Compressive Strength of Steel
Compressive Strength of Steel
(OP)
Greetings,
I am looking at a cantilevered rack system. So a pretty straight forward set of calculations. Or so I thought. For the rear vertical member (backbone as I call it) I have come up with a stress due to bending of 12,001 psi and a stress due to compression (from the weight of load and structure) of 2,338 psi. This would result in -14,339 psi compressive stress and 9,663 psi tensile stress at the edges of the "backbone". I typically design for a safety factor of at least 3. But, with this being made from standard structural steel components with a typical yield of 36ksi, I only get a safety factor of about 2.5 in compression.
I have two questions.
1.) Assuming my bending and compressive stresses are correct, you can add them together to get the resultant stresses as I did, correct?
2.) As long as question 1 is true, what is a typical value to use for the compressive strength of A36 steel? I have always used the yield stress of 36ksi. But I recently saw some numbers as low as 22,000 psi.
Thoughts?
I am looking at a cantilevered rack system. So a pretty straight forward set of calculations. Or so I thought. For the rear vertical member (backbone as I call it) I have come up with a stress due to bending of 12,001 psi and a stress due to compression (from the weight of load and structure) of 2,338 psi. This would result in -14,339 psi compressive stress and 9,663 psi tensile stress at the edges of the "backbone". I typically design for a safety factor of at least 3. But, with this being made from standard structural steel components with a typical yield of 36ksi, I only get a safety factor of about 2.5 in compression.
I have two questions.
1.) Assuming my bending and compressive stresses are correct, you can add them together to get the resultant stresses as I did, correct?
2.) As long as question 1 is true, what is a typical value to use for the compressive strength of A36 steel? I have always used the yield stress of 36ksi. But I recently saw some numbers as low as 22,000 psi.
Thoughts?





RE: Compressive Strength of Steel
I think you should have more than two questions. What about buckling and instability of the various members in this rack system? What about secondary loadings and stresses? What about the various connection details on this system, and the concentrated loads and stresses at these points? What supports the backbone, and what shape and size is it? What is the load on each shelf or level, is it a uniform load, or can it be applied as a point load out at the tip of the canti.? Should I ask a senior engineer or my boss for some help and guidance on this? Should I consult the AISC Steel Construction Manual on this? Can I even buy A36 material any longer?
RE: Compressive Strength of Steel
RE: Compressive Strength of Steel
1) yes, you can superimpose bending stress and axial stress.
2) depends, have you heard of crippling (thin sections can fail with a compression stress less than fcy).
personally 12001psi looks suspiciously like 12ksi (ie 5 significant digits ??)
Quando Omni Flunkus Moritati
RE: Compressive Strength of Steel
Bending Stress = My/I = 1,492,812*10.495/1,309 = 11,969 psi.
I will go ahead and look at crippling. Besides crippling and buckling, are there additional concerns for this area of concern I need to look at? What is the 22ksi compressive yield I saw on a few sights used for?
RE: Compressive Strength of Steel
From the original question, I thought this was a cold formed member. However, it is clear now that you should be using the design principles in the AISC Steel Construction Manual. Chapter H1 specifically deals with the design of doubly and singly symmetric members subject to flexure and axial force.
If you do not have a copy of this reference, AISC 360 is available as a free download. If in doubt, please consult with a structural engineer in your area. There can be a considerable amount of liability in the design of such structures, and good engineering practice is prudent.
RE: Compressive Strength of Steel
instead of crippling, you might consider the flanges as flat plates in compression, SS on 3 sides, free on the other.
getting back to your original problem ... if you want a SF of 3 and are only getting 2.5, then don't you want to up-size some of the structure ?
Quando Omni Flunkus Moritati
RE: Compressive Strength of Steel
RE: Compressive Strength of Steel
If you've got any substantial load supported, consider seismic design as well, and, if outdoors, wind loading.
RE: Compressive Strength of Steel
RE: Compressive Strength of Steel
Sorry for not being definitive. I don't want to go on a hunt for the information. It is available in engineering literature, I've found it myself before.