Question

find the center of gravity of an I section with top flange 100mm×20mm, web 200mm×30mm and bottom flange 300mm×40mm ​

Answer 1

Since, The I section is symmetrical about y-y' axis the center of gravity line on the axis.Then the section is divided into three Rectangle 1,2 and 3.

Let, The base of bottom flange be the axis of references.

Rectangle 1

a1= 300×40= 12000

y1 = 40/2 = 20

Rectangle 2

a2=200×30=6000

y2= 40+200/2= 140

Rectangle 3

a3 = 100× 20=2000

y3=40+200+20/2=250

we know that The distance between the center of gravity and the Base of the section.

ȳ= (a1 y1 + a2 y2 + a3 y3) ÷ ( a1+ a2 + a3)

= (12000×20+6000×140+2000×250) ÷ (12000+6000+2000

= 79 mm