Force measures for weld calculation

I want to try to extrapolate force (tension) from a welded structure to perform a calculus as prescribed by EN1993-1-8.

I want obtained the forces by measures of a simple truss loaded by transversally.

On each side of the green beam I want to simulate the presence of two filled weld with a=5mm.

I used two kind of measure: Force and Interface.
Looking on the Help it seems the proper one should be the force measure, but, in this case, I think both should be right.
Exept that the results are different, so which are the right?

Thanks

Bye