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Queensferry

Module 03

Structural forms, load paths and modelling

The building and the model are different objects. Knowing exactly which parts of the building the model does not contain is most of the skill.

What this module covers

  • Follow a load from the cladding to the foundations of a steel building
  • Distinguish a physical member from the analytical element that represents it
  • Say what each element type captures and, more importantly, what it misses
  • Classify a joint by its stiffness relative to the beam it connects
  • Explain why a connection detailed as simple may still attract moment
  • Account for eccentricity that the model has quietly removed

Lessons

  1. 3.1

    From building to model

    Every modelling decision throws something away. The skill is knowing what, and where it gets picked up again.

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  2. 3.2

    Joints are never pinned or rigid

    Those are the two ends of a scale. Everything real is in between, and a connection built stiffer than it was assumed will attract moment whether or not you asked it to.

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Module checkpoint

Check what you have taken in

6 questions

  1. Question 1

    A member carries 320 kN with the load line 52 mm from the modelled axis. What moment results, in kNm?

  2. Question 2

    A beam has I = 40 000 cm⁴ and spans 10.0 m. What is EI/L, in kNm/rad? Take E = 210 000 N/mm².

  3. Question 3

    A joint has ρ = 6 on a beam whose fixed-end moment is 200 kNm. What end moment develops, in kNm?

  4. Question 4

    For that same beam, if the simply supported midspan moment is 300 kNm, what is the midspan moment with the ρ = 6 joints, in kNm?

  5. Question 5

    A joint of 30 000 kNm/rad sits on a beam with EI/L = 6000 kNm/rad in a braced frame. What is the ratio, and does it classify as rigid?

  6. Question 6

    A beam is modelled centreline to centreline between 450 mm deep columns. The clear span is 9.1 m. By what percentage does the modelled span exceed the clear span?