Column Base Plate under Axial Load (AISC Design Guide 1)
The plan size and thickness of a concentrically-loaded column base plate.
Example
You enter
- Axial load Pu (kip) 400
- Concrete strength f'c (ksi) 4
- Plate yield Fy (ksi) 36
- Column depth d (in) 9.98
- Flange width bf (in) 10
- Plate width B (in) 14
- Plate length N (in) 14
You get
- A1 req 180.995
- Cantilever m (in) 2.2595
- Cantilever n (in) 3
- Cantilever n' (in) 2.4975
- Governing cantilever l 3.00 in
- Required plate thickness 1.06 in
Details, formula, and sources
The required concrete bearing area A1_req = Pu / (0.65 x 0.85 x f'c), the cantilever dimensions m, n, and n', and the thickness tp = l x sqrt(2 Pu / (0.90 Fy B N)). A W10x49 at 400 kips on a 14 in square A36 plate over 4 ksi concrete needs a 1-1/8 in plate; raise the load to 700 kips and the plate is flagged as too small in bearing. Concentric axial only; anchor rods and shear transfer are separate. A design aid, not a substitute for the engineer of record.
A1_req = Pu / (0.65 x 0.85 f'c); m = (N - 0.95 d)/2; n = (B - 0.80 bf)/2; n' = sqrt(d bf)/4; l = max(m, n, n'); tp = l sqrt(2 Pu / (0.90 Fy B N)).
AISC Design Guide 1 §3.1 and AISC 360-22 §J8, by name; the concrete bearing uses phi_c = 0.65 with the confinement factor taken as 1.0.
The base-plate bearing-area, cantilever, and thickness relations are published in AISC Design Guide 1 and AISC 360 §J8; the arithmetic is public.
Estimate. AHJ and licensed professional govern.
Field names used by the API: pu_kip, fc_ksi, fy_ksi, d_in, bf_in, b_in, n_in, a1_req, m, n, np, l, tp
- Bearing area A1_req = Pu / (0.65 x 0.85 f'c) with the confinement factor sqrt(A2/A1) = 1.0; a larger pier reduces the required plateAISC 360-22 J8
- Cantilever l l is the largest of m, n, and n' = sqrt(d bf)/4 (lambda = 1.0); the yield-line cantilever the plate must spanAISC Design Guide 1 §3.1
- Concentric only concentric axial compression; moment / uplift, the anchor rods, and concrete breakout are separate checksAISC Design Guide 1