Metal pipe stiffness.

[Bulldogio]

Could anyone inform me how to calculate the pipe bending stiffness and pipe hoop stiffness for metallic pipes. I have found formula's for the above but the reference material I have suggests that these formula's are for non-metallic pipes. Please help.

 

[BigInch]

I don't know what exact formulas you have, and assuming you are not talking about a reinforced concrete pipe for example, and if you are talking about stiffness in the classical beam bending sense, just substitute the values you have for Young's modulus for your non-metal for the metallic value.

Actual collapse loads may depend on out of roundness or other mechanical factors for which different materials may have different tolerance values.

Can you furnish more information as to what formulas you have and what exactly it is that you are actually trying to accomplish with your formulas?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Cockroach]

The analysis could be completed by Beam Theory, using a circular cross section of known outer and inner diameter. Obviously you also have an understanding of the length and boundry conditions, i.e. loads and supports.

I would complete the analysis in general terms, place a theoretical distributed load across the span and do the Bending Moment Diagram. Given the strength of material, you can easily derive an expression for shear, bending moment and deflection based on geometry of the pipe and the theoretical load.

Try finding a textbook from first year engineering static courses. Typically such a problem is worked out in detail from first principles as an example.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[stanier]

AS 2566.1 Standard for Buried Flexible Pipelines contains steel as well as non metallics. The equations are the same for both. The only information you need is OD, ID, modulus to work out the stiffness for analysis of a soil/pipe structure.
Go to

http://www.standards.org.au

and invest.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[Bulldogio]

BigInch, Cockroach and Stanier, thanks for you tips. BigInch the formulae I found was:-
Pipe bending stiffness = EI/(0.139r^3)
Where:-
E = pipe material modulus of elasticity
I = pipe wall moment of inertia per unit length.

I found this in reference material for thermoplastic piping. Nowhere in the reference material is pressure mentioned. Would applied pressure affect the pipe bending stiffness significantly? Obviously there would be some effect but at this time I am unaware of how much.

 

[desertfox]

Hi Bulldogio

The "I" value for a pipe assumed to be circular would be


"I"= Pi* (Do^4-Di^4)/(64)


where Do=outer diameter of pipe

Di= inner diameter of pipe


hope this helps

regards

desertfox

 

[desertfox]

Hi Bulldogio

I think the bending would come from the weight of the pipework not the internal pressure.
If one asssumes that a straight pipe subject to equal internal pressure is supported on simple supports all I can see is that the forces due to pressure would cancel out and your left with the weight of the pipe to cause sagging between the supports or am I missing something?


regards

desertfox

 

[BigInch]

Careful, he may be talking about bending transverse to the pipe axis and rigidity in the X-sectional direction (like for arching resistance for soil or vehicle loads from above)

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[desertfox]

Hi BigInch

True but we need to establish that.

Regards
desertfox

 

[Bulldogio]

Thanks, Desertfox & BigInch.
Every bit of information that comes through makes the muddy water clearer. The problem that I am trying to solve is transverse to the pipes longitudinal axis. However the X setion of the object for which I am trying to solve is more like a c section. A pipe with strengthening flanges if you will.

 

[rconner]

I think I have heard the structure it appears you are trying to describe referred as a "ring girder". Such structures, at least for steel pipe, have been discussed in AWWA Manual M11 and I suspect other references for many years (you could do a search with these key words).
I believe you are also correct in your hunch that flexible pipes can become in effect stiffer when they are pressurized, and maybe even able to carry more ring or other load in this condition; however, I believe this strengthening effect is most often ignored in many basic designs (after all, pipelines must initially in many cases carry loads before they are pressurized, and also commonly become de-pressurized at times thereafter.)

 

[BigInch]

Deflection in the structural bending sense is M/EI, as in deflection of a uniformly loaded beam would be w * L^3/384/E/I. Where E = Young's Modulus and I is moment of inertia of the cross section, the w * L^3 is uniform load x length^3. So a measure of the "stiffness" or resistance to a bending moment M deflection, would be = L^3/E/I

If you just had a point load at the top of an arch, M = P * e/2, E according to your material and I according to your shape "U" in a cross section a-a, you'd have something like this,

bending stress would be M * c/I and deflection would be M/EI.

The other bottom half of the pipe would tend to reduce M and the deflection by allowing Fr and Fl to be greater than zero, so this Moment calc. is a bit conservative.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com