Neutral Axis · Superposition · Composite Sections

Interactive Moment of Inertia Demo

Practice how the neutral axis is identified and how the section moment of inertia is built from simple pieces. Use the neutral-axis guess slider first, then reveal the result and inspect each area contribution.

Section family

Section type

The page uses the centroid relation for single-material sections and the E-weighted neutral-axis / effective inertia idea for composite sections.

Dimensions

Material settings

Neutral axis guess

Move the dashed line and guess the N.A. location from the bottom

Dashed orange line = your guess. Solid blue line = revealed neutral axis.

Cross-section and superposition view

Single material

Neutral axis from bottom

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Section result

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Interpretation

Guess first, then reveal.

Key connection

Your guess for N.A. from bottom

Your guess for I / Ieff

Contribution table

Each simple piece contributes its own centroidal inertia plus a parallel-axis term.

Zhao Qin at SU and ChatGPT 2026