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I beam or box beam for crane long travel, which is better? 11

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edison123

edison123

Electrical
Oct 23, 2002
4,413
IN
For a crane long travel along a factory length, in terms of load carrying and resisting torsion while the crane moves, is a I beam of hxw with one vertical web of thickness t is better than a box beam of same hxw with two vertical webs of thickness t each as shown below? Crane supplier claims I beam is better. Both are fabricated from structural steel.


Parts-of-an-I-Beam_htcmux.jpg



box-beams-250x250_pezfzk.jpg


Muthu
 
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He says the I beam will have vertical stiffeners welded on both sides of the web at every 750 mm to prevent torsion and better load carrying capacity. Is he right?

Muthu
 
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No. The stiffeners dont really add torsional stiffness to the I. Í-beams use surge girders, horizontal truss with the top flange
so that it eliminates the requirement for torsional stiffness/strength.
 
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Or the I beams can be capped by a channel that will span from column to column around its strong axis.
 
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Thanks, Steyn. The top of the beams is where the crane rail is and the crane runs along.

Is box type beam better at handling longitudinal torsion than I beam?

Muthu
 
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a box beam is better than an I beam under torsion loads.

an I beam is typically lighter than a box beam as it has a higher proportion of material in the caps (a box beam has two webs).

so if you don't have to worry about torsion loads but do worry about weight, then an I beam is probably the better choice.

You add stiffeners to the web, to help with shear buckling of the web, or another way .. you can have a thinner (lighter) web if you add stiffeners.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
 
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What are the support conditions? Torsion can be dependent on that piece as well.
Torsion would be handled better by the closed section generally speaking. Box beam.
 
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skeletron

Thanks.

The long travel crane beams rest on rigid structural columns made of two beams with angle crisscross ties. The crane runs at a height of 30 ft from ground. It's an indoor crane not exposed to elements



Muthu
 
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An I beam is more efficient for bending moment, but has less resistance to torsion than a box beam. So, the bottom line is, does an I-beam sized for the bending moment have adequate torsional resistance? If it does, there's no reason to fabricate a heavier box beam, that's also more difficult to fabricate. If the I-beam doesn't have sufficient torsional capacity, then it becomes a matter of what works best to provide torsional resistance - use the box beam or provide more bracing for the I-beam, with the addition of transverse beams, diaphragms or cross-frames and/or increasing the stiffness of the connection to the columns (this is where vertical stiffeners may be useful).

Rod Smith, P.E., The artist formerly known as HotRod10
 
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"Capped channel welded on the top flange is a compromise between a I beam and a box beam?" ... no, reinforcing the caps does not make a box section ... in fact it probably weakens the torsional strength, though it probably improves the lateral buckling of the cap.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
 
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Our plant columns are fairly close, so our rail beams are supported every 20'.
We have web stiffeners tied back to the beams at each location (welded to tap flange, the web, and bottom flange as well as the column).
There should be little torsion on the rail beams.
But if someone gets carried away with lateral moves or there is a drive symmetry issue is possible.
We hate using boxes because we can't inspect the inside.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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Skeletron noted "what are the support conditions?" and what sort of span are you looking at? and are there any cantilevers?

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
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"We hate using boxes because we can't inspect the inside." ... you can always cut inspection holes in the webs and use a borescope camera.

not saying it's a good idea, or needed, just answering a problem statement.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
 
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Even if there is torsional moment (there is, from side thrust) the I-beam is more efficient in this application. The top flange of a box will have to be heavily reinforced to support the crane rail, or you can put the crane rail above one of the vertical walls of the box, but then you induce more torsion into the beam. You can also likely make a rolled section work with an I section, but the box beam will have to be fabricated from plates, so it will cost more per ton. As ed said - hard to inspect, if it was my plant I would have choice words for an engineer who used a box section in this application.
 
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Thank you all for your tips.

The span between LT columns is 22 ft with a lift of 20 ft and no additional frames or ties are not possible due to the crane movement. The crane (60 ton) travels at about 2 to 5 meters/minute along the LT depending on the load. The total long travel is about 300 ft. The span of bridge is 45 ft.

Going by the consensus here, I beam (fabricated 620 x 300 x 10 mm) set up is more reliable and adding web stiffeners is enough to arrest the lateral movement, which was my main worry.

The whole discussion started because the bridge girder (cross travel) is double box type construction and I said why not do the same box type girder for the long travel also.

Muthu
 
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...adding web stiffeners is enough to arrest the lateral movement, which was my main worry.
Click to expand...

If you're referring to the addition of vertical web stiffeners at the columns, those would resist torsion at the column locations. Longitudinal stiffeners would help the flanges resist with lateral bending. Vertical web stiffeners at locations other than at the columns would not have any substantial effect on lateral or torsional resistance.

Rod Smith, P.E., The artist formerly known as HotRod10
 
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