TJI Floor Joist/ Wood Rafter Connection

[dumaszarktek]

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

 

[msquared48]

Yep - Everett, WA

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

 

[dumaszarktek]

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]

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]

Sorry, those are all too high by a factor of 2.

BA

 

[dhengr]

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]

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]

dhengr,

You are correct, as usual.

BA

 

[ToadJones]

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.