Drilled Pier Reinforcement Design 1

[CE475]

I'm trying to find out the best way to determine the required amount of steel for a circular drilled pier foundation. I was wondering if anyone has a suggestion for a reference for determining an effective "d" for the reinforcement placed in various circular patterns.

 

[WillisV]

The most accurate way would be to use an interaction diagram for a large circular column...

 

[bushel3]

One of the books my company uses is "Foundation Design" by Teng published in 1962 which is probably hard to find. The book gives a table of minimum reinforcement based on the diameter of the caisson. I believe "Principles of Foundation Engineering" by Das also answers this question, but I couldn't find it immediately. I would consult a Foundation Design book that covers deep foundations. This is a a problem common to geotechnical engineers and you may get a better response in the foundation engineering section under geotechnical engineers if you don't get the desired response here.

 

[apetr26542]

Title: ACI 336.3R-93: Design and Construction of Drilled Piers

 

[archeng59]

CRSI has a section near the back of the book for piers.

 

[miecz]

If you have the ACI Design Handbook for Columns, its easy to interpolate the tables for Circular Columns. Notice that for reinforcing ratios under 2%, its always conservative to neglect the axial force and use point "7". I usually start at a reinforcing ratio of .5%, as long as that meets ACI 10.5.

 

[HouseBoy]

What behavior are you trying to resist with the drilled piers?
Is it promarily axial load or is there more significant bending with the piers used for lateral load resistance such as on a hillside foundation? I've found that with the latter, PCA sells a software that allows good refinement of steel cages.

 

[CE475]

I am primarily interested in the design of the reinforcement for moment capacity, the interaction diagrams seem like a good idea, but I am curious if there is a way to do it iteratively. For instance could you simply find the depth of embeddment for each bar location and find your required steel that way?

 

[JAE]

Its important to remember that ACI 318 doesn't apply to drilled piers. ACI 336 is used instead.

For years, most of the drilled piers we designed (in South Texas) were reinforced with approximately 0.75% reinforcing (0.0075 x Gross Area of Pier)as a minimum and with a second criteria provided by the geotechnical engineer that attempted to deal with the potential uplift of the pier in expansive clay situations. This was usually a formula involving the pier circumference.

 

[WillisV]

CE475 - it doesn't really work that way for a section with various rebar depths as each bar experiences a different strain.

 

[minorchord2000]

We design many drilled shafts (as we call them here) for bridge supports at piers and abutments. We design the drilled shaft reinforcing using 6" of clearance from the ties or spiral ties to account for spongy concrete if the concrete is tremied using the polymer slurry system. If the shaft is placed "in the dry", we use 3 inches of clearance. We design using 3000 psi but we detail and specify that the contractor provide 4000 psi. We them use a program called COM 624P or LPile to determine the depth of embedment. Either the axial load or the lateral load on the shaft will govern its depth of embedment. We then search for the maximum axial and bending forces (increasing to Pu and Mu) and then compare these values to typical interaction curves at various levels of steel percentage. Usually the maximum moment in the shaft will occur typically about 3 times the shaft diamter below the design ground line. We then insure that the reinforcement chosen is sufficient to resist the maximum forces.