Question 1

How is the bearing pressure under a steel base plate calculated?

Accepted Answer

Bearing pressure fp = P / (B × N), where P is the column axial load and B × N is the base plate area. fp must not exceed 0.85f'c × (A2/A1)^0.5 per ACI 318-19.

Question 2

How is the required base plate thickness calculated per AISC Design Guide 1?

Accepted Answer

t ≥ l × √(2fp / (0.9Fy)), where l is the larger of the plate cantilever dimensions m or n (measured from column face to plate edge), and fp is the bearing pressure.

Question 3

What are the m and n dimensions in base plate design?

Accepted Answer

m = (N – 0.95d)/2 and n = (B – 0.80bf)/2, where d is the column depth and bf is the flange width. They represent the cantilever lengths of the plate beyond the column footprint.

Question 4

How are anchor bolts designed for a base plate?

Accepted Answer

Anchor bolts resist tension (uplift or overturning) and shear. Tension from bending is T = M/d – P/2 (when moment is large enough to cause uplift). Bolt capacity is checked per ACI 318-19 Chapter 17.

Question 5

What concrete strength is used for base plate bearing checks?

Accepted Answer

The bearing capacity is φ × 0.85f'c × A1 × √(A2/A1) ≤ φ × 1.7f'c × A1, where A1 is the plate area and A2 is the supporting concrete area within a frustum. φ = 0.65.

Step	Formula	Substitution	Result
B	B	350	350 mm
N	N	450	450 mm
Pu	Pu	800	800 kN

Step	Formula	Substitution	Result
fp	Pu/(B·N)	800/(350×450)	5.08 MPa
fp,max	0.85f'c	0.85×30	23.44 MPa	✓

Step	Formula	Substitution	Result
m	(N-0.95d)/2	(450-0.95×310)/2	78 mm
n	(B-0.8bf)/2	(350-0.8×166)/2	109 mm

Step	Formula	Substitution	Result
tp,req	tp,req	max(m, n) × √(2fp / 0.9Fy)	23.1 mm
tp,prov	tp	25	25 mm	✓

Step	Formula	Substitution	Result
B	B	350	350 mm
N	N	450	450 mm
Pu	Pu	800	800 kN

Base Plate

Base Plate Design

Loads

Column

Plate

Material

Base Plate Design

Given:

Bearing

Cantilevers

Plate Thickness

DCR

Base Plate

Base Plate Design

Loads

Column

Plate

Material

Base Plate Design

Given:

Bearing

Cantilevers

Plate Thickness

DCR