Valley Rafter - inclined loading

[Cjpwdesign]

This must be a pretty straight forward question but currently I am pulling my hair out to justify the following:
how does the computer software convert the dead load (no idea if it is the standard acting on slope or taking the plan area) to the inclined trapezoidal load as shown on the diagram..?
I would have thought calculating the overall load on plan giving a magnitude would then be applied to the inclined area to find the equivalent triangular height, if that makes sense. I hope I am not missing something so basic here..!

the valley plan geometry is:
main roof pitch 33.7', main roof length 1m
secondary roof pitch 45', secondary roof length 1.5m
valley rafter pitch 20', valley rafter plan length approx. 1.8m

dead load 1.75 kN/m2 however the software makes no explicit reference to whether a plan area load or on slope...

 

[XR250]

Honestly, I calculate valleys (and hips) as a beam with a triangular loading. The length being the horizontal projection and just use live and dead without changes due to the upward slope.

 

[ANE91]

4.4 Determinate Frame Analysis | Learn About Structures

learnaboutstructures.com

 

[phamENG]

If your secondary framing is spanning one way (like rafters), then it's triangular and not trapezoidal. You'll have zero at one end, and half the length of the connected rafter at the other.

 

[Cjpwdesign]

https://learnaboutstructures.com/Determinate-Frame-Analysis[

If your secondary framing is spanning one way (like rafters), then it's triangular and not trapezoidal. You'll have zero at one end, and half the length of the connected rafter at the other.

yes, i was only using trapezoidal load implying zero at the ridge end, to distinguish between that and a triangular load as found when analysing lintels.