I don’t have the benefit of all the latest codes and manuals, so I’m hard pressed to see the very same code sections or manual figures you guys are sighting. However, for that end connection, on the simple beam that we are talking about here, basically assuming only a shear reaction, non end moment connection; you have the very same forces from the building and beam acting on the connection wether it is a WT or a single shear plate, they are just taken out differently into the HSS. And, as I see it they both have some drawbacks or conditions which are kinda hard to rationalize from the stress or weld standpoint.
For the WT as a hanger with the web vertical and with a hanging load, you will have a prying action causing tension at the root of the fillets, not a good condition; as Rfruend shows in his Sec. A-A, if the only welds are out at the flg. tips to the supporting member. But, you can start to alleviate this prying action by welding across the cut flg. on both ends of the WT to the supporting member. Then the problem I have trouble rationalizing is a fairly high weld stress within an inch or two on either side of the WT web because of the way the stiff web transmits the load the weld on the cut end of the flg. For the single pl. hanger you can certainly get enough double sided weld btwn. the single pl. and the supporting member, a good weld detail too, but now the starts and stops (terminations) of these welds have the potential of becoming highly stressed or stress raisers if there are any undercuts or craters, particularly if the load is not perfectly vert.
With the WT as a shear connection on the HSS you have the same considerations. I would weld across the top of the WT flg. to minimize the prying action on the vert. welds out at the flg. tips. The weld hard spot at the WT web becomes softer because the HSS face pl. is flexible, but this should still be looked at. The forces applied to WT by the building and the simple beam are the same as those applied to the single shear pl. We assume the rotation (some fixed end moment) will be taken care of by the slotted holes, but maybe not if the nuts are tightened. Otherwise, you still have a moment applied to the connection as a function of the shear and its eccentricity, Rfruend’s sketch pretty much shows it as I see it.
You can do the very same sketch for the single shear pl., and now any end moment (RF’s, Td = M) plus Pe = another M, are acting with their max. stress in the shear pl., from any moment in the shear pl., right at the start or stop (terminations) of the double vert. shear welds, at the top. And, without great care in welding and inspecting this is hardly a better condition than the prying on the WT.
I think Connecteng pretty will summarizes the problem, or quandary, by saying some worked out examples and some figures seem to ignore some of the forces or couples which might be acting on the connection. However, the idea that “The design example in the HSS manual does not address this concern. It actual limits the flange thickness to provide beam end rotation.” seems to fly in the face of what we are discussing here. It seems that almost invariably we make a second problem by trying to fix the first problem, and it is left to us..., good, thinking engineers to try to pick the least of the evils, and then hope they don’t slot the holes in the wrong direction, or some such.