a non-engineer, and you are just going to guess at it and hope for the best? Hire a damn engineer! You are being irresponsible and negligent if you don't. You know there is a problem so solve it.


"I upped the plate to 2x8 with a row of 3 nails @ 4" o.c. with blocking below and a simpson A35. Nailing the plywood in the eaves at 4" o.c.

We are just going to have to see what happens.... "
msquared48 (Structural)
14 Apr 11 15:45
Just sick Toad...  You don't want to get this cr#$...

Simpson does make twist straps to cover this situation.  One or twoo at each joist should develop the necessary tension into the floor joist.  Place the twist straps on top of the 3/4 ply and nail off to the rafters.  You will need to place the straps before you place the top plate and rafters, but it can be done.

As mentioned above though, if you are not a structural engineer, and considering the fact that if it is not designed correctly, you will have a serious structural problem, I insist you engage a structural engineer to properly size and detail the connection.    

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

dumaszarktek (Structural)
14 Apr 11 16:17
Ok, I sent the detail over to another PE, I already had my structural engineer look at the dwgs and he said nothing, only asked me to specify the nail spacing for the plate i had left blank for him to design!...anyway, I like the twisted strap idea.

thanks for all the helpful comments.
msquared48 (Structural)
14 Apr 11 16:23
Might consider getting another structural...

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

ToadJones (Structural)
14 Apr 11 16:50
MSquared-

"Just sick Toad...  You don't want to get this cr#$...


What?  
msquared48 (Structural)
14 Apr 11 16:52
Got a real strange type of crud that is keeping me down for a good portion of the time here.  Nothing more.  

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

ToadJones (Structural)
14 Apr 11 17:10
Work wise or you are sick?

I thought I ticked you off somehow.  
msquared48 (Structural)
14 Apr 11 17:14
Just sick Toad.  Sorry if I gave you the misimpression.  

My son and grandkids have had this stuff for two weeks now and they are just on the downhill side of the curve.  Diane and I have only had it for about a week.  Saps all your energy and leaves you mentally drained.   

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

ToadJones (Structural)
14 Apr 11 17:21
Mike-
Honest to goodness, same thing here.

My two yr daughter has been a damn mess, in and out of the doctors, now I'm feeling it pretty good too. Miserable. It's been weeks now.  
dumaszarktek (Structural)
14 Apr 11 17:21
msquared are you on the west coast?..i hear something like that in LA
msquared48 (Structural)
14 Apr 11 19:05
Yep - Everett, WA

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

dumaszarktek (Structural)
16 Apr 11 11:04
what forumula do you all use for calculating thrust?, i had double what my engineer said, he came up with 388 lbs after the 1.15 reduction.
at any rate we have a design i have confidence in,



 
BAretired (Structural)
16 Apr 11 11:44
The vertical reaction at each end is wL/2.  If L is 27', V = 13.5w where w is the uniform load per lineal foot of rafter projected on a horizontal surface.

The horizontal thrust is 12/10 times as much or 0.6wL.

The axial force in the rafter is (10^2 + 12^2)^0.5/10 = 1.56 times as much or 0.78wL.

BA

BAretired (Structural)
16 Apr 11 11:48
Sorry, those are all too high by a factor of 2.   

BA

dhengr (Structural)
17 Apr 11 1:41
BA:
I think the rafter reaction on the wall is .5wL, and the axial load on the rafter is .78wL, but the rafter thrust is .3wL.

Assuming the OP'er. can put the 2x10 rafters on the 3/4" plywd. right over the TJI's, the 2x6 sill pl. on top of the plywd. may not be req'rd., or maybe should be standing on edge btwn. the rafters, as blocking.  He may want squash blocks at the webs of the TJI's.  Then use a concealed flange joist hanger (Simpson, LUC26Z or USP, JL26IF-TZ) laying horiz. on top of the plywd. to pick up the thrust, nailing through the plywd. and the top flg. of the TJI, and the rim board.  Cut the rafter seat cut, then over cut the plumb cut enough to receive the bearing seat of joist hanger (B = 1.75 - 1.875") above the rafter seat, just a saw kerf.
dumaszarktek (Structural)
17 Apr 11 5:03
My alternate engineer did add squash blocks, a 2x10 plate w/ (5)16d nails into the TJI and a simpson L90 on top of the plate to the rafters.(9" angle with 5 nails ea side, can take 500+ lbs of force.) I may still add somerthing else, I am concerned that the TJI flange could split if some clown does the nailing. If the squash blocks are face nailed to the web of the TJI, then blocking in between those could be
strong enough to nail into from above to help hold the plate down.  
BAretired (Structural)
17 Apr 11 9:29
dhengr,

You are correct, as usual.

BA

ToadJones (Structural)
17 Apr 11 18:43
dhengr has a pretty nice idea there with the concealed flange joist hangers....may want to over-cut the plumb cut with a jigsaw, sawzall, or handsaw as you'll have to over-cut pretty far with a circle saw to get the depth...running risk of a weak rafter tail.

I'm getting slightly different values for the vertical and thrust reactions...probably rounding.  

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