Skip to content
Queensferry

Module 14

Column bases and anchorages

Where steel design stops and concrete and anchor design begin. A base plate cannot spread pressure further than it can span, the tension side is a T-stub you have already met, and the shear is not carried by the bolts.

What this module covers

  • Explain why the concrete under a base plate is far stronger than fcd
  • Derive the effective bearing area from the plate's own bending capacity
  • Recognise the tension side of a base as a T-stub
  • Say why the governing case for holding-down bolts has the LEAST axial load
  • Explain how shear actually gets out of a base, and why not through the bolts
  • Say which base-fixity assumption is safe and which is dangerous

Lessons

  1. 14.1

    The base plate, and the concrete under it

    The concrete is stronger than you expect and the plate is weaker. Both facts come from the same place: how far a plate can reach before it runs out of bending capacity.

    Start lesson →
  2. 14.2

    Tension, shear, and how fixed a base really is

    The tension side is a T-stub. The shear goes out through friction, not the bolts. And the base is neither pinned nor fixed, which matters more than either.

    Start lesson →

Module checkpoint

Check what you have taken in

8 questions

  1. Question 1

    A 400 mm square plate sits on a 1600 mm square pad. What is the concentration factor, allowing for the cap of 3.0?

  2. Question 2

    A 20 mm plate in S355 bears at fjd = 30 N/mm². What is the effective projection c, in mm? Take γM0 = 1.0.

  3. Question 3

    A base plate's thickness is doubled. By what factor does the effective projection increase?

  4. Question 4

    A base has N = 500 kN and M = 120 kNm, with the compression centre 120 mm from the axis. Is there a tension side? Give the eccentricity in mm.

  5. Question 5

    A base carries 900 kN of axial compression. With Cf,d = 0.2, what shear can friction transfer, in kN?

  6. Question 6

    A base must transfer 100 kN of shear by friction alone at Cf,d = 0.2. What axial compression does that need, in kN?

  7. Question 7

    Which load combination usually governs the holding-down bolts of a column base?

  8. Question 8

    Why is assuming a pinned base safer than assuming a fixed one, when the truth is somewhere between?