Module 12
Composite beams
Two materials working together: strain compatibility, the modular ratio and the transformed-section method.
What this module covers
- Explain why strain is continuous across a bonded interface but stress is not
- Derive the transformed-section method from compatibility and equilibrium
- Use the modular ratio to convert one material into an equivalent area of another
- Find the neutral axis and stresses in a steel-reinforced timber beam
- Analyse a cracked reinforced-concrete section elastically
Lessons
Why the stiffer material takes more load, and the trick that makes the sums easy.
Start lesson →Cracked-section analysis: where the neutral axis goes when the concrete cannot pull.
Start lesson →Making a slab and a beam act as one member, and what it is worth.
Start lesson →
Module checkpoint
Check what you have taken in
3 questions
Question 1
In a transformed section, which quantity is multiplied by the modular ratio?
Question 2
A cracked RC section has Icr = 2.0 × 10⁹ mm⁴, x = 180 mm, d = 420 mm and n = 15. Under a moment of 120 kN·m, what is the steel stress?
Question 3
What is continuous across a perfectly bonded interface between two materials?