Design of Gussetted Base 11

DESIGN OF GUSSETTED BASE

Dr. K.U.MUTHU*

A Steel column of effective height 5m has to transmit an axial load of 2000KN. Design the

gusseted base. The size of the column is ISHB450. Adopt M20 concrete.

Bearing Strength of concrete=0.6fck=12N/mm2

Area Reqd= 2000x103=166.7x10

3

12

Length of base plate+ Column Depth+ 2 Cover plate thickness + 2 gusset plate thickness + 2

gusset plate + 2 gusset angle + 2 Projections = 450+2(06)+2(16)+2(115)+2(25)

=774mm say 780mm.

Breadth of plate = 166.7x103=213.7mm say 400mm

780

Use a base plate of 780x400mm

Upward pressure = 2000x103 = 6.4N/mm

2

780x400

DESIGN OF THICKNESS OF BASE PLATE:

Projection = 25+ 780-774 = 28mm.

2

Mxx=p x2

2

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= 6.4(100=28)2

2

Mxx = 52428.8N-mm.

52428.8 = 1.2 x 1 x 1 x t2

x 250 6 1.1 t=33.96mm

∴ t plate = 33.96-15

= 18.96 say 20mm.

At X1 – X1:

Mxx = p (l -2a) 2

-p a2

8 2 a=projection + angle width

a= 28+115 = 143mm.

Mxx=6.4(780 – 2x143)2

– (6.4x143)2

8 2

Mxx = 129792

129792= = 1.2 x 1 x 1 xt12

x 250 6 1.1

t1=53.44mm.

Due to approximation in boundary conditions;

Thickness = 0.5 x 53.44= 26.72mm say 28mm

Connection of gusset to the column

Assuming the ends of the column are machine cut,



Vdsb= fu x π x (db)2

√3 γmb 4

Using 16mm dia bolts;

Vdsb= 410 x π x 162 = 38KN

√3 1.25 4 1000

tf = 16mm ; thickness of gusset plate = 16mm. Vdpb= 2.5kb x dt x fu

√3 γmb

e= end distance = 40mm p=50mm. do=16+2=18mm. fub=410N/mm

2

We have e = 40 = 0.74

3do 54

p – 0.25 = 50 – 0.25 = 0.675 3do 54 fub= 1.0

fu Vdsb= 2.5 x0.675 x 16 x 12 x 410 =61.35KN √3x1.25 BOLT VALUE = 38KN

Number of blots = 500 = 13.15 38



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Design of Gussetted Base 11