Sizing an I-Beam That's Resting On The Ground 1

[psmi8905]

All,

I'm a mechanical engineer at a steel mill and today I was asked to design a rack which will hold steel coils (see the attached picture). The coil rack shown in the picture is in use at a sister mill whose coils weigh only 50,000 lbs whereas our coils weigh up to 90,000 lbs. As you can see, the beams are resting on the ground. I'm at a loss as to how to calculate the required beam size to support these coils. We have various sizes of W 14 on-site and would like to see if any of those sizes would suffice. The project originator would like to use a beam that would not require web stiffeners or "boxing in the beam" which would consist of a plate welded to on both sides of the beam flange. With that being said, do you guys have any advice for calculating the required beam section? I'm most worried about the beam's web failing. Keep in mind that the weight of the coil will be shared over two I-beams, just as the attached picture shows.


Stuff you may want to know:
1. The beam's bottom flange rests completely on the ground.
2. The beams will be tied together at both ends.
3. There will not be chocks in place between the coils, this allows us to use free rack space most efficiently.
4. There will not be a compressible "padding" on the top surface of the beam i.e. no wood or rubber.
5. The overall length of the rack will be 30 ft.
6. There will be 42" in the clear between the two parallel beam's flange edges.

 

[psmi8905]

Here's a picture of a loaded coil rack just for more clarification of what we're looking to do.

 

[fegenbush]

The reference you require is the AISC Steel Construction Manual (14th Edition is current). The loading scenario you have is a continuous beam with a uniform load (the ground) and a finite number of supports (the coils). This is upside-down from your case, but you will find tables for the orientation I present. A helpful reference for determining the moments and shears of the continuous beams is Moments, Shears, and Reactions for Continuous Highway Bridges published by AISC.

 

[Dougt115]

Side loading of the beams may also be of issue. If the ground is not flat the beams will just fold over sideways as they have no apparent cross bracing short of the I-beam itself. This can be modeled by computing the loading at an angle.

 

[GregLocock]

Guessing these racks are loaded via forklift or crane, size them for impact loads as well, in any direction.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[dvd]

beams on elastic foundations is a good search topic

 

[racookpe1978]

The side loading mentioned above happens because the very heavy coil appears to be supported only at both ends, thus there is a moment arm from the weight of the middle of the coil trying to bend each I beam (probably W14) and "kick-out" the WT's away from each other.

Do this: Use 3x WF 14, not 2. The moment arm rolling the two end beams is reduced to 1/4 it previous value, and the load trying to buckle each web of the WF14's is reduced to 66% its previous value. Your problem is simplified.

 

[JStephen]

Take a slice of beam a unit long, treat it as a little column fixed at the base, design the web accordingly; use appropriate K-factor for a top end that is free to sway sideways and rotate.
You could treat the ground as elastic; you could use uniform load distribution on the ground. With the elastic foundation, the reaction directly under a point load would be higher, which should reduce the moment in the beam. So assuming uniform loading on the soil side should be conservative. And you likely don't have elastic stiffness for the soil side anyway.

 

[Lou Scannon]

FWIW, it seems to me your loading case is not too dissimilar from a railway (minus the dynamics & high number of cycles), if that helps at all.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[dineshakabari]

As per my view based on bearing pressure limit of floor/surface on which beam resting, you have to workout the length up-to which applied load transferred to floor safely. Based on this UDL and worked out length you can work out bending moment on beam. Then by use of BM and sec-modulus you can work out induced stress in beam. This situation reverse of a beam having one support and uniform load applied for certain length of beam. Good luck !