Module 10
Shear in beams
Deriving τ = VQ/It, why shear stress is zero at the top and bottom faces, and why the web carries the shear.
What this module covers
- Explain why a vertical shear force also produces horizontal shear stress
- Derive τ = VQ/It from longitudinal equilibrium of a beam element
- Say what Q means and calculate it for common sections
- Explain why shear stress peaks at the neutral axis and vanishes at a free surface
- Use shear flow to size welds, bolts and other connectors
Lessons
The unbalanced push on a beam slice, and complementary shear.
Start lesson →From longitudinal equilibrium of an element to the shear stress at any level.
Start lesson →Why a channel twists when you load it through its centroid.
Start lesson →
Module checkpoint
Check what you have taken in
3 questions
Question 1
A rectangular beam 150 mm wide by 400 mm deep carries a shear force of 120 kN. What is the maximum shear stress?
Question 2
What does Q represent in τ = VQ/It?
Question 3
Why is shear flow used rather than shear stress when designing bolts joining a built-up beam?