Question about laterally loaded piles 2

[pelelo]

Hello Engineers,

I have been working on secant pile drilled shaft project and now i'm at the lateral analysis design stage, using LPILE.

As you may know, LPILE allows you to enter a section and compare its maximun bending moment with the maximum moment you get from your soil profile.

In order to compare both values, I was told I need to amplify my maximum moment I get from my soil profile by a factor of 1.75. I am not sure if this factor varies between project (e.g Secant pile wall, or deep foundation). I just would like to know where can i get more information about this amplification factor.

If anyone knows, please let me know.

Thanks

 

[GeoPaveTraffic]

Who told you to use the 1.75 factor? Ask them.

I'm only guessing hear, but I expect that the factor is a structural design load factor.

 

[dcarr82775]

For concrete piers Lpile calculates ultimate bending strengths. You MUST factor up the soil loads so they are ultimate (LRFD) level loads instead of service (ASD) loads if you are going to use Lpile to check the bending capacity of the shaft.

ACI 318 has a load factor of 1.6 for soil and a phi factor of 0.9 on bending. Combining the two gives a 1.77 factor which is close to the 1.75 you were told to use. That is my guess as to where the 1.75 comes from, but ask the person who told you to use it, hopefully they know

 

[pelelo]

dcarr82775, GeoPaveTraffic

That 1.75 came from some chapter in the LFRD code.

It makes more sense to me to use ACI 318, by amplifying the maximum bending moment by 1.6 and comparing this one to the max moment I get from the pile section using a reduction factor phi (0.9).

 

[VoyageofDiscovery]

Does lpile do non-linear analysis of the pile?

If not, ACI should have factors for moment magnification to be applied.

 

[pelelo]

Lpile does.

I am not sure if there is an option in which you can enter the factors.

 

[VoyageofDiscovery]

The moment magnification is not the 1.75 you referred to, so you may want to look into this separate structural issue.

I have not used LPile, if it doesn't do a non-linear analysis of the pile structural components, the input should be looked over by the structural engineer to see if it satisfies the structural considerations of the deep foundation. One of the structural issues I am thinking about is P-Delta effects.

 

[VoyageofDiscovery]

See link:

http://www.jmst.org.tw/marine/12-1/62-70.pdf

 

[dcarr82775]

If the piles have axial load I would agree p-delta should be done, but often these walls support very little axial gravity load so p-delta isn't required.

 

[molerat2210]

The loads should be factored separatey since LRFD may assign varying factors for various loads. For data entry into L-pile, convert all the forces on the wall into a single shear and moment.