BCGBC4010A Apply structural principles to residential low-rise constructions

Structural principles - Properties

Section properties

Calculating the radius of gyration
The equation for calculating the radius of gyration is ryy = the square root of I divided by A.
For the rectangle with dimension of b = 50 mm and d= 200 mm, Iyy = 2.08 x 106 mm4.
Question
Using this information calculate the value of the radius of gyration ryy about the y-y axis. 
A.	57.7 mm
B.	5.77 mm
C.	14.4 mm
D.	144 mm
The correct answer is C - 14.4 mm. ryy = the square root of, 2.08 x 106 mm4, divided by 10,000 mm2. The value of rxx is 57.7 mm compared with the value of ryy which is 14.4 mm.
Therefore the beam is more likely to buckle about the y-y axis as this has the smaller value of the radius of gyration.

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