Crossmember Size, and Placement

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I'm interested in the latest post about a trailer stress crack (have to see when the paint's cleaned off).My general inclination is to say that a centrally located crossmember, although small in height, should be somewhat resistant to stress problems.  My main reasoning is that the member in question is in the neutral part of the web, at least for bending stress associated with a vertical load.  Being an open channel shape, it shouldn't provide much resistance to torque during frame twisting.  Resistance to torque would definitely build stress at the welded joint.I've had success "nesting" smaller channel as intermediate crossmembers.  In other words........let's say a 5" main channel frame side rail, with a 4" channel crossmember welded to the web, no coping involved.  It's as tall as practicable, without having to interfere with the siderail flange.  (Try welding in a full height crossmember along a siderail, and watch the distortion you get along the frame.  Once you weld to the flange, it will distort the flange)I'm not a guru, or an engineer.  I simply follow industry standards.  I figure they've done the engineering for me.  I can merely try to understand the reasoning behind the accepted methods.It's rare to find flange-to-flange welded crossmembers in most commercially built trailers.  For example, the video shows a frame similar to my 18 wheeler flatbed.  Notice the small crossmembers.  In most cases, the only full height crossmember is at the axles, or the rear/front of the trailer.  And, I don't recall any of these near the axles being a full coped joint, they generally are a "nested" design.  The aluminum trailer in the video has a full height crossmember, bolted through the web, and flanges..........but that's aluminum.You won't find a frame more subject to torsional stresses than a semi trailer, yet this design prevails.http://bigtextrailerworld.com/gooseneck/  Little trailers are built much the same, and utilize "nested" crossmembers.  Videos 13, and 14, give a brief glimpse of frame construction.It's bad enough that you have to weld to the flange when installing floor supports (in a stacked design), or spring hangers.  The flange is pretty much a sacred cow, with good reason."Any day above ground is a good day"http://www.farmersamm.com/
Reply:On the trailer in question, I would have used a nested design at the spring hangers, or blocked the lower part of the channel with a full width piece of channel running from side to side attached to the front of the hanger.  Both methods are industry standards, although I don't favor the side-to-side method, and would avoid it unless forced to by circumstances."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Before I get out the door........................................As per the above post, and design at this point on the trailer..................The greatest stress at the front hanger (and I'm assuming the crack, if it is a crack, occurred at the front hanger location) is side loading.  Side loading???????????????????????Yup, side suspension forces encountered while making a tight turn.  The wheel scrubs due to this loading.  It's trying to overcome side loading.The channel at this point is trying to bend at the lower edge.  The above methods (post 2) are designed to deal with this side loading.  See the suspension details on the flatbed I built a while back, and you can see how to effectively deal with side loading.  The hanger is tied to the crossmember so it can't flex, and the crossmember reinforces the side rail.Be the metalOutta here"Any day above ground is a good day"http://www.farmersamm.com/
Reply:So why on the trailer in question would anyone weld across the flange? his channels are flange out leaving the nice flat back side of the channels for welding crossmembers to without any need to compromise the main beam flange. Thanks for posting the link to the semi trailer video as well. Altho there is very little in common with gooseneck or bumper pull trailers that are the most common subject here, it's nice to see that my advice to put a full height crossmember at the spring hangers and any bend in the frame is backed up by semi trailer manufactureres. Of course after 30 years of designing and fabricating many dozens of trailers of many different designs, I already knew that, but with so much bad advice being passed around by internet surfers who think they are experts after one or two builds it's good to get acurate info out there.In my experience, and again this is only from some 30 years experience in the field and not from any formal education on the subject, every manufacturer including me has their good and bad points. I like the Big Tex trailers and think that over all they are as good as it gets for comercial trailers. But even a good manufacturer can have problems as you can see in this pic I took of a Big Tex trailer a while back.As you can see the main rail has broken several times and been patched poorly trying to get it to stopp breaking. This is in the rear of the trailer where they added the beaver tail to the main rails and is not related to the crossmember issue, but does demonstrate that noone, even Big Tex, always gets it right.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:I think the reason the welds are cracking is the 7018 wasn't kept in a rod oven and used within 4 hours of contact of ambient air.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:Originally Posted by farmersammBefore I get out the door........................................As per the above post, and design at this point on the trailer..................The greatest stress at the front hanger (and I'm assuming the crack, if it is a crack, occurred at the front hanger location) is side loading.  Side loading???????????????????????Yup, side suspension forces encountered while making a tight turn.  The wheel scrubs due to this loading.  It's trying to overcome side loading.The channel at this point is trying to bend at the lower edge.  The above methods (post 2) are designed to deal with this side loading.  See the suspension details on the flatbed I built a while back, and you can see how to effectively deal with side loading.  The hanger is tied to the crossmember so it can't flex, and the crossmember reinforces the side rail.Be the metalOutta here
Reply:Your right. It is the rear axle, and again, its almost identical to welderjs picture he posted. I wont be able to get the pic with rust scraped until tomorrow.  Its the only part of the trailer where there is rust on a welded member. Its surely cracked~
Reply:Originally Posted by farmersammI'm interested in the latest post about a trailer stress crack (have to see when the paint's cleaned off).I've had success "nesting" smaller channel as intermediate crossmembers.  In other words........let's say a 5" main channel frame side rail, with a 4" channel crossmember welded to the web, no coping involved.  It's as tall as practicable, without having to interfere with the siderail flange.  (Try welding in a full height crossmember along a siderail, and watch the distortion you get along the frame.  Once you weld to the flange, it will distort the flange)
Reply:Originally Posted by AKweldshopI think the reason the welds are cracking is the 7018 wasn't kept in a rod oven and used within 4 hours of contact of ambient air.
Reply:Originally Posted by bratkid63One of my first trailer builds. (The cars in the photo ought to give an idea how long ago!) All 3" channel frame with a 2x3x1/4" box tube tounge. Full perimeter welds at all joints. Trailer size was 6x10 with a single 2000 lb axle. It was built to carry my Honda ATC's (way back when men were men and three wheels were all we needed on our ATV's lol). No distortion along the frame rails.
Reply:Originally Posted by bratkid63One of my first trailer builds. (The cars in the photo ought to give an idea how long ago!) All 3" channel frame with a 2x3x1/4" box tube tounge. Full perimeter welds at all joints. Trailer size was 6x10 with a single 2000 lb axle. It was built to carry my Honda ATC's (way back when men were men and three wheels were all we needed on our ATV's lol). No distortion along the frame rails.
Reply:Jon, I shoulda seen that was a rear hanger.  It's a slipper suspension. Whether the channel if facing away from a weld, or facing inwards and coped, a flange is still a flange Jon.  It doesn't matter which side of the channel you're on, it's still a flange at the upper/lower extremity of the web.  Backside/frontside, you're still talking about welding to the flange using your methods.I don't believe I ever said anything about welding "across" the flange, I simply said welding "to"/"on" the flange.  It's something I just don't like doing.  I know it's necessary at times, but I don't like it.  Matter of fact, Hutch (and probably Reyco) prohibits welding on the flange edges.  Welds are allowed transverse, and longitudinally, as long as the welds terminate within 1/2" of the edge of the flange, if I remember my numbers right.  It's their WP.I don't believe the moment at the front hangers is as crucial as, let's say the midpoint of the beam, when it comes to vertical loading, but it's a concentrated fatigue area I'd imagine.  The suspension area is relatively stiff compared to the rest of the beam.  The moment at the rear of the suspension would probably be more critical because it's a cantilever, so you have a bending moment smack dab where the hanger is attached, and quite a bit of fatigue at this point.You really don't have a choice when it comes to hanger attachment on these trailers, it is what it is.  It has to be welded to the flange.  I believe you only see bolts through the web on Class 8 truck hangers, been a while since I rebuilt one.  The flange is of major concern on HD applications.  I really believe the flange deserves respect in all applications.  That's my take on it anyways."Any day above ground is a good day"http://www.farmersamm.com/
Reply:https://www.trailerlocators.com/View%20Trailer%20GWSNPPer the Great Dane video:  Jon, maybe you didn't get to the steel trailer features on the video.  This is a common suspension setup, with a "nested" crossmember, not a full height crossmember  flange-to-flange.  Steel trailers are stronger than aluminum trailers, and designed accordingly."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by welderjWould you care to explain why you put the center rail in? I see no problem with it, I'm just curious why. I have seen other trailers done that way too.
Reply:Originally Posted by farmersammI must be going wrong somewhere.  I can't do something like that without it pulling.  The heat simply folds it at the joints.
Reply:Originally Posted by bratkid63I put it in so I would have a good location to weld in tie downs along the centerline of the trailer. Steel was cheap then, that center piece probably only added $10 to the cost of materials!
Reply:Originally Posted by farmersammhttps://www.trailerlocators.com/View%20Trailer%20GWSNPPer the Great Dane video:  Jon, maybe you didn't get to the steel trailer features on the video.  This is a common suspension setup, with a "nested" crossmember, not a full height crossmember  flange-to-flange.  Steel trailers are stronger than aluminum trailers, and designed accordingly.
Reply:Originally Posted by farmersammJon, I shoulda seen that was a rear hanger.  It's a slipper suspension. Whether the channel if facing away from a weld, or facing inwards and coped, a flange is still a flange Jon.  It doesn't matter which side of the channel you're on, it's still a flange at the upper/lower extremity of the web.  Backside/frontside, you're still talking about welding to the flange using your methods.I don't believe I ever said anything about welding "across" the flange, I simply said welding "to"/"on" the flange.  It's something I just don't like doing.  I know it's necessary at times, but I don't like it.  Matter of fact, Hutch (and probably Reyco) prohibits welding on the flange edges.  Welds are allowed transverse, and longitudinally, as long as the welds terminate within 1/2" of the edge of the flange, if I remember my numbers right.  It's their WP.I don't believe the moment at the front hangers is as crucial as, let's say the midpoint of the beam, when it comes to vertical loading, but it's a concentrated fatigue area I'd imagine.  The suspension area is relatively stiff compared to the rest of the beam.  The moment at the rear of the suspension would probably be more critical because it's a cantilever, so you have a bending moment smack dab where the hanger is attached, and quite a bit of fatigue at this point.You really don't have a choice when it comes to hanger attachment on these trailers, it is what it is.  It has to be welded to the flange.  I believe you only see bolts through the web on Class 8 truck hangers, been a while since I rebuilt one.  The flange is of major concern on HD applications.  I really believe the flange deserves respect in all applications.  That's my take on it anyways.
Reply:I think we're mostly on the same page about a lot of things Jon.The subframe for the suspension isn't part of the main beam by the way I figure.  It is like a slider, like you say.  But it is part of the entire assemblyThe stacked channel at this point is like a beam in its own small right, with a smaller crossmember on the bottom.  It's screwy, but I didn't want the stacked assembly to be un-reinforced, nor did I want to completely box it in with respect to both pieces of channel (main frame, and "slider").  It's a stiff area, and I didn't want it to be any stiffer than necessary.  I suppose it's one of the compromises you have to deal with on this kind of trailer where you have to lower the suspension to clear the deck.I did feel it was necessary to offset any side loads on the hangers, and this was the solution.  The 3" channel allowed for a place to tie the hangers in.  Pretty much like attaching a piece of channel to the hangers, directly in front/behind of the hanger.  I felt that the way I did it, made it possible to reinforce the hangers dead middle, instead of on the edges.  My gussets extend to within a socket thickness of the shackle bolt, it's that close clearance wise."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammI think we're mostly on the same page about a lot of things Jon.The subframe for the suspension isn't part of the main beam by the way I figure.  It is like a slider, like you say.  But it is part of the entire assemblyThe stacked channel at this point is like a beam in its own small right, with a smaller crossmember on the bottom.  It's screwy, but I didn't want the stacked assembly to be un-reinforced, nor did I want to completely box it in with respect to both pieces of channel (main frame, and "slider").  It's a stiff area, and I didn't want it to be any stiffer than necessary.  I suppose it's one of the compromises you have to deal with on this kind of trailer where you have to lower the suspension to clear the deck.I did feel it was necessary to offset any side loads on the hangers, and this was the solution.  The 3" channel allowed for a place to tie the hangers in.  Pretty much like attaching a piece of channel to the hangers, directly in front/behind of the hanger.  I felt that the way I did it, made it possible to reinforce the hangers dead middle, instead of on the edges.  My gussets extend to within a socket thickness of the shackle bolt, it's that close clearance wise.
Reply:I don't think these cracks ar not caused by the vertical. I think they are caused by the sideways loading during a turn. Particularly during backing if the trailer is nearly being pushed sideways. These effects are even higher if the trailer happens to be a triple axle.
Reply:Originally Posted by welderjOk, that makes sense then. I just couldn't figure out why you would cut all the crossmembers like that. But if you need tie downs there then I see the purpose. Thanks for that info, I always like to know why folks do things, you never know when a good idea will come up that I can use.
Reply:I have the day off today in St. Louis, so I decided to take a walk and check out just what the "industry standard" for crossmembers is in St. Louis. The results were interesting. I took pics so maybe we can put this to rest.The structure on this first one is made from tube and so are the crossmembers. It has one full height member at the center of the suspension and a 4" at the front and rear hangers on a triaxle setup. 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:This is a new trailer at the Jd construction equipment dealer across the street. Full height cross members at the spring hangers and the bend at the tongue.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:How about a Fontaine aluminum, full height at the suspension and several along the length.Last edited by welderj; 01-17-2015 at 01:57 PM.Yeah, I know, but it'll be ok!Lincoln Square wave 255Miller Vintage mig30a spoolgunThermal Dynamics Pacmaster 100xl plasmaSmith mc torchEllis 1600 band sawBenson, aluminum.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:Utility combo. Tied to the bottom rail, crossmembers tied to the top and full height stiffeners to tie it together.How about a heavy haul, lowered to allow clearance for the load, but tied both top and bottom and welded 100% and to the flange. 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:Transcraft Eagle, crossmember at the hanger with a gusset up to the deck crossmember and a full height stiffener for a backer welded 100%. They also add diagonal braces between the axles.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:I saved the best for last tho. I think it's the best because it shows what happens if you don't follow my advice. This one didn't have full height crossmembers from the factory and is broken and patched in all the places I predicted. Pictures don't lie. So tell us now, just what is the industry standard for crossmember placement and size?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:Came across this Great Dane just now. Attached ImagesYeah, I know, but it'll be ok!Lincoln Square wave 255Miller Vintage mig30a spoolgunThermal Dynamics Pacmaster 100xl plasmaSmith mc torchEllis 1600 band saw
Reply:Well from my chair it is hard to know what to believe, it must be entertaining though because I keep looking.  Well good luck with all of the trailer builds and if in doubt consult with an engineer, then you will be really screwed up.  I know this because when I ask an engineer I know less by the time he is done answering then when he began. Canner
Reply:I have welded enough transcraft trailers back together to ask you to not use them for any design considerations.    we NOT so lovingly refer to them as Transcrack or transcrap around here.Vantage 500's LN-25's, VI-400's, cobramatics, Miller migs, synch 350 LX, Powcon inverters, XMT's, 250 Ton Acurrpress 12' brake, 1/4" 10' Atlantic shear,Koikie plasma table W/ esab plasmas. marvel & hyd-mech saws, pirrana & metal muncher punches.
Reply:Originally Posted by DualieI have welded enough transcraft trailers back together to ask you to not use them for any design considerations.    we NOT so lovingly refer to them as Transcrack or transcrap around here.