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Help - Will My Bracket Design Work?

06/30/2012 2:14 AM

Hello,

I need a bracket to support a leveling jack for a travel trailer. (Actually I need 4 brackets to support 4 leveling jacks.)

The trailer has a 2" x 6" I beam for its frame. I need a bracket that will bolt to the bottom of the I beam, bend 90 degrees vertical, 5.5 inches up bend 90 degrees away from the I beam (parallel to the bottom of the I beam) to provide a 6 x 6 inch mounting plate for the jack. Hence the bracket needs to be 6 inches long, but could be longer.

The trailer weighs 6000 lbs. Distributed between 4 jacks, each mounting bracket must support a minimum of 1500 lbs. The brackets need to support this weight without significant deflection.

I'm thinking of 1/4 inch steel plate, either bent or welded. Sans gussets would be preferred.

I know nothing about this subject being a computer science and electrical engineer.

Any insights would be greatly appreciated.

Thanks in advance.

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#1

Re: help - will my bracket design work?

06/30/2012 3:45 AM

Welcome to the CR4 forum kmc...

One of the first things everyone is going to want is a section drawing of your beam and bracket. You can sketch one and shoot a photo with your phone... wait... you are the computer guy - you can do that stuff. A top and side view if you can make them will help. You can also post photos of the framing where you plan to attach.

Is your trailer a tag along or fifth wheel? Overall length? What is the spacing of the I-Beams you want to put the brackets on?

I hate to be the first reply and first to say... "hold that thought for a minute while we review what you are trying to do" but that's what happens here a lot.

CR4 responders (forum) need you (Original Poster or OP) to clear up some issues. First off - we need you to clarify that you either -

(1) already know from the trailer manufacturer that you can, indeed, level your trailer on jacks, or that

(2) you wrote "leveling jack" when you meant to say "stabilizing jack".

Very, very few, travel trailers have the frame stiffness required to allow leveling the trailer using anything other than the spring axles - certainly you can't level in the left-right direction. For example, if the driver's side is 2 inches low, you can't use a left front and left rear to jack up the entire left side two inches to make the floor level. You would need to block up the left side tires by 2 1/2 inches or maybe a bit more to get the trailer level. I'll explain the extra 1/2" later if you want.

The tongue jack is designed to level front-rear. So, unless you are replacing the tongue jack, then we have to be careful about what you are asking us to help you build.

I have owned four trailers and three motorhomes for a variety of reasons related to work and play. I've never been satisfied with the stability of the stabilizing jacks, so I feel your pain and want to be sure you get the right advice about attaching these stabilizer brackets... but I also want to try to help you get them on the trailer in the right places.

I can (mostly) picture the bracket you are describing from your word picture and I can tell you not to go that way for several reasons. Is your I-beam is supporting the floor, and there is no clearance above the beam?

(1) your design will torque the I-Beam and that's bad for your trailer floor.

(2) because of the springiness of the bracket rotation, your trailer won't be stable.

(3) the more you try to jack it up to make it stable, the more likely one or more of the jacks will not be doing its fair share as the load (you and others inside) move around inside the trailer.

(4) you will do all this work and find out your trailer still bounces in the middle because your jacks are at the corners and the majority of the weight is still sitting on the spring axles. And then you will start thinking about six jacks...

So - let's solve all those problems. Are you building this 5.5" drop bracket because you need the ground clearance to store the jack in the up position, along side the I-Beam? Are you using screw-scissor jacks or swing-away tongue jacks like on the front of utility trailers (you don't want those...) If we make this bracket, and inset the scissor jack the correct distance from nose and tail, will your jack screw handle reach the jack socket? Will you have to climb under the trailer in the mud to turn the handle because the jack is parallel to the beam and you really wish that handle attachment was facing the side of the trailer?

What if we can design you a bracket that mounts to the beam, allows you to remove the jack and stow it in a cargo compartment, and keeps the jacks from fouling with road grime/salt/mud, etc? Would that work for you? Do you want this to be quick and easy? There are electric jacks, and there are battery-powered-drill powered jacks, and there are manual turn-this-frozen-handle-over-200-times-in-the-rain jacks.

A few more things to consider - While your trailer may only weigh 6000 pounds empty, you need to add the weight of fresh water, waste water, people, and cargo and determine the Max Gross weight. And, remember that the front of the trailer is usually heavier by 10-20% sometimes more, than the rear, so that the proper tongue weight is applied to the tow vehicle. Sometimes we need bigger jacks up front than in back for that reason. And - you can't ever, never, plan to jack your trailer up off the ground using these stabilizer jack points - you'll break more stuff than I can list.

Okay, let's see some pics or drawings and we'll get you sleeping in something that doesn't rock like a bass boat in a 3 foot sea.

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#2

Re: help - will my bracket design work?

06/30/2012 3:49 AM

It really needs a sketch as 1/8 will do if it's well designed, but if it's cantilevered out then it will need to be much thicker. How thick is the web of the I beam?
No point bolting 1/4" cantilevered to an 1/8" web, it will just rip out the web.
The decsripion doesn't make sense to me, as if it bolts to the bottom and then bends up 90 degrees it isn't parallell to the bottom of the I beam any more.
E.g. Bottom of I beam is horizontal, plate bent up at 90 is now vertical...
Confused Cat
Del

PS.. Drat txmedic has just beat me to it with a much better post.... scampers off to hide in secret cat nest.

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#3
In reply to #2

Re: help - will my bracket design work?

06/30/2012 4:10 AM

Yes, Kitty, run and hide... Ha!!!

Seriously, I think what KMC is describing would be a "Z" bracket - bolted to the bottom flange with zero offset, 5.5" riser, and a 6" kick-out top plate to mount the jack.

Far too much axial torque on the beam, and too much on the bottom flange, and one big lever-spring that won't be too stable.

Worse, with that rise on the 6" beam, KMC could be punching holes in the floor of the trailer - 4-6 inches off to the side of the beam when the jack keeps a-pushin' and the beam stops a-liftin'

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#4
In reply to #3

Re: help - will my bracket design work?

06/30/2012 4:42 AM

...yeah, but other than that, the design id fine?
Del

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#5

Re: Help - Will My Bracket Design Work?

06/30/2012 10:59 AM

I think Tex has some very valid concerns here. GA from me!

I have further concerns: even with 4 brackets you may run into "web crippling" issues, where the web of the "I-beam" deforms under load. A lot depends on the location of the individual brackets, load distribution withing the trailer, and the length of the bracket.

You do know that the steel mills manufacture structural steel angles? Sure, you can buy a steel plate and then bend it, but why go through all the motions to do so when you can buy an easily available steel angle that can be purchased at a local steel fabricator.

Agree that you may need at least 6 "brackets" to support your trailer. I personally would use brackets no less than 8-inches in length, and at least 3/8-inches leg thickness just to provide enough Factor of Safety, otherwise the outstanding leg (horizontal leg under the I-beam) of a thinner angle will bend and/or the I-beam will deform significantly or fail.

Try finding a L6 x 3 1/2 x 3/8 x 8" long.

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#6

Re: Help - Will My Bracket Design Work?

06/30/2012 11:23 AM

I would look for screw jacks with brackets on the top to catch the trailer axle. Extend a jack handle to reach under the trailer. With two jacks and the tongue jack, you can level the trailer. Screw jacks don't collapse or slip like scissors jacks or hydraulic jacks.

Carry metal plates to put under the jacks if you are parked on soft soil.

One of these jacks would be necessary to change a flat on the trailer, anyway.

I keep two handy for when I do brake jobs on my vehicles, that way both wheels are up, so I can compare sides to make sure I have them the same, springs and such.

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#7

Re: Help - Will My Bracket Design Work?

06/30/2012 12:50 PM

Thanks for all the responses.

TXMedic3338 has it right. I was thinking about a 'z' bracket - only with right angles!

The trailer is a Dutchman Kodiak. The leveling system is a Bullseye leveling system that uses 4 auto-folding electric jacks rated at 6,000 lbs each. Both units were sold to me (and initially installed by) an authorized Dutchman dealer. (That doesn't mean they know what they are doing from an engineering perspective...)

The Bullseye system is sold as suitable for travel trailers, 5th wheels, motor homes, etc.

I really doubt Dutchman would "bless" installation of anything on their trailer, especially anything that puts strain on the frame. In fact I remember reading warnings about changing tires, disconnecting weight distribution hitches, etc. to CYA about damaging the frame. So the point about not being able to level the trailer via the frame may be totally valid.

I have no information about the trailer frame other than what I gleaned by measuring tape. Again, I doubt Dutchman will provide engineering specs on frame materials. (But I think I will ask. Can't hurt...)

I see lots of people with scissor jacks mounted under their rigs so they can manually level their units. And companies like Bullseye regularly sell their products for these applications. So maybe it is possible to level a trailer via the frame. (But now that it is mentioned, I am getting scarred of twisting the frame...)

The jacks are currently bolted to the bottom of the I beams. They hang too low for comfort. They also lack sufficient ground clearance to deploy on anything less than a nearly level pad. There should be about 6" of clearance between the unfolded-but-not-extended jack and level ground. I've got maybe 2". So if the pad and trailer are not nearly flat and level to start with, one or more of the jacks will not even unfold. Plus towing ground clearance has been seriously compromised.

So the jacks need to be raised. There is clearance between the frame I beam and the exterior of the trailer to "tuck them up" along side the I beam. The question is how to affix.

Angle stock bolted to the "web" (I assume that means the vertical portion) of the I beam is a possibility. Holes have already been drilled through the bottom rail of the I beam. I was hoping to reuse the holes. Hence my thought of a "z" bracket.

Plus I thought the vector of the load would be such that the bottom of the I beam would carry the lions share of the weight (being in the same horizontal plane as the jack mounting plate...). Just seemed to make sense given the current situation.

But as I said, I really don't know what I'm doing. My fear is that neither does my RV dealership. I would like to suggest a solution and/or be confident in the solution they provide.

How much torque to the I beam should I expect from a 6" bracket that's acting kinda like a lever bolted to the side of the I beam? Does it change if the bracket is bolted to the bottom rail (z bracket) or the web (angle bracket)?

Again, thanks for the help!

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#8
In reply to #7

Re: Help - Will My Bracket Design Work?

06/30/2012 1:02 PM

What you want will definitely put leverage strain on the frame, possibly damaging it. To avoid this strain, straps would have to go under the trailer to connect the Z brackets. For this kind of weight, I would also recommend gussets.

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#9
In reply to #7

Re: Help - Will My Bracket Design Work?

06/30/2012 7:10 PM

Yessir, KMC - if you do what you are talking about - you will kill your frame.

When you see the "other guys leveling their rigs" next time you are out - take a look - I bet the rig is either leveled by being parked on a level surface under the tires and axles, or the axles are jacked, or if you ask "how do you like your trailer" all the guys who jack with screw jacks to "level" the rig will also be the ones complaining about leaks in the windows, roof seams, A/C hatch, etc...

Now, if Dutchman okays the jacks that are already installed as "leveling devices" then that means they built the frame to take those loads. BUT - it doesn't mean you can apply the force from a different direction onto the beam.

Here's an example. Let's fill a thin gauge metal box(like air duct 18 gauge for example) 12" tall x 36" wide x 6" thick with sand. Pick the box up by applying an upward force with the palms of your hands on the bottom of the box. If the box holds the sand and doesn't have the walls bowing out, sit the box back down. Empty the sand.

Now, drill two 1/2" holes in the side of the box in the middle of the 12" height, six inches from each end. Insert a 6" bolt through from the inside, and run a nut up to the box on the outside to secure the bolt. Tighten that all you want... even put some washers on there if you feel like it. Re-fill with sand. Now pick the box up by lifting straight up (you can't let the bolts tilt even a little or you are cheating!!!) on the bolts. Box still intact? Hmmm. Probably not. That's the best picture I can give you in words of "Web Crippling" the side of the box will bend and distort, if not fail completely because it is not designed to have that force applied in that way. After vacuuming up the mess, tell us what happened.

Your offset jack idea will do the same thing (a bunch of other bad stuff also) when you offset the lifting point from the load point. Yes, what you are describing can be done and manufactured, but you really need an experienced RV frame mechanic and welding shop, plus the manufacturer's blessing before you go forward with this.

Alternately, you could look into sockets and pins that would allow you to drop the jacks off the frame, and return them to the proper location when needed. And, that will probably cost less than all this other fabrication and modification.

Good Luck and Send Pictures!!!

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#12
In reply to #7

Re: Help - Will My Bracket Design Work?

07/01/2012 10:03 AM

Hello KMC-

Where are you and who is your RV dealership? You are correct that the Bullseye system has the lifting capacity to pick your entire trailer up with its 24,000 pound capacity. I do like their anti-twist technology that always jacks both fronts, both rears, or one side or the other. I still wonder if the jack-to-trailer setup was done correctly. Again, pictures would help. I recommend that you do call Dutchmen and ask the factory techs about the setup you have. If they say 'yeah, we do this all the time' then you have at least part of your answer. If they say 'oh heck no' then some of us can help you start over - or Dutchmen can guide you to a RV dealer who does things right.

Which model of the Kodiak line do you have? Looking at pictures I can find of the Kodiak series online - I don't see any that would have the 2" clearance problems you are mentioning. If anything, they seem to be more of the "high riders" than for example an Airstream "low rider".

From your description of your ground clearance problem, I am wondering if you may have :

1) an axle problem or

2) your trailer is severely overloaded, or

3) your trailer-tow vehicle setup is out of whack. Do you use a leveling/stabilizing hitch system? What is your tow vehicle?

When parked on flat level ground - fairly flat city street or large parking lot, is the frame of your tow vehicle parallel to the pavement?

Is the frame of the trailer parallel to the pavement?

If not, part of your ground clearance problem might be your hitch/frame setup.

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#10

Re: Help - Will My Bracket Design Work?

07/01/2012 12:24 AM

Tractor Supply Company, Trailer ,wheel and tire. Most RV supply houses have what you need without reinventing the wheel.

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#11

Re: Help - Will My Bracket Design Work?

07/01/2012 5:24 AM

Before you go bolting anything to the bottom of the "I" beam bear in mind the ground clearance, one dodgy bump and you'll rip the jack off and maybe even damage the chassis. the best way is to fit the supports to the sides of the frame so when in an up position they don't protrude any further than whats already there. the most stable method of stopping any movement is to set the jacks at an angle to the centre line ie,45ยบ this way no matter which way it's being blown from there is always two jacks opposing it, I've done it and it works.

Bazzer.

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#13

Re: Help - Will My Bracket Design Work?

07/01/2012 10:14 AM

kmcintyre: There are complex solutions to all problems and then there are easy solutions to a lot of them. If you have room between the frame and the floor of the trailer, weld a U channel from one side of the frame to the other. It should be the same height as the frame and the same width as the mount for your jack on to the frame with the U pointed downward. You will then be able to mount your leveling jacks crosswise to the trailer and not torque your frame.

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#14

Re: Help - Will My Bracket Design Work?

07/01/2012 5:50 PM

Mr. Mcintyre, consider this...when you level out your trailer, you're not lifting the 6000 lb evenly. Therefore some jacks will see more than 1500 lb. It's not an issue for the Bullseye jacks but it makes a difference for the design of your brackets. You should also keep in mind that when you lift the trailer, the wheels and axles will "hang" from the frame. For this reason you want to place your jacks closer to the axles rather than towards the ends of the trailer. This will limit the bending on the framing. You shouldn't jack it up so high that the wheels come off the gorund anyway. Just enough to level it out and take some weight of the wheels. Your "Z" bracket idea is far too weak and will induce twisting on the beams as others have pointed out. I understand you want to nest the jacks up underneath the frames for more ground clearance but you still need to transfer the loads directly under the beams. You can do it using standard angles and bridge the beam sections. Similar to Byron's idea with the C-Channel but this way you support the bottom of the beams and transfer the loads more evenly. The jack bracket is simply a "U" shaped bent plate welded to the inside of the angle (or bolted). I don't know the dimensions of your trailer but the model below is 23' X 104". Jacks are 17' apart center to center. The first set of jacks is 68" from the front of the trailer frame. As you can see this model is a very simple frame (2 x 6 I-beam) with no re-reinforcement. Of course your trailer framing is far more robust with additional framing members. This model passed my analysis with a 6000 lb distributed load with room to spare and worst case deflection was less than 1/8". The angle iron is 4 x 4 x 3/8 thk. The jack bracket is 1/4" thk. Inside width is 7.5". This should be fairly simply to install and you can position it anywhere along the frame where you have open space. If you can't span the complete width of the trailer with one angle then just stop it under the next available I-beam. My suggestion would be to position the forward jacks just after the tow bar framing. The rear jacks could be placed in between the rear most axle and the end of the trailer. Keep in mind the jack legs will need to fit in between the angle iron in the folded position. I don't know if 7.5" is enough so it's just an example. Hope this helps you out.

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#15
In reply to #14

Re: Help - Will My Bracket Design Work?

07/01/2012 6:04 PM

TM-

This is a great idea!!!

One thing for KMC to consider would be to use your design but put the jacks on the outside of the frame, increasing the width between the jacks to increase the distance from the CG - reducing rocking even more?

Great job on the drawings. GA from me.

TX

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#16

Re: Help - Will My Bracket Design Work?

07/02/2012 12:28 AM

TerraMan, this is most excellent! GA from me as well. BTW TerraMan, what software is that you're using?

A couple of suggestions to refine the design:

1. I would be concerned with the clearance between the top of the bracket and the underside of the trailer flooring (sheathing?). It may difficult, if not impossible, to install the bolts, unless of course they're welded into place before you install the brackets. Instead of a 1/2-inch clearance you may have to provide additional room.

2. Provide horizontal welds at the top of the angles where they're in contact with the bracket vertical legs. In an installation such as this I suggest using 1/4-inch fillet welds throughout. The welding rod of choice would be E70XX electrodes if you're using ASTM A36 steel plate (to make the brackets) and the structural angles. Use at least a 1-inch weld "return" at each end of the horizontal welds to prevent fatigue cracking of the welds. If you cannot bend the steel plate, then I would suggest that you weld 3 pieces if steel together....provide at least 1/4" minimum overhang at the ends of the top plate and use 1/4" fillet welds throughout.

3. You may want to bolt the angles to the underside of the trailer frame for several reasons. First, it is a very difficult welding position upside down. Second, your don't want your beloved trailer to catch on fire! I suggest using at 5/8" pr 3/4" ASTM A325-F structural bolts here.....providing the proper torque value is essential here.

4. Make sure that you surface prep the steel before welding and priming and painting. Sand blasting would be the best, but if not, apply a readably available rust removing agent like Evapo-Rust or similar product, followed with a wire wheel or sanding disc attached to an angle grinder.

5. You may want to consider adding vertical 1/4" steel plates at each open side of the bracket for stiffening purposes. again, use the same welds and overhang at sides and the bottom of this plate if you can achieve the proper clearances between the bracket and the jack itself.

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#17
In reply to #16

Re: Help - Will My Bracket Design Work?

07/02/2012 4:15 PM

Thx for the GA Cap'n & Tex. You're right the design could be fine tuned. I based it on the OP's specs for a 6 x 6 mounting surface and minimum work since he mentioned he's a computer guy! If I were to do it myself I would weld all around and add additional reinforcement as you mentioned. I would reinforce the sides and top with one plate since the span between angle irons will most likely be larger than what I've shown. The jacks pivot and I'm assuming the screw motor goes with it when it folds up so that would have to fit inside the bent plate. I would also bolt the angle iron to the bottom of the trailer beam as you suggested but OP said it was a 2" flange. That doesn't leave any room for large bolts so...?

Anyway it's all guess work since we don't know what the jacks actually look like nor do we know what the trailer frames are (c-channel, I-beam, etc).

To answer your question Cap'n I use Catia V5 for design and analysis.

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#18
In reply to #17

Re: Help - Will My Bracket Design Work?

07/02/2012 5:33 PM

Wowsers, that latest 3D graphic is just incredible TerraMan!!!

Okay, Catia V5 by Dassault Systemes....much like ProE in a sense, but I'm sure it's much more useful for ME's and Manufacturing Engineers than my lowly CE self. LOL Still I am very intrigued by its capabilities!

And I bet it cost an arm & a leg (or two) or my first born to purchase....... Yeah, I can just imagine it's far far more expensive then my freebie Draftsight!!!! x 1000!!!!!

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#19
In reply to #17

Re: Help - Will My Bracket Design Work?

07/02/2012 10:30 PM

This looks like gross overkill to me. I don't have the drawing tool that you have, but if he just welds a u channel upside down to both sides of the frame he can use screw jacks longitudinally to the frame. Complexity is not always the best solution. I know by looking at your work that the concept is very good but it uses a lot more steel than a U channel. You are obviously thinking in the right direction and I commend you for that.

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#20
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Re: Help - Will My Bracket Design Work?

07/03/2012 1:42 AM

Yes, it's more complex than your c-channel solution but I was considering ease of installation and the OP's abilities given he's a computer guy and not a fabricator. Your c-channel would require careful welding to the frame and it would need to be cut to length accurately. I was looking for a way the OP can have something made up so he can just bolt it in place without welding to avoid the risk of damaging the trailer frame. He can install the jacks and use them to hold the angle iron securely to the bottom of the beams while drilling the holes. If holes already exist from the previous install then it would be even easier. Wish he would post some pics so we can see what we're dealing with.

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#21
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Re: Help - Will My Bracket Design Work?

07/03/2012 9:46 AM

You are absolutely right. It would only take some cutting to length from a steel retailer. Then some clamps to hold things in place while holes could be drilled. Then a trip to the hardware store to get some machine bolts and lock washers. A welder at a local welding shop could probably put the C or U channel in place in less than an hour. I guess it just is a matter of choosing how you want to spend your time and money. I think I would rather give the job to a good welder and go play golf while he is working on my trailer. If I need something engineered I will look you up.

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#22
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Re: Help - Will My Bracket Design Work?

07/03/2012 11:14 AM

So I guess a GA from you is out of the question ??...

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#24
In reply to #17

Re: Help - Will My Bracket Design Work?

07/04/2012 8:04 AM

Some frame material should not be welded on. They are made of high tensel steel heat treated to give the disired strengh ang flexibilties needed.

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#23

Re: Help - Will My Bracket Design Work?

07/03/2012 2:24 PM

Wow! So many great posts! Thank you.

So I contacted the trailer manufacturer. Dutchman basically punted, stating that any mods cancel the frame warrantee. But they did give me a contact for the frame manufacturer.

I have a request for frame specs and any recommendations placed at the frame manufacturer.

I contacted Bullseye. They indicated that initial clearance of 1 -2 " between the ground and the unfolded (but not extended) legs is typical. (Still doesn't help me if I'm on an unlevel dirt dry camp site.)

I'm taking the trailer back to the RV dealer later today. I'm going to ask them to look at adding a cross member that spans the frame and incorporates the equivalent of the left and right 'z" bracket concept to raise the front legs another 5 inches. If they weld it up out of 'c' channel as one solid member, from what I've read, I think it will go far to stiffen the front of the frame.

The rear jacks are already located near the rear axle. I think this is where the manufacturer instructs to place jacks when changing tires. I will confirm this, but if that is the case, the rear jacks might not be problematic(?).

BTW - the trailer is only 22' long and 8' wide. It has twin rear axles. it weighs 3900 lbs dry. I would never expect to raise the trailer off the ground, even though the Bullseye jacks are capable of doing so. The tires and axles should still carry a portion of the load when the leveler jacks are deployed.

Again, thanks for all the input. Further comments are welcome.

What is an GA? And where is a good place to park jpgs so they can be hyperlinked?

Thanks!

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#25

Re: Help - Will My Bracket Design Work?

08/02/2012 2:25 AM

It's been a long journey and it ain't over yet...

I just got back from a trip to a Thousand Trails campground. On a fairly level pad the trailer leveled fine, but the driver-side wheels were completely off the ground. Since nobody (trailer manufacturer, frame manufacturer, RV dealer, or Bullseye) would provide any blessing for the installation if the wheels were raised off the ground, it is clear that I need to provide more frame rigidity (or remove the leveling jacks).

BTW - the jacks are extremely cool. Easy to operate and the trailer was level and stable.

So I am thinking that two C channel cross members (6 x 2 x 1/4 8.2# A36 steel) bolted to the frame I-beams should be sufficient(?). Here's a rough drawing...

So what happens to the strength of the I-beam when I drill holes in the bottom and bolt up C channel to it? It is weaker or stronger in the area where the holes are drilled?I already have two holes per jack drilled in the I-beam. I will be drilling 8 more holes (2 per cross member end) into the I-beam to complete this installation.

Again, thanks for all the GAs!

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#26

Re: Help - Will My Bracket Design Work?

08/02/2012 2:56 AM

Another twist on my last post, here is a more elaborate cross member design that would allow me to mount the jacks along side the I-beam of the trailer frame. I'm sure these would cost more to have made and installed.

As stated on the drawing, there is an area of concern where the wings attach to the cross member. Will what I have work, or would I need to continue the C channel flat side up through the wing and then add a plate to the bottom of the wing (essentially boxing in the wing) to provide a flat mounting surface for the jack?

If I went with these cross members I would be left with 8 holes in my I-beams where the jacks are currently bolted on. Would I need to bolt on an additional steel plate where the jacks are currently mounted to stiffen up (reinforce) the I-beam?

Thanks again!

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#27
In reply to #26

Re: Help - Will My Bracket Design Work?

08/03/2012 12:45 AM

You will need to have some reinforcement at the 45 angle welds. That's not enough material in 1/4 inch, I don't think.

You might need 3/8 or thicker channel, plus some extra plates for more weld surface.

Since you'll be welding the channel, if you have a good welder doing the work, you might want to consider fabricating clamping brackets instead of drilling more holes in the frame. Two more holes on the bottom flange, near where the old holes are, probably is not a huge structural issue, but it could be a ridiculous huge warranty issue.

Hope that TerraMan sees this latest idea and chimes in with his stress analysis software. Why was his last drawing of the consensus plan not acceptable? Did it not fit, or something else?

Have you had any luck finding a "good" RV frame shop and asked how they would do this?

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#28

Re: Help - Will My Bracket Design Work?

08/05/2012 12:22 PM

The issue with TerraMan's drawing are the bottom of the trailer is fully insulated so the space between the I beam frame rails is a level plane. I do not know what infrastructure lives above the insulation. Further, while the jacks require a 6 x 6" mounting surface, they require additional area (about 19 x 6") for the leg to retract and fold up. Hence the jack can't be mounted in a box, as depicted. Good idea though.

The easiest way to mount a cross member would be to bolt it to the bottom of the I beams (spanning the approximate 6 feet of insulation). Using C channel made sense since I get the rigidity of two 45 members in one mountable cross member. Less parts probably mean less cost (labor) for installation.

If I start with a simple C channel spanning the I beam to add rigidity, but cut the cross member long enough, I can come back at a later time an add the wings shown in the second drawing to move the jacks out and up for better ground clearance (at extra expense).

I have no idea if A36 steel is the best material to use. C channel comes in a variety of sizes. My choice of 6 x 2 x 1/4 8.2# was purely arbitrary. (But not totally random...) There are heavier 6 x 2" channels to choose from, but weight is not desirable so if the 8.2# stock is sufficient...

The frame warrantee is toast at this point. Peace of mind that my frame is sufficiently reinforced is my goal.

Again, thanks for the great responses!

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#29
In reply to #28

Re: Help - Will My Bracket Design Work?

08/05/2012 6:23 PM

Mr. McIntyre, your installation limitations are clear regarding the insulation and the required room for the jacks. Having said this, your proposed "wing" idea will work...with a few simple tweaks. First off, reality is sometimes counter intuitive. The weak area in your design is not at the upper connection between the 2 short sections of c-channel. It's at the lower joint.

Image #1 below illustrates your design with 1300 load applied 5" from the flat face of the short vertical c-channel (C8.2). Max stress is 72000 psi which exceeds the tensile strength of A36. It's a localized stress but it will produce a crack the moment you put weight on it. The crack will propagate really fast and eventually will fail.

Image #2 shows the bending magnified 200X so you can visualize it. This bending needs to be eliminated somehow to lower the stresses in that corner.

Image #3 below is my suggestion for the c-channel configuration. I suggest not cutting the I-beam at 45 deg as you propose but leave the joints square and butt the ends together as shown. You end up with more material where it counts. Add two 1/4" gussets as shown. Resulting stresses at corner are now below the yield point of A36 steel but not by much. You need more safety factor for this thing to last.

Image #4 illustrates what you can do to almost completely eliminate the bending problem. Simply add two 1/2-13UNC tapped holes and hex bolts (length up to you) into the vertical c-channel near the top joint. After you install it onto the trailer, tighten the bolts against the face of the I-beam. This will prevent the vertical c-channel from bending under load. You can add some jams nuts to lock the bolts in place.

Image #5 shows the corner stress is almost completely eliminated. There is a peak in the analysis of 18000 psi but that's because it a sharp corner transition in that area. It's the way I modeled it and the surrounding area is below 5000 psi so it's not significant. Complicated to explain in detail but trust me!

You can clearly see the improvement in stress distribution and overall it's far more robust. Moving to a C7 x 9.8 channel also wouldn't hurt.

The existing holes in the trailer I-beam are not an issue. These mods should be easy for your welder to do. Good luck!

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#30

Re: Help - Will My Bracket Design Work?

08/05/2012 8:26 PM

I suggest that you not use a C6 x 8.2 (ASTM A36) as it will become overstressed significantly.

Nice modeling of the cross members, but sorry Terraman, you cannot use such a Tensile Stress limit (Fu), unless you want to get into Plastic State design and analysis as well as dealing with fatigue limits. Not advisable for a structural engineering standpoint.

According to the AISC Steel Manual (ASD), using ASTM A36 steel only gives you a Yield Stress (Fy) = 36 Ksi. Also, for extreme fiber compressive and tensile stresses due to Bending, use can only compare design stresses to the Allowable Bending Stresses (Fb), not Fu.

For channels bending about their major axis (not this case): Fb = 0.60 * Fy = 0.6 * 36 Ksi = 21.6 Ksi

Honestly, I believe a square or rectangular steel member would perform better than a C6X8.2. You could use ASTM A500, Grade B tube steel having Yield Stress (Fy) of 46 Ksi. This steel type is readably available from steel fabricators. you may want to look into TS 6 x 2 x thk., or TS 6 x 3 x thk. For welding issues, any thickness greater than 1/4" would be best.

The Allowable Bending Stress would be: Fb = 0.60 * Fy = 27.6 Ksi (for bending about the weak, or minor, axis)

But introducing the mitered sections at each end is asking for long term trouble as it introduces unwanted high stress areas, especially at the weakest link, the welds. I sure hope the OP has a friend that can weld with the best of them.

If you keep the maximum bending stresses down below 27 Ksi using TS rectangular sections, then you won't experience problems IMPO. If you need to absolutely go with the mitered ends as shown above, then I believe you will need to attach some side reinforcement plates for stress reduction. If they're A36 steel plates, then the maximum allowable Bending Stress in the reinf. plates alone should be limited to 18.0 Ksi (0.50 Fy), whereas the Allowable Shear Stress would be 16 Ksi (0.45 Fy).

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#33
In reply to #30

Re: Help - Will My Bracket Design Work?

08/05/2012 9:08 PM

Capn' I didn't use the tensile limit Fu in any calculation. I was simply pointing it out to OP that his design introduces stress at the corner which exceeds the tensile limit of A36 meaning...it will crack at the corner! Look at what I wrote in red for image #3. I'm well aware that we design to yeild and not tensile, wether it's civil or mechanical engineering.

I've been doing this for a while now.

My goal was to get a peak stress below 18000psi which is half of the allowable Fy (36000psi) for ASTM A36 = safety factor of 2:1 based on yield. Fatigue would be a concern with only a 2:1 for S.F but I don't think he jacks up the trailer that often so he should be fine. My suggestion reduced peak stresses below 18000psi and average stresses are around 7000psi. I also did not use 45 deg miter cuts. Look at the images again.

Your right OP would be better off using rect hss but that would defeat the purpose of what he is trying to accomplish...mount the jacks as high as possible!

If OP wants to use C-channel it can work as long as it's done right. His idea is fine but just needed some tweaking.

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#31

Re: Help - Will My Bracket Design Work?

08/05/2012 8:41 PM

Damn TerraMan! This is awesome! Thanks!

A few questions -

1) W.r.t. the two bolts that transfer load to the web of the I beam - is there any concern about punching through the web? Would it be wise to have the bolts tighten against a 6 x 5 x 1/4" plate fitted against the web of the I beam to distribute the load? Might a single bolt suffice?

2) Just to confirm - all your stress analysis was based on 1/4" channel and plate (gussets). The kind that weighs 8.2 lbs. per foot?

3) Is there any way to quantify how much additional "stiffness" adding the two C channel cross members will add to the trailer chassis? The I beams are approximately 22 ft long. The existing framing is all aluminum "studs" and (I assume) floor joists). I have no idea how much torque the stock frame can withstand without significant deflection. The crossmembers will be placed about 4 feet from each end of the I beam. Is it possible to estimate how much additional stress the design might support?

Thanks again!

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#34
In reply to #31

Re: Help - Will My Bracket Design Work?

08/05/2012 9:31 PM

To answer your questions:

1. It's the first time you mention aluminum and I thought your trailer beams were steel. Adding a steel plating as you suggested is a good idea. The load on each bolt is only about 700 lb. I don't recommned only 1 bolt because the c-channel wall is only .20 thick and there isn't sufficient thread to hold 1400 lb (700*2). Plus your pushing against an aluminum frame. Use two bolts. In fact ,you should install nuts on the inside (flat face) of the vertical c-channel and tighten them to the face. Let the nuts take the load and not the thread in the channel.

2. Yes. Channel is C6 x 8.2 and plate is 1/4".

3. You're not really torquing your frame by mounting the jacks this way. The c-channel connects one i-beam to the other. The force on the the left side jack torques the left frame to the left while right side goes right so they balance each other out. If the beams were not connected by the c-channel then it would be an issue but not the way you plan to do it.

Cheers!

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#32

Re: Help - Will My Bracket Design Work?

08/05/2012 8:57 PM

CaptMossie,

Thanks for your analysis. I don't really understand all the ratings (but I can learn). From a layman's vantage, are you saying the whole cross member and wing should be made of rectangular stock vs. C channel?

How would you suggest I bolt a hollow rectangular cross member to the existing I beam? Would I need an insert to insure the rectangle stock didn't collapse?

Would heavier C channel meet the more stringent ratings you are proposing?

Thanks

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#35
In reply to #32

Re: Help - Will My Bracket Design Work?

08/05/2012 9:37 PM

Heavier c-channel is of course better but you still need to weld it together the way I've shown for it to work efficiently. Capn's ratings are not more stringent. They are the same as mine. He just didn't read my post very carefully!

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#36

Re: Help - Will My Bracket Design Work?

08/05/2012 11:11 PM

TerraMan,

I'm pretty sure the I beam is steel, but the studs are aluminum. That said, a plate against the web seemed like a good idea. I was thinking two locknuts on the bolts that transfer load to the web of the I beam - one on each side of the wing vertical support. That way I don't have to worry about threading the C channel. (Flat and lock washers on each side too...) Sound reasonable?

Thanks for the analysis of the cross member. To be sure I understand, the cross members are more to keep each I beam stable and vertical, rather than providing corner-to-corner rigidity to keep the frame from twisting (torque-ing). The I beam itself provides rigidity front-to-back. The leveling system is designed to synchronize the jacks when lifting each side or front/rear. (In fact, the system is touted to synchronize all jacks to reduce stress while leveling...) So hopefully this additional measure will ensure the frame (and everything attached to it) stays stable.

I'm probably going to start with a simple cross member and leave the jacks bolted to the bottom of the I beam (as initially installed). I will add the wings if clearance becomes an issue as I do more dry camping.

Again, thanks for all the help. Kudos! GA! Eternal gratitude!

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#37
In reply to #36

Re: Help - Will My Bracket Design Work?

08/06/2012 12:55 AM

"...Sound reasonable?".

Yes it does.

"...To be sure I understand, the cross members are more to keep each I beam stable and vertical, rather than providing corner-to-corner rigidity..."

Exactly!

Cheers.

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