Bridge Crane designs and ideas...38' span

[LD1]

This is lateral torsional buckling that I was talking about. If you put bracing along the yardstick it wouldn't do that.


LD, you checked your posts and side carry beams that support the bridge right?

Yep. Posts will be 4x6x1/4 tube, carry beams will be S7x20. Posts will be 12' apart, with the side beams overhanging each by a foot and a half. They are 15' and a knee brace both directions by 1.5'. Effectivly limiting span to ~9'. And with the load distributed along a 4 or 6' "truck", there is no worries there.

 

[LD1]

With the span beam placed right at a post, and the chain fall in the center of the span beam I could pick 2-tons, with 3/1 safety factor.

I think it is more than that. At 5 ton I figured a 6:1 SF.

Stress = (1/2 beam depth x W x l)/(4 x i)

A 2-ton load would be 2470psi stress and 0.08" deflection.

Your side beams with a 3500# load (I added 1500 for 1/2 the weight of the bridge beam and hoist), 5780psi stress. Jumping to 2-ton would be 9000psi, still a 3:1 SF, and probably the stress would be less with it not being a point load, rather two loads at whatever spacing your rollers are at.

 

[Shield Arc]

Over the years Mike told several of my co-workers when he had to run the numbers for me. He upped the safety factor, because he felt I never told him the whole story.

 

[FarmWrench]

I don't know how your end trucks are set up. Why not use two beams and put the hoist between on a top running carriage. For the right price two s beams could become as box just for rigidity.

Other than you already have an underhung hoist, and you have no desire to save headroom.

 

[LD1]

I don't know how your end trucks are set up. Why not use two beams and put the hoist between on a top running carriage. For the right price two s beams could become as box just for rigidity.

Other than you already have an underhung hoist, and you have no desire to save headroom.

Im lost. Not sure what you are trying to say.

A bridge crane requires THREE beams.

Two side beams, and the bridge beam that the hoist goes on.

I have a 38' span and a 12' span. The 38' direction is the width of the shop. The 12' span is along the outer walls.

Rather than span 38' TWICE, I would like to only span it once. On this beam, there will be a 5-on trolley and 5-ton chain-fall. The two beams that comprise the 12' run will be along the outer walls, and have 40#/yd rail on top, in which "trucks" will ride that carry the 38' bridge beam.

Not sure why some are suggesting to reverse the design, That would require TWO 38' beams instead of just ONE. And TWO beams spaning accrpss the width of the shop that are NOT movable. How does that help with anything. I would rather have a single 38' span beam, which would cost half as much as 2 beams, and have the ability to push it all the way to the back if needed for clearance reasons.

 

[LD1]

Over the years Mike told several of my co-workers when he had to run the numbers for me. He upped the safety factor, because he felt I never told him the whole story.

So...how much have you lifted on this "1-ton" crane??

 

[Shield Arc]

So...how much have you lifted on this "1-ton" crane??

I don't really know. A buddy brought me a load of steel one time. I knew it was heavier than 1-ton. So I used the 3-ton manual chain fall.

One of the best things I did to my crane was to install a winch on top of the span beam for power travel. :cool2:

 

[otlski]

I do.

W27x114 for a 30' clear span and 10k hanging from it..................

That amounts to 3ksi stress and 0.079" deflection. So ~12:1 safety factor.

They even use that same beam on the 25' spans, which is over 14:1 safety, and 0.04" deflection.

Would have no issues at all pushing 15t on "their" 5 ton rated beam. Would only just slightly exceed a 5:1 safety. (like 4.8:1), and deflection just slightly more than 1/8" over 25'.

If YOU dint think that to be overbuilt, I'd hate to see the size of the floor joists in your house.:laughing: Are they made of 8x24 lumber, spanning no more than 12', and no more than 16" OC spacing.....

My opinion comes from my experience operating several of these cranes. Positioning 3000 to 8000 lb test masses and fixtures to within 0.010". Also being the guy working 20 feet in the air making the fine adjustments while the bouncing is occurring. The cranes are bouncy at much less than their rated load. When the load stops moving, the whole thing bounces 10 seconds before damping out. I ran the numbers, I agree with your safety factors. I have to guess that not just Gorbel but other crane manufacturers treat unintended off axis forces less casually. Must be a reason they are overbuilt because they would never sell any if the extra costs associated were frivolous. Anyway I was just a guy offering the OP (you?) a different perspective. I'll go back to my normally built house which I indeed built normally and enjoy the thread.

 

[farmer2009]

I'm just subscribing to this. One day I'll be building one so I'm making notes.

Shield Arc. What is supporting the ends of your side beams? From the picture they're just hanging in the air. I'm sure it's the picture angle.

 

[Shield Arc]

Shield Arc. What is supporting the ends of your side beams? From the picture they're just hanging in the air. I'm sure it's the picture angle.

At the ends of the rails, (40-feet long) I have 4-inch schedule 80 pipe. In the center of the rails I have 6" x 6" x 1/2" wall square tubbing. I got the majority of the iron to build the crane for free.