single pile cap

huangyhg

single pile cap
when i have a single pile cap for a column.  is there any parameter or rule of thumb considering the depth of the pilecap and the amount of reinforcement required???
if you analize it theres no punching shear on the pile cap, and there is no moment applied to it, except if there is an eccentricity applied to the pile cap by the column or by misplacement of the pile.

in my experience with the aashto code the minimum depth is the column diameter or smallest column dimension but not less than 30 inches.  also, hairpin bars are placed from one pile to the next in each direction.  generally, the bars are #6 (5/8").
i'm sure that various building codes allow for less depth but i can't recall the numbers offhand.
thanks for your reply qshake.  i have seen that on the bottom of the single pile cap you use a minimum reinforcemnt ratio, i think is 0.0018 just like a footing.  you use this reinforcement both ways on the bottom of the pilecap.
the pile cap is in pure compression and i think this bottom reinforcement is just to prevent mittigate any tension stresses that might affect the pile cap.  but if the pile cap is un pure compression, does the concrete f'c has to be checked to i think.  
minimum depth according to reynolds is as follows:
if pile dia. < 550mm, d= {(2 x dia.) + 100 }
if pile dia. > 550mm, d= 1/3 {( 8 x dia ) -600 }
but must be sufficient to meet anchorage - bond lengths of starter bars and both normal and punching shear requirements.
eccentricity in column will create moment in the pile cap.