Question for the Engineers Here.
My neighbor has a "Yarder", which is a piece of logging equipment. Here is a bit of information for those that may not be familiar with logging equipment, so you can get the gist of my question.
Here is a generic picture of a yarder, rigged up and logging:
My neighbor's is much smaller, and looks similar to this one:
The above pictured yarder is in the transport mode. When it is rigged up, the tube, or tower will be vertical like the one in the top picture.
The tube on my neighbor's yarder is round rather than square like the one in the bottom picture. His tube is about 24" in diameter, and it is 65' long/tall. I have no idea of the wall thickness, but would guess 1/2". His is a one piece tube, and does not telescope like the one in the top picture. That is a big machine with a 90' or 100' tube.
Anyway, the tube has a bend to it, and the state safety drones are loading their pants about it. It is a long sweeping bend that puts the top with the sheaves about 8" out of plumb. Most everybody seems to think it is from the machine sitting for long periods of time with the tube down in the transport mode, like the one in the lower picture. They say that the weight of the sheaves, and lines out on the end caused the tube to bent over time
My neighbor, and myself think it was made that way. While the bend does have the top bending toward the ground, it is long and gentle, and directly opposite the load applied to the tube when it is logging.
These two reasons along with the way steel acts, in my mind anyway, is why we think it is an intentional bend. In my mind, all steel is "spring steel" to a point. That's the idea of steel, isn't it? Steel has an elastic range in which it will deflect, and return to it's original shape. Only if it bends past it's particular elastic range does it permanently bend. My thinking tells me there is nowhere near enough weight on the end of that tube to cause a permanent bend.
The company that built the yarder is long, long(30+ years) out of business, so no chance of any information there.
Thoughts? Ideas?
Here is a generic picture of a yarder, rigged up and logging:
My neighbor's is much smaller, and looks similar to this one:
The above pictured yarder is in the transport mode. When it is rigged up, the tube, or tower will be vertical like the one in the top picture.
The tube on my neighbor's yarder is round rather than square like the one in the bottom picture. His tube is about 24" in diameter, and it is 65' long/tall. I have no idea of the wall thickness, but would guess 1/2". His is a one piece tube, and does not telescope like the one in the top picture. That is a big machine with a 90' or 100' tube.
Anyway, the tube has a bend to it, and the state safety drones are loading their pants about it. It is a long sweeping bend that puts the top with the sheaves about 8" out of plumb. Most everybody seems to think it is from the machine sitting for long periods of time with the tube down in the transport mode, like the one in the lower picture. They say that the weight of the sheaves, and lines out on the end caused the tube to bent over time
My neighbor, and myself think it was made that way. While the bend does have the top bending toward the ground, it is long and gentle, and directly opposite the load applied to the tube when it is logging.
These two reasons along with the way steel acts, in my mind anyway, is why we think it is an intentional bend. In my mind, all steel is "spring steel" to a point. That's the idea of steel, isn't it? Steel has an elastic range in which it will deflect, and return to it's original shape. Only if it bends past it's particular elastic range does it permanently bend. My thinking tells me there is nowhere near enough weight on the end of that tube to cause a permanent bend.
The company that built the yarder is long, long(30+ years) out of business, so no chance of any information there.
Thoughts? Ideas?
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That's some heavy duty stuff. My first thought is that sometime in the past it was overloaded and bent. Having said that, the overload must have been removed quickly or the bend would have become huge. The fact that it is a long bend doesn't sound like a typical failure though. Take a good look to see if that 8" offset provides any purpose during operation. You say a long bend (I don't know the direction of the bend)so does it extend to a point where the beam doesn't sit centered on it's forward support when down? I can't agree with the long sitting theory. 0 -
quote:Originally posted by cbxjeff
You say a long bend (I don't know the direction of the bend)so does it extend to a point where the beam doesn't sit centered on it's forward support when down? I can't agree with the long sitting theory.
If you look at the tube in the bottom picture, the bend would have the top of the tube bending toward the ground. Thus, then the machine is rigged up, and ready to log, the load on the tube will be directly opposite the bend, That is, the working load trying to pull the tube back to straight. It looks to me like it was some "camber" built into the tube to counteract the load forces when it's working.0 -
I am not an engineer but I did take civil engineering for a year and studied carbon steel for a while. The permanent deflection you mention is called the yield point. Every steel alloy has a yield point.
That is the point at witch it will give and not return to it's original shape. I learned this from straightening gun barrels. In my opinion the deflection you see in this boom is because it is horizontal position and is caused by the weight on the end. You would not see it in the vertical position. I was also in the operating engineers when I was a kid in my 20s and crane booms are the same way,0 -
quote:Originally posted by jerrywh818
In my opinion the deflection you see in this boom is because it is horizontal position and is caused by the weight on the end. You would not see it in the vertical position.
The problem is, the bend/deflection is still present when the tube is stood up. That's how the state safety people noticed it.0 -
HPD, I reread your original post and see the direction of bend now. Since I don't know just how this thing works, if what you say that the operational load is opposite the direction of bend you may be on to something there. Ever see an empty flatbed semi trailer - they are slightly arched. 0 -
I am an aeronautical engineer.
I dont think it would fly very well.
You?re welcome.
Scrape the paint front middle & center and have it x ray?d- you will be able to determine if the mterial has been unequally stressed.0 -
1.) Whip up some documents on the web for owners manual and state the bend is natural.
2.) Kind of reminds me of the ole Magazine stored full or empty saga0 -
"and directly opposite the load applied to the tube when it is logging."
It sounds like it was engineered that way originally, so that the load would want to pull against the arc, and want to straighten the tube- much like you would span a joist board with the crown up.
Your neighbor might have to pay a structural engineer for a report to clear it with the state inspectors or talking heads.0 -
What brand and model of Yarder? 0 -
Question the company that made the rig. 0 -
quote:Originally posted by flyingcolumn
What brand and model of Yarder?
Tillman, I don't remember the model
quote:JimmyJack Posted
Question the company that made the rig. That company has been out of business for over 30 years.0 -
Properly rigged, there should not be much of a horizontal load on the tube, only a vertical load applied by the guy wires and the working load.
The problem is that the applied vertical load is not concentrically supported.
Are there guy wires supporting the center section of the tube, or do they only attach at the top?
Frankly, an 8" bow in a 24" diameter tube that is 65' long is not a huge deal. Also, there is a definite possibility that the bow was caused by the tube resting in the travel position for 30+ years. Vibration combined with a stress much lower than the yield stress can cause some realignment of the grain in the steel, relieving stress and resulting in the bow that you see.
We have used vibratory stress relieving of large weldments on occasion, and a fabricated structure will move noticeably during the process without the overall structure being loaded at all.0 -
Tried to edit my earlier reply and deleted it instead. I think it's fatigue.
Suggest you read this: https://www.asminternational.org/documents/10192/1849770/05224G_Chapter14.pdf
If there is stress cracking it will be evident. May have to remove paint to see it.0 -
quote:Originally posted by Mr. Perfect
Tried to edit my earlier reply and deleted it instead. I think it's fatigue.
Suggest you read this: https://www.asminternational.org/documents/10192/1849770/05224G_Chapter14.pdf
If there is stress cracking it will be evident. May have to remove paint to see it.
Mental or metal fatigue?[:)]
Someone can check my math, but if rigidly supported from one end, a 65' long steel tube, 24" diameter x 1/2" wall will droop 6.75" due to its own weight.
Weight = 8,400 Lbs.
Modulus of Elasticity = 29x10(6)
Moment of Inertia = 2545 in(3).
Depending upon where it is supported during transit, stresses could be fairly high at the support points.0 -
quote:Originally posted by Don McManus
quote:Originally posted by Mr. Perfect
Tried to edit my earlier reply and deleted it instead. I think it's fatigue.
Suggest you read this: https://www.asminternational.org/documents/10192/1849770/05224G_Chapter14.pdf
If there is stress cracking it will be evident. May have to remove paint to see it.
Mental or metal fatigue?[:)]
You ask like you care. [:(][^]0 -
Has anyone looked at a new "flatbed" trailer lately? They are bowed and we have several concrete bridges in my area that have been assembled with "bowed" beams. Kind of like driving on a roller coaster, which I hate. 0 -
software engineering type.... that won't compile. It is a hardware issue.
Next ticket please.0 -
quote:Originally posted by cbxjeff
HPD, I reread your original post and see the direction of bend now. Since I don't know just how this thing works, if what you say that the operational load is opposite the direction of bend you may be on to something there. Ever see an empty flatbed semi trailer - they are slightly arched.
^^^^^^This0 -
quote:Originally posted by Don McManus
quote:Originally posted by Mr. Perfect
Tried to edit my earlier reply and deleted it instead. I think it's fatigue.
Suggest you read this: https://www.asminternational.org/documents/10192/1849770/05224G_Chapter14.pdf
If there is stress cracking it will be evident. May have to remove paint to see it.
Mental or metal fatigue?[:)]
Someone can check my math, but if rigidly supported from one end, a 65' long steel tube, 24" diameter x 1/2" wall will droop 6.75" due to its own weight.
Weight = 8,400 Lbs.
Modulus of Elasticity = 29x10(6)
Moment of Inertia = 2545 in(3).
Depending upon where it is supported during transit, stresses could be fairly high at the support points.
Checked your math. I get 6.47" for A36 Steel (that weighs 8,062lb), but it is likely something a bit stronger than A36, though that's pretty common for structural steel. https://www.amesweb.info/StructuralAnalysisBeams/Structural_Analysis_Beams.aspx0 -
I vote for metal fatigue. 0 -
Just rub a little viagra on it!
Should straighten it right out!0 -
is the center of the bend near the support point ? if so would indicate that the bend was cause from being transported and stored horizontally. 0 -
is the center of the bend near the support point ? if so would indicate that the bend was cause from being transported and stored horizontally. 0 -
How long has it been stored in that position, and how many tail holds does it have? Does he know if the yarder has ever lost a tail hold and shocked the sky line? Also, what type of sky car is he running? 0 -
If horizontal storage for transport or yard storage has caused such a droop...
Wouldn't you just take it off it's base and rotate it 180? and reinstall it...
If you did this at the end of every season would that eliminate any propensity to droop in any specific direction...
I'm am not an engineer but that would seem to be the simplest way to avoid the issue...
If you reversed the horizontal stressing by flipping it upside down how long would it take to return to true - would adding some weight or stress though cable down force cause it to straighten out...
If the area in question if fatigued or stressed near or at the failure point would a Rockwell hardness test indicate some loss of springiness or elasticity???
Surely this is not the only functional intact unit of this brand and model in north America - there must be pictures only of one or more being used - for comparison purposes.
Does that make any sense or have my pain meds turned my brain into pudding
Mike0 -
The load pushes down and with a bend there is a very real potential for a catostrophic failure. That said, I doubt anything would ever happen but if there was a foot of bend would it be unsafe? The question is how much bend is too much. .10 inches? 12? 8?
I don?t think I ever went in the engineering building at school. So fwiw I could imagine a way to get some of that bend out... it would involve a bulldozer and a log pile....0 -
Not an engineer, but I liked this thread so much that I had to throw my $0.02 in.
If it were my call, I would just use the darn thing. From what I understand the stress will be "pulling the tube straight" when in use.
Whether or not the engineers designed the bend into the tube, I think it is an advantage if anything. (If in fact the load will be "pulling the tube straight.")
I do think that finding out whether or not the tube is made with some bend in it on purpose would help in deciding how to store it in the future like somebody else mentioned the idea of rotating it periodically.0 -
I guess if money were no object an x-ray inspection or magnetic particle inspection wouldn't hurt. 0 -
quote:Originally posted by Flying Clay Disk
The curvature that some of you are referring to is called "camber". Camber is intentionally introduced to some structural members to deal with mid-span loads when the structural member is in a horizontal position. Camber is not used in vertical members (or very rarely).
Theoretically, if all the guy lines are anchored properly, there shouldn't be any significant horizontal load on the boom, only vertical. (Well, other than the shiv at the very top, above the guy-line anchor points).
That said, here's why the safety 'drones' don't like it...as the vertical load increases there is nothing to counteract the bend in the mast from increasing, and the vertical load is not directly over the base. The load gets there eventually, but it creates a horizontal or rotational force on the base getting there. So there's a bending moment mid-span on the tower with nothing to counteract it.
Under extreme (but not maximum) loads the mast would fail in the center and collapse due to the down force not being equally applied around the circumference of the circular mast structure. In other words, one side of the mast would be in compression and the other side would be in tension (or less compression). It doesn't matter what direction the timber is coming from, the loads would be the same, all the load should be vertical only (this is why yarders work at all to begin with), otherwise the yarder itself would just overturn.
Cylindrical structural members fail in very strange ways when vertical loads are applied to them with any contributing rotational force.
Because we don't know the exact characteristics of the boom in question, or how it transfers the load to the ground (exactly), it's not possible to say whether the bend will be a problem or not. The one thing I can tell you for certain is, there is no place for camber in a vertical member for that type of application.
This ^^^^^^^^^^^
His last sentence says it all. I have stood up many "bent" 110 ft
stadium light poles. When planted into the ground, we made sure
they were straight. A temporary chamber while shipping on trucks
laying down was always checked out before standing them into the holes.
I just checked my old pdf on the poles we used. While we had prestressed concrete poles, it will give you an idea about bends.
Allowed 1/4" per 10 feet of length!!!
Here is some "light" reading if you dare....
http://www.coldrocks.com/reference/rus20160517/UEP_Bulletin_1724E-206.pdf0 -
quote:Originally posted by Flying Clay Disk
The curvature that some of you are referring to is called "camber". Camber is intentionally introduced to some structural members to deal with mid-span loads when the structural member is in a horizontal position. Camber is not used in vertical members (or very rarely).
Theoretically, if all the guy lines are anchored properly, there shouldn't be any significant horizontal load on the boom, only vertical. (Well, other than the shiv at the very top, above the guy-line anchor points).
That said, here's why the safety 'drones' don't like it...as the vertical load increases there is nothing to counteract the bend in the mast from increasing, and the vertical load is not directly over the base. The load gets there eventually, but it creates a horizontal or rotational force on the base getting there. So there's a bending moment mid-span on the tower with nothing to counteract it.
Under extreme (but not maximum) loads the mast would fail in the center and collapse due to the down force not being equally applied around the circumference of the circular mast structure. In other words, one side of the mast would be in compression and the other side would be in tension (or less compression). It doesn't matter what direction the timber is coming from, the loads would be the same, all the load should be vertical only (this is why yarders work at all to begin with), otherwise the yarder itself would just overturn.
Cylindrical structural members fail in very strange ways when vertical loads are applied to them with any contributing rotational force.
Because we don't know the exact characteristics of the boom in question, or how it transfers the load to the ground (exactly), it's not possible to say whether the bend will be a problem or not. The one thing I can tell you for certain is, there is no place for camber in a vertical member for that type of application.
A reasonable analysis.
The fact that the bow is only 8" in a 24" diameter piece, however mitigates much of the problem.
While the load is not concentric with the center of the tube, it is well within the confines of the tube and will therefore not result in any tensile load on the convex side of the tube. The compressive load on the concave side will be greater than on the convex side.
Now, if the sheaves are on the convex side of the tube the applied load will be moved back towards the center of the tube, resulting in a more concentric load.
It is entirely possible that the boom was designed this way to better center the vertical load.
It is also entirely possible that 30+ years of horizontal loading while traveling less than perfect logging trails resulted in some grain re-alignment that allowed for the bow.
In either case, I personally do not see an issue, provided there is not evidence of damage on the concave side.
The failure mode of this tube will in all likelihood be the buckling of the concave surface, not at tensile failure of the convex surface.
I wouldn't stand within a 65' radius while the rig is under load, but would assume that is a fairly standard practice anyway.0
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