×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

ACIP Pile Reinforcing Design

ACIP Pile Reinforcing Design

ACIP Pile Reinforcing Design

(OP)
If the geotech. engineer is designing the ACIP(Augered Cast-In-Place) piles, who determines if steel reinforcing is required and who designes the depth of the cage and size of the reinforcing.  If structural designs the reinforcing, what methods are used.  Are there any guidelines or references.  Looking for how this is normally handled.

RE: ACIP Pile Reinforcing Design

Typically, we (the structural engineer) usually call out the steel reinforcing in auger cast piles. We have some standard pile reinforcing details that we use unless there is something unusual about the pile ie: it is taking unusually high lateral loads or eccentricities.

For example: for 16" diamter piles we have a cage of 4-#6 bars around the perimeter with #3 ties. This cage extends 20 into the pile and 2'-6" into the pile cap. We also place 1 full length (usually a #9) bar down the entire length of the pile. The exterior cage is to handle any accidental or incidental bending on the pile from lateral loads or eccentricities. The center bar is to provide ductile continuity down the entire length of the pile and to engage the entire pile when we are counting on it to resist uplift.

Others, I'm sure have different standards and opinions on the subject. Just how our office does this.

RE: ACIP Pile Reinforcing Design

The geotech should provide you with deflection and moment graphs for the different load conditions assumed and the head restraint (fixed or free).  The pile reinforcing should be designed for the moments in the pile.  You need the max steel at the max moment.  At some point along the pile there is a point of fixity...no moment.  Usually the reinforcing cage will extend past this point a short distance.  Don't know exactly what this distance is.  I have only seen center bars placed in a pile for uplift only and they have been full length like lkjh345 said.

RE: ACIP Pile Reinforcing Design

(OP)
lkjh345 you mentioned 16" diameter piles.  Do you know off hand what capacity a 16" is normally used for,.....I guess I am asking what is a common size pile diameter that you would expect for say, 40 tons, 12", 14", 16"?

RE: ACIP Pile Reinforcing Design

Barring something unusual in the Geotech report or in the loading of the pile, we usually assume a 16" Auger pile is good for 100 tons (200 kips). See Section 1810.3 of IBC 2006. Assuming 3,000 psi grout, this works out to 200 kips or 100 tons.

(Full disclosure: Our local building department has modified 1810.3 to allow for the maximum stress to be only 25% of the f'c. We therefore typically use 4,000 psi grout to get back to the 100 ton capacity for a 16" diameter.)

We estimate the length based on parameters of skin friction and end bearing set by the Geotech. Final length is determined in the feild by the Geotech rep.

Uplift resistance is based on parameters given by the Geotech.

I have seen 14" diameter ACIP piles. I personally have never called for or seen anything smaller than a 14" dimater piles. Doesn't mean they are not out there, just have never seen them used around my area.

Might check with a local installer to see what the smallest they typically do in your area.

RE: ACIP Pile Reinforcing Design

(OP)
lkjh345 thanks for your help.  I have only specified wood piles where the diameter is about 12", where I spaced them 2'6" or 3'-0" apart for a two-pile  pile cap.  What is the minimum recommended spacing for 16" diameter ACIP piles.

RE: ACIP Pile Reinforcing Design

Talk to the geotech for spacing.  He will probably tell you 3 times the diameter..that is usually standard.  Any closer and you start to get group action, which reduces the capacity of the piles.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources