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arched or cambered trailer frames
3

arched or cambered trailer frames

arched or cambered trailer frames

(OP)
We were having a discussion today about the purpose of cambered main rails on trailers that haul around heavy equipment.
One fellow felt that the beam was stiffer as a result of the camber.
I thought it would have little or no effect on stiffnes unless a tension member went from end to end.  So the arch is to end up with a flat floor or good ground clearance.

RE: arched or cambered trailer frames

First off, the frame rail goes from one end of the trailer to the other, so it does go end to end, and the bottom flange is in tension under load.

Now, my qualifier.  I am not a structural engineer, and maybe this should be posted in a fourm where they live, but the arched trailer is done on purpose to enable the beams to carry the load properly.

It is magical to see an arched trailer being loaded with with a point load, steel coils come to mind as one of best of examples, and the frame rails flatten out, only to return to their original arch upon having the load removed.

Now the structural guys will have to explain all the statics and stress and strain that goes with all that.

As I remember it, the bottom flange of the frame rail goes into a heck of a tension, and as your friend says, gets stiffer.

Same for heavy haul trailers, etc.  It has to do with the load carrying characteristics of the trailer, and nothing to do with ground clearance.  

In theory, a properly designed, properly loaded trailer frame will be perfectly horizontal, and the ground clearance will be equal all around the trailer.

If you are going to make the case that an "un-arched" trailer would 'sag' in the middle, and hence reduce ground clearance, I guess it could be made, but I don't think that is the case at all, based on experience with trailer manufacturers.

rmw

RE: arched or cambered trailer frames

If you are going to make the case that an "un-arched" trailer would 'sag' in the middle, and hence reduce ground clearance, I guess it could be made, but I don't think that is the case at all, based on experience with trailer manufacturers.

Oh really?  'cause that's exactly the case I was going to make.  Ground clearance doesn't sound like as much of a concern to me as a flat deck, though.  A flat deck "looks right", whereas a sagging deck looks overloaded.  If you made the trailer flatten out as it approached design load, then a sagging trailer would be overloaded, and more easily spotted.  Then again, if I remember my vehicle stability course, a distributed load is worse for trailer stability (something to do with comparing J to m*a*b), and a trailer will sag less under a distributed load.

Back in school we went over beam bending, and I don't recall the stiffness varying significantly vs deflection, as you suggest above ("...gets stiffer").  


RE: arched or cambered trailer frames

Quite probably because railroad flat cars have always been build with positive camber.

Structurally I don't think there is any real need to design for positive camber when empty.

RE: arched or cambered trailer frames

You really see the benefit of prestress when you're dealing with a very low deck low loader.

This time last year, I watched a trailer (which had started out with 3 or 4 inches of ground clearance) sag right onto the vehicle park as a new type of load was craned onto it.  There followed an afternoon of (somebody else's) clever work with a gas torch to reshape the beam and adapt it to the new load.

Even if you don't ground out, heavy trailers which sag are far more likely to attract unwelcome attention from people with awkward questions to ask about axle weights.

A.

RE: arched or cambered trailer frames

I'm guessing that the camber is provided so that a person with no engineering skills needs no measurements to decide when the trailer has pretty much reached its design load; the deck gets flat.

The beam doesn't get stiffer from the camber.  The ground clearance argument has some validity, especially for lowboys, but there's no structural reason that the trailer couldn't start out flat when unloaded.  But if that were so, truckers and loaders and load enforcement people would waste endless hours arguing about how much negative camber was acceptable for a given trailer with a given load.

Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

RE: arched or cambered trailer frames

Support provided to a large, rigid flat-bottomed load is better and deck unit loading is more uniform if the deck is flat under load.  I suspect that full-length contact between load and deck has something to do with friction damping of the spring (trailer beam) - mass (load) system as well.

Norm

RE: arched or cambered trailer frames

I have a hard time believing that the sole reason is asthethics.  I have seen the work that it takes to custom fabricate one of these arched beams, and you could make a trailer a heck of a lot cheaper with straight beams.

RE: arched or cambered trailer frames

Maybe the bottom half of the beams are actually preloaded to compression so that when a load is applied the bottom goes from compression to tension?  Doing this would lower the stresses on the top and bottom surfaces of the beams when placed under load.  This could be done if the beams are 2 piece with the top section arched and stress relieved and then welded to a flat bottom section.  

RE: arched or cambered trailer frames

Since this post firstr came up, I have been trying to remember the exact reasons for this.  As I remember, it is to minimize the strain (and resulting stress).  With an arched bed loaded to near-level, the top half is under compression and the bottom half is under tension.  If the bed had gone from unloaded and level to level and sagging under the same load, the tension strain on the bottom of the bed would be greater.

RE: arched or cambered trailer frames

I wish some structural eng'r would come over here from the structural forum and answer this.  I think TheTick has come the closest, but I want to add two more things to the conversation.

One is, not only do you have the static loading of the trailer beams, there is the dynamic loading.  Back to my 50,000 lb single steel coil loaded amidships on an arched trailer that brings it from its fully arched position to a level position, but then think about what this pair of beams is undergoing as this rig bounces down the road at 70 mph on the kind of roads that I have to use.

Now all of a sudden the stress and strin of this beam under load takes on some real intersting characteristics.

Secondly, ever notice that the ultra long concrete bridge beams that can be seen from time to time being trucked down the road are arched??

rmw

RE: arched or cambered trailer frames

To be honest I think the Tick's explanation is awful (sorry mate).

Using simple beam theory the stress and strain in simple bending  is proportional to the distance of the fibre from the neutral axis of the section. The large scale curvature of the beam does not affect this. If you don't like beam theory then replace the beam by a simple warren truss, and you'll see the same effect, in a manner that can be calculated by a mechie (grin).

Having said that, I have no better alternative except: If you had a long stiff heavy load, and placed it on a flat beam, it would only touch at the ends.

If the beam is curved then it initially contacts in the middle, and then as the beam bends the contact load will be distributed to some extent along the length of the beam or load.

I don't particularly like this explanation, it seems to rely too much on perfect matching of the load and the stiffness of the beam.

 



Cheers

Greg Locock

RE: arched or cambered trailer frames

Thread507-58876

You may find this useful.

Regards.

RE: arched or cambered trailer frames

Pre-cambering of beams (and trusses) is for deflection control.  You would need a large amount of camber for a beam to behave as an arch!

RE: arched or cambered trailer frames

And most importantly the end conditions - pinned or fixed.

RE: arched or cambered trailer frames

I think GregLocock is petty close to the money:

A bit of camber in a beam does not make it stronger or stiffer, unless there is sufficient "arching" to generate arch behaviour AND you have some means of preventing the ends from spreading, such as a tension tie. Neither condition applies to a cambered trailer rail, so it will deflect just as much as if it was dead flat.

A trailer body which hogs slightly in the middle looks OK. A trailer body with 50 mm of sag at midspan looks overloaded. Try and convince the police and other road users that your trailer is not overloaded when they can see it sagging!

If you put a long "rigid" load onto a precambered trailer, it will force the trailer to deflect down until the whole load is more or less uniformly spread over the length of the trailer. If the trailer is initially flat or sagged, the load will probably be totally concentrated at the ends, which will be stiffer than the midspan.

Sometimes, this is exactly what is intended. Check out a typical container trailer. Containers are designed to carry all their loads by the corner blocks, not by distributing the load along their length. The container sits on the trailer at its 4 corners only, with clear daylight between the bottom of the container and the top of the trailer. The trailer body retains its camber even when fully loaded in this case, because all of the loads go straight down though the corner blocks into the chassis and suspension, and none goes to the trailer rails.

RE: arched or cambered trailer frames

I, too, think Greg has pretty much nailed it.  It is primarily an aesthetic issue...with deflection being the key.  If you pre-camber a member to an expected deflection, you can reduce the member size (thus weight), if deflection is the primary controlling factor.

IvyMike makes a good point about the "notice" factor....if it looks overloaded, it will draw suspicion, thus the authorities are more likely to take a look....keep in mind that overloaded trailers are a source of income to the government...they charge for overweight vehicles (handsomely in some cases) because of the "impact" that additional load has on the life of a pavement structure.

RE: arched or cambered trailer frames

I'll agree with Ron, and restate the obvious.

Trailer beams are cambered to save money.

There are many factors to be considered in designing a structural member. Quite often, the smallest member capable of supporting the load is not adequate due to reasons of serviceability i.e. too much deflection, obvious movement, etc.

I am not a designer of semi trailers, but if I could use a smaller member with added camber, versus a larger and heavier member, I'd go with the lighter, and spend the bonus money I got for allowing a higher load rating on the trailer due to lower self weight on a nice little vacation.

SO, having camber in a truck trailer potentially allows for a smaller member to be used without seeing the negative visual effects of deflection, and thus allows a light trailer weight and larger allowable shipping loads for a given gross vehicle weight.

The extra cost for cambering the beam is made up by the difference in beam size, and more so by the larger allowable payload of the trailer.

How about that?

Daniel Toon

RE: arched or cambered trailer frames

More agreement with recent posts (and with original post by Tmoose): it's a deflection thing.

Regarding some details raised in earlier posts:

Trailer beam resists load like a "beam", not an arch; besides the camber being too small for arch action, there's no mechanism to resist horizontal arch thrust.

Camber of beam doesn't increase stiffness, so relative deflection from unloaded condition isn't different between cambered and uncambered beams. But benefits from deflecting from the unloaded cambered shape include the "notice factor", and perhaps low trailer clearance during suspension compression over bumps--both mentioned in previous posts.

Cambered concrete beams mentioned earlier similar to trailer beams (load-induced deflection superimposed on pre-deflected shape), but different too: Camber in concrete beams achieved by prestressing eccentric tendons in beam to introduce net compression on unloaded beam, causing more favorable (to concrete) stress distribution under load. This is neither helpful nor feasible for steel beams.

RE: arched or cambered trailer frames

Another structural input - just to confirm a few points that have been posed above:

1.  Agree that this isn't an arch issue.
2.  Agree that cambering doesn't do anything to reduce stress or deflection....just changes where the deflection starts.
3.  Agree SOMEWHAT with the "notice the sag" point, but I think the following is another consideration:

The types of loads placed on the flatbeds are sometimes quite long, extending the full length of the trailer.   If the load is fairly long, and the trailer frame is not cambered, then the load will cause a downward (smile-shaped) curve whereby the ENDS of the loaded element will become point loads, and the loaded element would be required to span from end to end, placing stress and bending in the load.

With a cambered beam, as the load is applied, the beam becomes MORE straight, not LESS straight, and there would be a tendency for the load to be more uniformly supported.  Shims can always be used so this may not be a totally valid point, but it seems right.

Also, with a uniformly loaded frame, as the trailer goes over bumps and swales, I would think that a more uniformly loaded frame would not be as susceptible to cyclic excitation where the deflections would be magnified from free swings in deflections....again - I don't have any special knowledge in this - but it also seems to make sense.

RE: arched or cambered trailer frames

Sorry JAE, but I have to disagree.  If a long container was placed on a flat trailer, the container would not push the trailer down such that the container was point loaded on the ends.  If there is no contact, there is no load to push it down and there is no end point loading.

On the flip side of that coin, if a flat-bottom container is placed on a cambered-beam trailer and does not have the weight to load it to flat, the container will be point loaded in the middle (one point only).  This would be far more unstable no matter how many tie-downs you use and, in addition, shipping containers are designed to be loaded at the corners and not in the middle.  You would likely damage the container.

Just my opinion.

RE: arched or cambered trailer frames

Regarding contact with the (platform) trailer, normally, in this country, at least, where possible, the load does not actually contact the trailer, but is either placed on wooden beams, or special load carrying devices (such as are used with the aforementioned steel coil.)

It is not uncommon to see long pipe or tubing loads that are supported strategically at the point above or near the fifty wheel, and above or near the centerline between the suspension attachment points.  This some time makes the camber of the trailer rails obvious, because the straighness of the long load highlights the "arch" of the cambered rails.

For the purpose of this conversation, the word "arch" applys to the fact that a trailer frame is cambered, not ARCH in the sense of what structural engineers think of.  There is no capstone in the middle of a trailer.

Good discussion.  Good answers.  Thanks to the structural participants for answering the call.

rmw

RE: arched or cambered trailer frames

Loads on trailers rarely are configured such that they actually span anything.  They are most often a series of point loads, even if they are long items such as pipes and the like.  Further, they contribute nothing to the stiffness or structural resistance of the load/trailer deck interface.  As such, the reaction points are only the 5th wheel and the axle(s), leaving free deflection in the middle.  The use of a cambered main frame allows smaller, lighter members to be used thus decreasing costs and weight.  As JAE noted, the deflection characteristics don't change, its just where they start that changes.  That's important for the points mentioned about aesthetics and the need to reduce the "notice" factor.

RE: arched or cambered trailer frames

Gensetguy - I would respectfully disagree with you.  

ANY beam loaded with twin point loads, say at the third points or quarter points would ALWAYS deflect downward in a reverse arc - this is simple statics and mechanics of a beam.  

Two point loads DO make a downward arch, which WOULD produce a gap below a rigid element on the bed.  I can get the actual deflection formula if you'd like to see it.(don't have it handy right now)

But the element would have to be rigid enough to span across the distance.  This would produce a condition where the supported load would have to either span the distance between the ends (if it was rigid enough) or sag along with the trailer until the "span" of the loaded element was reduced such that it would still span over a smaller gap.

I believe you are correct about the reverse condition, where the camber is not quite overcome by the load and the element is supported in the center, or probably end up with one end in the air.

But the subsequent comments are also valid, I think, in the multiple loaded pieces are the norm.

Perhaps someone else could comment on another thought I had - that the camber keeps the hitch mechanism in a proper angle to maintain the connection?  Any validity in that?

RE: arched or cambered trailer frames

My doubts..

I am not fully sure that it is an Industry-wide accepted practice to camber the truck/wagon/trailer  beams. There is not any clear advantage and at the same time cambering is a costly exercise. It is also difficult to believe that the deflection is actually perceptible to an observer (cop)just by looking at the loaded trucks.

Tmoose can verify whether it is indeed so that these trailer beams are invariably cambered.

RE: arched or cambered trailer frames

JAE....the "hitch" mechanism of a 5th wheel hitch can rotate over 15 degrees, so it should be able to accommodate most any level of deflection.

flame...the deflection, particularly in aluminum trailers, can be quite pronounced under load when the smaller sections are used.  Comparing older trailers to newer ones shows the significant size reduction in the main frames.  Further, older trailers were 34 to 40 feet in length while newer ones are 40-45 feet long, have slide-adjustable axle trucks, and must often endure the fatigue of 500,000 road miles or more.

Container trailers are usually much shorter and stiffer than the trailers discussed.  They are designed for the containers and are built for short distance logistics, not long-haul, over the road considerations.  I doubt you would see much if any deflection in a "container" trailer.

RE: arched or cambered trailer frames

JAE - After thinking about it last night, I now have to agree with you.  I was thinking about a conatiner that spanned the entire length of the trailer (fifth wheel to axles) and that is very unlikely.  Containers of this type have specialized trailers.

Speaking with an engineer who has experience in this design (dealing with the regulations and such), at least in the case of a low-boy trailer, the reason is ground clearance.  There is a minimum required clearance (from the DOT) and if you are under it, you are ticketed.  Another vote for ground clearance.

RE: arched or cambered trailer frames

There are other issues that involve ground clearance other than dimensions dictated by regulation and inspectors "eyeballs" and that is rail road track clearance.  In the USA, at least, a commercial driver license (CDL) holder can get a major 'ding' on his driving record (along with the monetary fine) if he/she high centers on a Rail Road crossing.  I can attest to this as a CDL holder, and I have to be aware of that proviso should I choose to operate a commercial motor vehicle, which I do from time to time.

Now, understanding the industry is part of the answer, too.  In the truck transportation industry in most developed countries of the world, weight, that is to say 'payload' capacity is EVERYTHING!!!!  Therefore any design consideration (arched or cambered beams) that would produce a smaller, and hence, lighter frame member is a  feature that would set you apart from the competition.

And, Ron, not to be picky, but the truck/trailers in our country can be expected to go several millions of miles before they find the scrap heap.  Your point is excellent otherwise in emphasing that they have to be built tough.

Flame,  I have carefully used the word 'platform' trailers in these posts, because, I, like you, am unaware of any cambering of the frames on other than flat beds, low boys, drop decks, etc.  And, not every style of platform trailer out there has a cambered frame.  Pulp wood hauling trailers, for example, have to be built so stout in order to survive the rigors of going into the woods to be loaded, that some of the lightweight designs where you find the cambered beams would never survive the twisting and torsional loads put on the frame members.

The cambered beams are especially prevelent in trailers that are designed to carry point loads.  This would include the 50,000 steel coil I keep mentioning, or a low boy that may have a huge transformer sitting in the middle of a long span.

Those parts of the discussion I can vouch for, the conversation regarding the engineering behind reason for the cambering is what I am benefiting from here.

rmw



RE: arched or cambered trailer frames

Ground clearance doesn't really matter for a regular flatbed trailer, though, and these are still cambered.

I'll concede that I may not have the correct reasoning behind arching trailers.  All I remember is that we spent about half of a mechanics of materials class discussing it.  There was more than aesthetics at stake.

RE: arched or cambered trailer frames

I know from personal experience that drivers judge the weight on their truck by both spring and trailer bed deflection.

It is a lot easier to determine by simple visual inspection that the trailer is still arched or flat. It is a lot harder to determine it is sagged to a predetermined level.

Many trucks are loaded where no scales are available, so the drivers ability to estimate the load is really an important issue, at least in rural Australia

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: arched or cambered trailer frames

(OP)
"Tmoose can verify whether it is indeed so that these trailer beams are invariably cambered."

All I know about trailers is what I see drivin' down the road.  I would have said I've seen plenty of the real long ones that are cambered, whether they are up high, or close to ground to haul a 'dozer.  The beam/frame I was talking about would be handling the load all alone, without a cable or rod tension strut paced several inches off the bottom of the rail, like an old trolley.

Actually the cambered trailer was an example thrown into the tail end of a conversation. I had "invited" myself into it when I thought I heard My boss and the new project engineer discussing cambering as a means of stiffening a part of a simple part.  

I had thought a bit about almost the same topic almost 20 years earlier.  We were thinking of using bowed rafters for the house we were planning to build.  I was talking to an outfit that offers them as part of kits.  The proprietor or maybe his wife tossed out a catchy statement something like "curved parts are stonger.  Always were. Always will be."  As it looked (and looks) to me like there is little or no arch action in a typical framed roof whether the rafters are bowed or straight, I researched the subject a little more. I believe According to the "Timber Construction manual" laminated wooden rafters or beams are actually a little weaker in bending than straight laminated beams.  The reason is because each of the laminating strips were straight before being bent cold and glued together.  For the rest of their life they are trying to straighten out, but are prevented from doing so by the convex/concave glue joint.  So the extreme fibers on the concave face are in tension when the rafter/beam is just sitting there, and adding real load to the convex side adds to their non-zero starting tension.

RE: arched or cambered trailer frames

There is a lot of talk in the above about cambering being expensive. I know nothing about vehicle trailers but find this hard to believe. Even if a significant cost could be associated with cambering it is only one process among the many required to form a trailer.

I'd guess that cambering offers SOME material savings, SOME benefit to the 'laymen' who have to load the trailers, and SOME improvements in the way ground clearance is achieved (if not the actual ground clearance required.

Another thought, a cambered surface will shed water...

RE: arched or cambered trailer frames

The cambered beams are actually three plates.  One with a double arch (think of the waste in drop), a top plate, and a bottom plate.  The center web is cut and the top and bottom flange are heated or in some other way bent around the arced web.  Then (making sure it is square to the world) the three pieces are welded up (most of the time they are stitched).

This seems a lot more expensive than an extruded I-Beam to me.

RE: arched or cambered trailer frames

"This seems a lot more expensive than an extruded I-Beam to me."

True, but for lots of trailer designs, a rolled section isn't ideal anyway - fabricating a beam allows the shape and dimensions to be tailored at will (and varied along the length of the beam).

Imagine the junction between the gooseneck and main deck on a stepframe trailer - this is a real stress point.  With fabricated rails, you can make it so that the web is one continuous piece of metal all round the transition.  With rolled section, you're looking at having to put welds in all the wrong places.

Similarly, with fabricated raves, you can build in details like wheel arches without compromising the structure too badly.

A.

RE: arched or cambered trailer frames

Rather belately, I had a bit of a trickle of brains to the head.

So far, we've talked a lot about big individual loads.

Driving home the other evening, I passed a trailer carrying a large number of tall boxes, each pushed flush against the next.  It struck me that any sag in the trailer would make these loads touch and fret at the top, while separating them at the bottom making them hard to secure.

Maybe not the primary reason for the camber, but certainly one to make you glad it's there.

A.

RE: arched or cambered trailer frames

Trailer frame main rails are cambered by taking a rosebud on the oxy/acy torch and heating the the rails in about the middle, this brings the ends up when it cools. Then when the rest of the camper is built, or the car/equip. whatever is loaded on the frame,it goes to a fairly straight shape.
It's not done by mech. bending as far as I know. They just typically use the principle of heating a member on one side only to red hot and this makes it settle into curve.
Unless it is a really light trailer, carrying a load on it w/out camber would probably make the ends to sag downward visibly.
I have seen this done to re-straighten(re-camber) a large mobile home frame by welding beads along frame rails with a stick welder, you see a lot of this in Elkhart Indiana-believe me!

RE: arched or cambered trailer frames

Hi Guys,

I'm a newbie here, so I hope I don't step on too many technical toes in this message.  :)

I would like to respectfully disagree with all of the given reasons why trailer frames are cambered.  I think the real answer is something else.

Everything wears out.  Tires wear, brake linings wear, brake drums wear out, light bulbs burn out, paint wears out, and believe it or not...trailer frames wear out!  Trailer manufacturers realize that over extended time/miles/bumps/overloading the frame rails will tend to relax.  So to make their frames last longer, they are built with a positive camber.  The more camber, the longer the service life of the trailer.  

Having some engineering background, having worked for a small volume trailer manufacturer and having been around the trucking industry, all cause me to believe in my above stated opinion regarding trailer camber.

In the trucking industry, a flatbed trailer that has lost its camber is called a "sway-back".  I think the term is a carry over from the old west describing a horse with a bad back.  Sway-back trailers are not very valuable/useful/desirable in the trucking industry, ie the service life is out of them.

Many times trailer frames are made out of T1 steel which typically comes in plate form.  T1 is much stronger than A36 steel which I beams are commonly formed from.  So to make a strong trailer frame, 3 pieces of T1 steel are used, the top flange, the web, and the bottom flange.  A good trailer manufacurer welds all 3 together with a certain amount of camber.  Trailers made from A36 I beams are not strong and are heavy.  Heavy equals less payload.  However on some applications like the skeleton frame under container boxes the frames do not carry much weight and therefore can be made out of the cheapest steel available (usually A36).  Container boxes are self-supporting and focus their weight to the hard points in the corners which are typically immediately above the fifth wheel and rear axles of the trailer hence the trailer frame bares no weight.

As you notice flatbed trailers on the road, look to see how they are loaded.  Let me give you an example using bricks.  I good driver will have 2 piles of bricks on his trailer.  The first bunch will be as far foward as possible (above the fifth wheel) and the second bunch as far back as possible (above the trailer axles).  This method of loading puts the least amount of load on the middle of the trailer which stresses the trailer frame the least which causes the trailer to last longer.  A poor driver puts all the bricks in one bunch and in the middle, stressing the frame the most and "wears out" the frame slightly faster than the good driver.

Lastly, being somewhat associated with the trucking industry in the past, you guys have seriously overestimated law enforcements ability to detect overweighted commerical vehicles.  Weighmasters and police are really inexperienced regarding this topic.  With cambered trailers and air ride suspensions, it is almost impossible to detect an overloaded vehicle.  The only thing to look for is the amount of tires are squatting...and this is difficult thing to do visually.  And with cb radios, cell phones, and truckstop gossip, many overloaded trucks bypass scales and/or pass by scales when they are closed.  The overloading issue is furthermore confused because different states have differing weight laws.  The whole thing is a colossial governmental reglatory mess, ie tax dollars at work.

Anyway, these are my thoughts, I could be wrong, (heck...most of the time I am wrong) but I think the bending/cycle fatigue/service life of the frame rails is the primary purpose for the camber.

Wayne
bulldozermaki@gmail.com

RE: arched or cambered trailer frames

The camber of the frames will have no (significant) effect on their fatigue life.

Cheers

Greg Locock

RE: arched or cambered trailer frames

Wayne,

I'm glad to see it's not just here that regulatory enforcement is a mess.

For Heavy (Special Types) haulage in the UK, you have to give a couple of working days' notice of your load and route.

Once you've got clearance on that, you're not allowed to deviate from that route - and the legend says that at least one haulier has got away with telling the traffic policeman that this prevents him from diverting to the nearest weighbridge.

A.

RE: arched or cambered trailer frames

Hey

  Good topic! I work at a company were we build mobile home frames, and it is a similiar process, with the same goals in mind as a tractor trailer frame. Adding camber to a frame does stiffen the metal if it is burned in with a welder in a arched position. And having the camber in the frame helps distibute the weight across the frame( how much would be hard to say). Having camber in a frame allows that beam to hold heavier loads than it would if it was staight. By cambering a frame you can get  a stronger frame for less money. As far as the placement of the load on a frame, consider the wear and tear on it and the truck. Some loads even though they may be smaller can still have quite a bit of weight(bricks for ex.), could ride different from one frame to another. The camber of the frame should be a issue for clearance except for maybe on a lowboy. Just some thoughts for you to consider. I'm a newbie to this site,but I have enjoyed all of your committs.  
         

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