load analysis steel pipe 2

[tlh0598]

Can someone give me an idea of how to calculate load capacity on a steel pipe with a certain OD at a given length? Are there calculators online I could use?

TIA

 

[minorchord2000]

Are you talking about a steel column? with the pipe as a vertical member?

If so, there are allowable load tables in the AISC manual for different pipe diameters,wall thicknesses and different KL values.

 

[BigInch]

And wall thickness. Pipe shapes are relatively strong and the axial load you can place on a steel pipe usually depends on the buckling length. At a certain length, a small load will bow the column out and it will start bending and typically fail very quickly. Buckling length depends on how the ends of the column are held from rotating. Bracing is added to columns to keep them from bowing out and failing in that manner. Buckling is a well known phenomenon and there are formulas around to do it. However, I wouldn't recommend designing columns for any important structure, if you don't have some training and experience at it. That, because column failure by buckling is catastrophic, meaning usually it happens very fast with what can be significant consequences to life and property.

I don't know of any java applets around that do it, but I'm sure you could find one if you look hard enough.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[tlh0598]

Sorry, I should have been a bit more detailed. I am going to build a small bridge (25-30') out of some structural pipe I have. The OD ranges from 2 3/8" to 5.5". At any rate, the idea was to build a bridge based on a warren truss. Without going into extreme detailed analysis I was hoping to determine the load capacity for the long base members without a truss design and see what the difference is with a truss design.

 

[BigInch]

Used as beams, (bending design only) maybe you could walk across it.... carefully. With a truss, you have a chance, to make it using those sizes, but probably only for walking across, no driving. 2" pipes are good in tension, but not so much for compression. The taller the truss, the lesser the chord loads, but you will reach the buckling lengths of your 2" braces sooner or later. When that happens, you won't be able to raise the top chord any higher to reduce the chord loads any further while still mataining adequate bracing.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[tlh0598]

Well my thought was that I could use multiple long members (5.5" OD) to distribute the load. I really need to be able to drive a tractor across and some vehicles. The material I have available are these steel drill stems. Thanks for your replies.

 

[Dinosaur]

I don't think you are going to be able to get there from here. Tractors and vehicles are going to need a substantial deck to ride upon. The deck load alone, may come close to the weight of the vehicle. When you add it all up, you are going to have a more substantial structure than I think you expect.

Even if you pursue this, you are going to need a qualified welder and many fittings to make the joints. I recommend you contact a prefab bridge producer before getting too much farther. CONSPAN manufacturers precast concrete bridge products that can easily span 30 feet, but are designed for substantially more than a tractor. U S Bridge manufactures prefab steel trusses. Their off the shelf stuff would likely also be more substantial, but they may be able to produce something closer to your needs. Good Luck

 

[Tomfh]

How many 5.5s do you have? Maybe you could bolt or weld pairs together producing beams that look like the number 8 in cross-section. They would probably span the required distance.

 

[tlh0598]

That is an option as well. I need to take a detailed look at the span and the existing bridge (what portions can be reused etc). A welder that made some gates from the same material took a look at the span and said he could "build a bridge to support a cement truck". Being that he has made cattleguards and small bridges for many years, I would think he probably could. He would charge close to 5k for welding assuming I provide the material (the pipe I listed above). I wanted to find some ways to analyze the load (more as an exercise in preparation for the EIT exam) to see for sure that a vehicle bridge could be made.

 

[BigInch]

OMG

Moment = 5000 lbs * 30 ft * 12 in/ft * 1/2

Bending stress, Fb = Moment/Section_modulus, I estimate that it should have an allowable of around 18 ksi for "unknown" pipe.

Where section_modulus = I/r
I = moment of intertia
c = radius to outside of pipe

calculate "I" here,

http://www.processassociates.com/process/basics/pipeprop.htm

Needs adequate lateral bracing.

Now, how much do you really need that tractor across the stream?


Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[trainguy]

Hire a structural engineer.

Or, maybe I should post the following on the Electrical Engineering forum:

Guys:

Although I'm a structural engineer, I need to design a substation, to power my home and 5 neighbors' homes. I have a Costco generator, and approx. 50 feet of wire. Any tips?

tg

 

[BigInch]

Look, this guy is gonna' do this thing one way or another. Might as well get enough pipes lined up. Not all farmers hire engineers to build a barn or design a dam for a stock tank. They find some guy that can weld or better yet, teach them to weld too.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[tlh0598]

Well, first of all, this is a low priority side project to do on a family farm where we do some deer hunting. Beyond that, this is a very unique opportunity to apply some learned principles of engineering but more importantly learn much more. I am not asking anyone to do any work for me, simply point me in the right direction and offer advice along the way. We aren't talking about a 250' bridge for passenger trains here. Anyway, I appreciate the direction I have gotten thus far.

 

[PT999]

Since this only an exersize in preparation for the PE exam:

Download RamAdvance's demo version, and see what happens when you design your frame, and put vehicle load on it.

 

[SlideRuleEra]

Like PT999 says, this sounds like a learning experience. I'll give you an "off-the-wall" suggestion. Download "Design of Steel Bridges" at this link (500 pages, about 12 MB)

http://library.case.edu/ksl/ecoll/books/kundes00/kundes00.pdf

Excellent book, the problem is it was written in 1915. Probably 90% of it has only historical interest or is far too specific, but you may learn a lot from the remaining 10%.

http://www.SlideRuleEra.net

 

[rb1957]

i figure we're dealing with about 450000 in.lbs (5000 lbs in the middle of a 30ft span). if the 5.5" pipe has a wall thickness of 0.25" and you have 4 side-by-side the maximum stress is about 18ksi (which should be reasonable for some unknown steel).

how are you going to make a decking to distribute the load ?

maybe you could align 2 pairs of pipes to make two tracks, but that sounds a bit dodgy. you'd need to join them together (welds). maybe nest one of your smaller pipes between two large ones; also add some small ones as cross bracing.

maybe you'll be alright ... good luck !

 

[tlh0598]

I will need some time to work through some things based on the last few posts. I am not sure if RAM Advanse will be much of an option for me as I am not familiar with the program at all. I did download an evaluation copy but its not exactly like working in AutoCAD or other such programs.

 

[BigInch]

And only a 3" deflection PL^3/48/E/I (with the 4 pipes and 0.25 WT). Be sure to weld some good X bracing across the 5" bottoms. Use the 2" for that. So where's the deck and the railing coming from?

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[tlh0598]

we have no railing on the existing bridge (that has been up for probably 80 years). I have to make a trip out there to check out the existing bridge and what can be reused. I planned on putting some wood 2x6 planks across to make a track to drive over (as opposed to a cattle guard style which would make it pretty bumpy). At any rate, I am making a trip to evaluate all materials and existing conditions next Saturday.