local flange bending stress of monorail crane 2

[LeonCC]

Using AISC Design Guide 7 and CMAA 74 to calculate the local flange bending stress of monorail crane gives two significantly different results. The stress from CMAA 74 is about 40~50% larger than the number from AISC (David T. Ricker). Anybody know what's going on here? shouldn't them run out two similar results?

 

[le99]

The two methods could have different assumptions on - 1) location of the wheel load, 2) longitudinal distribution length (effective width), and 3) loading considered, 4) safety factor.

 

[canwesteng]

Is there a new version of DG7 with local stresses in monorails out? I don't think that is in the 2nd edition

 

[centondollar]

Here's a wild guess: one method considers the effect of warping (which creates bimoment and thus additional normal stress in the entire section), and the other method does not consider warping.

stress(outermost flange fiber in tension) = + (M_/I_z)*y +- P/A + (B / I_w)*w(s) (bending + axial compression + warping , where B = bimoment and w(s) = sectorial coordinate and I_w = warping constant).

 

[OH_PA_AISC]

All;

This question comes up from time to time. Old post from 2002 sums it up. Credit to RockEngineer (Structural).

Key point: CMAA 74 just gives you an equation and no background.

RockEngineer (Structural)25 Jun 02 14:59

If you have access to old copies of the magazine "Modern Steel Construction" put out by AISC the Dec 1999 issue has a good article on calculating lower flange loading for underhung cranes on page 9 in the steel interchange section. The answer was by David T. Ricker who was a premier crane structural engineer for many years. His method gives slightly different answers than the CMAA 74 but you have an idea how you came up with your answer. CMAA 74 just gives you an equation and no background. If you don't have access to the article I can probably fax it to you depending on where you are in the world.

Thanks for reading.

 

[dik]

Can you post a snapshot of that page? Thanks, if you are able to.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[canwesteng]

Because I looked it up anyway, here it is

https://www.aisc.org/globalassets/modern-steel/archives/1999/12/1999v12_interchange.pdf

I think the answer by Ricker is conservative, but it does leave the determination of biaxal stress out. I'm combining the flange stresses with the global bending moment stresses when I design monorails (when loaded at centre span). I think checking tension in the web in particular is a bit overly conservative, even though it won't really control design.

 

[dik]

Thanks very much...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik