Building my bridge crane

[SPYDERLK]

First of all take this info for what you paid for it. Which was nothing. In other words its for discussion only.

Attached you will find FEA of OPs spliced beam... using tapered and square scab plates. Note hot spots at points of scab plate. With that being said, highest stress is at butt welds between two beams and not at scab plates.

Also I've included approx safety factor at 10,000 lbs with indicated loading... around 1.1. OP should inspect rail at butt weld joint for possible fractures. Proceed at your own risk. Not sure what you are gonna rate this crane at but be careful. Cranes are serious business.

Good day.

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Perhaps you know what that all means; while I have to guess. Aside from WTF on the color code and symbols and other jargon, my guess is that you have made assumptions about scab thickness, taper start point away from the butt weld, and taper angles.

... Why would the butt welds be an issue? The scab plates span them and spare the butt welds from excessive stress by sharing the load.

 

[SPYDERLK]

I spliced an I beam together in my shop when I removed a wall after I welded it, I used square scabs but plug welded them and welded just the top and bottom.

A little different than the OP's bridge crane though because the top of the beam is attached to the rafters preventing deflection side to side, making it much less likely to fail.

You are talking a torsional issue here. ... A light round tubular member split and welded into the web would make the beam rigid enuf torsionally. -- Not necessary at the 5k max loading LD1 has in mind.
,,,larry

 

[LD1]

Got the first set of braces/gussets up. Probably gonna do 2 more on each side out of square tube going from the truck to the top flange, but a few feet out away from the rail beam. Still have to do the knee braces on the columns yet.

First of all take this info for what you paid for it. Which was nothing. In other words its for discussion only.

Attached you will find FEA of OPs spliced beam... using tapered and square scab plates. Note hot spots at points of scab plate. With that being said, highest stress is at butt welds between two beams and not at scab plates.

Also I've included approx safety factor at 10,000 lbs with indicated loading... around 1.1. OP should inspect rail at butt weld joint for possible fractures. Proceed at your own risk. Not sure what you are gonna rate this crane at but be careful. Cranes are serious business.

Good day.

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Not really gonna have a hard and fast rating. Just a personal garage, to lift whatever I have in mind. But figuring on calling it 5k. What do you figure is safe based on what you know?

As to the plates....Never measured the actual thickness with calipers. But Guessing the web plates are either 1/4" or 5/16" and the flange plates are 1/2"

 

[dragoneggs]

Looking good LD! I'm getting more jealous each time you post.

 

[jwmorris]

You are talking a torsional issue here. ... A light round tubular member split and welded into the web would make the beam rigid enuf torsionally. -- Not necessary at the 5k max loading LD1 has in mind.
,,,larry

Yes, an I beam will fail much quicker when it is allowed to flex side to side or torsional, like the FEA posted by projectking note the beam buckles not at the joint rather in the center where it is allowed to flex. The addition of a horizontal truss along the top would make it much stronger.

Not unlike the truss on a sheet metal brake.

The beam will fail when it lays over a "diamond" at the top of the beam would keep it vertical and make it much stronger, while not inhibiting trolley movement below.

It is simple if you look at it simply, the wider the beam the less likely it is to deflect side to side. Take a yard stick and flex it by both ends it is strong vertically but will flop side to side with little pressure make it a "T" or "H" and the wider you make the horizontal sections, the stronger it gets in that direction.

 

[ProjectKing]

Perhaps you know what that all means; while I have to guess. Aside from WTF on the color code and symbols and other jargon, my guess is that you have made assumptions about scab thickness, taper start point away from the butt weld, and taper angles. ... Why would the butt welds be an issue? The scab plates span them and spare the butt welds from excessive stress by sharing the load.

Blue to red is low to high stress.

I used w16 beam same as OP speced. Scab plates are 1/2" thick. Beam ends are beveled for 100% butt weld. Scab plate angles are approximated from pic OP posted.

Even though the beam is welded together and scabbed the joint is still the highest point of stress. Stress will always find weak spot. Similar to nicking a piece of wire and then bending it. It will break at the nick.

The key to reducing stress is having a uniform structural member free of any defects. A continuous I-beam is a perfect example.

 

[ProjectKing]

Got the first set of braces/gussets up. Probably gonna do 2 more on each side out of square tube going from the truck to the top flange, but a few feet out away from the rail beam. Still have to do the knee braces on the columns yet. <img src="http://www.tractorbynet.com/forums/files/build-yourself/448302-building-my-bridge-crane-img_20151124_175911081-jpg"/><img src="http://www.tractorbynet.com/forums/files/build-yourself/448303-building-my-bridge-crane-img_20151124_175920590-jpg"/><img src="http://www.tractorbynet.com/forums/files/build-yourself/448304-building-my-bridge-crane-part_1448407569003_1448407569082-jpg"/> Not really gonna have a hard and fast rating. Just a personal garage, to lift whatever I have in mind. But figuring on calling it 5k. What do you figure is safe based on what you know? As to the plates....Never measured the actual thickness with calipers. But Guessing the web plates are either 1/4" or 5/16" and the flange plates are 1/2"

Nice looking work!

I'll decline to say what a rating should be. It depends on entire structure. You probably should load test slightly above your rated weight to make sure everything is okay. 37' span ( I think that's what you said)... Is a pretty big distance with supports only on ends. Some cranes with this kinda span will also use a center runway rail for support. But it all depends on how much load you pick up.

I'm very impressed you are making this bridge crane yourself. Awesome DIY project!!!

 

[dstig1]

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As an engineer, I understand and appreciate the concerns. The OP seems to know more or less what he is doing, and has consulted decent sources, so it appears he is in decent shape, though things like this are always a bit trickier than they may appear to the inexperienced. Shield Arc had the benefit of an engineer that does this stuff daily for his design, and years of, umm, "hobby" welding behind him.

Nonetheless, I think I can appreciate the irony of the somewhat-mutant-fish-shaped Von Mises stress plot on the "fish plate", probably more than most... :laughing::shark: Especially since no one else mentioned it...

LD1 - I hope you aren't going to cantilever that hoist out past the ends of the posts by much more than a couple inches....

 

[bigdeano]

ProjectKing,

I have a couple questions on your FEA solution. It looks like you have constrained the ends of the beam in X and Y directions instead of only in Y direction like the OPs crane. The beam won't bend near the end like that in real life. Also it looks like the load is not in the center. Any reason for that? I used to do FEA quite a few years ago. It doesn't look right to me. Just wondering.

 

[LD1]

Blue to red is low to high stress.

I used w16 beam same as OP speced. Scab plates are 1/2" thick. Beam ends are beveled for 100% butt weld. Scab plate angles are approximated from pic OP posted.

Even though the beam is welded together and scabbed the joint is still the highest point of stress. Stress will always find weak spot. Similar to nicking a piece of wire and then bending it. It will break at the nick.

The key to reducing stress is having a uniform structural member free of any defects. A continuous I-beam is a perfect example.

Details are a bit off if you care to run the program again.

ITs not a 16" beam. Its a W18x60. The plates are 5/16" thick for the webs and 1/2" on the flanges. The total beam length is 38', and setting on 6" wide end trucks, the beam over-hangs by about 2" on each one. So the span is basically 36'8" total from truck edge to truck edge.

The trucks are 6x6x1/4" tube and 48" axle to axle.

The gussets connecting beam to truck are 18" high, 18" along the bottom and the same 5/16 plate used to plate the web.

The splice in the beam is not at center. It was a 25' stick and 13' stick welded together.

Trucks are running on 40# rail track, and one side sits on W8x24 beam, the other sits on W8x31 beam. Columns are 118" tall and W10x33 and 15' apart center to center. 12x12x1/2" thick pads on the bottom, held with 4 anchors that are 3/4". Top pad is 1/2" 8x10 welded to the column.

LD1 - I hope you aren't going to cantilever that hoist out past the ends of the posts by much more than a couple inches....

Yes it has the ability to cantilever out about 18-20". Thats beam center can be 18" or so beyond the post. I would have put the post at the end of the rail beam, except my window is in the way. MY calculations show that there is greater stresses and deflection with the trucks right in the middle of the rail beam rather than a little cantilever. And everything checks out okay WITHOUT gussets. Once they go in, there should certainly be no worries.

The knee braces would be something like this