chord force, timber construction 2

[DoubleStud]

Hey fine folks. Typically I design houses with many interior walls and wall jogs where I am not as worried about lateral forces. Now I am designing a big detached garage with no wall in the middle. I just want to make sure I am not missing anything. For the purpose of this post, I just simplified the dimension and the force. Let's look at the wind blowing North South. I know the load is not suppose to be equally distributed because it is a gable end. I just went to the mid height of the gable and use that height. I use the simplified method from ASCE. Let's just say I have 250 plf.
Based on Table 4.2b of the wind and seismic provision, using minimum 7/16 panel with 8d nail Case 1 can get me 0.5 x 715 = 357.5 plf. OK

Moment = (250 plf x 75^2 )/8 = 175781 LB FT
b = 50 ft
T = C = M/B = 3500 LB

Hem fir #2 tension = 525 psi x 1.6 (duration factor = 840
tension capacity of 2x6 top plate = 1.5x5.5x840 = 6930 lb. 2x6 chord is OK
splice nailing use 16d. Table 11N NDS 16d 1.5" side member on hem-fir #2 = 122 lb x 1.6 (duration factor) = 195 lb.
3500/195 = 18 nails. I am going to specify 2 rows of (10)-16d nails at overlap

How do I get this 3500 tension right at the peak of the gable? Do I need to specify a strap at the peak that can have 3500 lb tension capacity?

Now the walls on the west and east will take 250x75/2 = 9375 lb at each shear wall. I have enough walls to resist this, I should be OK. Do I need to worry about this diaphragm spanning 75 ft? Do I need to check for deflection somehow? Do I need to make the series of beam and column at the ridge as moment frame to break the span of the diaphragm to 37.5 ft instead?

 

[XR250]

I believe this is usually ignored but it would not be difficult to throw a few straps at each end.
Depending on the location of the openings, the structure likely defaults to a three-sided building load path if needed.

 

[DoubleStud]

XR250, do you have an example for 3 sided building? What is taking the chord tension force where there is no wall?

 

[XR250]

https://www.structuremag.org/?p=19733

There are no chords in a 3-sided design.

 

[DaveAtkins]

If you divide your roof diaphragm into two three sided diaphragms, there are not chord forces. Instead, the unbalanced moment in each half diaphragm is resisted by the two shear walls perpendicular to the direction of the applied load.

DaveAtkins

 

[DoubleStud]

Dave, I am not sure I followed. I will keep researching.

 

[ChorasDen]

He's getting at that it is designed similar to a c-channel, on your drawing, if the bottom edge is neglected and the diaphragm is treated as 3-sided, then any standard diaphragm forces into the diaphragm from the left and right direction would be resisted by the shear wall at the top of the drawing. However, the walls on the left and right will need to be engaged to resist the torsional forces that will develop due to rotation around the center of rigidity.