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Queensferry

Module 05

Shear, bond, anchorage, laps and torsion

The failures that are sudden. A truss you can derive, an empirical formula you cannot, and the reason a bar must be given length before it can be given a force.

What this module covers

  • Explain why a diagonal crack forms, and why the failure is brittle
  • Derive the variable-angle truss from equilibrium alone
  • Choose a strut angle, and say what you are trading when you do
  • Distinguish the empirical concrete term from the mechanical truss term
  • Design links for a beam, and check the struts do not crush
  • Derive the anchorage length from a force balance on one bar
  • Curtail a bar correctly, accounting for both the shift and the anchorage
  • Distinguish equilibrium torsion from compatibility torsion, and design for the first

Lessons

  1. 5.1

    Why shear is the dangerous one

    Diagonal tension, brittle failure, and why a beam without links gives no warning at all.

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  2. 5.2

    The variable-angle truss

    Once the web has cracked, the beam is a truss. Derive it by cutting, and the design equations fall out.

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  3. 5.3

    Bond, anchorage and laps

    A bar can only be given a force over a length. Get that length wrong and the flexural design is worthless.

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  4. 5.4

    Torsion

    The same truss, wrapped round a tube — and the one question you must answer before designing for it at all.

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Module checkpoint

Check what you have taken in

7 questions

  1. Question 1

    What is physically happening when a beam 'fails in shear'?

  2. Question 2

    A beam has bw = 300 mm, d = 450 mm, C30/37 (fcd = 17 N/mm²). At cot θ = 2.5, what is VRd,max, in kN?

  3. Question 3

    For a beam with z = 405 mm, fywd = 434.8 N/mm² and cot θ = 2.5, what shear can H8 two-leg links at 175 mm centres carry, in kN? Take Asw = 100.5 mm².

  4. Question 4

    A beam needs 250 kN of shear resistance. VRd,c is 95 kN. How much shear must the links be designed for?

  5. Question 5

    An H20 bar in C30/37, good bond conditions, stressed to 435 N/mm² with fbd = 3.04 N/mm². What is lb,rqd, in mm?

  6. Question 6

    A beam has z = 495 mm and is designed at cot θ = 2.5. What is the shift distance al that the bending moment diagram must be displaced by, in mm?

  7. Question 7

    Two beams are identical except that one has d = 250 mm and the other d = 1000 mm. Which has the higher shear STRESS capacity vRd,c, all else equal?