Vertical Compression Strength of Different Hollow Rods

[Rev. Cheeseman]

Which one is stronger in vertical compression? A cylindrical hollow rod or a hollow rod, that is made from the same material as the cylindrical hollow rod, with twisted construction around the middle part?

If a hollow rod has less cross sectional area than an another hollow rod but the one with less cross sectional area has more mass and heavier, which one has the higher compressive strength?

 

[DaveC426913]

what do you think? What research have you done to find an answer?

 

[Rev. Cheeseman]

I think the cylindrical hollow rod is stronger and the hollow rod with less cross sectional area but with higher weight is stronger.

 

[Baluncore]

A cylindrical hollow rod or a hollow rod, that is made from the same material as the cylindrical hollow rod, with twisted construction around the middle part?

What is meant by "twisted construction".

If a hollow rod has less cross sectional area than an another hollow rod but the one with less cross sectional area has more mass and heavier, which one has the higher compressive strength?

Mass, or weight, does not determine relative compressive strength between different materials. Consider titanium and lead.

A solid section is more likely to buckle under compression, than is a hollow section of the same sectional area and material. For short rods it should not matter.
https://en.wikipedia.org/wiki/Second_moment_of_area#Annulus_centered_at_origin

 

[jrmichler]

I think the cylindrical hollow rod is stronger and the hollow rod with less cross sectional area but with higher weight is stronger.

Thinking has nothing to do with this, but an engineering calculation does. The vertical compression strength of a column is dependent on the compressive yield strength of the material, the modulus of elasticity, the area moment of inertia, the slenderness ratio, and the fixity of each end. Search Euler column to learn how these factors interrelate, and how to do the calculations. The Wikipedia hit has a good summary of Euler columns, and mentions short columns. It is a good place to start.

 

[Rev. Cheeseman]

What is meant by "twisted construction".


Mass, or weight, does not determine relative compressive strength between different materials. Consider titanium and lead.

A solid section is more likely to buckle under compression, than is a hollow section of the same sectional area and material. For short rods it should not matter.
https://en.wikipedia.org/wiki/Second_moment_of_area#Annulus_centered_at_origin

Twisted like this https://images.app.goo.gl/iur2RnMA3Njmj2x27 but only around the middle part.

The hollow rod will be stronger if the solid rod and hollow rod have the same mass, right?

 

[Baluncore]

Twisted like this https://images.app.goo.gl/iur2RnMA3Njmj2x27 but only around the middle part.

So, we are not considering a simple rod or a tube, but a high-rise building constructed with an internal structural framework.

 

[Rev. Cheeseman]

So, we are not considering a simple rod or a tube, but a high-rise building constructed with an internal structural framework.

A hollow rod but with a twisted construction around the middle part, like a humerus.

 

[Bystander]

A hollow rod but with a twisted construction around the middle part, like a humerus.

Such as, "

https://sportingclassicsdaily.com/damascus-barreled-shotguns-are-safe-to-shoot/

?"

 

[A.T.]

A hollow rod but with a twisted construction around the middle part, like a humerus.

As explained to you in the previous threads, bones are loaded mostly by the muscles and thus optimized for that distributed load pattern, not for pure compression.

 

[Baluncore]

A hollow rod but with a twisted construction around the middle part, like a humerus.

To survive without damage, bones must flex and twist during normal activities. Strength under axial compression is not everything, indeed it is a liability.

Considering axial torque, given a hollow tube, a solid rod, and a ribbon, all with the same sectional areas, the most rigid will be the "torque tube", followed by the solid round rod, "sway bar", while the most flexible will be the ribbon.

By twisting the ribbon through half of a turn along its length, it will have maximum flexibility in all directions. There is a compromise where multiple parallel ribbons run through the twisting structure, making a flexible hybrid of the tube, from two or three ribbons.

A slight bow along the length of the structure will, when subjected to high axial loads, allow flexing, reducing shock damage to the end ball-joints.

I think you will find that the humerus has evolved to employ all those features, increasing its compliance with, rather than opposition to, the live forces normally encountered.

 

[Rev. Cheeseman]

Such as, "

https://sportingclassicsdaily.com/damascus-barreled-shotguns-are-safe-to-shoot/

?"

Sorry, no.

 

[Rev. Cheeseman]

As explained to you in the previous threads, bones are loaded mostly by the muscles and thus optimized for that distributed load pattern, not for pure compression.

Imagine if we hit something with a hollow rod with a twisted construction around its middle part like a humerus, by ramming it into something hard. Just to see how much impact force along its longitudinal or axial direction it can take

 

[Rev. Cheeseman]

To survive without damage, bones must flex and twist during normal activities. Strength under axial compression is not everything, indeed it is a liability.

Considering axial torque, given a hollow tube, a solid rod, and a ribbon, all with the same sectional areas, the most rigid will be the "torque tube", followed by the solid round rod, "sway bar", while the most flexible will be the ribbon.

By twisting the ribbon through half of a turn along its length, it will have maximum flexibility in all directions. There is a compromise where multiple parallel ribbons run through the twisting structure, making a flexible hybrid of the tube, from two or three ribbons.

A slight bow along the length of the structure will, when subjected to high axial loads, allow flexing, reducing shock damage to the end ball-joints.

I think you will find that the humerus has evolved to employ all those features, increasing its compliance with, rather than opposition to, the live forces normally encountered.

So, the normal hollow rod is stronger in axial compression than a hollow rod with twisted construction around its middle part like a humerus? Assuming if we hit something hard by ramming the hollow rod with twisted construction at its middle part

 

[Baluncore]

Assuming if we hit something hard by ramming the hollow rod with twisted construction at its middle part

It happens quite often, so hopefully, the mode of failure will be stable, one which can heal without needing to be set, or needing invasive surgery.
https://en.wikipedia.org/wiki/Greenstick_fracture

 

[Rev. Cheeseman]

It happens quite often, so hopefully, the mode of failure will be stable, one which can heal without needing to be set, or needing invasive surgery.
https://en.wikipedia.org/wiki/Greenstick_fracture

Between a humerus with no twisted construction and a humerus with twisted construction around its midpart, the humerus with no twisted construction will be stronger in axial compression. Is that correct

 

[Baluncore]

Between a humerus with no twisted construction and a humerus with twisted construction around its midpart, the humerus with no twisted construction will be stronger in axial compression. Is that correct

All other things being equal, the middle of the humerus will be stronger without the twist.

The joints will be more susceptible to damage, and the ends will be more likely to break cleanly off. Surgical intervention will be required for any break of the humerus, because, without the twist, it has no flexibility at any point. "Safe" spiral fractures will no longer occur in children, as they will fracture cleanly, more will sustain compound fractures, with infections to the bone, requiring emergency amputation before death.

 

[Rev. Cheeseman]

All other things being equal, the middle of the humerus will be stronger without the twist.

The joints will be more susceptible to damage, and the ends will be more likely to break cleanly off. Surgical intervention will be required for any break of the humerus, because, without the twist, it has no flexibility at any point. "Safe" spiral fractures will no longer occur in children, as they will fracture cleanly, more will sustain compound fractures, with infections to the bone, requiring emergency amputation before death.

Thank you.

 

[Rev. Cheeseman]

Last question. A long bone whether it is a femur, tibia, humerus, etc. with less cross sectional area but have more mineral content will be stronger than a long bone with more cross sectional area but less mineral content. Is this correct

 

[Rev. Cheeseman]

Thoughts?

 

[Baluncore]

I paraphrase:
"A long bone whether it is a femur, tibia, humerus, etc."
"with less cross-sectional area, but more mineral content"
"will be stronger than a long bone"
"with more cross-sectional area, but less mineral content."
"Correct?"

Thoughts?

Define "stronger", in what dimension, under what circumstances ?

Ignoring the material, a greater sectional area, will be more rigid and less flexible.

Higher mineral content will make it heavier. It will also be more brittle, so will tend to shatter, causing compound fractures. It will not be so well-matched to the joints, so joint damage and torn tendons and ligaments are more likely.

 

[Rev. Cheeseman]

I paraphrase:
"A long bone whether it is a femur, tibia, humerus, etc."
"with less cross-sectional area, but more mineral content"
"will be stronger than a long bone"
"with more cross-sectional area, but less mineral content."
"Correct?"

Define "stronger", in what dimension, under what circumstances ?

Ignoring the material, a greater sectional area, will be more rigid and less flexible.

Higher mineral content will make it heavier. It will also be more brittle, so will tend to shatter, causing compound fractures. It will not be so well-matched to the joints, so joint damage and torn tendons and ligaments are more likely.

This is in the context of pure axial compression. Isn't a long bone such as a femur with thinner cortical thicknesses and smaller outer diameter (smaller cross-sectional area) but with higher mineral content (therefore heavier weight) will be stronger than a femur with less mineral content despite having thicker cortical thicknesses and larger outer diameter (larger cross-sectional area)?

Usually higher mineral content equal to stronger bones.

 

[Baluncore]

Usually higher mineral content equal to stronger bones.

That may be important in a violent Neanderthal environment, where physical fights determine outcomes, but having an intelligent brain, and using it to avoid conflict, is a better investment in the community. Training a few young males as soldiers, for the defence of the community, will help protect the women and children, who share the same genetics, but are most unlikely to have high mineral content in their bones.

Coming up with a statement, that considers only one dimension, is a pointless exercise. Every bone in the body, has been optimised, by long experience through many generations, to benefit the genes across every dimension of the varied environment.

You can conclude and believe what you want, but your failure to accept the complexity of the whole, makes your simplistic conclusion, without caveats, inapplicable to the real world.

 

[Rev. Cheeseman]

That may be important in a violent Neanderthal environment, where physical fights determine outcomes, but having an intelligent brain, and using it to avoid conflict, is a better investment in the community. Training a few young males as soldiers, for the defence of the community, will help protect the women and children, who share the same genetics, but are most unlikely to have high mineral content in their bones.

Coming up with a statement, that considers only one dimension, is a pointless exercise. Every bone in the body, has been optimised, by long experience through many generations, to benefit the genes across every dimension of the varied environment.

You can conclude and believe what you want, but your failure to accept the complexity of the whole, makes your simplistic conclusion, without caveats, inapplicable to the real world.

Ok so therefore the lighter less dense and more porous femur with thicker cortical thickness and larger outer diameter is stronger in pure axial compression than the heavier denser compact femur with thinner cortical thickness and smaller outer diameter

What do you think @russ_watters

 

[jrmichler]

You can conclude and believe what you want, but your failure to accept the complexity of the whole, makes your simplistic conclusion, without caveats, inapplicable to the real world.

Because @Baluncore so nicely sums up this thread, it is being closed.

The vertical compression strength of a column is dependent on the compressive yield strength of the material, the modulus of elasticity, the area moment of inertia, the slenderness ratio, and the fixity of each end. Search Euler column to learn how these factors interrelate, and how to do the calculations.

The quote above lists five factors that affect the compressive strength of a column. All five must be considered, and leaving any one of them out makes comparisons invalid.

Thread closed.