Embedment/Extension of Piles into the Pile Cap... 2

[vooter]

I posted this in the Marine/Ocean Engineering forum, but no one was biting...

I'm looking into rules/requirements for just how much a pile should extend into its pile cap. The piles are steel H-Piles.

AASHTO Bridge Manual says 6 in, but 9 in is desirable for a bent cap (which is more like what I have). 12 in is required for pile caps.
CSRI Handbook (I have the 1984 edition handy) says 6 in.
One of my concrete textbooks says 6 in to 12 in
US Steel H-Pile manual shows 6 in
Most of my Ocean Engineering books indicate through figures a minimum 6 in embedment.
Ditto for the NAVFAC and USACE manuals.

From inspection reports, it looks like my existing pier was constructed with a 12 in embedment...

Any comments are most appreciated, thanks in advance!

 

[SlideRuleEra]

vooter - I have seen, and used, a whole range of numbers similar to what you have found. Most of the time it does not seem to make any significant difference. A few thoughts on the matter:

Have enough concrete in the cap, above the top of the pile, so that punching shear thru the cap is not a concern.

More embeddment in the cap should help improve "fixity" for column loading calculations.

For uplift or seismic loading, more embeddment (within reason) should be better.

http://www.SlideRuleEra.net

 

[vooter]

Thank you, sir!

CRSI (1984) has this to say, "Pile caps are an important structural element somewhat neglected in handbooks on steel because they are reinforced concrete and in handbooks on concrete in the range where steel piles are used..."

 

[MichSt]

vooter,

My experience with piles is all in bridge design and the embedment depth I use is typically the min required by the governing DOT specs. For pile caps I’ve seen 1’ to 1.5’ min embedment when more than one row of piles is used and 2’ to 2.5’ min embedment when a single row of piles is used (this is in Michigan and Ohio where we have no seismic concerns).

I haven’t designed a pile supported bent, but here’s a pile bent standard used for continuous slab bridges in Ohio:

http://www.dot.state.oh.us/se/standard/english/revisions/07-19-02 mailing/pdf/2002cms/cpp294.pdf.

Note the use of ties around the end of the piles to help confine the concrete at the pile tip and improve the transfer of forces at the pile/bent joint.

I also echo SRE’s comment to make sure you have enough concrete above your piles to prevent punching shear failure.

 

[vooter]

MichSt, you're a "star," too.

Interesting detail; HP 12X53 has a 1 ft 6 in embedment into the cap. The cap itself, though is 2 ft deep.

 

[MichSt]

Yes, when I saw that 1.5’ embed with only 2’ thick cap that got my attention too. But, I think with the slab on top of the cap, which is probably 18” min, there should be enough concrete on top of the piles to prevent punching shear failure. This detail is only used for short span bridges so the vertical loads on the piles would not be that large. The 1.5’ embed may be that large to ensure moment transfer.

This continuous slab on pile supported bents bridge type is an ODOT favorite for rural bridges over farm drains and other small water crossings. It’s very quick and cheap to build.

By the way...what is your pile bent being used for?

 

[vooter]

"By the way...what is your pile bent being used for?"

I'm working on analyzing an existing marine facility's pier. No maintenance has been done on it in 30 years (it was built 30 years ago...), no one has the slightest idea where any as-builts/record drawings are; yet the thing still stands and is heavily used.

I have very little bridge experience, yet that's where the info for this kind of construction detail seems to be. After my work is complete, I'll still have very little bridge experience, but it's still a bit more than I have right now.