Bending moment due to wind on threaded tubular

[oneeyedwitchdoctor]

I am working on a problem that invloves a threaded tubular that is situated vertically with the lower end being screwed into a base part, the upper end of the tubing is blanked off. I am trying to analyse the effect the bending moment caused by the wind will have on the integrity of the assembly.
The tubing is pressurised, so this will induce a tensile force on the threaded joint, which is easily calculated, however I am unsure as to who to relate the bending stress caused by wind velocity to the tensile stress that the joint is already subjected to.
I seen some literature regarding bending loads on threaded fasteners and it merely stated that the bending stress should be added to the tensile stress, but would like some other opinions as I am unsure as to whether this is a simplification that applies to small threaded fasteners speciffically.

Thanks in advance

 

[hydtools]

The stress caused by bending is algebraically added to the tensile stress in the joint.

The stress on the windward side is tensile and is additive to the joint stress. The stress on the lee side is compressive and subtractive from the joint stress.

The weight of the tubing may also need to be considered, if significant. It will produce a compressive stress.

All stesses are supperposed to get the final result.

Ted

 

[oneeyedwitchdoctor]

Sorry I have should have said in the original post, but what is confusing me is that the weak point of the threaded connection is the shear across the teeth. Hence it seems oversimplisitc to algebracally add the stress induced from the bending moment. Does this change what has been said in the previous reply

 

[dvd]

This connection sounds ill-advised. The threaded connection should be used to seal the tubing. I recommend developing a support which resists the wind-moment independently from the sealing threads.

 

[oneeyedwitchdoctor]

the tubing thread is not a sealing thread, there is an o-ring on the pin situated in such a way that any radial loading should not affect the integrity of the seal. I am concerned with the mechanical integrity of the connecting thread. I have calculated the maximum permissable force based on the shear rating of the teeth, and the bearing rating on the teeth, and found that the shear rating is the critical one. Given that I know the working load on the joint and also the worst case bedning moment, I want to know how to relate both of these stresses together such that I can verify the integrity of the threaded connection

 

[rb1957]

if you're screwing the tube into a base, won't the interface between the tube and the base react the moment (at least on the compression side).

the shear rating of the thread considers a complete circumference, no? i'd consider a segment of the thread (maybe start with 30 deg) ... i know the axail load applied (1/12th of the total), i know the moment reaction (sum the bending stresses over the arc), and i know the rating (1/12). consider larger and smaller segments. if you overload for a small segment, then is it reasonable to say that plasticiity will redistribute this peak load over a wider (acceptable) segment ?