Help with frame modification

[MtnDon]

yes on the triangle plates, they should stiffen up lateral forces. Is that end of the A-member welded very solidly to the main frame rail? I see what looks like a plate on the bottom. A bent plate welded onto the A-member and welded to the main frame rail, like an angle iron with an obtuse angle, would supply more strength to vertical bending forces.


You do have a lot of steel in that floor. If you want I can run the numbers for tube deflection. Just need the size and wall thickness, length of tubes and spacing. It appears you have more than enough of those cross tubes.

[angib]

How about this?

Hmmm, that's probably OK, though not as strong as what was there before - it is still putting a twisting load on each tongue member, over the length between the first and second cross-members The two triangular pieces do absolutely nothing at all, so skip those.

Plan B would be to add a new cross-member directly under the existing cross-member and running from side to side (well, the very ends can be tapered away). This would then allow the centre of the existing cross-member to be cut away and the new cross-member would then connect to two sides firmly together below floor level. At a guess a 2x2 box welded to the bottom of the existing sheet metal inverted-U would be as strong as the U.

[48Rob]

Okay,

After thinking it through a bit more, here are a couple new thoughts;

The tongue is 2" higher than the save piece.
I only need 27" of the center of the front plate removed.
This picture may help to explain;



The tongue rails are 2" above the bottom of the main frame rails, and save piece. So if I cut out the front plate, I can leave 2" of it intact. Since there is a 2" gap between the save piece and the tongue rails I can weld in a 2x2 box tube connecting it to all.
Since I only need 27" in the center of the 42" long front plate removed, it can be cut at an angle for more strength.

The 2 x 2 tube that Andrew suggested under the main frame rails, can now be added/welded to the 2" portion of the original front plate that will not be cut out.
Does that make sense, and add back enough of the lost strength?

Rob

[angib]

That looks fine structurally - and has the benefit of being fairly tidy, too.

[48Rob]

Thanks Andrew.

Should the 2x2 tube be welded to the bottom of the tongue rails, or should I tie them together with plates?
Welding on the bottom of the tongue at that stress point may weaken it or will leaving most of the front plate intact be enough?


Rob

[MtnDon]

FWIW, my welding mentor, an structural engineer, always said that using angle plates as I drew before was stronger than a simple bead weld where the two pieces met. The angle plate spreads the forces out over a larger area.

[48Rob]

Don,

Thank you!

Glad all you guys are willing to hep, it is appreciated.

Rob