Structural role of the chair rail?

[musigenesis]

I was wondering if the chair rail plays a role in stiffening the walls of a bus, or whether it is literally there only to support the chairs bolted to it. I am curious about this because I am planning a floor repair job that will leave the walls unsupported by the floor for about a ten-foot span between the fuel tank tube (back right) and a spot about three feet in front of the wheel wells (the rusted floor here will be entirely cut away).

I am worried that the walls will have a tendency to droop, counteracted only by the stiffness provided by the outer siding and the windows (which may be sufficient, I dunno). The chair rail will be intact over this span on both sides and would normally add stiffness, but it is mostly cut away for the wheel wells. Do I perhaps need to weld a long plate to the channels just above the wheel wells, to compensate for the wheel well cutouts in the chair rails?

[o1marc]

They are very much part of the structural rigidity of the body. The chair rail panel wraps down under the floor. The ribs are held off the floor by about 1/2" and secured with an "L" bracket to the floor. These ribs are then secured to the chair rail and prevent them from racking front to back.

[musigenesis]

Originally Posted by o1marc

They are very much part of the structural rigidity of the body. The chair rail panel wraps down under the floor. The ribs are held off the floor by about 1/2" and secured with an "L" bracket to the floor. These ribs are then secured to the chair rail and prevent them from racking front to back.

So I wonder over how long of a span, then, that chair rail would prevent the wall from drooping if it was not supported underneath by any floor structure. And it wouldn't be continuous over the span I'm talking about anyway, since the bottom part of the chair rail is cut away for the wheel wells. I think I would at least need to weld a reinforcing plate across the channels above the wheel wells, and perhaps this plate would actually need to span this entire floorless section (my bus won't actually have no floor here, but the replacement floor will not bear any of the wall load).