load analysis steel pipe

huangyhg

load analysis steel pipe
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
are you talking about a steel column?  with the pipe as a vertical   
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!
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   
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!
well my thought was that i could use multiple long   
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
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.
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.
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,
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