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Hello all, Working on Pile found

Hello all, Working on Pile found

Hello all, Working on Pile found

(OP)
Hello all,

Working on Pile foundation substructure. I have determined total lateral force in X and Z directions acting on the group of piles.

Was provided 1" deflection and 3" deflection lateral resistance by Geotech with a P multiplier of 0.8. Is it Geotech's responsibility to incorporate the correct P multiplier in the L pile based on pile layout? I think based on the layout and AASHTO table, the p multiplier will be less than 0.8 for my layout.

1st question - Can I take the avg. P multiplier for Row 1 and 2, provide it to Geotech and then compare the resistance of a single pile provided by Geotech against a load on the single pile?

2nd question - Geotech provided lateral resistance for pinned and fixed conditions. The general rule of thumb is to embed the pile 2.5D into the cap to make it a fixed connection. Is there any design or calcs I can use to determine the embedment into the pile cap for the fixed condition since my cap cannot accommodate 2.5D? Also, I used RC pier for analysis and the software cannot define fixed conditions at the Pile head. Will there be additional moments I need to add to the pile due to fixity?

3rd question - If I decide to use 3" deflection lateral resistance, does that mean my pile needs to be able to withstand moment due to 3" deflection?


Sorry for long post and Thanks in advance.

RE: Hello all, Working on Pile found

My input on the 2nd question is that 2.5D seems excessive. Maybe pipe piles are different than H-piles, but full scale testing of HP12x53's showed that 12" of embedment (1.0D) was sufficient to produce a plastic hinge in the piles without damaging the cap.

For the 3rd question, you're not likely to reach 3" of deflection without the pile forming a plastic hinge, unless the embedment soil is very soft. We usually find the resistance provided by the soil (passive pressure case) against the side of the footing to be adequate for the lateral load. If it's not, yes, you'd have to make sure the piles don't yield under lateral load, except for the seismic load case, if damage is allowed, and it's considered an acceptable monetary risk (it would be a huge repair cost but an unlikely event).

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Hello all, Working on Pile found

The P multiplyer of 0.8 for lateral capacity is too high. For 24 inch pile, you are at a 108/24 = 4.5D in long direction and 2.5D in short direction.

Therefore your P multipliers should be 0.35 and 0.2, approx, respectively. Its the geotechs responsibility, but if you notice something wrong its your responsibility to highlight it to them.

And yes, you can take overall average of group efficiency.

RE: Hello all, Working on Pile found

This type of analysis requires close coordination between the Geotech and the structural to get it right. However, the Geotech is only responsible for what is included in their scope of work. As a result, you may need to amend the Geotechs contract to get this completed.

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