Required Flexural Reinforcement for Drilled Pier Design

[ach985]

We do a lot of drilled pier designs, and are trying to determine a better way to determine the required flexural reinforcement for the pier. The structures that we are supporting are relatively lightly loaded axial loads (usually around 5 kips) and the base moment is typically around 50 kip*ft. With those loading conditions the design is laterally controlled and we believe should be treated more like a beam than a column. Our problem is that ACI 318 clearly states that it is not supposed to be used for drilled pier foundation designs and to use ACI 336, but ACI 336 doesn’t have any reinforcement design information to my knowledge…The way that we currently do it is with an equation out of an old book by Wang & Salmon “Reinforced Concrete Design” and use the max of the flex. Steel required and Asmin. We were hoping to be able to find a way to find flexural reinforcement for a circular section in a newer resource. If you could provide any help or insight it would be greatly appreciated. Thanks a lot!

 

[dcarr82775]

I have always used 318 for this scenario. A concrete section in bending doesn't care that ACI put some disclaimer at the front end of their document. I think the pier behavior in high shear scenarios probably wanders away from 2 sqrt shear, but for axial and bending just use 318. I believe AASHTO provides direction, but I avoid opening that tome at all costs.

 

[Lion06]

ACI 336.3R-93 (maybe this has changed in a more recent edition) explicitly states in 3.3 that ACI 318 may be used for the strength design of drilled piers. I have always used ACI 318 strength design method to design drilled piers.