Any structural / material engineers on here? Need help with steel selection

[ogasman]

The question, what is stronger an I beam or a square tube?  I need advise on what to use for the mast on a power hammer.  I have a choice of a six inch square tube that is .58" thick.  The I beam is 10" x 5".  The main web is .62", with the sides tapering from .62" at the center to .37" at the edges.  The hammer I'm building uses a T shaped mast in the center welded to a flat base.  On the top of the T you mount a truck leaf spring.  One side of the spring you mount a rod to a flywheel on the electric motor, the other side is the slide for the actual hammer.

Thanks
Paul

[FERoadster]

Not a structural engineer but I made my own English wheel with the backbone (Mast) out of 3/8" 6 X 10 I-Beam. When doing a test I found that the I-Beam would twist but not bend. To fix it I welded a W pattern of 1/4 by 2" strap inside each side then plated it with 1/4 X 10". The top tube is 3/8 inch 6 inch square with an angled  rib from the top.

With leg the adjuster and base it's over 800 lb. I put a hook on the top so I can lift it with a cherry picker.
Also made my own modified bead roller. It started out as a Harbor Freight roller.
To answer your question I'd use the 6" square, from my own experience.
Richard >>> FERoadster

[WConley]

The I-Beam is designed for bending in one direction only.  With a box tube, you'll get the best performance in torsion and bending in all directions.

It sounds like that box tube you selected is plenty stout for your needs!

- Bill

[pbf777]

The question, what is stronger an I beam or a square tube?

     The absolute correct answer is going to require a true structural engineer;  but my amateur observations and with economies of steel material usage in the comparison, that "I"-beam designs are generally of superior strength in perpendicular loading when in proper orientation, and do well in draw and compression in length, but as indicated previously do poorly in other planes and particularly in twist, were as square tube works better in multi-directional loading but would require greater material usage to equal the "I"-beam when in it's proper realm.     

     I'm not aware as to the true engineering of your hammer but, with a leaf-spring, an electric motor, a rotating flywheel, and an oscillating tool in motion, not to mention the intermittent impact load & unloading, all I can say is you will need much more steel structure than one might initially invision, of course unless you are a structural engineer!     

     Scott.

[frnkeore]

Industrial machinery is generally over built by 100-200% (or more), especially impact stuff.

I like Richards approach of reinforcing the I beam. Bearings and pivots also need to be taken into account, with a higher strength, hardened material.

[427mach1]

Engineer with 34+ years of experience, was licensed as a Professional Engineer in the state of Georgia for 25+ years.  Lots of good information given above, so I can only add a little theory to the mix.  In order to minimize bending, you want a high moment of inertia.  In order to resist torsional (twisting) deflection, you want a high polar moment of inertia.  Looking through standard beam tables, it appears that the I-beam as described by the OP is actually known as an S-beam.  The dimensions given are close to those of an S10-35 beam, which is 10 inches tall and weighs 35 lbs per foot.  It has a moment of inertia about the x-axis of Ix = 147 inch^4 and along the y-axis it is Iy = 8.36 inch^4.  The polar moment of inertia for this beam would be the sum of those two quantities, or J = 155.36 in^4.  The square tube has an Ix = 62.27 and Iy = 62.27 and a J = 124.54.  Normally the best shape to resist torsional deflection is circular, i.e. round tubing (that's why driveshafts are round rather than square) but that wasn't one of the options given.  The square tube would normally be better for torsion but since the S-beam is so much larger, in this case it is better than the square tube in bending in one axis and better in torsion.  The S-beam would not be a good choice if the loading is in the y axis.  It all depends on the design and how the structure is loaded.  If you would like to send me a drawing of your power hammer, I would be happy to look at it and give you my suggestions.

[ogasman]

These are the basic drawings of the hammer.

[ogasman]

More pictures.

[427mach1]

You've got the design manual, what material is suggested?  I think either the S-beam or square tubing would work, as there doesn't appear to be much torsion involved, all the loads are in one plane.  Construction would probably be easier with the square tube and 6 x 6 is fairly robust.

[ogasman]

The manual states either a square tube or an I beam, does not state which is better.  Kind of a general guide, more than an exact recipe.  I have both sitting in the shop.  Just trying to figure  the best one for the application.  I have a 7 hp motor for the build.  It is bigger than what is called for in the build specs, but it is what I have.

Thanks for the help
Paul

[427mach1]

Either would work but I think I would go with the square tube.  There shouldn't be any side loads involved but I don't like the low Iy of the S-beam and harmonics can sometimes do weird things.

[FERoadster]

Being  a welder, welding the outside of a square tube is way more basic than welding inside corners of an I-Beam
Just my take on this. Otherwise for max strength(But a lot of work) mimic my mods. to the I-Beam for the E-Wheel.
Richard