Single Span Crane Beam with Cantilever and Cap Channel 1

[dik]

Does anyone have a good link to the design of a Crane beam that has a single span with a cantilever. The beam is an S Shape, and there is a C Section welded to the top. The crane is on the bottom flange. Concern is LTB of the combined section for the 8' cantilever. I can work it out, but was hoping for a 'canned' example that I can use. As usual, thanks in advance.

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

-Dik

 

[dik]

Can anyone post the formula for x. I think it is in a Galambos publication from 1968. It's related to calculating the torsional sectional properties for a channel.

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

-Dik

 

[ProgrammingPE]

Determining the centroid for a C section can be complicated since the flanges are sloped and there's fillets. The values are tabulated in AISC's Steel Construction Manual, Table 1-5. You can calculate the value ignoring the sloped flanges and fillets using the following formula, but you will get a larger value since more area is accounted for in the tips of the flanges:

x = (w*(d-2*t)*w/2 + 2*(t*b*b/2)) / (w*(d-2*t) + 2*(t*b))
(Dimension is from the back face of the channel)

Alternatively, you can use the formula for shear center found here.

c = b²*h²*t/(4*Ix)
(Dimension is from the center of the channel web)

How do you then use this for the combined S Shape and C Section? (The Steel Construction Manual tabulates some of the combined properties in Table 1-20, but not the torsional properties.)

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[dik]

Thanks...

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

-Dik

 

[GC_Hopi]

Check out the steel tools website there are excels and examples for runway beams. Link

 

[dik]

GC... I've downloaded a bunch of files to look at... thanks.

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

-Dik

 

[WARose]

You may want to check out a AISC Journal article: 'Design of Crane Runway Beam with Channel Cap', by: Ellifritt & Lue, 2nd Quarter 1998. They consider the case of the LTB value of the combined section.

The cantilever presents another issue. Good articles (by AISC) I've seen on that are:

'Allowable Bending Stresses for Overhanging Monorails' by: Tanner (1985)
'Lateral-Torsional Buckling of Wide Flange Cantilever Beams' by: Dowsell (2004)

 

[dik]

Thanks, Bill

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

-Dik

 

[DCBII]

The purpose of the cap channel is to provide lateral support for the compression flange as the crane applies side thrust. In the case of a cantilever, the compression flange is on the bottom, and the cap channel is ineffective. I would treat it like an ordinary S beam.

You have 2 issues to watch in your situation:
1. Torsion in the cross-section. AISC Design Guide 9 outlines a simplified approach to analyzing for torsion. You can treat the the torsional moment as a force couple acting on the weak axis of the two "half" sections.
2. The laterally unbraced length of the cantilever is longer than the actual unbraced length. Generally it behaves as if it's 3 times as long, but there are more accurate methods for determining the unbraced length outlined in AISC Engineering Journal articles for cantilevered monorails.

 

[dik]

That's the way I considered it, due to the long cantilever... but wanted to expand my crane beam program from a simple span. Your second issue was what prompted the post because I was really concerned. The reason for refining my program. Treating it as a torsional couple is one of the ways of Galambos. The crane has a 3T capacity. Another issue is the backspan is 'short' and there is uplift. The assembly is running on a couple of 'rails' and has to be anchored (magnets?). Still some issues to resolve. I like weird problems and they seem to find me... else I just grow old... It sort of looks like...

Thanks

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

-Dik