Lateral deflection calcs for Auger Cast Piles 3

[jfleischman]

I am tasked with the structural portion of an auger cast secant wall retaining structure. I have received all of the design moments, anchor forces, shears, etc. from the geotech. The controlling criteria, however, seems to be the deflection. Because of buried utilities in the vicinity, the Owner has specified a rather stringent maximum deflection for the wall.

At present, the pile design is expected to be 18" diameter ACP (at the client's request). For moment capacity, it appears as though an HP12 will be adequate in lieu of a reinforcing cage, but the I for this section alone is inadequate for the deflection calcs.

Are there any published analysis methods for determining the moment of inertia of a round ACP with an embedded H-pile? I "know" the composite section will be sufficient, but I need to be able to prove it on paper. A Google search has thus far been fruitless.

TIA

 

[dcarr82775]

To be composite you must have some kind of shear connectors, you can not just assume it will act compositely. After that just calculate the area of concrete you have in compression beyond the steel flange and design it as a composite beam.

In my experience the contractor always prefers a larger shaft with a larger steel beam to a smaller shaft and a smaller steel beam with studs is cost is the only factor.

 

[jfleischman]

Thanks. I know I also need to provide ties or spirals in accordance with ACI 10.13.7. I think that by the time I add studs and longitudinal reinforcing, the contractor may reconsider a larger diameter.

 

[molerat2210]

I usually use L-pile or Com624 for calculation deflection of concrete shaft with embedded H-pile. The I of H-piles is published by the pile makers. We often covert the I of the H-pile into an equivalent rebar cage so we can use the software.

 

[FixedEarth]

You can limit your deflection at the ground surface by one of the following (most beneficial first):

Increasing pier diameter
Use HP beam with largest Sx that can still fit in the shaft
Increase f'c of the mix
Remove and replace upper 5B soils with slurry (this increases lateral subgrade reaction value).

If you increase the pier diameter and discount the I of the HP beam you should be o.k. with deflection. Ultimately your design is based on Mu and not induced Moment in the pier. Alternatively, you can get the equations form Foundation Design by Cernica and set up a spreadsheet so that each row has the composite E and I values.

 

[jfleischman]

Alas, I have no control over the soils, which are, unfortunately, lousy. Or, as my geotech calls it, "baby poop". I already have as big an H-Pile as I can get in there, and I have access to L-Pile (which prior to now I didn't know would do an encased H-Pile, so thanks for that tidbit.)

Aside from the specific project requirements, however, I was mostly wondering if there is a generic, non-software analysis method for determining the properties of a circular cracked section with either rebar or encased steel section. I mean, they wrote the software based on an existing algorithm, right?

 

[PEinc]

http://www.dot.state.fl.us/structures/proglib.shtm

Look around in this Florida DOT site for a free program.

http://www.PeirceEngineering.com