Pile Uplift capacity under seismic loads

[BAGW]

Hi,

I have a Seismic uplift force of 200kips. The skin friction is 100psi. When I calculate the embed depth for the pile, the force to be used is 0.7x200 = 140kips right (ASD seismic equation 0.6D+0.7E). As 100psi provided by geotech engineer will be a service limit.

Thanks

 

[BridgeSmith]

If your seismic loading is calculated per ASD, and so is your capacity, I don't believe there would be any reduction. It's been awhile since I've done anything ASD, so I could be wrong on that. If you're mixing ultimate loads (LFD or LRFD) with capacities calculated by ASD, you're into engineering judgment territory there.

Is your 100 psi a typo? 100 psf seems reasonable, but 100 psi (14.4 ksf) would be way higher than I've ever seen for a friction value in soil, even for a concrete CIP shaft (drilled shaft).

 

[EDub24]

You should talk with the geotech. If the 100 psf has factors of safety built in then I don’t see why you can’t use the reduction. With that said i’m used to geotechs giving me pile values with no safety factors forcing me to use ultimate loads.

 

[BAGW]

Thanks