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Foundation DesignACI 318-19 Sections 13.4, 22.2, 22.5, and 22.6

Pile Cap Design

Design a pile cap supporting a column over a group of driven or drilled piles. Distributes the factored column loads to individual piles, checks that no pile is overloaded, evaluates two-way (punching) shear around the column and around individual corner piles, and designs the cap flexural reinforcement. Handles 2-pile, 3-pile, 4-pile, and 6-pile configurations.

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What this calculates

Individual pile reactions under axial load and moment (Pi = P/n ± M·xi/Σxi²), maximum pile reaction vs. allowable pile capacity, two-way punching shear around the column and around corner piles on critical perimeters at d/2, one-way shear at d from the column face, and required top and bottom reinforcement in both directions.

Inputs

Factored Axial LoadPu[kip]

Total factored axial load from the column

Factored MomentMu[kip·ft]

Factored moment at the column base (if any)

Number of Pilesn

Number of piles in the group (2, 3, 4, or 6)

Pile Spacings[ft]

Center-to-center pile spacing

Allowable Pile CapacityQa[kip]

Allowable axial capacity per pile

Pile DiameterD_pile[in]

Pile diameter or width

Column Widthc[in]

Column dimension

Cap Thicknessh[in]

Pile cap total thickness

Concrete Strengthf'c[psi]

Cap concrete compressive strength

Steel Yield Strengthfy[ksi]

Reinforcement yield strength

Outputs

Maximum Pile ReactionPmax[kip]

Maximum factored pile reaction

Pile UtilizationPmax/Qa

Maximum pile load vs. allowable capacity

Column Punching Shear RatioVu/φVc (col)

Two-way shear ratio at column critical perimeter

Required Bottom Steel (long)As,long[in^2]

Required bottom reinforcement in the long direction

Required Bottom Steel (short)As,short[in^2]

Required bottom reinforcement in the short direction

Methodology

Pile reactions per statics: Pi = Pu/n ± Mu·xi/Σxi² where xi is each pile's distance from the centroid. Punching shear around the column per ACI 318-19 Section 22.6, with the critical perimeter at d/2 from the column face. If corner piles are within d/2 of the cap edge, individual pile punching is also checked. Flexure designed at the column face as a cantilever with pile reactions as point loads. Minimum cap depth is typically 3 ft for transfer length. Reinforcement per ACI 318-19 Section 22.2.

Code References

ACI 318-19 Sections 13.4, 22.2, 22.5, and 22.6

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