Pile Cap Design

Pile reactions from the rigid-cap eccentric-load equation, punching (two-way) shear at every pile and column pedestal, one-way (beam) shear, and Whitney-block flexural design with auto bar selection, for a 1-20 pile, 1-8 column cap by ACI 318-08.

ACI 318-08

Pile layout

Layout

Pile countSpacingSin

Pile shapePile diameterDin

Allowable pile capacitykipRotationdeg

Auto edge distance

Cap geometry

Depth modeAuto thickness (0.7S, min 12 in)

Cap centre shift xinCap centre shift yin

Materials & reinforcement

f'cpsifypsiCoverin

Bar size XBar size YTop bar size

Auto-select bottom bars

Options

Include column moments3-pile diagonal strips (single-column triangular cap)Compute minimum depth per check (slower)

Columns

Number of columns

Column A (fixed at the origin)

WidthcxinDepthcyin

Service PPskipService Mxkip.ftService Mykip.ft

Ultimate PPukipUltimate Mxkip.ftUltimate Mykip.ft

Everything you have entered is in the address bar, so the link reproduces this exact calculation.

d = 30.00 in · 7 checks · all pass

Plan view

Effective depth

30.00 in

Cap thickness

34.0 in

Max. ultimate pile reaction

97.5 kip

Governing DCR

0.65

Section views

Bottom bars shown: 11-#8 @ 7.70 in (running across this cut). Top: minimum temperature/shrinkage mat; no negative span demand governs.

Pile reactions

Pile	x (in)	y (in)	P service (kip)	P ultimate (kip)
P1	-24.0	-24.0	65.0	82.5
P2	24.0	-24.0	65.0	88.8
P3	-24.0	24.0	65.0	91.3
P4	24.0	24.0	65.0	97.5

Design checks

Check	Ref	Demand	Capacity	DCR	Governs	Status
Pile Capacity (Service)	Geotech. Allowable / CRSI Guide	65.0 kip	100.0 kip	0.65	Ps/n +/- sum(M.c)/sum(c^2) (service)	PASS
Punching Shear (per pile)	ACI Section 11.11.2.1	97.5 kip	457.8 kip	0.21	Eq. 11-33 (perimeter truncated at cap edge)	PASS
Column A — Beam Shear (X-dir)	ACI Section 11.2.1	0.0 kip	239.1 kip	0.00	Eq. 11-3 bw = 84 in; critical section at d from pedestal face, x = 45 in	PASS
Column A — Beam Shear (Y-dir)	ACI Section 11.2.1	0.0 kip	239.1 kip	0.00	Eq. 11-3 bw = 84 in; critical section at d from pedestal face, y = 45 in	PASS
Column A — Punching Shear at Pedestal	ACI Section 11.11.2.1 (area-prorated pile inclusion)	85.9 kip	1366.1 kip	0.06	Eq. 11-33 b0 = 240 in; pile contribution weighted by fraction of area outside the d/2 perimeter	PASS
Column A — Flexure (X-dir)	ACI Section 10.3	139.7 kip.ft	1137.5 kip.ft	0.12	Whitney block b = 84 in (11-#8 @ 7.70 in)	PASS
Column A — Flexure (Y-dir)	ACI Section 10.3	141.6 kip.ft	1137.5 kip.ft	0.12	Whitney block b = 84 in (11-#8 @ 7.70 in)	PASS

Design strips

Strip	Piles	Max V (kip)	φVc (kip)	Shear	Max M (kip.ft)	φMn (kip.ft)	Flexure	Rebar
X1 @ 0 in, w=full	2	186.3	239.1	PASS	347.5	1100.6	PASS	42-#4 @ 1.89 in
Y1 @ 0 in, w=full	2	188.8	239.1	PASS	342.5	1100.6	PASS	42-#4 @ 1.89 in

Calculation

1Pile group centroid and eccentric reactions
$R_i = \frac{P}{n} \pm \frac{M_x(y_i - \bar y)}{\sum(y-\bar y)^2} \pm \frac{M_y(x_i - \bar x)}{\sum(x-\bar x)^2}$
$P_{max,ult} = 97.5,\quad P_{min,ult} = 82.5$
$P_{max,ult}$ 97.5 kip
2Effective depth
$d = t - \text{cover} - d_b$
$d = 34.00 - 3.00 - 1.000 = 30.00$
$d$ 30.00 in

Notes

Governing check: Pile Capacity (Service) — DCR = 0.65, Ps/n +/- sum(M.c)/sum(c^2) (service)
All 7 design checks pass.

What this calculator does not check

This is a single design-load-case check (one factored Pu/Mu and one service Ps/Ms per column), not a full pile-cap design across multiple load combinations.
Group effects (pile-to-pile interaction, block failure, negative skin friction) are not checked — pile capacities are taken as entered.
ETABS/analysis-software load import is not available in this port — enter each column's governing loads directly.
No published worked example has been reproduced against this port; verification is internal cross-checks with the original tool's own engine, disclosed as such.

Results are for preliminary sizing and educational use. They are not a design and must be reviewed, verified and sealed by a licensed or registered engineer before being used in construction.

pile-cap-design v1.0.0 · ACI 318-08 · input ae23e28189dba902