Difference of truss axial force between load assigning on member and membrane slab

[Anousit]

Dear all. I compared axial force of two same truss in Etabs but difference in load assigning method.
1. assigned load on rafter (Top chorde)
2. used area load on membrane slab
The result of 2nd method shows that the axial force of top and bottom chord are too difference (around 6 KN and 21 KN, respectively), while the resulf of 1st method are 16 KN and 19 KN, respectively.
I think that the 1st method is more correct and logistic. Pleas help me that what is wrong with the 2nd model?

 

[Agent666]

Try sharing your etabs files for each case, without any screenshots or printouts it may be a bit hard to diagnose.

But you do need to be careful regarding using shell elements with frames, in so far as depending on the type of shell element it will carry axial load (sharing out the loads that would otherwise be in the truss top chord.