# Steel strengths

I'm doing a bit of research for a story, so let me apologize in advance if this doesn't fit the mandate of your groups. I won't repost if I
I'm trying to find a formula or a chart that'll help me figure out average/ideal steel strengths given a bar of a certain diameter. For instance, how thick of a rod of steel would a person need to keep it from buckling when a super-human applied a ton of pressure. I realize there are different types of steel, purities, etc., which is why I thought there might be a kind of slide-rule-esque chart for figuring X-type for Y-weight is Z-thickness.
Any help would be appreciated. I've Googled and checked Wikipedia, but the best they seem to have is related tooling equipment and melting points, respectively, which is interesting but not what I need. Again, thank you in advance for your help!
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Andrew Burton
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It sounds like you need some basic info on the different ways that steel is "strong" or not, Andrew. There are people here who will fill you in.
First, though, steel ranges in tensile strength from around 40,000 pounds per square inch to over 300,000 psi, depending on the grade. When you talk about buckling you raise the question of whether you're aware of the shape effects of steel under compressive loads. It isn't just the strength of the steel that's at issue; it's the ratio of the length to cross-sectional area, and the section shape.
In other words it may sound like you're asking a simple question but you're not. You could start by telling us what kind of steel shapes you're talking about (round bars? tubes? I-beams?) and how the load is applied.
-- Ed Huntress
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Ed Huntress wrote:

Yes. I figured my Googling was being such a dismal failure because of my lack of knowing the right context in which to search. Thank you for confirming this. (Seriously, thank you, because that lets me know I need to research metallurgy in general to learn the basic terms.)

The shape I have in mind is a rectangular frame made up of four solid, round bars. The longer two of these pipes are six feet, the shorter are four feet, and it's assumed that the weld points at the corners are equal in strength to the bars (I'm not sure how that holds up in the real world, though). The pressure that will be applied comes from a super-human strapped in the middle, with their limbs attached to the four corners, trying bend at the waist. I'm assuming the "buckling" as I call it would most likely happen at the middle on the longer bars, maybe in the shorter ones.
Mostly I'm trying to figure if the super-human can exert roughly one ton of pressure at the four corners, how thick would the bars need to be not to buckle. Steel might not even be the ideal metal for this situation, I was just hoping to use it as a good enough example to get pointed in the right direction. Thank you!
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Andrew Burton
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I would make a frame from tubes, buckling properties of structural tube
http://www.corusconstruction.com/en/design_and_innovation/structural_design/the_blue_book/axial_&_bending/british_standard_sections/chs_celsius /

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David Deuchar wrote:

http://www.corusconstruction.com/en/design_and_innovation/structural_design/the_blue_book/axial_&_bending/british_standard_sections/chs_celsius /
Thanks!
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Andrew Burton
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The problem is that the frame could bend, crush, or buckle depending on how the load is applied.
If the short sides were the hands and the feet, the long sides one hand and one foot:
If the person tried to do a situp it would be a bending moment, that is a function of the length of the tube and the section modulus.
If the person tried to just compress either the sides or the ends, it could buckle or crush. Buckling is when the bar bends like a fishing rod. Crushing is what an aluminum can does when you hit it on your forehead. For steel, buckling occurs when the length to diameter ratio exceeds 89:1
Andrew Burton wrote:

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Except that there appears to be no contact with the center of the body, so that would probably not do much.

What I would consider the most likely maneuver to succeed would be if the super-being tried pulling one hand and the diagonally opposite foot towards the center of his body, thus deforming it in such a way as to cause the other two corners to move outward -- if there is any slack allowed for this. Alternating hand-foot pairs would continue to flex it, perhaps leading to metal fatigue.
To protect against this, you would want another piece of steel as a diagonal brace between two opposite corners -- but this might then provide a possible contact with the mid body, thus offering more possible failure modes.
As someone else suggested, square tube (with adequate wall thickness) would be almost as strong as solid steel of the same dimensions -- and a lot lighter. It is also stronger than the same weight of steel in the form of a solid bar (thus of smaller diameter.
Does the weight of the frame matter for the purposes of the story, or are you assuming that the means exists to transfer all the weight needed? Can the super-being be kept unconscious for long enough to allow the frame to be poured full of cement and allowed to set before he/she/it starts applying that super strength to the frame?
I would also suggest that the frame be suspended by steel cables so the being does not have access to any surface to use to help concentrate the strength.
Good Luck,         DoN.
P.S.    What format of work will this be? Book? Comic book/graphics     novel? Movie/animation? (Not that it really matters to the     question you asked, but I'm wondering in what format to expect     to eventually find this?
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DoN. Nichols wrote:

Plain text actually, strictly an amateur endeavor. If I can ever pull all these facts together and understand them, it'll show up in one of the "Lady Lawful & Doctor Developer" stories here:
http://haven.eyrie.org/~dvandom/ASH/history.html
Thanks for the useful info!
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Andrew Burton
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O.K. Bookmarked to read the rest later.

You're welcome. Best fo luck with it.
Enjoy,         DoN.
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As David said, the most efficient shape, in terms of strength for weight, is hollow tube. The *least* efficient shape is solid bar. However, solid bar would result in the smallest *diameter* for the structural members, at a very large penalty in weight.
There is one thing to clear up about strength, and then you'll be off and running with the formulas. The tubes, probably, or the bars, certainly, will spring in or out long before you approach the strength of the steel. The limit will be based on the diameter of the member relative to its length, and the *stiffness* of the bar or tube.
All grades of steel have the same stiffness. But they can have radically different strength. What this means in your application is that any grade of steel, strong or weak, will spring in or out (it will happen along the longer bars) with the same load. However, a stronger steel will bend and then spring back fully, while a weaker steel will bend and stay partly bent.
This is not a trivial structural situation, and you'll probably have more questions. If this is a real situation you'll want to make sure you get it right. If it's a literary one, you probably can b.s. your way through it. <g>
-- Ed Huntress
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Here's a link that will give you some flavor of what you're asking.
http://physics.uwstout.edu/statstr/Statics/index.htm
This is part of undergraduate mechanical engineering. I recall encountering the problem of plastic buckling of a frame (assembly of beams) in a graduate level course in plasticity. Very likely, whole books have been written on the subject.
Knowing the shape and size of the frame, the size and shape of the members comprising the frame, the nature of the joints between members, the stress vs strain relation (and perhaps other properties) that characterize the material, and the nature, magnitude, direction and point(s) of application for each of the applied loads, a qualified structural analyst might be able to construct such a chart, providing that an assumption of relatively small deflections is valid. Change any of the above and you may have a whole different chart. Encounter a different failure mode (e.g., brittle fracture) and it's a whole different analysis. If the aspect ratio of member cross-sections exceed certain limits other modes of buckling may prevail, etc, etc. If the frame is not a fairly simple configuration, a finite element computer analysis might be required. The context of the problem usually dictates the level of sophistication required and the level of resources to be expended.
Incidentally you're confusing force and pressure, the latter, like stress, being measured in force per unit area.
David Merrill

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"David Merrill" wrote: (clip)Incidentally you're confusing force and pressure, the latter, like stress, being measured in force per unit area. (clip) ^^^^^^^^^^^^^^^^^^ Also, in an earlier post, confusing pipe with solid bar. Andrew, why don't you write about something you know?
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That link doesn't seem to be working this morning; here's the whole search with some alternatives.
David Merrill

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David Merrill wrote:

That link was spectacular! Thank you.
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Andrew Burton
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Andrew Burton wrote:

Has it come to this?
An engineer turning to the usenet for his doctoral thesis homework?
:-)
Cheers Trevor Jones
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On Sun, 28 Oct 2007 04:31:42 -0000, snipped-for-privacy@gmail.com wrote:

Did you really, truly google "steel strength"? I just did and got 1,890,000 hits.
Bruce-in-Bangkok (Note:displayed e-mail address is a spam trap)
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A Guide to Esoteric Technology

Great now can u sort out some good useful ones as the o/p obviously is a busy sole and doesn't have time to sift through the results.
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snipped-for-privacy@gmail.com wrote:

The quality of the steel usually doesn't enter into the solution until you get into very SHORT columns--the limiting factor is the L/r ratio-- (which is the length / by the slenderness ratio.. long skinny columns fail by buckling)---Short fat columns fail by deformation at their Yield Strength--similar to the same size bar in tension.
This is a very simple explanation for a problem that might require quite a bit of mathematical calculations.
Jerry
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A Guide to Esoteric Technology

Exactly; Google for Euler buckling and once you understand that you may be able to formulate a better question.
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