Computing the rebars on ACP Piles (reduction and amplification factors) 1

[pelelo]

Engineers,

The way how i have seen in the past that senior engineers calculate the rebars for Auger Cast Piles is by selecting a section (e.g 10 #8 bars, and select f'c and f'y). Based on that, LPILE (lateral pile analysis software), generates the interaction diagram for such section.

In the interaction diagram, using the downward pile capacity, they are able to select the ultimate moment (Mult). Then, they factorize Mult by a a factor (0.9) to get the M fact.

This Mfact is then compared to the moment coming from the soils and specific lateral force (Mmax). At the same time, Mmax is amplified by a factor of 1.75, which will result in an amplified moment (Mampl).

Finally, there is a comparison between Mfact and Mmax, and if Mfact is > Mmax, then the section is ok.

My question is, does anyone knows the specific codes that provide such reduction and amplification factors? (0.9 and 1.75)?

Please advise.

 

[r13]

Mult is the nominal moment capacity of the pile, it is adjusted downward by the strength reduction factor, ø = 0.9, to the permissible design strength, which is not to be exceeded by the calculated/actual factored moment, Mu. Mu is derived from the factored lateral earth pressure. The code treats the lateral earth pressure as live load, depends on the code you are using, in the US, the factor is 1.6 according to ACI. The 1.75 factor can be required by your code, or it could be a conservative practice by your company.

 

[pelelo]

Thanks a lot r13.

Do you by chance know any good reference that provide examples of this calculations?

 

[r13]

I don't have design example readily available. However, I found an article, and the reference code (ACI336.3R), that can help you to better understand the aspects of the design. You may also find that AASHTO has many useful information on the design of auger-cast-piles.
Link, Link