flatbed trailer I-beam sizing

[sparky55]

I am trying to build a low boy flatbed trailer and need help in sizing the I-beam.<BR>The trailer I-beams (2)&nbsp;will be 38' long and 7' apart. The axle will be at the very back<BR>&nbsp;and be able to be raised or lowered to allow frame to sit&nbsp;on the ground when loaded.<BR>when traveling on the highway the load is a 5000lb.&nbsp;horizontal tank. When on location<BR>it is filled with&nbsp;168,000lbs. of water.&nbsp;At this point the frame is sitting completely on the<BR> ground. The location&nbsp;has been graded&nbsp;and leveled to a point of 1"&nbsp;ridges or&nbsp;valleys in <BR>the length of the trailer.&nbsp;<BR>&nbsp;What size I-beam would be best for this application.<BR>Thanks<BR>Sparky55

[PinkertonD]

Hi Sparky and welcome to the forum, and I guess I will be the bad cop. If you have to ask that here, you probably should get an Engineer to design it. The DMV will require Engineering proof of the design safety before Registering and allowing it on their roads.

The concept itself offers a lot of engineering challenges including having the wheel-set right at the back so it can kneel. You need to take into consideration the flexing when traveling empty, side and wind loads depending on how high the tank is.

You should also check with the DMV to see that a 38'-plus length trailer can be used without over-size vehicle permits.

I strongly suggest you get an Engineer very conversant and experienced with long and heavy vehicle design, to take this on for you.

OK, now waiting for the good cop to chime in.

[jboggs]

Dave,
I saw this one earlier and was wondering who would be the bad guy here. Congratulations on stepping up to the plate and preserving your reputation! Curmudgeons unite!

Sparky,
If you will scan over other similar inquiries on this forum you will see that unfortunately we often have to dissappoint posters with requests about strength of structural items. The reasons are numerous, and valid. Frankly, it would be near impossible for you to include enough information in posts on this forum to allow a competent engineer to design this frame (or even just size one member) for you.

One more thing - as we all know "crap" happens. Picture this: When the lawyers for the injured children in the van that was damaged when something in your trailer failed asks for your design documentation, do you really want to say, "Well the guys on this on-line engineering forum thought it would be good enough." We are recommending the safest course of action for you here.

You need the direct assistance of an experienced engineer competent in this field. Ask around. I'll bet you can find it somewhere nearby.
Joe

[dalecyr]

Sparky:
To answer your original question, you should use the calculator on this site:
http://www.engineersedge.com/beam_be...flection_1.htm

leave the Modulus of Elasticity where it defaults to, 30,000.

pick an I beam from this table:
http://www.engineersedge.com/standar...properties.htm

you are looking for a beam with a Moment of Inertia that will give you an acceptable deflection at center.
so you will be playing with the Moment of Inertia number.
but start at, oh, say 60 or so.
(other good cops will chime in and help refine this number)


you said your uniformly distributed load was 5000, supported by two beams,
so 2500 per beam.
distance x you dont care about.
you said length (l) was 456 inches.

for distance to neutral axis use half the height of the intended I beam,
the one you picked from the properties table above.

hit the calculate button, and note the Maximum Deflection at Center.

others will offer their opinions on an acceptable deflection.

none of the above is meant to detract from Dave's warnings.
but you may find the cost of a beam that will do the job to be excessive.

and i'll add my own cautions:
you will have to decide the safety factor you want to use in your design.
the trailer may support a 5000 pound load sitting at a stop sign,
but when (not if) you hit a bump / pot hole / etc.;
or swerve to avoid an accident, you are putting amazing stress on your components.

from this forum you may get an idea of what the design will look like,
but engage a pro to (at least) review the design.


and finally...
be careful taking advice from anonymous people on the internet.
including me.

[PinkertonD]

I saw this one earlier and was wondering who would be the bad guy here.

JB, I saw it earlier and went away and then came back, then went away...

Finally could not help myself, and decided to weigh in with the bad news.

Bah humbug to Christmas, while I am at it.

[sparky55]

I just read my post and wondered how anyone could understand my questions with all the crazy letters and commas scattered throughout. So let me try again this is a light weight frac tank. The current frac tanks weigh 28,000 pounds empty and 168,000 pounds when sitting on site full of water. These tanks are built by dragon.com. ,grizzly.co
and many others. They are 45 ft long and 9 ft btall by 8.5' wide. My frac tank weighs in at 5000 pounds empty when being pulled down the road. The weight factor only applies when tank is loaded in static location at that point the entire frame is sitting on the ground. My question is this, what size I-beam is needed to support the weight
of the tank when it is full but sitting inplace until emptied.

[Kelly_Bramble]

My question is this, what size I-beam is needed to support the weight
of the tank when it is full but sitting inplace until emptied.

With the information given "Big".... To do a statics analysis somebody is going to need a lot more information. Can you provide a free-body diagram with dimensional information on where this W or S flange is supported and how the loading is distributed? Do you know what the structural materials needs to be?

Not a simple question you're asking..

http://en.wikipedia.org/wiki/Free_body_diagram

To get an ideal on loading configurations see: http://www.engineersedge.com/beam-deflection-menu.htm

[RWOLFEJR]

Attachment 157

Try looking here...
www.truckpaper.com
There are a bunch of gently used frac tank trailers for sale there for less than you'll have in materials.

[PinkertonD]

With the information given "Big".... To do a statics analysis somebody is going to need a lot more information.

Absolutely correct Kelly.

Maybe I am becoming even more grumpy in my old age, but it amazes me that some people think they can distil something like a 38' trailer down to the sizing of two main I-beams and they have the trailer. The fact that it is sitting on the ground when loaded does not mean that the beams will not bend, unless you are sitting it on the deck of an aircraft carrier or a reinforced, pre-stressed concrete plinth maybe 3-feet thick.

I, and some others here have spent many years studying the Engineering craft in Universities, and then many dozens more years perfecting the skills to use those hard-learned doctrines. It stuns me that anyone can consider a trailer coping with 168,000-lbs of anything can be so simply defined as the "size" of I-beams.

The educated people here are shying away from direct help for a very good reason. It is certainly not to feather the nest of our fellow Engineers with income for them, it is because the project is very complex, even though it might eventually look just like two I-beams.

At the risk of being repetitive, Sparky, get an experienced Engineer on the job or throw good money after bad in wasted steel cost, manufacturing time and maybe even human lives.

Bah, humbug.

[PinkertonD]

The current frac tanks weigh 28,000 pounds empty

Hi Sparky, on a more practical note, this comment of yours got me thinking. Why would anyone spend the money and steel to build such a big trailer. Thinking...thinking...thinking...

Posit, suddenly the gas runs out unexpectedly and there is still 15,000 gallons in the tank. What do they do? Do they get 3 x 5000-gallon road tankers and load it off for the next site, OR do they hook up a tractor and haul it off with 15,00 gallons inside?

I think I may be getting close to an answer there. I am always amazed at when I think I have just invented something, I do a Patent search and some shoe salesman in Georgia working from his garage in 1932, had the same idea.

[RWOLFEJR]

Ah yes Necessity...the mother of all invention...

Apparently Sparky is seeing a better mousetrap.

Without being inside of your head and knowing what your plan is for this tank and the entire structure it's impossible to give you an answer... but... I'll toss this out there for you ponder. A consideration in your design might be to add vertical pieces to an H beam to add compressive strength to it while loaded and be able to keep the size / weight down. Smaller beam adequate for your empty trailer and fill in the H shape every foot or so to add resistance to buckle or twist when loaded.

[sparky55]

Aha, now we are seeing the forest not the trees. I do believe it is a better mousetrap. While I do have a patent pending on the mousetrap I thought a little more info on the trailer structure would be helpful. My current plans due to lack of engineering and design knowlege is to oversize frame which means 14" I-beams with cross bracing.
This just adds weight and additional material cost. I just thought you guys could help with some estimates not hard design of the trailer.

[RWOLFEJR]

First thing I'd do is have a good long look at the current 28,000-ish lb. trailers that are operating without any problems today. You never said whether or not you too will be loading with the same 140,000 lbs. of weight? If your goal is a lighter trailer for the transport to and from but still need the frame to handle 140,000 + your trailer weight of 5,000 instead of the current 28,000... Then you might want to go with basically same / same for the frame since the difference of 168,000 total vs. 145,000 total isn't going to reduce your strength requirements all that much. A 14% decrease in load might only be a structural material weight reduction of 1... maybe 3%??? ... Where weight = dollars...

The traveling empty trailer beam strength for a 28,000 lb. trailer vs. the required beam strength of a 5,000 will certainly afford to be some amount less... but the loaded beam probably not so much?

So now you've got me wondering are we talking a plastic tank... maybe a big bladder in a cage? Have you seen the big bladders that are being used now?

I'm guessing you're looking at something light enough that a less expensive smaller vehicle (pick-up with a fifth wheel?) can haul the trailers in and out with lower operating costs? Inquiring minds want to know...

Maybe instead of the wheels kneeling you could go with the entire frame with the wheels lifting to allow the tank cradles / bladder / whatever, to sit directly on the ground? Like a walking beam set up... When empty run your screws or whatever to lower the frame and axles to lift the tank?

Just thinking out loud...

That reminds me of a short story...
Once upon a long time ago... up until about 12 years ago when I lost my dad... I used to go to him with an idea and say "You know, I was thinking... If we..." And he'd always interrupt me with... "Oh no... We're in trouble now!!"

If I've sparked (get it... Sparked... Sparky...) any new ideas that you may end up incorporating into your design I like money... and Budweiser... and pretty women a lot. Feel free to remunerate as you see fit... Or not is fine too...

[sparky55]

RWOLFEJR you are way to scary. How about a tank of Bud and a pretty lady jumping out with a hand full of money. I really do appreciate the idea on trailer design and you are correct about need to reduce weight. I will have the same loaded stationary weight. The axle issue has been resolved with hydraulics.
Thanks again

[PinkertonD]

How about a tank of Bud and a pretty lady jumping out with a hand full of money

OK, if beer, money and neked wimen are involved, I'd like to get into this too.

RJ, has already mentioned an idea about sitting the tank on the ground. Another occurred to me to ask, how many of these trailers are likely to be on site? If more than one, then consider the rear wheel set as a dolly complete that slides in and is pinned. At the rear end, it will have a hinged A-frame hitch for a 2" ball.

Have trailer jack-legs at both ends. Lift the front and unhook from the turntable. Go to the back, take the weight almost off the wheels with the jack-legs and hook the truck to the A-frame, remove pin(s) and drive off to get the next trailer.

One expensive wheel set fits many trailers. No hydraulics involved unless you wanted to use hydraulic jack-legs.

Dale gave you some insight into calculating beam size.

p.s. Just kidding about compensation. Good luck with the project but I still think you should be using an Engineer as he/she would be coming up with these ideas and suggestions, and possibly a myriad more based on their vast experience with projects like this.

[sparky55]

Thanks to all for the suggestions, I am trying to locate an engineer in Texas that has trailer design experience. One of the problems I have had when contacting
trailer builders has been this idea that we have always built it this way. Sometimes you can teach an old dog new tricks, sometimes it is better to get a new dog.