In my view:
1. It will only resist torsion by warping of the flanges due to a partially broken load path (see next point).
2. It is unable to resist St Venant Torsion i.e. J=4A0/(ds/t) type for a box section. For a single box there is a broken load path for the circulatory shear forces.
3. It will be able to resist a minor axis moment, but not be able to resist a major axis moment.
If you want to weld it that way I'd be very careful with your support conditions in your model (and preferably weld it all around instead).
Appreciate all your comments. WF solution is not gonna work in my case since I need torsion resistance. The beam is actually framing at an angle to the end plate which makes it more difficult.
Guess I'm gonna design it fully fixed and weld it all around.
Will wrap the plate connection around the support concrete beam and bolt away from the edge.
We usually do angles top and bottom of the hss and weld the top angle toes only to the plate and to the beam. This allows them to flex.
You'll find this connection for seated beam connections where the top angle is just used for rollover restraint. let me know if i should attach a sketch but it beats designing the beam for the moments.
