Flexural Design

The design of the flexural reinforcement used to resist the moments in the pile cap are outlined in the Section 5.12.3. Due to the unique nature of pile caps they need to be checked using both the slab and beam reinforcement limits.

The required reinforcement area is selected as follows: (From CRSI p13-18)

if A_s > 200/ f_ybd, Use A_s (Sec. 9.6.1.2)
if A_s > 200/ f_ybd < 4/3 A_s, use min (200 / f_ybd, 4/3 A_s) (Sec. 9.6.1.2)
if 0.0018bh < 4/3 A_s < 200/ f_ybd, Use 4/3 A_s (Sec. 24.4.3.2)
if 4/3 A_s < 0.0018bh < 200/ f_ybd, Use 0.0018bh (Sec. 24.4.3.2)

Note use 0.0020 instead of 0.0018 if f_y< 60 ksi

The pile axial forces replace the soil stress (Section 5.12.3) when calculating the force inducing the moment at the column face. The centroid of the force is calculated based on the effective centroid of the pile axial loads. The moment is taken as the distance from the pile force centroid to the column face + the maximum construction tolerance. This helps account for construction tolerances in the location of the piles or the column.

Top reinforcement is only provided if at least one pile is in tension.

In all cases the slab reinforcement criteria are used.