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# Shoring - Section Moment of Inertia

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## Shoring - Section Moment of Inertia

(OP)
Could somebody help me how to calculate the moment of inertia for a composite section of steel pipe pile and shotcrete.  I need to have the EI for the wall section as seen in the attached file.

For simplicity I have assumed that shotcrete thickness is one half of the pipe diameter.

I have obtained various values and wanted to check if something is going wrong.

http://files.engineering.com/getfile.aspx?folder=7cf7bffd-4652-479e-bc40-40ddf7ea196e&file=Wall_Section.xls

### RE: Shoring - Section Moment of Inertia

It's similar to how you calculate the transformed moment of inertia for reinforced concrete.  Convert everything to the same material using the modular ratio (E1/E2).  Then calculate the moment of inertia as you do for any oddly shaped object.  Calculate the moment of inertia for each shape and the use the parallel axis theorem to combine...

### RE: Shoring - Section Moment of Inertia

(OP)
I presume moment of inertia should be against the new neutral axis of the unifies section.

How can I convert strll pipe pile section to equivalent concrete. If E/E' = 8 then is the equal wall thickness 8 times.

### RE: Shoring - Section Moment of Inertia

This same question has recently been asked in another forum.  This is not a composite section and a composite moment of inertia means nothing for this application.

You have two separate materials not acting in a composite manner.  Treat the system as a simply supported one-way concrete slab without reinforcement (your bending capacity will be very low), hopefully transferring shear to the pipes which will then be subject to bending from the slab reactions.

### RE: Shoring - Section Moment of Inertia

I agree with Ron.  The connection between the shotcrete and pipe piles probably will not be stiff enough to exhibit composite action.  The pipes will bend and the shotcrete will go along for the ride.

### RE: Shoring - Section Moment of Inertia

I totally agree with Ron, and PEinc too.

If you want any composite action, the shotcrete wall would have to be connected with horizontal shear studs welded to the pipe, extending into the wall, where most of the wall was at the front face of the pipe.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

### RE: Shoring - Section Moment of Inertia

(OP)
msquared48: do you mean the shotcrete be on the active saide of the pipe cross section.

### RE: Shoring - Section Moment of Inertia

In do't know what you mean by active here.

I mean on the compression side of the pile, the side most removed from the soil load.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

### RE: Shoring - Section Moment of Inertia

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