Moment of Inertia - Corrugated Metal Pipe (CMP)
Moment of Inertia - Corrugated Metal Pipe (CMP)
(OP)
I have a 16 gauge 24 in. diameter corrugated metal pipe with 2-2/3’’ x ½’’ corrugation. For my analysis I'm looking for the moment of inertia in units of inches^4. The tables that I have found give me 1.892 x10^-3 (in.^4/in) for the CMP dimensions. This seems like a very low value and I'm not exactly sure what the per inch is for in.^4/in. I've hear it called the moment of inertia per unit length of cross section of the pipe wall but I'm not sure what dimension they're talking about. Everything I have tried gives me very low values for I. Is the I for a CMP this size usually really low (like 0.454 in^4)?






RE: Moment of Inertia - Corrugated Metal Pipe (CMP)
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment of Inertia - Corrugated Metal Pipe (CMP)
RE: Moment of Inertia - Corrugated Metal Pipe (CMP)
What application is this?
RE: Moment of Inertia - Corrugated Metal Pipe (CMP)
If you are interested in the bending stiffness of the whole pipe about a transverse axis you can't just use the geometric properties because in this direction the buckles greatly reduce the stiffness. I don't know how it is done, my guess would be that it is based on testing rather than a theoretical approach.
Where did the 0.454 number come from?
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: Moment of Inertia - Corrugated Metal Pipe (CMP)
RE: Moment of Inertia - Corrugated Metal Pipe (CMP)
1) It will be low as discussed above.
2) With sand in the interstitial space, it won't act compositely with the pile.
If you wanted to estimate the E x Ix of the CMP, I would recommend this procedure:
1) Calculate an Ix based on the sheet thickness and the average diameter of the CMP.
2) Modify your E value to account for the "accordion" effect that the the corrugations would have on axial stiffness.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment of Inertia - Corrugated Metal Pipe (CMP)
Also consider what it is you are checking. If you want maximum deflections and bending moments in the pile then you should use lower bound pile stiffness, so ignore the pipe and reduce the soil stiffness (or treat it as unsupported over the top 20 feet). If you want maximum shear forces at the top of the pile then you should use an upper bound stiffness, so ignore the effect of the loose sand. If the upper or lower bound analyses produce unacceptable results you will have to look at it closer.
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/