Structural Engineering & Statics
where the load goes
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Interaction — the series

One essay so far on this idea, and more questions about it than one essay answers.
  1. Two ways to fail, and the curve between them. The exact plastic interaction between axial force and moment for two sections of identical area, both normalised by their own squash load and their own plastic moment. The rectangle stands 25.0% of its plastic moment outside the straight line at an axial ratio of 0.50; The I-section stands 6.0% of its plastic moment outside the straight line at an axial ratio of 0.12. Every section here is symmetric about its centroid, so the equal-area axis and the centroid coincide and it makes no difference which the moments are taken about. The straight line is the rule that says the two capacities share out in proportion, and everything between it and a curve is capacity that rule gives away.

    Two ways to fail, and the curve between them

    A column carrying both compression and bending has two capacities and a rule for sharing them out. The rule is a straight line, the truth is a curve, and for a rectangle the straight line gives away a quarter of the plastic moment at half the squash load.

    part 1 · materials

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