Welds on vertical steel tubing?

[HGC]

There has been a lot of talk about broken vertical welds to the chassis frame on some Tiffin MHs. It seems that Tiffin only welds one side of the post to the frame and I am concerned that they should be welded on both sides of the post. There are some opinions that say the welds should be welded on one side only to allow for flexing. Wanted to tap into the eclectic knowledge of Irv2 members to get their opinions and also to find out if other manufacturers do the same. Seems this a real engineering question and maybe we need expert opinions on this type of ,and placement of these welds. Would love to hear from experienced members on this debate. And whether I would be wrong to have a chassis welding company add additional welds and bracing.Thanks for your interest and response.

[NvGuy]

This is an excellent question for the real engineers out there.
My shop floor engineering training taught me that you don't want things completely welded, some flex is needed, but it sure would be nice to hear some actual engineering explanation.

[RRR]

Most of the welds that I have seen by the manufacturer, either horzonal or vertical, have plenty of room for flex due to the poor quality of the welds.

[JIMBO34PA]

HGC; I had some of my welds redone already but they were in the RF corner. from all the other posts it appears its always the weld that gives up.What is strange is some of my tubes are bridged on the sides with angle iron and some are just welded to frame . Go figure? Never seen a picture of a torn or ripped square tube . Curious if weld separates from frame or square tubes. Jim

[FIRE UP]

Well gang,
Been welding for decades in all kinds of scenarios. Never been an engineer per say but, have designed and built quite a few things and have never had a failure yet. My question would be to this situation is, if the areas in question have reputation for breaking welds, is there THAT MUCH flexing in those areas that, you cannot weld the other side of the tubing? If so, somethings seriously wrong with the original engineering since they keep breaking.
If one was to weld the other side, just where MIGHT be the next possible break? Does the original design in that area NEED to flex that much? Sure don't sound right to me.
Scott

[ThePowells]

Originally Posted by FIRE UP

Well gang,
Been welding for decades in all kinds of scenarios. Never been an engineer per say but, have designed and built quite a few things and have never had a failure yet. My question would be to this situation is, if the areas in question have reputation for breaking welds, is there THAT MUCH flexing in those areas that, you cannot weld the other side of the tubing? If so, somethings seriously wrong with the original engineering since they keep breaking.
If one was to weld the other side, just where MIGHT be the next possible break? Does the original design in that area NEED to flex that much? Sure don't sound right to me.
Scott

What he said!

[grindstone01]

Welds are usually the weakest point of the frame, so it makes sense to weld all seams. Also welding will make the steel/aluminum brittle due to the high heat which is not a good area to promote flexing.

[HGC]

Thanks for the replies! So I have heard that welds are much stronger than the actual steel welded to, so why are some of these cracking and should we reweld the offending weld and add additional weld points or just reweld the failed weld? What really has me concerned is the weight of the box on these steel pillars and what would happen in any type of accident that would compound the stress on them ten fold with gforces from a rear ended, frontal, or roll over condition when they are not holding up under normal driving conditions. Would like to have our unit as safe as possible and not have the house literally slip off the frame in a crash.
I think this thread is valuable in the sense of helping those of us susceptible to any dangerous situations do to this potential danger. Not trying to do any bashing of manufacturers but rather promoting self help in assessing solutions. Thanks for your help. Are there any structural engineers familiar with this type of tubular design?

[FIRE UP]

Originally Posted by HGC

Thanks for the replies! So I have heard that welds are much stronger than the actual steel welded to, so why are some of these cracking and should we reweld the offending weld and add additional weld points or just reweld the failed weld? What really has me concerned is the weight of the box on these steel pillars and what would happen in any type of accident that would compound the stress on them ten fold with gforces from a rear ended, frontal, or roll over condition when they are not holding up under normal driving conditions. Would like to have our unit as safe as possible and not have the house literally slip off the frame in a crash.
I think this thread is valuable in the sense of helping those of us susceptible to any dangerous situations do to this potential danger. Not trying to do any bashing of manufacturers but rather promoting self help in assessing solutions. Thanks for your help. Are there any structural engineers familiar with this type of tubular design?

HGC,
First off, unlike automotive crash tests to determine structural strengths, weakness's, build characteristics and more, I know of no motorhome crash tests to determine such parameters. Waaaaaaaaay too many build differences to make a general consensus report. So, with all that jargon said, your thoughts on just what your motor home would do, and how it would react in an accident is, for the most part, impossible to predict.

Have you seen many RV accidents, roll-overs, run-off-the-road due to tire failures and more, what you see in ALL OF THEM is a pile of match box matches. There is no strength in the "Box" of the main unit. Sure, it supports wall paneling, some cabinets and a few things like that. But, to draw any conclusions as to what kind of reaction your BOX will have, in ANY given accident scenario is again, pretty much impossible other than, it's going to break up.

Now, some coach builders MAY put more structural reliability than others, depending on how high up in the food chain they are. Long story short, If I were you, and had broken welds, the coach is OBVIOUSLY out of any sort of warranty so, I'd weld them back up, and, reinforce with additional welds when and where needed and, even add braces and gussets where applicable. I mean, what have you got to loose, it's already broke, do something BETTER than they did.
Scott

[100Akers]

Ok, folks, here goes. I am a Professional Engineer and a AWS certified welder, and have spent the last 35 years fixing and reinforcing steel buildings.
A properly designed and executed weld will be stronger than the surrounding steel. If a weld fails, either the design or the execution is faulty, or the structure has been overloaded beyond the forces it was designed for. If the same weld fails on multiple structures due to overload, then obviously the assumed design forces are wrong. Bottom line - if a weld fails somebody screwed up.
Single sided welds are common on statically loaded structures, but generally not recommended where vibration and cyclic loading occurs. In my opinion a vehicle falls in this category and I would not recommend a single sided weld. Sure, they're cheaper, but not recommended.
If the fabricator or designer is saying a single sided weld is being used to allow more flexibility in the joint, my response is that is only a matter of time before that weld will fail.
I am not familiar with the particular problem raised by the OP, so can't comment on their welds specifically. But in general, it sounds like either the whole box needs stiffening, or the welds need to be repaired with due regard for fatigue.

[HGC]

Thanks for your replies on this matter. As I said, this is a problem for some and when it happens can drop the box down onto to the frame crushing anything in it's way and lopsiding the whole RV. Tiffin has a 10yr structural warranty but I really would like to offset that type of repair, since it requires jacking the box up from the frame and adding new welds and bracing. There is an OP in the Tiffin forum who seems to have had most of the welds fail with a drooping chassis and after all of the work at Tiffin has not been able to have it properly repaired to the original spec. So if you are capable, I feel it is a good idea to check chassis to box frame welds.
So keep your replies and opinions coming. It is an important issue to some. Thanks all and lets keep RVin. (safely)

[Charlie 5320]

If it were mine, I'd make sure to line the weld back up if it has sagged, and reweld it. I'd also be checking for breaking of other welds. One thing for sure if the welds are breaking it is moving, and I have a hard time believing the manufacture has that in design. More like negligence in manufacturing, NOT taking enough time to make sure it is done right to begin with.

[olcarguy]

I'm a Millwright, we're the guy's that make the plans that the engineers make work..... If I owned this rig, then I would weld three sides of the tubing leaving the bottom open. This will give it enough strength and alow and condensation a way to drain.

[ThePowells]

Originally Posted by olcarguy

I'm a Millwright, we're the guy's that make the plans that the engineers make work..... If I owned this rig, then I would weld three sides of the tubing leaving the bottom open. This will give it enough strength and alow and condensation a way to drain.

Fireup and Olcarguy,

Look at the pics on this thread and share your opinion please.

http://www.irv2.com/forums/f121/2017...cs-362441.html