Hi everyone,
I usually use a seat connexion, an angle on which I sit the HSS. Check if the seat needs to be reinforced with stiffner plate. And I also add a small plate (for one bolt), welded on the column to be bolted to the side of the HSS beam. This is very useful for lateral support while erecting. HOWEVER, do not forget that the bolt holes must be either oversized or sloted to give enough leeway for erection or else you'll have erectors torch slotting the holes on site so they'll be able to pin the beams.
Have a good one guys