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Queensferry

Module 10

Columns and structural walls

Axial load and moment together, the interaction diagram that governs them, and what happens when the column is slender enough to notice its own deflection.

What this module covers

  • Explain why axial load and moment interact rather than adding
  • Read an M–N interaction diagram, and find the balance point on it
  • Say why a modest axial compression increases the moment capacity
  • Distinguish the ductile and brittle sides of the diagram
  • Decide whether a column is short or slender, and why the answer depends on load
  • Calculate a second-order moment by the nominal-curvature method

Lessons

  1. 10.1

    Axial load and moment together

    Why the two cannot be checked separately, and what the interaction diagram is really showing.

    Start lesson →
  2. 10.2

    Slenderness and second-order effects

    When a column starts to notice its own deflection — and why that depends on how hard it is being pushed.

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Module checkpoint

Check what you have taken in

6 questions

  1. Question 1

    Why does a modest axial compression increase a column section's moment capacity?

  2. Question 2

    A 400 × 400 column with 2454 mm² of steel, C30/37 (fcd = 17.0, fyd = 434.8 N/mm²). What is its squash load, in kN?

  3. Question 3

    A 300 mm square column has an effective length of 2.7 m. What is λ?

  4. Question 4

    Two identical columns, one at the top storey and one at the bottom of a ten-storey building. Which statement is correct?

  5. Question 5

    A 450 mm deep column carries 2000 kN with Ac = 180,000 mm² and fcd = 17.0 N/mm². Give λlim, taking A = 0.7, B = 1.1, C = 0.7.

  6. Question 6

    What is the minimum design eccentricity for a 600 mm deep column, in mm?