"Jim Wilkins" writes:

This is a half section of my present gantry hoist track splice
design. C is the 4" channel, V the 3/8" thick central splice plate
between the channels, H the 3/8" thick horizontal splice plate under
the tension flanges and A the angle iron splice above the compression
flanges.

My question is how to weld the inverted T joint between V and H. I
think an inside fillet weld will deform H upward and require grinding
off the sharp and square lower corners of the channel. Is a row of
plug or slot welds in H a reasonable alternative to avoid distortion
and interference?

The 6" high vertical center plate V alone has nearly the same Ixx as
the two channels so I don't think welding it to H is essential but
connecting them should make the joint stiffer and one-man assembly
easier. The angle A on top bolts to V and C afterwards, and gives the
central hanger shackle pin more bearing area than V alone would.

VA
VA
VA
VAAAAAA
VCCCCCC
VC
VC
VC
VC
VC
VCCCCCC
HHHHHH

Is what you aim for structurally necessary or helpful is a good first
question given the work involved...

OK - using your notation and adding W for weld


...
VC
VC
VCCCCCC
WHHHHHW

So you now have the "H" as two strips with the inner edge bevelled
about 30deg.
Set with a root gap at least equal to the middle "V" plate. Wider and
you "get" some of the "C" channel.
Weld-up. Left and right corners and if necessary middle run for first
layer, then fill.

If "H" is a tension "doubler", not otherwise part of the beam "Second
Moment of Area", then just fillets at the ends would do?
Maybe small fillets along sides, out to edges of the "C" (channel)
sections?