Fender Pile Axial Capacity 1

[STH003]

Anyone know why an engineer would spec out a fender pile to have 1,900 kips of axial capacity? I would think EI, Ma and radial compression would be the most important design criteria for a fender pile.

Question is going around the office since this spec doesn't seem to make sense.

 

[SlideRuleEra]

Perhaps it's his round-about way of specifying an embeddment length. If a geotech report is available, then he would know (approximately) at what depth a certain axial capacity would be developed.

If the pile is battered, such as being in a dolphin, axial capacity would be needed to resist horizontal force.

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[STH003]

Ah, thanks SlideRule. Embedment depth would make sense in most cases, and I think that may be what the engineer was going for, but IMO 1,900 kips is a bit high, since these piles are not battered and are only 16" diameter, so even a solid concrete pile @5000psi wouldn't have that axial capacity.

Hope they are not planning on these being structural and fender piles. Pick up some pretty nasty P-delta effects if they are....

 

[cessna98j]

I agree that it seems to be an out of place spec for a fender pile - I've never designed a fender pile to take ANY axial load, but 1900K is very significant and would overload any 16" pile regardless of unbraced length I would think.

Although its rare, I've seen prestressed piles used as fender piles before. Was thinking maybe it could be a jacking force on a prestressed pile, but even that seems very high for a 16" pile.

Can you question the engineer's reasoning for this?

 

[STH003]

I have, and they say that NO competitor has been able to meet that spec with a fender pile, and that they plan on using axial capacity as a secondary evaluation as to which customer's piling they want to go with, if 2 competitors seem a deadlock tie.

I would think if no one is meeting the spec, that would raise a red flag....

 

[cessna98j]

Yeah seems like pretty strange evaluation criteria to me - and where in the world did they come up with 1900K?

Let's assume its a solid cross section, for a 16" pile that load equates to a stress of roughly 9.45 ksi. Good luck finding any concrete or timber pile that's going to handle that. A 16" steel pile with a 1/2" wall thickness would be stressed to nearly 80ksi. Most steel piles I've seen have a yield of 35ksi, although higher strength steel is available (read more expensive).

That's like going car shopping and finding 2 similar cars at identical prices, then telling each salesman you'll buy their car if they can guarantee it to 1,900,000,000 miles... I just don't see it happening