Question 1

What section properties does AXIS calculate?

Accepted Answer

AXIS calculates: gross area A, centroid location (ȳ), moment of inertia I about both axes, section modulus S = I/c, radius of gyration r = √(I/A), and plastic modulus Z for common cross-sections.

Question 2

How is the moment of inertia of a composite section calculated?

Accepted Answer

Using the parallel axis theorem: I = Σ(Ii + Ai × di²), where Ii is the moment of inertia of each element about its own centroid and di is the distance from the element centroid to the composite centroid.

Question 3

What is the section modulus and why is it important?

Accepted Answer

Section modulus S = I/c determines the elastic bending stress: σ = M/S. A larger S means lower stress for the same moment. S is used in steel beam design to select W-shapes from the AISC Manual.

Question 4

What is the radius of gyration r and how is it used?

Accepted Answer

r = √(I/A). It measures the distribution of area relative to the centroid axis. In column design, KL/r is the slenderness ratio that determines which buckling equation applies per AISC 360-22.

Question 5

What is the plastic section modulus Z and when is it used?

Accepted Answer

Z = ΣAi × di (area above/below plastic neutral axis × distance to centroid). Used in LRFD: Mp = Fy × Z is the plastic moment capacity of compact steel sections per AISC 360-22.

Step	Formula	Substitution	Result
Type	type	-	rectangular
A	area	formula	150,000 mm²

Step	Formula	Substitution	Result
Type	type	-	rectangular
A	area	formula	150,000 mm²

Section Properties