I Beam flex???

[DrDan]

I am putting in an overhead crane in my shop and have a question. The shop is 30' wide X 40' long. We have no problem supporting 4" I Beam by hooking on to 2" X 6" trusses spaced 7.5' OC. Lots of support especially since these beams will be alongside the walls. Now here's the problem. We will be running a bridge across the 30' width and hooking it onto the I beams running alonside the walls on each side. This bridge will roll on the two I beams with steel rollers rated at 1.5 ton. On the bridge will be another trolley (steel rollers) that will go back and forth with the lift mounted to it. The I beam used for the bridge can't flex much more than 3/8" when the lift is picking up a ton or the trolly will roll to the center. The idea is to be able to get this lift anywhere in the shop. I am also being told that we won't need any power drive on the bridge since the steel wheels roll so easy on the steel I beam. Anyone know how much 4" or 6" I beam 30' long will flex when supported by the ends and a ton is hung on the center?

DrDan

 

[rlw]

The formula for a deflection of a beam supported on the ends with a centered load is: (Force * length^3) / (48 * E * I)
E = modulus of elasticity
I = moment of inertia.

For structural steel, E = 29 Mpsi
I is calculated from the dimensions of the beam

I looked in a book for standard I beam data. There are 2 sizes listed for both the 4" and 6" I beam.
a) 4" beam with .193 thick web - I=6.08 in^4
b) 4" beam with .326 thick web - I=6.79 in^4
c) 6" beam with .232 thick web - I=22.1 in^4
d) 6" beam with .465 thick web - I=26.3 in^4

Putting the numbers into the formula:
(2000 * 360^3)/(48 * 29E6 * I)
This reduces to:
67/I
Therefore using the I values from above:
a) 11.02 in
b) 9.87 in
c) 3.0 in
d) 2.54 in

Clearly neither the 4" or 6" beam will meet your 3/8" max deflection requirement.

Using the reduced formula above, and 3/8", and solving for an I value: 67/I = .375, we get I=178.7

I went back to the beam tables and looked for the minimum sized beam that had an I value greater than 172. The minimum sized beam that will meet your requirements is a 12" beam. The book I have lists four different web sizes for a 12" beam (.350, .428, .462, .687). Any of these will work.
The dimensions for the .350 web beam are:
Flange width = 5.0 in
flange thickness = .491 in
I = 218
Its designation is S12 x 31.8.
This beam weights 31.8 #/ft, therefore 30 ft = 954 # beam.

If you really want to use the best 6" beam from above, we can put all the numbers into the equation and solve for max weight at 3/8" deflection. The answer: 294# is the max weight you could suspend at the center and have 3/8" deflection. -- Not a very useful crane.

You may need to look at the supporting 4" beams as well, to make sure they can take all the loads.

 

[RobS]

Nice work rlw, I was finding the same but didn't find pre-calculated moment numbers for the beams, only a formula which was giving me fits. There is probably a calculator somewhere on the 'net to do all this with dropdowns or something.

Whatever the case DrDan, you do want to be extra careful when designing for overhead lifting. Check with your local crane and hoist dealer and maybe they can give you some help /w3tcompact/icons/smile.gif

 

[MikePA]

<font color=blue>Check with your local crane and hoist dealer and maybe they can give you some help</font color=blue>

Just don't check with <A target="_blank" HREF=http://www.tractorbynet.com/forumfiles/35-210572-whoops02.jpg>these</A> guys (from another post on TBN). /w3tcompact/icons/laugh.gif

 

[RobS]

Ouch! I'm a big crane fan and have come across various crane failure pictures over the years. They are typically pretty spectacular. Several years ago we had a large lattice boom crawler crane fall into the river while working on a bridge project. Fortunately, the operator was not hurt but the extraction was even more impressive than the planned lift /w3tcompact/icons/smile.gif

 

[BB_TX]

rlw - On a similar note, I have been trying to figure the best way to build a bridge across a creek to get my tractor across. I need a span of about 24' and the tractor weighs about 3500#. From your numbers, looks like two 12" I beams would safely support that weight. I would space the I beams where they would be approximately under the wheels on each side. And also have the appropriate cross bracing between the I beams to prevent rolling.

 

[gerard]

bbx - try and find an old flatbed trailer. If you can get it to the area all you need to do is cut the rear axels off and you have a ready made bridge 8 feet wide x 35-40 feet long and strnog enough to drive over. I've read in Farm Show Magazine of people getting trailers for $150 and even welding two together to makde a wider bridge.

 

[DrDan]

Thank you rlw... That gives me some "food for thought". In actuality I will only be lifting less than 1000# (more often 300-500#), so now I can get some better ideas of my limitations. Actually the 6" looks like it would do it!

You see, I am in a wheelchair and do a lot of bowl turning on the lathe and handle lots of stumps that must be split and then moved to the lathe and chucked up. LOL You should see the underpinnings on my lathe! Of course I can settle for 6 to 8" bowls. I don't get my "jolly's" uless it's 20" or greater!

I'll be back to you later. Gotta go to work!

DrDan

 

[Anonymous Poster]

DrDan,

How about a couple photos of your larger bowls...maybe in the photos forum?

Love to see them and a pic of the lathe you turn them on too!

Bill in Pgh, PA

 

[dmccarty]

DrDan,

To bad you are in Ohio. I got plenty of stumps for you. Just
come and get 'em. /w3tcompact/icons/smile.gif

I to would like to see what you have made. I've got some
large 36+ inch oak stump that would make a heck of a bowl.
/w3tcompact/icons/smile.gif

I'm real impressed that people figured out the span data for
you. The other to consider is how you are going to support
the beam. You mention the trusses but could the handle
the load. The other option is to build the structures under
the beam ends.

I know enough to be dangerous and I bought some wood
engineering texts and standards manuals a few months ago
to study some building ideas I came up with. From a dollar
perspective I would have been better off just paying an
Engineer but I wanted the books, span tables, and knowledge.

But you might want to talk to a Engineer. A friend at work
had a concern with a house he was buying and the Engineer
was a few hundred dollars to look at the problem and design
a solution. The Engineer's stamped solution was MUCH
cheaper than what various contractors bids. A couple
hundred dollars for the Engineers solutions to multiple
thousand dollars for the contractors......

Let me know when you want the stumps!
Dan McCarty