JBarca wrote:
...From researching this, Artic Fox uses weld bead in the upper flange area to create camber in the frame behind the axles when new. They use to weld approx 2 to 3" weld bead on the top flange at an angle as they showed in their 2007 camper brochures. My buddies 2 year old Fox, has the weld bead on the inside radius of the upper flange. He can't tell if the bead is on top or not as the camper is sitting on it. They may have changed their methods. On his camper, this is only in the axle area on the upper flange.
I'm assuming they are using that heat shrink to force the frame rail upper flange into compression. Since the upper flange is in compression, it can take more stress as the top flange is normally in tension overhung off the back of the axles. You have to pull all that compression stress to zero before the tension starts, thus creating more beam holding power. I do not know this for fact, but I can see the science adding it to that it will work like that. Point is, they do this all the time and have learned the technique. And the fact there is no camper on top of the frame.
Give me a day or 2 and I'll have my plan up to see.
Thanks
John
The actual mechanics of what is happening is hard to explain but my understanding is the primary mechanism is volumetric change due to thermal expansion. When you apply a weld you are apply weld material along with a lot of localized heat, locally all of the material adjacent to the weld attempts to expand. This expansion is constrained by the adjacent unheated material, in the simplified case of a beam, the heated side needs to expand in volume but the unheated side is resisting this expansion. This results in the wall of the material expanding tangentially and not longitudinally. When the beam cools, the opposite occurs but due to the time duration and way the stresses redistribute, the material at the heated then cooled section will now be physically slightly thicker and slightly shorter. This will result in a net camber/distortion due to the material at the top pulling the bottom into tension. Sorry for the side track as this doesn't address you issue at hand.
I wish I could spend more time looking at your issue but quickly looking thru your pictures it appears you may want to look into verifying if you have a local buckling of the flange problem. This would show up in places of high moment (bottom flange adjacent to the rear spring hanger at the rear cantilever) or wherever the flange has be impacted or distorted due to jacking.
The typical strength failure mode of slender I type sections is local in nature. Looking at a section subject primarily to moment, it is going to be the flange in compression buckling causing overall flexural failure. So, whatever fix you end up coming up with make sure to straighten any of the distorted flanges and brace appropriately.
Also, I find when looking at fixes I always try to keep in mind that deflection and strength, although related, are issues that need to be addressed separately. You may want to step back and determine if you have a lack of strength issue or a stiffness (deflection) problem.
