Structural support for a GMC 4108

[Chaz]

Hey folks,
  I am installing a larger genny in my AC bay and I have to run it port - starboard instead of fore - aft. I have to cut the bulkhead out that runs fore - aft so it will fit. Some people believe that bulkhead is structural, some don't. I'm thinking it is after looking at what the floor is in that area (Basically and open void on drivers side and the corrugated floor stops at the back bulkhead) , so I am going to put 3 - 4"x6" aluminum "I" beams in. 2 will be in the very bottom of the "open void" on the drivers side and one will be in the middle above the floor so the genny can sit on it. All will be tried to bulkheads.
  What do you think?? Strong enough?? Or should I go for another one above the genny?? It would be cramped but doable. I tend to overkill my projects but I'd like your opinions.

  Thanx again,
   Chaz
 

[kyle4501]

A picture of the area in question and a sketch will be helpfull to understand where you are placing the replacement parts. And YES, the bulkheads ARE structural. (I rode in a converted Scenicruiser that the owner/ converter bragged on how over built they were, so he removed all that unnecessary stuff - You could see the bus swaying & racking as it rode down the road! It had more rattles than a baby store.    )

It matters where the replacement pieces are added & how they are attached.

To be done right, you need to understand what the loads are & how they are being taken by the part you are removing - then you can install a replacement structure to properly handle the load.

With your skill set, you shouldn't have any problem to do this right.

[Chaz]

Thanx Kyle.
Unfortunately.... just before I started typing this post I taped up the box with my camera in it. I have to send it off for repair since I left it out in the rain.    Seems my "Blonde-ness" struck again. 

So... sorry, no pix. I'll try to explain it, but you about have to have a Buffalo or know enough about them to visualize what I am saying. And then the hard part......... understands Chaz-izms.  lol

But I understand what you are saying. I'm no structural engineer but I have a lot of fabrication experience. And from judging what the fore/aft bulkhead accomplished (assuming it was structural and not just a wall for mounting AC stuff) "I think" placing two beams low in the "open void" (lack of a floor) on the drivers side - one of them outboard to the side of the bus as far as possible and the other inboard about 2' to the other edge of the void -  then the third pretty close to the center of the bus but higher up in the bay for the generator to sit on as the floor supports are higher on the drivers side and I will be using treated tongue and groove for that floor so it will be even higher. A 4" beam is about perfect to match the hieghts.

I hope that whole mess makes sense to some of you. I think it's about the best I can do to explain it. I know a sketch would do no justice.

Oh, and I plan on stainless steel bolting plates to the walls and then weld the beams to the plates. I figure the bolts will give me the "flex", if you will, of what the rivets would give. It gives more surface area for the beams and it's also easier to tuck the beams in that way and weld them.

Thanx for the input!
   Chaz

[bevans6]

I would think that you would need to triangulate the load flow through that void, to prevent lozenging.   that's if it's structural in the first place, and it sounds like it is.  Your beams top and bottom normally wouldn't create the required stiffness.

Brian

[robertglines1]

loads transferr at a 45 degree angle...thats the way I calculate...sounds like your on top of it...maybe buy underwater rated camera

[kyle4501]

just remember, when it comes to structures, a triangle is stronger than a square or rectangle.

see how much stronger a square is when you turn it into 2 triangles by adding a diagonal

[Chaz]

Hmmmmm...
Triangulation is a good thought. I don't know that it would be necessary in this case but it sure couldn't hurt!!! I'm all about overkill. And I have the space to do it in with the lower two beams. Once I get the genny in there, I might look at a gusset or two here and there.
It's a bummer I don't have a camera to show you guys what i got but I think you sorta get it.

Thanx Gents,
   Chaz