How much weight will a piece of steel tubing, 2"x2"x1/4" support at the end of a 3 foot unsupported span?

[mr. cob]

Howdy All,

I am in the process of starting to design my Smart Car, deck.  I usually over-engineer stuff so I am looking for some kind of chart or a formula that can be used to calculate how much weight a particular type of structural steel can support at the end of a 3 foot long span only supported at one end.  For example, if I build a deck that 8 foot 4 inches wide and use 2"x2" square tubing that is a 1/4" thick that is laid across two pieces of channel iron that are 33 inches apart that would leave 33.5 inches of the tubing protruding beyond where it is supported by the channel iron.  Now that I have you confused, how much weight can be hung at the end of the square tube without it failing in any way?

If I use 2,000 pounds as the weight of the Smart Car, that means that the load that will have to be supported in four places that protrude beyond the channel iron is 500 pounds each.  So if I were to place a piece of 2"x2" square tubing every 12inches that would give at least two pieces of 2"x2" square tubing under each tire of the Smart Car.  My thinking that a piece of 2"x2" square tubing every foot topped with 3/16" steel plate should be WAY OVER KILL to support a Smart Car, but I AM NOT AN ENGINEER.  So if someone could point me toward some sort of chart or simple formula that could be used to figure the load bearing capacity of square tubing, channel iron and I-beam it sure would be helpful.  Thanks.

Dave

 

[Moresmoke]

Someone elsee can feel free to check my numbers, its been a long time since strength of materials class.

Using 10000 psi as the max allowable stress, I get 272 lbs per tube.  I use 10000 psi, as it minimizes the chance of fatigue cracking. You should be alright considering the deck adds strength, the neighboring cross members take part of the load, and assuming there is an outside  rail, that will also support the cross member.

[mr. cob]

3 minutes ago, Moresmoke said:

Someone elsee can feel free to check my numbers, its been a long time since strength of materials class.

Using 10000 psi as the max allowable stress, I get 272 lbs per tube.  I use 10000 psi, as it minimizes the chance of fatigue cracking. You should be alright considering the deck adds strength, the neighboring cross members take part of the load, and assuming there is an outside  rail, that will also support the cross member.

Howdy Moresmoke,

Yes, there will be an outside rail to tie everything together.  My thinking was that the tubing coupled with the deck should be more then enough for the load but I just wanted to get the opinion of others before I start buying-cutting steel.  Thanks for your reply.

Dave

[GlennWest]

Mine rides on 4" channel iron and 3/16" decking. Channel welded to angle iron bolted to chassis. 

[mr. cob]

11 minutes ago, GlennWest said:

Mine rides on 4" channel iron and 3/16" decking. Channel welded to angle iron bolted to chassis. 

Howdy Glenn,

I was thinking of using 6 inch channel iron, making two rails of the channel iron that will run the full lenght of the bed then use the square tubing for cross stringers.

I DON'T want to use chains but I want to build this deck so that will be clearance for chains should I ever find myself in a situation where I need them.  My thinking is the 6 inch wide channel stood on edge would give me the lift I need to have the stringers far enough away from the tires so that I could reach in there to install chains if needed.  I don't want the top of the deck surface to go any higher above the truck frame then 8 inches in order to keep the break over angle as small as possible to make loading and unloading the Smart Car, easy.

I am interested in how others have approached this situation.

Dave

[GlennWest]

Keeping it low has a disavantage also. Not enough room for ramps. I built a storage unit at rear of my truck beneath deck for ramps because of this. I have room for chains. 

[mr. cob]

Just now, GlennWest said:

Keeping it low has a disavantage also. Not enough room for ramps. I built a storage unit at rear of my truck beneath deck for ramps because of this. 

Howdy Glenn,

That is my plan, I have enough room behind the rear axle under the truck frame to build a ramp storage box.

Dave

[GlennWest]

I did at first carried mine on top of bed. Seems like it was less work to use that way vs where they are now. Jfyi

[mr. cob]

8 minutes ago, GlennWest said:

I did at first carried mine on top of bed. Seems like it was less work to use that way vs where they are now. Jfyi

Howdy Glenn,

I would be nice if a person could just slide the darn ramps under the Smart Car, if they would fit I havn't figured out an EASY way to secure them when traveling.  If I can come up with an easy-simple way to carry them under the Smart Car, that is the way I would prefer to do it.

Dave

[GlennWest]

Raise the car. Wouldn't take much. Four pieces of channel laying down maybe. 

[I'mdonewiththis forum]

48 minutes ago, mr. cob said:

Howdy Glenn,

I would be nice if a person could just slide the darn ramps under the Smart Car, if they would fit I havn't figured out an EASY way to secure them when traveling.  If I can come up with an easy-simple way to carry them under the Smart Car, that is the way I would prefer to do it.

Dave

Dave, I saw one Smart that was sitting on 2x6 boards just for the reason you want. There was some rubber (think mudflaps) under the bottom ramp and a piece under the ends of the top ramp with a 2" ratchet strap holding them down length wise. It looked to be a simple way of doing what you want.

[mr. cob]

6 minutes ago, Mntom said:

Dave, I saw one Smart that was sitting on 2x6 boards just for the reason you want. There was some rubber (think mudflaps) under the bottom ramp and a piece under the ends of the top ramp with a 2" ratchet strap holding them down length wise. It looked to be a simple way of doing what you want.

Howdy Tom,

I am trying to picture in my mind how the ramps are being held down.  Putting the car up on the 2x6's would raise the car off the deck but it would also increase the break over angle, much like raising the entire deck from 8 inches to 10, actually 9.5 as a 2 inch thick piece of lumber is actually only 1.5 inches think.  Maybe I am not visualizing what your saying correctly.

Dave

[I'mdonewiththis forum]

I guess the blocks were placed just before the car was completely loaded. They didn't run the length of the car, but were about 12" long.

[mr. cob]

19 minutes ago, Mntom said:

I guess the blocks were placed just before the car was completely loaded. They didn't run the length of the car, but were about 12" long.

Howdy Tom,

OK, now its becoming clear.  Once I get the deck built, I can mess around with different ways to store the ramps.  I looked at a photo of Glenn's ramp storage behind the axle, I have the room to do this same type of storage only I would build a weather proof box to keep them in, I travel through to much nasty weather to leave them open to all the crud that would be thrown up off the road by the tires.

Dave

[GlennWest]

They would slide out and in better also. I will at least put metal in bottom. Haven't been in a park recently where I can do such.

[Parrformance]

17 hours ago, mr. cob said:

Howdy Glenn,

I would be nice if a person could just slide the darn ramps under the Smart Car, if they would fit I havn't figured out an EASY way to secure them when traveling.  If I can come up with an easy-simple way to carry them under the Smart Car, that is the way I would prefer to do it.

Dave

 

 

[NoDirectionHome]

Back to the question.  First off there are some things that aren't considered.  The Smart wheelbase is only ~74"so overhang is only 20".  Weight distribution is 45/55 so I used 600 lbs for the highest single tire load.  Now you need to multiply by "G" load, so let's assume 1200 lbs. max load at a tire.  
    That calculates to ~26000 lbs stress and ~.125" deflection.  A large margin of safety by any view using 55 ksi steel.

[mr. cob]

27 minutes ago, NoDirectionHome said:

Back to the question.  First off there are some things that aren't considered.  The Smart wheelbase is only ~74"so overhang is only 20".  Weight distribution is 45/55 so I used 600 lbs for the highest single tire load.  Now you need to multiply by "G" load, so let's assume 1200 lbs. max load at a tire.  
    That calculates to ~26000 lbs stress and ~.125" deflection.  A large margin of safety by any view using 55 ksi steel.

Howdy NDH,

Can you share where and how you got this information, I am sure it would of use to not only myself but many who face these types of questions when building something like a Smart Car deck or any other addition to their truck that involves weight, stress and strength of materials need for the project. 

I am "assuming" that you were using the tubing and dimensions in my first post when making these calculations.

Thank you for this information.

Dave

[SuiteSuccess]

Dave,

I’ll be at my truck today or tomorrow and I will get some pics of my setup.  I store the ramps under the smart and raise the car with blocks under the rear/front tires after car has already negotiated the break over. (I load front of car to drivers side). Built couple of wheel dollies that attach to the ramp to maneuver under smart and set back end of ramps on two cutting boards (plastic)from WalMart.  Couple of “X” straps front and back of ramps to secure and good to go.

[Jack Mayer]

There are many ways to store ramps. The simplest way is what Carl (SUitesuccess) describes above. That is the way it has been done by many people since smart's were carried. The easiest way to raise the car is with permanent steel stock that raises the car off the deck. You can use 2" and it works well. A lock mechanism that is easy to use is critical. 

[mr. cob]

3 hours ago, SuiteSuccess said:

Dave,

I’ll be at my truck today or tomorrow and I will get some pics of my setup.  I store the ramps under the smart and raise the car with blocks under the rear/front tires after car has already negotiated the break over. (I load front of car to drivers side). Built couple of wheel dollies that attach to the ramp to maneuver under smart and set back end of ramps on two cutting boards (plastic)from WalMart.  Couple of “X” straps front and back of ramps to secure and good to go.

Howdy SS,

Thanks for your post, photos would be great.

Dave

[mr. cob]

2 hours ago, Jack Mayer said:

There are many ways to store ramps. The simplest way is what Carl (SUitesuccess) describes above. That is the way it has been done by many people since smart's were carried. The easiest way to raise the car is with permanent steel stock that raises the car off the deck. You can use 2" and it works well. A lock mechanism that is easy to use is critical. 

Howdy Jack,

Thanks for your reply, I am looking forward to Carl's photos.  I wish I had paid more attention to Smart Car, decks while at the rallies but until I decided to join in the party of Smart Car, carriers it really wasn't of any importance to me.  Live and learn as they say.

Dave

[noteven]

My AmeriDeck loader is rated for 2000 lbs payload strapped upon its deck. You load on the ground. The hydraulic arm hooks the deck onto the truck. It’s deck is 2x2x1/4 tubing about 18” apart the long way and 1/8” maybe checker plate for the deck. I’ve decked a 1600 lbs Kubota tractor with it and it doesn’t deflect or strain with the load at all. 

Walking on the ground to tie stuff down is beauty.

It’s not on my KW it’s a pickup twuck model. But with a little modification it could work...

Dave - imagine a side loader on the Petercar 

[SuiteSuccess]

Dave,

Understand none of this is elegant but it is functional.  This block is a spare.  The ones I use are black.

Chocks are raised two inches.

Roller for ramps (end that I’m pushing under car.  One for each ramp and I leave them on while traveling.  Height of wheels only about half inch above ramp end).

Walmart cutting boards that I set other end of ramp on to keep from rubbing bed.  However going to change to rubber “feet” that I will attach to one end. I “X” the straps front and back to center the ramps under the car.

Like I said not elegant but it works.

[mr. cob]

11 minutes ago, noteven said:

My AmeriDeck loader is rated for 2000 lbs payload strapped upon its deck. You load on the ground. The hydraulic arm hooks the deck onto the truck. It’s deck is 2x2x1/4 tubing about 18” apart the long way and 1/8” maybe checker plate for the deck. I’ve decked a 1600 lbs Kubota tractor with it and it doesn’t deflect or strain with the load at all. 

Walking on the ground to tie stuff down is beauty.

It’s not on my KW it’s a pickup twuck model. But with a little modification it could work...

Dave - imagine a side loader on the Petercar 

Howdy noteven,

If I were a rich man,  I'd just drive the Pete up to Canada or now to Kansas and have either Gregg or Jack work their magic and install one of them fancy hydraulic loaders.  As it is I have been pestering Gregg and Jack with endless questions and scan the RV Haulers videos for clues on how to do this in a simple, CHEAP manner suitable to my needs.  Your post makes me feel good about my choice of structural materials to use, I am sure what I end up with will be over kill but I think I have the horse power to carry it.

Dave