how to calc transp moment of I for reinf conc filled-steel pipe pile

[geotechM]

I need to know how to calculate the transposed moment of intertia for a steel pipe pile, filled with reinforced concrete that will be laterally loaded (will have flexure). I have tried n=Es/Ec, then n*As=(pi/4)*(Dtr^2 - D^2) to get the Dtr (transposed diam). then using Dtr to calculate Itr. Then used the E for concrete to input into L-pile.

Someone else suggested 2007 AASHTO 6.9.5.1, but this is for columns with out flexure. 6.12.2.3 doesn't give formulas for I.

Am I missing something here? Any help would be appreciated.

 

[BAretired]

I(transposed) = I(pipe) + I(concrete)*Ec/Es

BA

 

[geotechM]

That gives me less that either? should it be times Es/Ec?

 

[PMR06]

You need to multiply I by n. In essence, the transformed section is an ellipse, stretched in the axis multiplied by n. The transformed section is not a circle with diameter affected by n.

 

[paddingtongreen]

"That gives me less that either? should it be times Es/Ec?"

BAretired's formula transforms the concrete to steel. I don't know why you think it gives you less than either, it is I(pipe) plus I(concrete transformed to steel equivalent).

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[BAretired]

I gave you the transformed area in terms of steel. If you want the transformed area in terms of concrete, it would be:

I(transformed) = I(pipe)*Es/Ec + I(concrete)

BA

 

[PMR06]

Whether transforming the conc piece to steel or vice-versa, you have to obey the following:

E(conc)I(conc) = E(steel)I(steel)

You "transform" the piece by dividing one of the E's to the other side.

 

[csd72]

Gents, what about allowance for cracking of the concrete in the tension zone?

doesnt anyone google anymore?

http://www.ctsee.org.tw/出版品/200310/ee0401-05.pdf

 

[BAretired]

Here are some additional links:

http://www.google.co.uk/search?q=co...=en&sourceid=gd&rlz=1Q1IRFA_enCA356CA356&aq=t

BA

 

[geotechM]

maybe I should have mentioned it will not actually perform as a column, but one of many independant piles strung together with horizontal wale beams. For a fender system design to resist forces from a vessel. So no axial load (besides self weight).

I think I(transformed) = I(pipe)*Es/Ec + I(concrete) is what I want because a program that caclulates this internally is giving me something very similar. Thanks for all of your help.

 

[sundale]

How is strain compatibility (no slip) shear transfer justified between the smooth inner wall of the steel pipe and poured concrete that has perhaps shrunk?

 

[BAretired]

If there is no axial load, then forget about the contribution of the concrete. Use the properties of the steel only.

BA

 

[csd72]

The reference I gave should still be valid with no axial load.

 

[Lion06]

sundale-

There doesn't need to be strain compatibility if you're just algebraicly adding the MOI's. You just need to make sure they deflect together (so they share load according to their relative stiffnesses). This behavior implies that there is slip between the surfaces. It's all a moot point though, because, as csd points out, the concrete will crack.

 

[paddingtongreen]

The only way I can see is to consider the pipe and the reinforced concrete to act separately but deflect the same amount. You can then add their stiffness's and, if necessary, dummy up an equivalent member for your structural analysis program. The presence of the concrete does improve resistance to buckling.

If it was me though, I would go with BA's suggestion and consider only the pipe and regard the concrete as gravy.

Michael.
Timing has a lot to do with the outcome of a rain dance.