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Combining Primary and Secondary Stress in Monorail

Combining Primary and Secondary Stress in Monorail

Combining Primary and Secondary Stress in Monorail

(OP)
I'm looking into the monorail design procedures.. do you combine the secondary stresses from flange bending and web tension with the primary bending and axial stresses? I'm looking at Alex Tomanavich's spreadsheet from steeltools.org, and it looks like he does not and I'm a bit concerned about it. And if so, is the stress ratio of actual/capacity < 1 suffice, or is there other factors for combining these stresses?

FYI, I have looked at past threads and haven't really found anything on this.. I don't mean to repeat something that's already been answered.

Thanks!

RE: Combining Primary and Secondary Stress in Monorail

My first thought is yes, you must. How can you ignore real stresses that occur in various directions at the same time? Even if one of the inputs might be transient (or not). Ever seen a load left hanging from a monorail while everyone takes a lunch break? Unless you have some test results indicating these can be ignored as combining, I would recommend that you do so.
Dave

Thaidavid

RE: Combining Primary and Secondary Stress in Monorail

You definitely have to account for the stresses due to the beam bending at the same time as the stresses due to the flange local bending. Take a look at CMAA Specification #74 which gives you equations for determining the stress due to the local bending of the flanges as well as a formula for combining the stresses (it is based off of von Mises yield criterion, not unity).

Taking a quick look at the Tomanavich spreadsheet, it appears to me that the spreadsheet is already combining the beam bending stress with the flange local bending stress. Look at the formula for sigma,t0 which uses the square root of sigma,x sigma,z and tau,xz. It appears that sigma,z adds fbx and fby to sigma,z0 (fbx and fby are from the simple span equations and sigma,z0 is from the local flange bending equation). It doesn't appear to be including the overhang bending stress so just be careful if that's going to control your design.

www.structuralcentral.com

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