Steel · Bases, anchors & embedded plates

Fixed column base plate with anchor bolts calculator

Axial load plus moment: stress-block length, anchor tension, bearing stress, and plate thickness on both the compression and tension sides.

Standard: AISC Design Guide 1 rectangular stress block · AS 4100 Cl 9.3 · AS 3600 bearing

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Input	Value	Unit
Axial compression N*	300	kN
Base moment M*	120	kNm
Plate width B	400	mm
Plate length D (in moment direction)	550	mm
Plate centre to anchor line	220	mm
Anchor bolts on tension side	2
Anchor bolt size	M24
Anchor grade	4.6/S
Column depth	310	mm
Concrete f′c	32	MPa
Confinement √(A2/A1) (≤ 2)	1.5
Plate grade	Grade 250 plate
Plate thickness	45	mm

Result	Value	Unit
Bolt diameter df	24.00	mm
Bolt tensile strength fuf	400.0	MPa
Tensile stress area As	353.0	mm²
Core area Ac (threads)	324.0	mm²
Shank area Ao	452.0	mm²
Plate yield stress fy (AS/NZS 3678)	250.0	MPa
Plate tensile strength fu	410.0	MPa
Eccentricity M/N	400.0	mm
Design bearing stress φ0.85 f′c √(A2/A1)	24.48	MPa
f + D/2	495.0	mm
Discriminant (≥ 0 → solution)	207,035	mm²
Bearing length Y	39.99	mm
Anchor tension total	91.57	kN
Anchor tension capacity (group)	225.9	kN
Peak bearing stress	24.48	MPa
Plate cantilever m = (D − 0.95dc)/2	127.8	mm
t req (compression side)	43.30	mm
t req (tension side) √(4 T x/(φ fy B))	16.26	mm

Diagram for the worked example

Bolt diameter df = CHOOSE(4,12,16,20,24,30,36) = 24 mm
Bolt tensile strength fuf = IF(1=1,400,830) = 400 MPa
Tensile stress area As = CHOOSE(4,84.3,157,245,353,561,817) = 353 mm²
Core area Ac (threads) = CHOOSE(4,76.2,144,225,324,519,759) = 324 mm²
Shank area Ao = CHOOSE(4,113,201,314,452,707,1018) = 452 mm²
Plate yield stress fy (AS/NZS 3678) = CHOOSE(1,IF(45<=8,280,IF(45<=12,260,250)),IF(45<=8,320,IF(45<=12,310,IF(45<=20,300,280))),IF(45<=12,360,IF(45<=20,350,340))) = 250 MPa
Plate tensile strength fu = CHOOSE(1,410,430,450) = 410 MPa
Eccentricity M/N = 120*1000/300 = 400 mm
Design bearing stress φ0.85 f′c √(A2/A1) = 0.6*0.85*32*MIN(2,1.5) = 24.48 MPa
f + D/2 = 220+550/2 = 495 mm
Discriminant (≥ 0 → solution) = 495^2-2*300*1000*(400+220)/(24.48*400) = 2.070e+5 mm²
Bearing length Y = IF(400<=550/6,550,495-SQRT(MAX(0,2.070e+5))) = 39.989 mm
Anchor tension total = IF(400<=550/6,0,24.48*400*39.989/1000-300) = 91.575 kN
Anchor tension capacity (group) = 2*0.8*353*400/1000 = 225.92 kN
Peak bearing stress = IF(400<=550/6,300*1000/(400*550)*(1+6*400/550),24.48) = 24.48 MPa
Plate cantilever m = (D − 0.95dc)/2 = (550-0.95*310)/2 = 127.75 mm
t req (compression side) = IF(39.989>=127.75,SQRT(2*24.48*127.75^2/(0.9*250)),SQRT(4*24.48*39.989*(127.75-39.989/2)/(0.9*250))) = 43.305 mm
t req (tension side) √(4 T x/(φ fy B)) = SQRT(4*91.575*1000*MAX(0,220-310/2)/(0.9*250*400)) = 16.265 mm

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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.