BCGBC4010A Apply structural principles to residential low-rise constructions

Structural principles - Properties

Section properties

Comparing beam A and beam B
Question 1
What is the value of Ixx for beam A?
A.	0.333 x 106 mm4
B.	3.33 x 106 mm4
C.	33.3 x 106 mm4 
D.	2.08 x 106 mm4
The correct answer is C - 33.3 x 106 mm4. 
Using the formula Ixx = b x d3/12 with values b = 50 and d = 200 then Ixx = 50 x 2003/12.

Question 2
What is the value of Ixx for beam B?
A.	20.8 x 106 mm4
B.	2.08 x 106 mm4
C.	0.208 x 106 mm4
D.	33.3 x 106 mm4
The correct answer is B - 2.08 x 106 mm4. 
Using the formula Ixx = b x d3/12 with values b = 200, d = 50, then Ixx = 200 x 503/12.
Beam A has moment of inertia Ixx = 33.3 x 106 mm4.
Beam B has moment of inertia Ixx = 2.08 x 106 mm4. 
As the moment of inertia for beam A is greater than the moment of inertia for beam B, beam A is stiffer than beam B even though they are exactly the same shape and cross-section.

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