Chain Catenary

[someengineer]

Hello,

Does anyone have any experience with chain catenaries in water and how it affects a reaction loads and deflections?

For example,
Say you have an anchor in the bottom of a lake. There is a heavy chain tied to it, which is tied to a dock (the other end of the dock is pinned). If there is an applied lateral load onto the dock, how much load is absorbed in the chain catenary and how much will be transferred to the anchor?

Will the anchor only take load if the chain is taught? How much will the catenary affect the lateral movement of the dock?

If anyone has any insight into this it would be appreciated.

Thanks!

 

[youngstructural]

The chain will take load only when taught, but that doesn't mean the chain will be straight... The water will slow the movement of the chain, but will not fundamentally change the design reactions. There are also formulae available for the friction and mechanical drag on a chain being pulled through water. Check a Naval Architecture text...

Anyway, about the shape of the chain: In fact the chain will NOT be straight, but it will still transfer your load. A very senior and respected Kiwi Structural Engineer friend of mine (Arthur Tyndall) is a suspension structure specialist. If you need anything in particular about this situation, please post again and I'll give him a call.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[dgkhan]

When chain is hanged from two points and allowed to fall under self weight than it follows the shape of catenary curve.
In your case increasing water pressure is also effecting the shape of chain besides it will act more like axial column and less of beam.
Another thought is the tension in chain will determine the stiffness in chain and portion of load taken depends upon relative stiffness.

 

[someengineer]

youngstructural

Thank you very much for your comment, it was helpful. I will be investigating the design of this over the next week. I appreciate you offer to talk to your collegue. If i run into any problems I may have to take you up on it!

Thanks again.

 

[civilperson]

If any part of the chain is on the bottom, then ALL the load on the anchor is Horizontal. This is why chain is used near the anchor.
The angle of the chain at the attachment to the dock is exactly in the line of force effecting the dock, with both a horizontal and a vertical component.

 

[kelowna]

This is a catenary problem, as it has been poited out. The fact that it is under water only changes the weight of the chain, from which you have to substract the upward pressure from the water (Archimedes). Otherwise, no difference.

I would suggest you get familiar with the catenary formulation and most of your questions will become clearer.

 

[someengineer]

Thanks civilperson and kelowna for your help.

I will take all your advice into consideration.

 

[csd72]

Equlibrium still applies i.e. sum of reactions equals sum of forces.

For a roughly horizontal chain with a horizontal force applied to it:

Horizontal component of end reaction=horizontal force applied,
Vertical component of end reaction=half the weight of the chain.

This is why chains tend to straighten up under load - in order to balance this equilibrium.