Statics

Moment of Inertia (Area)

The second moment of an area about an axis, which measures how strongly a cross-section resists bending.

The area moment of inertia I = ∫y² dA grows with the square of each element’s distance from the axis, so material placed far from the neutral axis counts for much more than material near it. That is why a wide-flange beam puts most of its steel in the flanges. A rectangle about its centroidal axis has I = bh³/12.

For composite shapes, the parallel-axis theorem moves each part’s own centroidal moment of inertia to the common axis: I = I_c + A·d². Forgetting the A·d² term, or measuring d from the wrong axis, is the usual error.

How much of the FE Civil exam is Statics?