Bearing stiffeners on crane-runway beams 2

[GalileoG]

Hello all!

I am designing a crane runway beam and it seems like I will need bearing stiffeners to prevent web crippling/yielding. My question would be, how would I space these bearing stiffeners? The crane of course moves through the length of the beam, making web crippling/yielding a problem throughout the length. Would I have to choose a beam with a thicker web as opposed to using bearing stiffeners? If not, I ask again, how do I determine a suitable spacing for these stiffeners? Thanks!

 

[oneintheeye]

isnt the web buckling (crippling) resistance dependent on stiffener spacing? Therefore they would need to be spaced as required and not continuous as you imply in your question.

 

[GalileoG]

The equation that I am using w(N + 10t)Fy do not have stiffener spacing in it.

I didn't mean the stiffeners have to be placed continuously.

 

[youngstructural]

It's very rare to need stiffeners along the length of a crane rail unless the loads are very significant. Have you considered the distribution of the load through the rail and the top flange? Presuming you have, and the loads still are too high, I would think (just a gut feeling) that it might be best to increase the web thickness rather than install spaced stiffeners along the length of the beam. Labour is nearly always the more expensive option, particularly when you are probably using the same (or more) material in your stiffeners.

There is a great publication from CISC called "Crane Supporting Steel Structures Design Guide" by R.A. MacCrimmon. It is an excellent resource, complete with design examples and model detailing. I would encourage you to obtain a copy if you are going to be doing many crane rails. Available as a free download from

http://www.cisc-icca.ca/publications/technical/design/craneguide/

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[youngstructural]

That seems to now be a link to a draft version of the second edition. If you're uncomfortable using a draft let me know, I still have an electronic copy of the First Edition (also freely available, when it was on that page).

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[JAE]

Agree that bearing stiffners along the length isn't a good idea. First, if you take the stiffners down to the bottom (tension) flange, you have fatigue concerns with the stiffner to plate weld.

Second, the cost of adding all those stiffners is higher than the cost of a thicker web.

 

[GalileoG]

Thanks all!

I will change the profile of the beam to one that has adequate web thickness.

To youngstructural:

I'm looking at the first design example right now and one thing that is standing out is that the book calculates "Mi" and also the equation that they used for "Mu" is quite different than S16. Are these equations from AISC? Thanks!

 

[GalileoG]

It is page 91 of the draft of the second version.

 

[youngstructural]

clansman:

This is indeed from AISC; Please see "Design Method", p. 35 for an explanation of the term Mi... Essentially it is Mu.

Hope that helps!

Regards,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[youngstructural]

Pardon me, Mi is a LIMITED Mu...

I should really read my previews more carefully!

Sorry for any possible confusion...

Regards,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[GalileoG]

Thanks A TON, friend! This book from CISC is really helpful! I'm set.

 

[GalileoG]

By the way, are you a University of Carleton graduate? I'm a University of Ottawa graduate, took a few courses at Carleton though. Great civil engineering department.

 

[GalileoG]

Err..meant Carleton University (not University of Carleton)

 

[youngstructural]

I am a Carleton U grad, and took a couple of courses at the University of Ottawa; Quite a good civil deparment at your school as well. And don't worry about the U of Carleton thing, I'm forever saying Ottawa University for your school. I thought John Gardiner was an excellent Prof for Advanced Reinforced Concrete Design.

I haven't practiced in Canada for a few years now, but am a P.Eng. (Ontario). Working on getting my CPEng (New Zealand) right now... Will probably write the IStructE exam while I'm down here as well.

Are you still practicing in Canada?

And no worries at all; More than glad to help out. That should be why we're all here. *smiles*

Cheers,

YS



B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[hokie66]

The CISC publication that YS gave us is a fine reference. Especially the pictures. This is a nice compilation of a lot of experience. There are a lot of traps for young players in designing mill buildings and crane runways, and studying the details presented in this paper and understanding why things are done in certain ways will help to avoid repeating mistakes that have led to a lot of grief.

As to the original question about bearing stiffeners, I agree with YS and JAE that they are not normally needed along the beam. Stiffeners are usually required at the columns. Runway beams for heavy duty cranes, particularly hot metal cranes, are frequently fabricated welded girders, and these usually do have web stiffeners.

 

[youngstructural]

Agree with Hokie66 about the stiffeners at the columns, but I would add that I would include them even if the analysis showed they were not necessary. They stiffen the overall assembly and that is quite desirable for a crane rail system. I don't know if I would even be able to back up my gut feeling analytically, however I would not want any possibility of flange/web interface rotation. Just my two cents.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[csd72]

I agree with YS, how is the top flange restrained otherwise?

 

[hokie66]

The stiffeners are not for top flange restraint, they are to reinforce the web. The top flange is restrained by a flexible connection to the building column. Details vary depending on the type of column: corbel, stepped column, or separate crane column. The details in the CISC paper show some options.

 

[apsix]

" if you take the stiffeners down to the bottom (tension) flange, you have fatigue concerns with the stiffener to plate weld."
In my experience that's why web stiffeners are normally stopped short of the bottom flange. I've also seen details where the stiffeners are machined to fit tight to the underside of the top flange and only welded to the web, again for fatigue concerns.

Hokie
The stiffeners do have some beneficial effect on the bending in the web due to load eccentricity (eg AS4100.18, Cl.5.7.3.4).

 

[hokie66]

Yes, but YS and I were just talking about the stiffeners at the end of the beam, not intermediate stiffeners. For load eccentricity except for heavy duty crane runways with welded plate girders, it is best just to use a heavier section.