Pile Cap and Grade Beam

[ataman]

Hi,

I did a detail for a structure which requires piles. I believe I did the conventional detail which has the grade beams sitting on the top of the pile cap.

Due to certain site constraints, the contractor has asked be to consider a detail with the grade beam framing into the pile cap. Any comments on this? I believe that there is more danger of having eccentrically loaded piles since I don't have the depth of the pile cap to work with.

Any feedback would be great.

Thanks

 

[mrengineer]

We do this a lot in our area. A lot of times you can trench form the grade beams and pile caps, and do monolithic pour. Run grade beam reinforcing continuous thru the cap. Not sure why you feel eccentricity is more of a concern?

Keep an eye on top of pile cap elevation where roof drains come down.

I typically make sure the bottom of the pile cap is a little below the bottom of the grade beam so that the grade beam reinforcing can run over the pile cap reinforcing.

 

[271828]

Backing up mrengineer: That's often done and works fine.

 

[archeng59]

agree with mrengineer and 271828

 

[CJPW]

Dont see why eccentricity would be a problem. All depends on the pile arrangement within the pile cap (triangular cf rectangular etc.). As mentioned above just run the rebar through the pile cap.

 

[MikeT14]

Agree with mrengineer, 271827, and archeng59. That is typically how we design our foundation systems. It allows for easier forming (ie cheaper) and monolithic pour. If you don't want to lower the bottom of the pier cap, adjust your clear cover in either the cap or the grade beam to allow the reinforcing to bypass without any conflicts. I will add however, that unless you have unusual loading, most bottom bars in a grade beam can be displaced a bar diameter up or down through the cap as this typically is a zero positive moment area without a significant impact on the strength of the beam.

 

[ataman]

thanks everyone