Stress found during trailer inspection

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I found this stress crack during trailer inspection today. Been there a while fromWhat I can tell. This trailer is getting overhauled and I will do the prep work then have a pro burn it in. Suggestions?I'm thinking removing the cross member, v out the crack, fill, then fishplate. Should we fishplate the whole area up to the other shackle hangers too while its apart for more strength?  Then replace the cross member over the fishplate? Plate both sides?  Fishplate size, thickness and location suggestions welcome!Trailer member is 8" tall Channel. Attached Images
Reply:good catch.
Reply:Anything you do to it will be more then adequate.....Just saying.Just a couple welders, big hammers, grinders, and torches.Work will free you.Men in dirty jeans built this country, while men in clean suits have destroyed it. Trump/Carson 2016-2024
Reply:Maybe I'm not looking at the pictures hard enough, but are you sure the steel is cracking or did it just flex and crack the paint?First thing to do is clean the metal around the area so you (we) can get a better look at the condition.GravelThe difference between theory and practice is that in theory there is no difference.
Reply:Originally Posted by GravelMaybe I'm not looking at the pictures hard enough, but are you sure the steel is cracking or did it just flex and crack the paint?First thing to do is clean the metal around the area so you (we) can get a better look at the condition.
Reply:I would think if you see one crack there likely will be a few more.
Reply:I csn see it on other side of web. When reversing loaded that axle gets some stress. It was used by previous owner too Searched redt of trailer high and low. This is only structural flaw. Lemme go get pic from other side.
Reply:Grind it through, weld it up - rattle can paint and good to go! Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Surely the paint is flaked but the crack is a hair longer than the cross member wide. Old rust no new fractures anywhere. The rear axle takes a beating reversing loaded. I recon it was perfect conditions to initiate flaw. Both other cross members show no sign of rust cracks or flaws. There's only two midship Attached Images
Reply:Definitely clean off the paint with a wire brush or something...Too hard to guess what is going on.
Reply:Ok sry. Report tommorrow.
Reply:This is why I preach full height crossmembers at each spring hanger and any bend in the frame. You can patch it with a plate if you like and probly get by, but if you want it fixed right you will replace that crossmember with one that attaches to both the top and bottom flanges of the main rail. This is a perfect example of what I tried to convince everyone will happen when you attach crossmembers to only the web alowing the flanges to move flexing the web til it cracks. Here are the pics of the trailer I  posted before on Samm's trailer build, notice that the cracks are almost identical to those in this trailer.This also is demonstrated in the post about the aluminum boat trailer repair by William McCormick. You can get by if you find a way to get the existing crossmember tied to both the top and bottom flanges with gussets or something, but if you don't get attached you will likely have a return of the problem. That was also demonstrated in William's post as his repair was at least the second one for that trailer.Yeah, I know, but it'll be ok!Lincoln Square wave 255Miller Vintage mig30a spoolgunThermal Dynamics Pacmaster 100xl plasmaSmith mc torchEllis 1600 band saw
Reply:Wow look at that. Im not against doing it right. The whole deck of the trailer is getting rebuilt so whats a cross member to the equation. Your evaluation makes total sense.  Do you have  a picture on how to properly trim the cross member to touch all points on longsill?
Reply:I think you need to get the paint off to see what's really going on.  It looks more like the paint is delaminating at this point.  The steel can also delaminate when exposed to the elements for long periods.  HAZ zones are funny about the way they take paint sometimesThe crossmember is very small in relation to the main channel, that's a bit odd.  Wouldn't think it would be an effective crossmember.  I nested 4" channel inside 5" channel when it came to the crossmember, similar to my factory built 24K gooseneck as far as size ratio of the crossmember to side rail.In Jon's pics, the crack was on a loaded floor support which also happened to be a partial bulkhead/crossmember."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Jons pics are identical to mine. Ill still flake off paint and get ya a pic tomorrow. Brain fart too. The channel doesnt need to be coped. Doh!Last edited by brendonv; 01-14-2015 at 06:20 PM.
Reply:Originally Posted by brendonvWow look at that. Im not against doing it right. The whole deck of the trailer is getting rebuilt so whats a cross member to the equation. Your evaluation makes total sense.  Do you have  a picture on how to properly trim the cross member to touch all points on longsill?
Reply:I cope C-channel the same way as I cope beams. Cut both flanges back, so the web will touch the web of the other shape. Snip the top and bottom of the web so it will fit the radius of the heel of the web and flange. I bevel the flanges and web, then weld all the way around. Attached ImagesDon’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:Thanks for those pics Any issues if we used rectangle tubing?  I have some 2x8 coming in.
Reply:Originally Posted by brendonvThanks for those pics Any issues if we used rectangle tubing?  I have some 2x8 coming in.
Reply:Can you briefly explain torque tube..  Ive heard it before but unaware of meaning...To clear up things I've seen mentioned it another thread. This is at rear axle. Trailer is 15000 gvw. Pic of rust removed tomorrow. Was too dark today. But as mentioned, its identical to welderj's picture.
Reply:A torque tube is a term used when a trailer manufacturer builds a trailer from flexible material like channel, I-beam, angle, but then doesn't like the flexibility so they tie a tube of some sort, sometimes several tubes, to the main rails to help stop the normal flexing of the trailer frame. If your unfamiliar, tubes are very resistant to twisting and flexing, much more so that channels and such. The problem with you putting a tube in where the cracks are is that it would not likely be strong enough alone to do the job, which would leave the two types of frame fighting each other leading to more fatigue cracking. I also don't think your main rails are strong enough to take the extra stress of fighting the tube while also carrying the load. In this case I think you are better off to use a simmilar material to what's already there.Here is a pic of a torque tube in a Big Tex trailer.Yeah, I know, but it'll be ok!Lincoln Square wave 255Miller Vintage mig30a spoolgunThermal Dynamics Pacmaster 100xl plasmaSmith mc torchEllis 1600 band saw
Reply:Thank you. Ive heard the term regarding my rear mount aerial lift. It has a torque box.Makes sense.
Reply:what you are seeing there is a shear failure of the main beam.  as the shackle tries to push or pull laterally and the crossmember is resisting that movement, the shear in the main beam exceeds the beam's shear capacity.Welder J's solutions are spot on ... I would follow his advice.as I look at it, I see 3 options.  from best to least best:1. grind and weld crack. consider plating the beam, and add a full height cross member2. grind and weld crack, consider plating the beam, add gussets from the shackle to the shackle to the existing cross member.3. grind and weld crack, consider plating the beam, lower existing cross member such that it is adjacent to the shackle.option 1 probably costs the mostoption 2 is probably the cheapestoption 3 is, for all intents and purposes, silly - but likely acceptable.Personally, I don't see the problem with using the 2x8 tube, so long as it goes all the way down to the shackle, and so long as it is the same width as the shackle.  If it is narrower than the shackle you will still have a shear problem, albeit a different shear problem.  If it were me, I'd be tempted to just weld in the tube on the sides, and leave the top and bottom un-welded with a snug fit.but, with that being said, "J" has been doing this for awhile, and push come to shove, I'd probably defer to experience.JMOLast edited by Meborder; 01-16-2015 at 01:42 PM.
Reply:and just because it's bothering the crap out of me: Attached ImagesLast edited by Meborder; 01-16-2015 at 01:48 PM.
Reply:Originally Posted by Meborderwhat you are seeing there is a shear failure of the main beam.  as the shackle tries to push or pull laterally and the crossmember is resisting that movement, the shear in the main beam exceeds the beam's shear capacity.Welder J's solutions are spot on ... I would follow his advice.as I look at it, I see 3 options.  from best to least best:1. grind and weld crack. consider plating the beam, and add a full height cross member2. grind and weld crack, consider plating the beam, add gussets from the shackle to the shackle to the existing cross member.3. grind and weld crack, consider plating the beam, lower existing cross member such that it is adjacent to the shackle.option 1 probably costs the mostoption 2 is probably the cheapestoption 3 is, for all intents and purposes, silly - but likely acceptable.Personally, I don't see the problem with using the 2x8 tube, so long as it goes all the way down to the shackle, and so long as it is the same width as the shackle.  If it is narrower than the shackle you will still have a shear problem, albeit a different shear problem.  If it were me, I'd be tempted to just weld in the tube on the sides, and leave the top and bottom un-welded with a snug fit.but, with that being said, "J" has been doing this for awhile, and push come to shove, I'd probably defer to experience.JMOThis is my first post here.I think welderj is correct on what  is happening and how to stiffen the area. I have had two travel trailers that had angle iron welded at each hanger the way he deacribed.
Reply:"And I thank you for the kind words and backup"You're confusing threads Jon.I have no problem with Solution #2, neither should you or anyone else I'd imagine.  There's already a good deal of weld at the hanger, other than additional stored stress from the gusset it ought to work.  As long as the gusset is notched at the inside corner it'd be as good as anything."Any day above ground is a good day"http://www.farmersamm.com/
Reply:I do take issue with a full height crossmember attached to the flanges.  Aside from being a waste of material, completely superfluous, it's bad design.Speaking of shear, a full height crossmember welded solid top to bottom, will create a shear issue.  Vertical shear.  You've monkeyed with both flanges, and added a full length HAZ directly through the web, and flange, top to bottom."Any day above ground is a good day"http://www.farmersamm.com/
Reply:This adulation of full height crossmembers confounds me."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Let me put it to you this way.Rear of the rear hanger, the beam is cantilevered.  Lot of stress at the area where the hanger is located.Your moment is at the hanger.  This is a simple analysis from a bit ago.  I'm getting ready to build a single axle trailer with minimal structure.  It's simple in that the mid support isn't really a true representation of spring hangers.  I've centered the support in the middle of the hangers just for a fast look when I did it.There's a lot going on at that "hanger/axle", it's worth considering IMHOGotta get going.  K'kins gets home in about 1 1/2 hours, and I haven't done the dishes, or completed loading the truck for tomorrow"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammLet me put it to you this way.Rear of the rear hanger, the beam is cantilevered.  Lot of stress at the area where the hanger is located.Your moment is at the hanger.  This is a simple analysis from a bit ago.  I'm getting ready to build a single axle trailer with minimal structure.  It's simple in that the mid support isn't really a true representation of spring hangers.  I've centered the support in the middle of the hangers just for a fast look when I did it.There's a lot going on at that "hanger/axle", it's worth considering IMHOGotta get going.  K'kins gets home in about 1 1/2 hours, and I haven't done the dishes, or completed loading the truck for tomorrow
Reply:Originally Posted by farmersammThis adulation of full height crossmembers confounds me.
Reply:Originally Posted by farmersammI do take issue with a full height crossmember attached to the flanges.  Aside from being a waste of material, completely superfluous, it's bad design.Speaking of shear, a full height crossmember welded solid top to bottom, will create a shear issue.  Vertical shear.  You've monkeyed with both flanges, and added a full length HAZ directly through the web, and flange, top to bottom.
Reply:Originally Posted by welderjThe tube would work good as far as you are looking at it. The problem with the tube comes when an uneven load is applied, such as a single round bale or pallet set on a front corner of the trailer. This trailer will sag in that corner, and rightfully so, but that tube will try to resist that torquing of the frame. When that happens I think he could get into trouble. But it would work fine as far as the side to side forces. And if all the loads are evenly loaded he would be ok too.And I thank you for the kind words and backup.
Reply:Originally Posted by farmersamm"And I thank you for the kind words and backup"You're confusing threads Jon.I have no problem with Solution #2, neither should you or anyone else I'd imagine.  There's already a good deal of weld at the hanger, other than additional stored stress from the gusset it ought to work.  As long as the gusset is notched at the inside corner it'd be as good as anything.
Reply:Remove paint.  Grind out crack on inside of frame.  Weld it.  Grind crack on outside of frame.  Weld it.  If you aren't happy with that, you might consider a gusset here.  Just keep in mind that a channel frame will flex and beefing up one area may just cause a crack somewhere else.  Venture forth at your own risk. Attached ImagesMy name's not Jim....