Column Base Plate Design
Size a steel column base plate for axial compression and moment. For small moments (e ≤ B/6), uniform bearing governs and the plate cantilevers beyond the column footprint. For large moments (e > B/6), a portion of the plate lifts off and anchor bolts resist tension. Computes required plate thickness using the critical section bending method from AISC Design Guide 1 and checks concrete bearing per ACI 318-19 Section 22.8.
What this calculates
Required plate plan dimensions (N × B), eccentricity e = Mu/Pu, bearing stress distribution (uniform or triangular), cantilever projections (m, n, λn'), required plate thickness tp from the governing cantilever, anchor bolt tension demand Tu, and concrete bearing capacity φc·Pp with area ratio enhancement (A2/A1).
Inputs
Factored axial compression
Factored base moment
Factored horizontal shear at the base
Column section depth
Column flange width
Foundation concrete compressive strength
Base plate steel yield strength (36 ksi typical for A36)
Anchor bolt diameter
Anchor bolt material (e.g. F1554 Grade 36/55/105)
Outputs
Required base plate width
Required base plate length
Required base plate thickness
Load eccentricity Mu/Pu
Maximum concrete bearing stress
Required anchor bolt tension (0 if e ≤ B/6)
Shear per anchor bolt (or friction check)
Methodology
Per AISC Design Guide 1 (3rd Edition): Plate dimensions N × B sized for bearing and column clearance. For concentric compression (e ≤ B/6), uniform bearing fp = Pu/(N·B) ≤ φc·0.85·f'c·√(A2/A1), and plate thickness tp = l·√(2fp/(φ·Fy)) where l = max(m, n, λn'). For large eccentricity (e > B/6), iterative solution for bearing length Y and anchor bolt tension Tu using equilibrium. Concrete bearing per ACI 318-19 Section 22.8.3.2 with φc = 0.65. Area ratio A2/A1 ≤ 2.0.
Code References
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